Prince Lab Publications

Edward F. and Irene Thiele Pimley Professor of Neurology and the Neurological Sciences

Publications

  • Partial TrkB receptor activation suppresses cortical epileptogenesis through actions on parvalbumin interneurons NEUROBIOLOGY OF DISEASE Gu, F., Parada, I., Yang, T., Longo, F. M., Prince, D. A. 2018; 113: 45–58

    Abstract

    Post-traumatic epilepsy is one of the most common and difficult to treat forms of acquired epilepsy worldwide. Currently, there is no effective way to prevent post-traumatic epileptogenesis. It is known that abnormalities of interneurons, particularly parvalbumin-containing interneurons, play a critical role in epileptogenesis following traumatic brain injury. Thus, enhancing the function of existing parvalbumin interneurons might provide a logical therapeutic approach to prevention of post-traumatic epilepsy. The known positive effects of brain-derived neurotrophic factor on interneuronal growth and function through activation of its receptor tropomyosin receptor kinase B, and its decrease after traumatic brain injury, led us to hypothesize that enhancing trophic support might improve parvalbumin interneuronal function and decrease epileptogenesis. To test this hypothesis, we used the partial neocortical isolation ('undercut', UC) model of posttraumatic epileptogenesis in mature rats that were treated for 2 weeks, beginning on the day of injury, with LM22A-4, a newly designed partial agonist at the tropomyosin receptor kinase B. Effects of treatment were assessed with Western blots to measure pAKT/AKT; immunocytochemistry and whole cell patch clamp recordings to examine functional and structural properties of GABAergic interneurons; field potential recordings of epileptiform discharges in vitro; and video-EEG recordings of PTZ-induced seizures in vivo. Results showed that LM22A-4 treatment 1) increased pyramidal cell perisomatic immunoreactivity for VGAT, GAD65 and parvalbumin; 2) increased the density of close appositions of VGAT/gephyrin immunoreactive puncta (putative inhibitory synapses) on pyramidal cell somata; 3) increased the frequency of mIPSCs in pyramidal cells; and 4) decreased the incidence of spontaneous and evoked epileptiform discharges in vitro. 5) Treatment of rats with PTX BD4-3, another partial TrkB receptor agonist, reduced the incidence of bicuculline-induced ictal episodes in vitro and PTZ induced electrographic and behavioral ictal episodes in vivo. 6) Inactivation of TrkB receptors in undercut TrkBF616A mice with 1NMPP1 abolished both LM22A-4-induced effects on mIPSCs and on increased perisomatic VGAT-IR. Results indicate that chronic activation of the tropomyosin receptor kinase B by a partial agonist after cortical injury can enhance structural and functional measures of GABAergic inhibition and suppress posttraumatic epileptogenesis. Although the full agonist effects of brain-derived neurotrophic factor and tropomyosin receptor kinase B activation in epilepsy models have been controversial, the present results indicate that such trophic activation by a partial agonist may potentially serve as an effective therapeutic option for prophylactic treatment of posttraumatic epileptogenesis, and treatment of other neurological and psychiatric disorders whose pathogenesis involves impaired parvalbumin interneuronal function.

    View details for PubMedID 29408225

  • Structural alterations in fast-spiking GABAergic interneurons in a model of posttraumatic neocortical epileptogenesis NEUROBIOLOGY OF DISEASE Gu, F., Parada, I., Shen, F., Li, J., Bacci, A., Graber, K., Taghavi, R., Scalise, K., Schwartzkroin, P., Wenzel, J., Prince, D. A. 2017; 108: 100–114

    Abstract

    Electrophysiological experiments in the partial cortical isolation ("undercut" or "UC") model of injury-induced neocortical epileptogenesis have shown alterations in GABAergic synaptic transmission attributable to abnormalities in presynaptic terminals. To determine whether the decreased inhibition was associated with structural abnormalities in GABAergic interneurons, we used immunocytochemical techniques, confocal microscopy and EM in UC and control sensorimotor rat cortex to analyze structural alterations in fast-spiking parvalbumin-containing interneurons and pyramidal (Pyr) cells of layer V. Principle findings were: 1) there were no decreases in counts of parvalbumin (PV)- or GABA-immunoreactive interneurons in UC cortex, however there were significant reductions in expression of VGAT and GAD-65 and -67 in halos of GABAergic terminals around Pyr somata in layer V. 2) Consistent with previous results, somatic size and density of Pyr cells was decreased in infragranular layers of UC cortex. 3) Dendrites of biocytin-filled FS interneurons were significantly decreased in volume. 4) There were decreases in the size and VGAT content of GABAergic boutons in axons of biocytin-filled FS cells in the UC, together with a decrease in colocalization with postsynaptic gephyrin, suggesting a reduction in GABAergic synapses. Quantitative EM of layer V Pyr somata confirmed the reduction in inhibitory synapses. 5) There were marked and lasting reductions in brain derived neurotrophic factor (BDNF)-IR and -mRNA in Pyr cells and decreased TrkB-IR on PV cells in UC cortex. 6) Results lead to the hypothesis that reduction in trophic support by BDNF derived from Pyr cells may contribute to the regressive changes in axonal terminals and dendrites of FS cells in the UC cortex and decreased GABAergic inhibition.Injury to cortical structures is a major cause of epilepsy, accounting for about 20% of cases in the general population, with an incidence as high as ~50% among brain-injured personnel in wartime. Loss of GABAergic inhibitory interneurons is a significant pathophysiological factor associated with epileptogenesis following brain trauma and other etiologies. Results of these experiments show that the largest population of cortical interneurons, the parvalbumin-containing fast-spiking (FS) interneurons, are preserved in the partial neocortical isolation model of partial epilepsy. However, axonal terminals of these cells are structurally abnormal, have decreased content of GABA synthetic enzymes and vesicular GABA transporter and make fewer synapses onto pyramidal neurons. These structural abnormalities underlie defects in GABAergic neurotransmission that are a key pathophysiological factor in epileptogenesis found in electrophysiological experiments. BDNF, and its TrkB receptor, key factors for maintenance of interneurons and pyramidal neurons, are decreased in the injured cortex. Results suggest that supplying BDNF to the injured epileptogenic brain may reverse the structural and functional abnormalities in the parvalbumin FS interneurons and provide an antiepileptogenic therapy.

    View details for DOI 10.1016/j.nbd.2017.08.008

    View details for Web of Science ID 000414723000009

    View details for PubMedID 28823934

    View details for PubMedCentralID PMC5927780

  • TGF beta signaling is associated with changes in inflammatory gene expression and perineuronal net degradation around inhibitory neurons following various neurological insults SCIENTIFIC REPORTS Kim, S., Senatorov, V. V., Morrissey, C. S., Lippmann, K., Vazquez, O., Milikovsky, D. Z., Gu, F., Parada, I., Prince, D. A., Becker, A. J., Heinemann, U., Friedman, A., Kaufer, D. 2017; 7: 7711

    Abstract

    Brain damage due to stroke or traumatic brain injury (TBI), both leading causes of serious long-term disability, often leads to the development of epilepsy. Patients who develop post-injury epilepsy tend to have poor functional outcomes. Emerging evidence highlights a potential role for blood-brain barrier (BBB) dysfunction in the development of post-injury epilepsy. However, common mechanisms underlying the pathological hyperexcitability are largely unknown. Here, we show that comparative transcriptome analyses predict remodeling of extracellular matrix (ECM) as a common response to different types of injuries. ECM-related transcriptional changes were induced by the serum protein albumin via TGFβ signaling in primary astrocytes. In accordance with transcriptional responses, we found persistent degradation of protective ECM structures called perineuronal nets (PNNs) around fast-spiking inhibitory interneurons, in a rat model of TBI as well as in brains of human epileptic patients. Exposure of a naïve brain to albumin was sufficient to induce the transcriptional and translational upregulation of molecules related to ECM remodeling and the persistent breakdown of PNNs around fast-spiking inhibitory interneurons, which was contingent on TGFβ signaling activation. Our findings provide insights on how albumin extravasation that occurs upon BBB dysfunction in various brain injuries can predispose neural circuitry to the development of chronic inhibition deficits.

    View details for PubMedID 28794441

  • Epileptiform activity and behavioral arrests in mice overexpressing the calcium channel subunit a2d-1. Neurobiology of disease Faria, L. C., Gu, F., Parada, I., Barres, B., David Luo, Z., Prince, D. A. 2017

    Abstract

    The alpha2delta-1 subunit (α2δ-1) of voltage-gated calcium channels is a receptor for astrocyte-secreted thrombospondins that promote developmental synaptogenesis. Alpha2delta-1 receptors are upregulated in models of injury-induced peripheral pain and epileptogenic neocortical trauma associated with an enhancement of excitatory synaptic connectivity. These results lead to the hypothesis that overexpression of α2δ-1 alone in neocortex of uninjured transgenic (TG) mice might result in increased excitatory connectivity and consequent cortical hyperexcitability and epileptiform activity. Whole cell recordings from layer V pyramidal neurons in somatosensory cortical slices of TG mice showed increased frequency and amplitude of miniature and spontaneous EPSCs and prolonged bursts of polysynaptic EPSCs. Epileptiform field potentials were evoked in layers II/III and V of brain slices from TG mice, but not controls. Dual immunoreactivity for Vglut-2 and PSD95 showed increased density of close appositions in TG mice compared to controls, suggesting an increased number of excitatory synapses. Video-EEG monitoring showed that 13/13 implanted TG mice aged >P21, but not controls, had frequent abnormal spontaneous epileptiform events, consisting of variable duration, high amplitude bi-hemispheric irregular bursts of delta activity, spikes and sharp waves lasting many seconds, with a variable peak frequency of ~1-3Hz, associated with behavioral arrest. The epileptiform EEG abnormalities and behavioral arrests were reversibly eliminated by treatment with i.p. ethosuximide. Behavioral seizures, consisting of ~15-30s duration episodes of rigid arched tail and head and body extension, followed by loss of balance and falling, frequently occurred in adult TG mice during recovery from isoflurane-induced anesthesia, but were rare in WT mice. Results show that over-expression of α2δ-1 subunits increases cortical excitatory connectivity and leads to neocortical hyperexcitability and epileptiform activity associated with behavioral arrests in adult TG mice. Similar increases in expression of α2δ-1 in models of cortical injury may play an important role in epileptogenesis.Binding of astrocytic-secreted thrombospondins to their α2δ-1 receptor facilitates excitatory synapse formation and excitatory transmission during cortical development and after injury. Upregulation of α2δ-1 is present in models of injury-induced pain and epileptogenic cortical trauma, along with many other molecular alterations. Here we show that overexpression of α2δ-1 alone in TG mice can enhance excitatory connectivity in neocortex and lead to neural circuit hyperexcitability and episodes of electrographic epileptiform activity, associated with behavioral arrests in transgenic mice. α2δ-1 is the high-affinity receptor for gabapentinoids and a potential target for prophylactic treatment of posttraumatic epilepsy and other disorders in which excessive aberrant excitatory connectivity is a pathophysiological feature.

    View details for DOI 10.1016/j.nbd.2017.01.009

    View details for PubMedID 28193459

  • Aberrant excitatory rewiring of layer V pyramidal neurons early after neocortical trauma NEUROBIOLOGY OF DISEASE Takahashi, D. K., Gu, F., Parada, I., Vyas, S., Prince, D. A. 2016; 91: 166-181

    Abstract

    Lesioned neuronal circuits form new functional connections after a traumatic brain injury (TBI). In humans and animal models, aberrant excitatory connections that form after TBI may contribute to the pathogenesis of post-traumatic epilepsy. Partial neocortical isolation ("undercut" or "UC") leads to altered neuronal circuitry and network hyperexcitability recorded in vivo and in brain slices from chronically lesioned neocortex. Recent data suggest a critical period for maladaptive excitatory circuit formation within the first 3days post UC injury (Graber and Prince 1999, 2004; Li et al. 2011, 2012b). The present study focuses on alterations in excitatory connectivity within this critical period. Immunoreactivity (IR) for growth-associated protein (GAP)-43 was increased in the UC cortex 3days after injury. Some GAP-43-expressing excitatory terminals targeted the somata of layer V pyramidal (Pyr) neurons, a domain usually innervated predominantly by inhibitory terminals. Immunocytochemical analysis of pre- and postsynaptic markers showed that putative excitatory synapses were present on somata of these neurons in UC neocortex. Excitatory postsynaptic currents from UC layer V Pyr cells displayed properties consistent with perisomatic inputs and also reflected an increase in the number of synaptic contacts. Laser scanning photostimulation (LSPS) experiments demonstrated reorganized excitatory connectivity after injury within the UC. Concurrent with these changes, spontaneous epileptiform bursts developed in UC slices. Results suggest that aberrant reorganization of excitatory connectivity contributes to early neocortical hyperexcitability in this model. The findings are relevant for understanding the pathophysiology of neocortical post-traumatic epileptogenesis and are important in terms of the timing of potential prophylactic treatments.

    View details for DOI 10.1016/j.nbd.2016.03.003

    View details for Web of Science ID 000375885600015

    View details for PubMedID 26956396

    View details for PubMedCentralID PMC4860078

  • Antiepileptogenic repair of excitatory and inhibitory synaptic connectivity after neocortical trauma NEUROBIOLOGY OF EPILEPSY: FROM GENES TO NETWORKS Prince, D. A., Gu, F., Parada, I. 2016; 226: 209-227

    Abstract

    The "final common path" to epileptogenesis induced by cortical trauma and disease processes ultimately depends on changes in relative weights of excitatory and inhibitory synaptic activities in neuronal networks. Results of two experiments summarized here provide proof in principle that prophylaxis of posttraumatic epileptogenesis can result when antiepileptogenic treatments are focused on basic underlying synaptic mechanisms. (1) Brief gabapentin treatment after injury limits new excitatory synapse formation by preventing binding of thrombospondins to α2δ-1 receptors, resulting in long-lasting effects that limit aberrant excitatory connectivity and decrease epileptogenesis. (2) Fast-spiking (FS) interneurons are structurally and functionally abnormal in the partial cortical isolation and other models of epileptogenesis. Brain-derived neurotrophic factor (BDNF) supports growth and maintenance of GABAergic neurons during brain development, leading to the hypothesis that it might favorably affect injured interneurons. Partial activation of BDNF TrkB receptors with a small molecule reverses structural abnormalities in FS interneuronal terminals, increases the frequency of mIPSCs, and increases probability of GABA release. These changes are associated with significantly reduced spontaneous and evoked epileptiform bursts in vitro and increased threshold for pentylenetetrazole-induced seizures in vivo. Each of these treatments offers a potential promising approach to prophylaxis of injury-induced cortical epileptogenesis.

    View details for DOI 10.1016/bs.pbr.2016.03.013

    View details for Web of Science ID 000382284800010

    View details for PubMedID 27323945

  • Excitatory and inhibitory synaptic connectivity to layer V fast-spiking interneurons in the freeze lesion model of cortical microgyria JOURNAL OF NEUROPHYSIOLOGY Jin, X., Jiang, K., Prince, D. A. 2014; 112 (7): 1703-1713

    Abstract

    A variety of major developmental cortical malformations are closely associated with clinically intractable epilepsy. Pathophysiological aspects of one such disorder, human polymicrogyria, can be modeled by making neocortical freeze lesions (FL) in neonatal rodents, resulting in the formation of microgyri. Previous studies showed enhanced excitatory and inhibitory synaptic transmission and connectivity in cortical layer V pyramidal neurons in the paramicrogyral cortex. In young adult transgenic mice that express green fluorescent protein (GFP) specifically in parvalbumin positive fast-spiking (FS) interneurons, we used laser scanning photostimulation (LSPS) of caged glutamate to map excitatory and inhibitory synaptic connectivity onto FS interneurons in layer V of paramicrogyral cortex in control and FL groups. The proportion of uncaging sites from which excitatory postsynaptic currents (EPSCs) could be evoked (hotspot ratio) increased slightly but significantly in FS cells of the FL vs. control cortex, while the mean amplitude of LSPS-evoked EPSCs at hotspots did not change. In contrast, the hotspot ratio of inhibitory postsynaptic currents (IPSCs) was significantly decreased in FS neurons of the FL cortex. These alterations in synaptic inputs onto FS interneurons may result in an enhanced inhibitory output. We conclude that alterations in synaptic connectivity to cortical layer V FS interneurons do not contribute to hyperexcitability of the FL model. Instead, the enhanced inhibitory output from these neurons may partially offset an earlier demonstrated increase in synaptic excitation of pyramidal cells and thereby maintain a relative balance between excitation and inhibition in the affected cortical circuitry.

    View details for DOI 10.1152/jn.00854.2013

    View details for Web of Science ID 000343226600011

    View details for PubMedID 24990567

    View details for PubMedCentralID PMC4157179

  • How Do We Make Models That Are Useful in Understanding Partial Epilepsies? Workshop on Issues in Clinical Epileptology - A View from the Bench held in honor of Phil Prince, D. A. SPRINGER. 2014: 233–241

    Abstract

    The goals of constructing epilepsy models are (1) to develop approaches to prophylaxis of epileptogenesis following cortical injury; (2) to devise selective treatments for established epilepsies based on underlying pathophysiological mechanisms; and (3) use of a disease (epilepsy) model to explore brain molecular, cellular and circuit properties. Modeling a particular epilepsy syndrome requires detailed knowledge of key clinical phenomenology and results of human experiments that can be addressed in critically designed laboratory protocols. Contributions to understanding mechanisms and treatment of neurological disorders has often come from research not focused on a specific disease-relevant issue. Much of the foundation for current research in epilepsy falls into this category. Too strict a definition of the relevance of an experimental model to progress in preventing or curing epilepsy may, in the long run, slow progress. Inadequate exploration of the experimental target and basic laboratory results in a given model can lead to a failed effort and false negative or positive results. Models should be chosen based on the specific issues to be addressed rather than on convenience of use. Multiple variables including maturational age, species and strain, lesion type, severity and location, latency from injury to experiment and genetic background will affect results. A number of key issues in clinical and basic research in partial epilepsies remain to be addressed including the mechanisms active during the latent period following injury, susceptibility factors that predispose to epileptogenesis, injury - induced adaptive versus maladaptive changes, mechanisms of pharmaco-resistance and strategies to deal with multiple pathophysiological processes occurring in parallel.

    View details for Web of Science ID 000346021700020

    View details for PubMedID 25012380

  • Remodeling of dendrites and spines in the C1q knockout model of genetic epilepsy EPILEPSIA Ma, Y., Ramachandran, A., Ford, N., Parada, I., Prince, D. A. 2013; 54 (7): 1232-1239

    Abstract

    PURPOSE: To determine whether developmental synaptic pruning defects in epileptic C1q-knockout (KO) mice are accompanied by postsynaptic abnormalities in dendrites and/or spines. METHODS: Immunofluorescence staining was performed on biocytin-filled layer Vb pyramidal neurons in sensorimotor cortex. Basal dendritic arbors and their spines were reconstructed with NEUROLUCIDA software, and their morphologic characteristics were quantitated in Neuroexplorer. KEY FINDINGS: Seven to nine completely filled pyramidal neurons were analyzed from the wild-type (WT) and C1q KO groups. Compared to WT controls, KO mice showed significant structural modifications in their basal dendrites including (1) higher density of dendritic spines (0.60 ± 0.03/μm vs. 0.49 ± 0.03/μm dendritic length in WT, p < 0.05); (2) remarkably increased occurrence of thin spines (0.26 ± 0.02/μm vs. 0.14 ± 0.02/μm dendritic length in control, p < 0.01); (3) longer dendritic length (2,680 ± 159 μm vs. 2,119 ± 108 μm in control); and (4) increased branching (22.6 ± 1.9 vs. 16.2 ± 1.3 in WT at 80 μm from soma center, p < 0.05; 12.4 ± 1.4 vs. 8.2 ± 0.6 in WT at 120 μm from soma center, respectively, p < 0.05). Dual immunolabeling demonstrated the expression of putative glutamate receptor 2 (GluR2) on some thin spines. These dendritic alterations are likely postsynaptic structural consequences of failure of synaptic pruning in the C1q KO mice. SIGNIFICANCE: Failure to prune excessive excitatory synapses in C1q KO mice is a likely mechanism underlying abnormalities in postsynaptic dendrites, including increased branching and alterations in spine type and density. It is also possible that seizure activity contributes to these abnormalities. These structural abnormalities, together with increased numbers of excitatory synapses, likely contribute to epileptogenesis in C1q KO mice.

    View details for DOI 10.1111/epi.12195

    View details for Web of Science ID 000321110100012

    View details for PubMedID 23621154

  • Gabapentin decreases epileptiform discharges in a chronic model of neocortical trauma NEUROBIOLOGY OF DISEASE Li, H., Graber, K. D., Jin, S., McDonald, W., Barres, B. A., Prince, D. A. 2012; 48 (3): 429-438

    Abstract

    Gabapentin (GBP) is an anticonvulsant that acts at the α2δ-1 submit of the L-type calcium channel. It is recently reported that GBP is a potent inhibitor of thrombospondin (TSP)-induced excitatory synapse formation in vitro and in vivo. Here we studied effects of chronic GBP administration on epileptogenesis in the partial cortical isolation ("undercut") model of posttraumatic epilepsy, in which abnormal axonal sprouting and aberrant synaptogenesis contribute to occurrence of epileptiform discharges. Results showed that 1) the incidence of evoked epileptiform discharges in undercut cortical slices studied 1 day or ~2 weeks after the last GBP dose, was significantly reduced by GBP treatments, beginning on the day of injury; 2) the expression of GFAP and TSP1 protein, as well as the number of FJC stained cells was decreased in GBP treated undercut animals; 3) in vivo GBP treatment of rats with undercuts for 3 or 7 days decreased the density of vGlut1-PSD95 close appositions (presumed synapses) in comparison to saline treated controls with similar lesions;4) the electrophysiological data are compatible with the above anatomical changes, showing decreases in mEPSC and sEPSC frequency in the GBP treated animals. These results indicate that chronic administration of GBP after cortical injury is antiepileptogenic in the undercut model of post-traumatic epilepsy, perhaps by both neuroprotective actions and decreases in excitatory synapse formation. The findings may suggest the potential use of GBP as an antiepileptogenic agent following traumatic brain injury.

    View details for DOI 10.1016/j.nbd.2012.06.019

    View details for Web of Science ID 000309694000017

    View details for PubMedID 22766033

    View details for PubMedCentralID PMC3461125

  • Finding a better drug for epilepsy: Antiepileptogenesis targets EPILEPSIA Kobow, K., Auvin, S., Jensen, F., Loescher, W., Mody, I., Potschka, H., Prince, D., Sierra, A., Simonato, M., Pitkaenen, A., Nehlig, A., Rho, J. M. 2012; 53 (11): 1868-1876

    Abstract

    For several decades, both in vitro and in vivo models of seizures and epilepsy have been employed to unravel the molecular and cellular mechanisms underlying the occurrence of spontaneous recurrent seizures (SRS)-the defining hallmark of the epileptic brain. However, despite great advances in our understanding of seizure genesis, investigators have yet to develop reliable biomarkers and surrogate markers of the epileptogenic process. Sadly, the pathogenic mechanisms that produce the epileptic condition, especially after precipitating events such as head trauma, inflammation, or prolonged febrile convulsions, are poorly understood. A major challenge has been the inherent complexity and heterogeneity of known epileptic syndromes and the differential genetic susceptibilities exhibited by patients at risk. Therefore, it is unlikely that there is only one fundamental pathophysiologic mechanism shared by all the epilepsies. Identification of antiepileptogenesis targets has been an overarching goal over the last decade, as current anticonvulsant medications appear to influence only the acute process of ictogenesis. Clearly, there is an urgent need to develop novel therapeutic interventions that are disease modifying-therapies that either completely or partially prevent the emergence of SRS. An important secondary goal is to develop new treatments that can also lessen the burden of epilepsy comorbidities (e.g., cognitive impairment, mood disorders) by preventing or reducing the deleterious changes during the epileptogenic process. This review summarizes novel antiepileptogenesis targets that were critically discussed at the XIth Workshop on the Neurobiology of Epilepsy (WONOEP XI) meeting in Grottaferrata, Italy. Further, emerging neurometabolic links among several target mechanisms and highlights of the panel discussion are presented.

    View details for DOI 10.1111/j.1528-1167.2012.03716.x

    View details for Web of Science ID 000310975400006

    View details for PubMedID 23061663

  • Functional alterations in GABAergic fast-spiking interneurons in chronically injured epileptogenic neocortex NEUROBIOLOGY OF DISEASE Ma, Y., Prince, D. A. 2012; 47 (1): 102-113

    Abstract

    Progress toward developing effective prophylaxis and treatment of posttraumatic epilepsy depends on a detailed understanding of the basic underlying mechanisms. One important factor contributing to epileptogenesis is decreased efficacy of GABAergic inhibition. Here we tested the hypothesis that the output of neocortical fast-spiking (FS) interneurons onto postsynaptic targets would be decreased in the undercut (UC) model of chronic posttraumatic epileptogenesis. Using dual whole-cell recordings in layer IV barrel cortex, we found a marked increase in the failure rate and a very large reduction in the amplitude of unitary inhibitory postsynaptic currents (uIPSCs) from FS cells to excitatory regular spiking (RS) neurons and neighboring FS cells. Assessment of the paired pulse ratio and presumed quantal release showed that there was a significant, but relatively modest, decrease in synaptic release probability and a non-significant reduction in quantal size. A reduced density of boutons on axons of biocytin-filled UC FS cells, together with a higher coefficient of variation of uIPSC amplitude in RS cells, suggested that the number of functional synapses presynaptically formed by FS cells may be reduced. Given the marked reduction in synaptic strength, other defects in the presynaptic vesicle release machinery likely occur, as well.

    View details for DOI 10.1016/j.nbd.2012.03.027

    View details for Web of Science ID 000304791700010

    View details for PubMedID 22484482

    View details for PubMedCentralID PMC3416869

  • Interneuronal calcium channel abnormalities in posttraumatic epileptogenic neocortex NEUROBIOLOGY OF DISEASE Faria, L. C., Parada, I., Prince, D. A. 2012; 45 (2): 821-828

    Abstract

    Decreased release probability (Pr) and increased failure rate for monosynaptic inhibitory postsynaptic currents (IPSCs) indicate abnormalities in presynaptic inhibitory terminals on pyramidal (Pyr) neurons of the undercut (UC) model of posttraumatic epileptogenesis. These indices of inhibition are normalized in high [Ca++] ACSF, suggesting dysfunction of Ca2+ channels in GABAergic terminals. We tested this hypothesis using selective blockers of P/Q and N-type Ca2+ channels whose activation underlies transmitter release in cortical inhibitory terminals. Pharmacologically isolated monosynaptic IPSCs were evoked in layer V Pyr cells by extracellular stimuli in adult rat sensorimotor cortical slices. Local perfusion of 0.2/1 μM ω-agatoxin IVa and/or 1 μM ω-conotoxin GVIA was used to block P/Q and N-type calcium channels, respectively. In control layer V Pyr cells, peak amplitude of eIPSCs was decreased by ~50% after treatment with either 1 μM ω-conotoxin GVIA or 1 μM ω-agatoxin IVa. In contrast, there was a lack of sensitivity to 1 μM ω-conotoxin GVIA in UCs. Immunocytochemical results confirmed decreased perisomatic density of N-channels on Pyr cells in UCs. We suggest that decreased calcium influx via N-type channels in presynaptic GABAergic terminals is a mechanism contributing to decreased inhibitory input onto layer V Pyr cells in this model of cortical posttraumatic epileptogenesis.

    View details for DOI 10.1016/j.nbd.2011.11.006

    View details for Web of Science ID 000299500200017

    View details for PubMedID 22172650

    View details for PubMedCentralID PMC3409879

  • Targets for preventing epilepsy following cortical injury NEUROSCIENCE LETTERS Li, H., McDonald, W., Parada, I., Faria, L., Graber, K., Takahashi, D. K., Ma, Y., Prince, D. 2011; 497 (3): 172-176

    Abstract

    Prophylaxis of posttraumatic epilepsy will require a detailed knowledge of the epileptogenic pathophysiological processes that follow brain injury. Results from studies of experimental models and human epilepsy highlight alterations in GABAergic interneurons and formation of excessive new excitatory synaptic connectivity as prominent targets for prophylactic therapies. Promising laboratory results suggest that it will be possible to experimentally modify these aberrant processes and interfere with epileptogenesis. However, a number of key issues must be addressed before these results can be used to frame clinical antiepileptogenic therapy.

    View details for DOI 10.1016/j.neulet.2011.02.042

    View details for Web of Science ID 000292411600004

    View details for PubMedID 21354270

    View details for PubMedCentralID PMC3409878

  • Reorganization of Inhibitory Synaptic Circuits in Rodent Chronically Injured Epileptogenic Neocortex CEREBRAL CORTEX Jin, X., Huguenard, J. R., Prince, D. A. 2011; 21 (5): 1094-1104

    Abstract

    Reduced synaptic inhibition is an important factor contributing to posttraumatic epileptogenesis. Axonal sprouting and enhanced excitatory synaptic connectivity onto rodent layer V pyramidal (Pyr) neurons occur in epileptogenic partially isolated (undercut) neocortex. To determine if enhanced excitation also affects inhibitory circuits, we used laser scanning photostimulation of caged glutamate and whole-cell recordings from GAD67-GFP-expressing mouse fast spiking (FS) interneurons and Pyr cells in control and undercut in vitro slices to map excitatory and inhibitory synaptic inputs. Results are 1) the region-normalized excitatory postsynaptic current (EPSC) amplitudes and proportion of uncaging sites from which EPSCs could be evoked (hotspot ratio) "increased" significantly in FS cells of undercut slices; 2) in contrast, these parameters were significantly "decreased" for inhibitory postsynaptic currents (IPSCs) in undercut FS cells; and 3) in rat layer V Pyr neurons, we found significant decreases in IPSCs in undercut versus control Pyr neurons. The decreases were mainly located in layers II and IV, suggesting a reduction in the efficacy of interlaminar synaptic inhibition. Results suggest that there is significant synaptic reorganization in this model of posttraumatic epilepsy, resulting in increased excitatory drive and reduced inhibitory input to FS interneurons that should enhance their inhibitory output and, in part, offset similar alterations in innervation of Pyr cells.

    View details for DOI 10.1093/cercor/bhq181

    View details for Web of Science ID 000289578900012

    View details for PubMedID 20855494

    View details for PubMedCentralID PMC3077430

  • Neocortical posttraumatic epileptogenesis EPILEPSIA Prince, D. A., Parada, I., Li, H., McDonald, W., Graber, K. 2010; 51: 30-30

    Abstract

    Development of new excitatory connectivity and decreases in GABAergic inhibition are mechanisms underlying posttraumatic epileptogenesis in animal models. Experimental strategies that interfere with these processes, applied between the trauma andseizure onset, are antiepileptogenic in the laboratory, and have promise for prophylaxis of epileptogenesis after cortical injury in man. For an expanded treatment of this topic see Jasper's Basic Mechanisms of the Epilepsies, Fourth Edition (Noebels JL, Avoli M, Rogawski MA, Olsen RW, Delgado-Escueta AV, eds) published by Oxford University Press. Available on NCBI Bookshelf.

    View details for DOI 10.1111/j.1528-1167.2010.02816.x

    View details for Web of Science ID 000285388600025

    View details for PubMedCentralID PMC3082392

  • Differential effects of Na plus -K plus ATPase blockade on cortical layer V neurons JOURNAL OF PHYSIOLOGY-LONDON Anderson, T. R., Huguenard, J. R., Prince, D. A. 2010; 588 (22): 4401-4414

    Abstract

    Sodium-potassium ATPase ('Na(+)-K(+) ATPase') contributes to the maintenance of the resting membrane potential and the transmembrane gradients for Na(+) and K(+) in neurons. Activation of Na(+)-K(+) ATPase may be important in controlling increases in intracellular sodium during periods of increased neuronal activity. Down-regulation of Na(+)-K(+) ATPase activity is implicated in numerous CNS disorders, including epilepsy. Although Na(+)-K(+) ATPase is present in all neurons, little is known about its activity in different subclasses of neocortical cells. We assessed the physiological properties of Na(+)-K(+) ATPase in fast-spiking (FS) interneurons and pyramidal (PYR) cells to test the hypothesis that Na(+)-K(+) ATPase activity would be relatively greater in neurons that generated high frequency action potentials (the FS cells). Whole-cell patch clamp recordings were made from FS and PYR neurons in layer V of rat sensorimotor cortical slices maintained in vitro using standard techniques. Bath perfusion of Na(+)-K(+) ATPase antagonists (ouabain or dihydro-ouabain) induced either a membrane depolarization in current clamp, or inward current under voltage clamp in both cell types. PYR neurons were divided into two subpopulations based on the amplitude of the voltage or current shift in response to Na(+)-K(+) ATPase blockade. The two PYR cell groups did not differ significantly in electrophysiological properties including resting membrane potential, firing pattern, input resistance and capacitance. Membrane voltage responses of FS cells to Na(+)-K(+) ATPase blockade were intermediate between the two PYR cell groups (P < 0.05). The resting Na(+)-K(+) ATPase current density in FS interneurons, assessed by application of blockers, was 3- to 7-fold larger than in either group of PYR neurons. Na(+)-K(+) ATPase activity was increased either through direct Na(+) loading via the patch pipette or by focal application of glutamate (20 mM puffs). Under these conditions FS interneurons exhibited the largest increase in Na(+)-K(+) ATPase activity. We conclude that resting Na(+)-K(+) ATPase activity and sensitivity to changes in internal Na(+) concentration vary between and within classes of cortical neurons. These differences may have important consequences in pathophysiological disorders associated with down-regulation of Na(+)-K(+) ATPase and hyperexcitability within cortical networks.

    View details for DOI 10.1113/jphysiol.2010.191858

    View details for Web of Science ID 000284276000011

    View details for PubMedID 20819946

    View details for PubMedCentralID PMC3008847

  • Excitatory Input Onto Hilar Somatostatin Interneurons Is Increased in a Chronic Model of Epilepsy JOURNAL OF NEUROPHYSIOLOGY Halabisky, B., Parada, I., Buckmaster, P. S., Prince, D. A. 2010; 104 (4): 2214-2223

    Abstract

    The density of somatostatin (SOM)-containing GABAergic interneurons in the hilus of the dentate gyrus is significantly decreased in both human and experimental temporal lobe epilepsy. We used the pilocarpine model of status epilepticus and temporal lobe epilepsy in mice to study anatomical and electrophysiological properties of surviving somatostatin interneurons and determine whether compensatory functional changes occur that might offset loss of other inhibitory neurons. Using standard patch-clamp techniques and pipettes containing biocytin, whole cell recordings were obtained in hippocampal slices maintained in vitro. Hilar SOM cells containing enhanced green fluorescent protein (EGFP) were identified with fluorescent and infrared differential interference contrast video microscopy in epileptic and control GIN (EGFP-expressing Inhibitory Neurons) mice. Results showed that SOM cells from epileptic mice had 1) significant increases in somatic area and dendritic length; 2) changes in membrane properties, including a small but significant decrease in resting membrane potential, and increases in time constant and whole cell capacitance; 3) increased frequency of slowly rising spontaneous excitatory postsynaptic currents (sEPSCs) due primarily to increased mEPSC frequency, without changes in the probability of release; 4) increased evoked EPSC amplitude; and 5) increased spontaneous action potential generation in cell-attached recordings. Results suggest an increase in excitatory innervation, perhaps on distal dendrites, considering the slower rising EPSCs and increased output of hilar SOM cells in this model of epilepsy. In sum, these changes would be expected to increase the inhibitory output of surviving SOM interneurons and in part compensate for interneuronal loss in the epileptogenic hippocampus.

    View details for DOI 10.1152/jn.00147.2010

    View details for Web of Science ID 000282649900037

    View details for PubMedID 20631216

  • Desynchronization of Neocortical Networks by Asynchronous Release of GABA at Autaptic and Synaptic Contacts from Fast-Spiking Interneurons PLOS BIOLOGY Manseau, F., Marinelli, S., Mendez, P., Schwaller, B., Prince, D. A., Huguenard, J. R., Bacci, A. 2010; 8 (9)

    Abstract

    Networks of specific inhibitory interneurons regulate principal cell firing in several forms of neocortical activity. Fast-spiking (FS) interneurons are potently self-inhibited by GABAergic autaptic transmission, allowing them to precisely control their own firing dynamics and timing. Here we show that in FS interneurons, high-frequency trains of action potentials can generate a delayed and prolonged GABAergic self-inhibition due to sustained asynchronous release at FS-cell autapses. Asynchronous release of GABA is simultaneously recorded in connected pyramidal (P) neurons. Asynchronous and synchronous autaptic release show differential presynaptic Ca(2+) sensitivity, suggesting that they rely on different Ca(2+) sensors and/or involve distinct pools of vesicles. In addition, asynchronous release is modulated by the endogenous Ca(2+) buffer parvalbumin. Functionally, asynchronous release decreases FS-cell spike reliability and reduces the ability of P neurons to integrate incoming stimuli into precise firing. Since each FS cell contacts many P neurons, asynchronous release from a single interneuron may desynchronize a large portion of the local network and disrupt cortical information processing.

    View details for DOI 10.1371/journal.pbio.1000492

    View details for Web of Science ID 000282279200011

    View details for PubMedID 20927409

  • Presynaptic Inhibitory Terminals Are Functionally Abnormal in a Rat Model of Posttraumatic Epilepsy JOURNAL OF NEUROPHYSIOLOGY Faria, L. C., Prince, D. A. 2010; 104 (1): 280-290

    Abstract

    Partially isolated "undercut" neocortex with intact pial circulation is a well-established model of posttraumatic epileptogenesis. Results of previous experiments showed a decreased frequency of miniature inhibitory postsynaptic currents (mIPSCs) in layer V pyramidal (Pyr) neurons of undercuts. We further examined possible functional abnormalities in GABAergic inhibition in rat epileptogenic neocortical slices in vitro by recording whole cell monosynaptic IPSCs in layer V Pyr cells and fast-spiking (FS) GABAergic interneurons using a paired pulse paradigm. Compared with controls, IPSCs in Pyr neurons of injured slices showed increased threshold and decreased peak amplitude at threshold, decreased input/output slopes, increased failure rates, and a shift from paired pulse depression toward paired pulse facilitation (increased paired pulse ratio or PPR). Increasing [Ca(2+)](o) from 2 to 4 mM partially reversed these abnormalities in Pyr cells of the epileptogenic tissue. IPSCs onto FS cells also had an increased PPR and failures. Blockade of GABA(B) receptors did not affect the paired results. These findings suggest that there are functional alterations in GABAergic presynaptic terminals onto both Pyr and FS cells in this model of posttraumatic epileptogenesis.

    View details for DOI 10.1152/jn.00351.2010

    View details for Web of Science ID 000279586400026

    View details for PubMedID 20484536

    View details for PubMedCentralID PMC2904216

  • Enhanced synaptic connectivity and epilepsy in C1q knockout mice PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Chu, Y., Jin, X., Parada, I., Pesic, A., Stevens, B., Barres, B., Prince, D. A. 2010; 107 (17): 7975-7980

    Abstract

    Excessive CNS synapses are eliminated during development to establish mature patterns of neuronal connectivity. A complement cascade protein, C1q, is involved in this process. Mice deficient in C1q fail to refine retinogeniculate connections resulting in excessive retinal innervation of lateral geniculate neurons. We hypothesized that C1q knockout (KO) mice would exhibit defects in neocortical synapse elimination resulting in enhanced excitatory synaptic connectivity and epileptiform activity. We recorded spontaneous and evoked field potential activity in neocortical slices and obtained video-EEG recordings from implanted C1q KO and wild-type (WT) mice. We also used laser scanning photostimulation of caged glutamate and whole cell recordings to map excitatory and inhibitory synaptic connectivity. Spontaneous and evoked epileptiform field potentials occurred at multiple sites in neocortical slices from C1q KO, but not WT mice. Laser mapping experiments in C1q KO slices showed that the proportion of glutamate uncaging sites from which excitatory postsynaptic currents (EPSCs) could be evoked ("hotspot ratio") increased significantly in layer IV and layer V, although EPSC amplitudes were unaltered. Density of axonal boutons was significantly increased in layer V pyramidal neurons of C1q KO mice. Implanted KO mice had frequent behavioral seizures consisting of behavioral arrest associated with bihemispheric spikes and slow wave activity lasting from 5 to 30 s. Results indicate that epileptogenesis in C1q KO mice is related to a genetically determined failure to prune excessive excitatory synapses during development.

    View details for DOI 10.1073/pnas.0913449107

    View details for Web of Science ID 000277088700067

    View details for PubMedID 20375278

    View details for PubMedCentralID PMC2867906

  • Focal Cortical Infarcts Alter Intrinsic Excitability and Synaptic Excitation in the Reticular Thalamic Nucleus JOURNAL OF NEUROSCIENCE Paz, J. T., Christian, C. A., Parada, I., Prince, D. A., Huguenard, J. R. 2010; 30 (15): 5465-5479

    Abstract

    Focal cortical injuries result in death of cortical neurons and their efferents and ultimately in death or damage of thalamocortical relay (TCR) neurons that project to the affected cortical area. Neurons of the inhibitory reticular thalamic nucleus (nRT) receive excitatory inputs from corticothalamic and thalamocortical axons and are thus denervated by such injuries, yet nRT cells generally survive these insults to a greater degree than TCR cells. nRT cells inhibit TCR cells, regulate thalamocortical transmission, and generate cerebral rhythms including those involved in thalamocortical epilepsies. The survival and reorganization of nRT after cortical injury would determine recovery of thalamocortical circuits after injury. However, the physiological properties and connectivity of the survivors remain unknown. To study possible alterations in nRT neurons, we used the rat photothrombosis model of cortical stroke. Using in vitro patch-clamp recordings at various times after the photothrombotic injury, we show that localized strokes in the somatosensory cortex induce long-term reductions in intrinsic excitability and evoked synaptic excitation of nRT cells by the end of the first week after the injury. We find that nRT neurons in injured rats show (1) decreased membrane input resistance, (2) reduced low-threshold calcium burst responses, and (3) weaker evoked excitatory synaptic responses. Such alterations in nRT cellular excitability could lead to loss of nRT-mediated inhibition in relay nuclei, increased output of surviving TCR cells, and enhanced thalamocortical excitation, which may facilitate recovery of thalamic and cortical sensory circuits. In addition, such changes could be maladaptive, leading to injury-induced epilepsy.

    View details for DOI 10.1523/JNEUROSCI.5083-09.2010

    View details for Web of Science ID 000276685100033

    View details for PubMedID 20392967

    View details for PubMedCentralID PMC2861582

  • Neocortical Posttraumatic Epileptogenesis. Epilepsia Prince, D. A., Parada, I. n., Li, H. n., McDonald, W. n., Graber, K. n. 2010; 51 Suppl 5: 30

    Abstract

    Development of new excitatory connectivity and decreases in GABAergic inhibition are mechanisms underlying posttraumatic epileptogenesis in animal models. Experimental strategies that interfere with these processes, applied between the trauma andseizure onset, are antiepileptogenic in the laboratory, and have promise for prophylaxis of epileptogenesis after cortical injury in man. For an expanded treatment of this topic see Jasper's Basic Mechanisms of the Epilepsies, Fourth Edition (Noebels JL, Avoli M, Rogawski MA, Olsen RW, Delgado-Escueta AV, eds) published by Oxford University Press. Available on NCBI Bookshelf.

    View details for PubMedID 22056919

    View details for PubMedCentralID PMC3082392

  • Neocortical posttraumatic epileptogenesis. Epilepsia Prince, D. A., Parada, I. n., Li, H. n., McDonald, W. n., Graber, K. n. 2010; 51 Suppl s5: 30

    Abstract

    Development of new excitatory connectivity and decreases in γ-aminobutyric acid (GABA)ergic inhibition are mechanisms underlying posttraumatic epileptogenesis in animal models. Experimental strategies that interfere with these processes, applied between the trauma and seizure onset, are antiepileptogenic in the laboratory, and have promise for prophylaxis of epileptogenesis after cortical injury in humans. For an expanded treatment of this topic see Jasper's Basic Mechanisms of the Epilepsies, Fourth Edition (Noebels JL, Avoli M, Rogawski MA, Olsen RW, Delgado-Escueta AV, eds) National Library of Medicine Bookshelf [NCBI] at http://www.ncbi.nlm.nih.gov/books).

    View details for PubMedID 21158780

  • Surviving Hilar Somatostatin Interneurons Enlarge, Sprout Axons, and Form New Synapses with Granule Cells in a Mouse Model of Temporal Lobe Epilepsy JOURNAL OF NEUROSCIENCE Zhang, W., Yamawaki, R., Wen, X., Uhl, J., Diaz, J., Prince, D. A., Buckmaster, P. S. 2009; 29 (45): 14247-14256

    Abstract

    In temporal lobe epilepsy, seizures initiate in or near the hippocampus, which frequently displays loss of neurons, including inhibitory interneurons. It is unclear whether surviving interneurons function normally, are impaired, or develop compensatory mechanisms. We evaluated GABAergic interneurons in the hilus of the dentate gyrus of epileptic pilocarpine-treated GIN mice, specifically a subpopulation of somatostatin interneurons that expresses enhanced green fluorescence protein (GFP). GFP-immunocytochemistry and stereological analyses revealed substantial loss of GFP-positive hilar neurons (GPHNs) but increased GFP-positive axon length per dentate gyrus in epileptic mice. Individual biocytin-labeled GPHNs in hippocampal slices from epileptic mice also had larger somata, more axon in the molecular layer, and longer dendrites than controls. Dual whole-cell patch recording was used to test for monosynaptic connections from hilar GPHNs to granule cells. Unitary IPSCs (uIPSCs) recorded in control and epileptic mice had similar average rise times, amplitudes, charge transfers, and decay times. However, the probability of finding monosynaptically connected pairs and evoking uIPSCs was 2.6 times higher in epileptic mice compared to controls. Together, these findings suggest that surviving hilar somatostatin interneurons enlarge, extend dendrites, sprout axon collaterals in the molecular layer, and form new synapses with granule cells. These epilepsy-related changes in cellular morphology and connectivity may be mechanisms for surviving hilar interneurons to inhibit more granule cells and compensate for the loss of vulnerable interneurons.

    View details for DOI 10.1523/JNEUROSCI.3842-09.2009

    View details for Web of Science ID 000271664000019

    View details for PubMedID 19906972

    View details for PubMedCentralID PMC2802278

  • DOES GABAPENTIN PREVENT POSTTRAUMATIC EPILEPTOGENESIS? 63rd Annual Meeting of the American-Epilepsy-Society Li, H., Graber, K. D., Prince, D. A. WILEY-BLACKWELL PUBLISHING, INC. 2009: 350–351
  • TEMPORAL AND TOPOGRAPHIC ALTERATIONS IN EXPRESSION OF THE alpha 3 ISOFORM OF Na+,K+-ATPase IN THE RAT FREEZE LESION MODEL OF MICROGYRIA AND EPILEPTOGENESIS NEUROSCIENCE Chu, Y., Parada, I., Prince, D. A. 2009; 162 (2): 339-348

    Abstract

    Na(+),K(+)-ATPase contributes to the asymmetrical distribution of sodium and potassium ions across the plasma membrane and to maintenance of the membrane potential in many types of cells. Alterations in this protein may play a significant role in many human neurological disorders, including epilepsy. We studied expression of the alpha3 isoform of Na(+),K(+)-ATPase in the freeze lesion (FL) microgyrus model of developmental epileptogenesis to test the hypothesis that it is downregulated following neonatal cortical injury. FL and sham-operated rat brains were examined at postnatal day (P)7, P10, P14, P21-28 and P50-60 after placement of a transcranial freeze lesion at P0 or P1. Immunohistochemistry and in situ hybridization were used to assess the expression of the alpha3 isoform of Na(+),K(+)-ATPase (termed alpha3, or alpha3 subunit below) in neuropil and the perisomatic areas of pyramidal cells and parvalbumin-containing interneurons. There was a significant decrease (P<0.05) in alpha3 subunit immunoreactivity (IR) in the neuropil of FL cortical layer V of the P14 and P21-28 groups that extended up to 360 mum from the border of the microgyrus, an area that typically exhibits evoked epileptiform activity. Alpha-3 was decreased in the perisomatic area of pyramidal but not parvalbumin-containing cells in P21-28 FL animals. A reduction in alpha3 mRNA was observed in the neuropil of FL cortical layer V up to 1610 mum from the microgyral edge. The developmental time course for expression of the alpha3 subunit between P7 and P60 was examined in naive rat cortices and results showed that there was a significant increase in alpha3 IR between P7 and P10. The significant decreases in Na(+),K(+)-ATPase in the paramicrogyral cortex may contribute to epileptogenesis.

    View details for DOI 10.1016/j.neuroscience.2009.04.003

    View details for Web of Science ID 000267787500012

    View details for PubMedID 19362129

  • Epilepsy following cortical injury: Cellular and molecular mechanisms as targets for potential prophylaxis EPILEPSIA Prince, D. A., Parada, I., Scalise, K., Graber, K., Jin, X., Shen, F. 2009; 50: 30-40

    Abstract

    The sequelae of traumatic brain injury, including posttraumatic epilepsy, represent a major societal problem. Significant resources are required to develop a better understanding of the underlying pathophysiologic mechanisms as targets for potential prophylactic therapies. Posttraumatic epilepsy undoubtedly involves numerous pathogenic factors that develop more or less in parallel. We have highlighted two potential "prime movers": disinhibition and development of new functional excitatory connectivity, which occur in a number of animal models and some forms of epilepsy in humans. Previous experiments have shown that tetrodotoxin (TTX) applied to injured cortex during a critical period early after lesion placement can prevent epileptogenesis in the partial cortical ("undercut") model of posttraumatic epilepsy. Here we show that such treatment markedly attenuates histologic indices of axonal and terminal sprouting and presumably associated aberrant excitatory connectivity. A second finding in the undercut model is a decrease in spontaneous inhibitory events. Current experiments show that this is accompanied by regressive alterations in fast-spiking gamma-aminobutyric acid (GABA)ergic interneurons, including shrinkage of dendrites, marked decreases in axonal length, structural changes in inhibitory boutons, and loss of inhibitory synapses on pyramidal cells. Other data support the hypothesis that these anatomic abnormalities may result from loss of trophic support normally provided to interneurons by brain-derived neurotrophic factor (BDNF). Approaches that prevent these two pathophysiologic mechanisms may offer avenues for prophylaxis for posttraumatic epilepsy. However, major issues such as the role of these processes in functional recovery from injury and the timing of the critical period(s) for application of potential therapies in humans need to be resolved.

    View details for DOI 10.1111/j.1528-1167.2008.02008.x

    View details for Web of Science ID 000262827500006

    View details for PubMedID 19187292

    View details for PubMedCentralID PMC2710960

  • The Endocannabinoid 2-Arachidonoylglycerol Is Responsible for the Slow Self-Inhibition in Neocortical Interneurons JOURNAL OF NEUROSCIENCE Marinelli, S., Pacioni, S., Bisogno, T., Di Marzo, V., Prince, D. A., Huguenard, J. R., Bacci, A. 2008; 28 (50): 13532-13541

    Abstract

    In the CNS, endocannabinoids are identified mainly as two endogenous lipids: anandamide, the ethanolamide of arachidonic acid, and 2-arachidonoylglycerol (2-AG). Endocannabinoids are known to inhibit transmitter release from presynaptic terminals; however we have recently demonstrated that they are also involved in slow self-inhibition (SSI) of layer V low-threshold spiking (LTS) interneurons in rat somatosensory cortex. SSI is induced by repetitive firing in LTS cells, which can express either cholecystokinin or somatostatin. SSI is triggered by an endocannabinoid-dependent activation of a prolonged somatodendritic K(+) conductance and associated hyperpolarization in the same cell. The synthesis of both endocannabinoids is dependent on elevated [Ca(2+)](i) such as occurs during sustained neuronal activity. To establish whether 2-AG mediates autocrine LTS-SSI, we blocked its biosynthesis from phospholipase C (PLC) and diacylglycerol lipases (DAGLs). Current-clamp recordings from LTS interneurons in acute neocortical slices showed that inclusion of DAGL inhibitors in the whole-cell pipette prevented the long-lasting hyperpolarization triggered by LTS cell repetitive firing. Similarly, extracellular applications of a PLC inhibitor prevented SSI in LTS interneurons. Moreover, metabotropic glutamate receptor-dependent activation of PLC produced a long-lasting hyperpolarization which was prevented by the CB1 antagonist AM251, as well as by PLC and DAGL inhibitors. The loss of SSI in the presence of intracellular DAGL blockers confirms that endocannabinoid production occurs in the same interneuron undergoing the persistent hyperpolarization. Since DAGLs produce no endocannabinoid other than 2-AG, these results identify this compound as the autocrine mediator responsible for the postsynaptic slow self-inhibition of neocortical LTS interneurons.

    View details for DOI 10.1523/JNEUROSCI.0847-08.2008

    View details for Web of Science ID 000261601800018

    View details for PubMedID 19074027

  • SPONTANEOUS EPILEPTIFORM ACTIVITY AND ENHANCED EXCITATORY SYNAPTIC CONNECTIVITY IN C1Q KNOCK- OUT MICE 62nd Annual Meeting of the American-Epilepsy-Society/2nd Biennial North American Regional Epilepsy Congress Chu, Y., Jin, X., Parada, I., Stevens, B., Prince, D. A. WILEY-BLACKWELL. 2008: 476–476
  • Alterations in excitatory synaptic activation of neocortical fast-spiking interneurons in a model of posttraumatic epileptogenesis 61st Annual Meeting of the American-Epilepsy-Society Jin, X., Huguenard, J., Prince, D. WILEY-BLACKWELL. 2007: 120–120
  • Sick axons and epileptogenesis 61st Annual Meeting of the American-Epilepsy-Society Prince, D. A., McCormick, D. A., Gutierrez, R. WILEY-BLACKWELL. 2007: 409–409
  • Modulation of epileptiform activity by glutamine and system A transport in a model of post-traumatic epilepsy NEUROBIOLOGY OF DISEASE Tani, H., Bandrowski, A. E., Parada, I., Wynn, M., Huguenard, J. R., Prince, D. A., Reimer, R. J. 2007; 25 (2): 230-238

    Abstract

    Epileptic activity arises from an imbalance in excitatory and inhibitory synaptic transmission. To determine if alterations in the metabolism of glutamate, the primary excitatory neurotransmitter, might contribute to epilepsy we directly and indirectly modified levels of glutamine, an immediate precursor of synaptically released glutamate, in the rat neocortical undercut model of hyperexcitability and epilepsy. We show that slices from injured cortex take up glutamine more readily than control slices, and an increased expression of the system A transporters SNAT1 and SNAT2 likely underlies this difference. We also examined the effect of exogenous glutamine on evoked and spontaneous activity and found that addition of physiological concentrations of glutamine to perfusate of slices isolated from injured cortex increased the incidence and decreased the refractory period of epileptiform potentials. By contrast, exogenous glutamine increased the amplitude of evoked potentials in normal cortex, but did not induce epileptiform potentials. Addition of physiological concentrations of glutamine to perfusate of slices isolated from injured cortex greatly increased abnormal spontaneous activity in the form of events resembling spreading depression, again while having no effect on slices from normal cortex. Interestingly, similar spreading depression like events were noted in control slices at supraphysiological levels of glutamine. In the undercut cortex addition of methylaminoisobutyric acid (MeAIB), an inhibitor of the system A glutamine transporters attenuated all physiological effects of added glutamine suggesting that uptake through these transporters is required for the effect of glutamine. Our findings support a role for glutamine transport through SNAT1 and/or SNAT2 in the maintenance of abnormal activity in this in vitro model of epileptogenesis and suggest that system A transport and glutamine metabolism are potential targets for pharmacological intervention in seizures and epilepsy.

    View details for DOI 10.1016/j.nbd.2006.08.025

    View details for Web of Science ID 000243981400002

    View details for PubMedID 17070687

    View details for PubMedCentralID PMC1952182

  • Electrophysiological classification of somatostatin-positive interneurons in mouse sensorimotor cortex JOURNAL OF NEUROPHYSIOLOGY Halabisky, B., Shen, F., Huguenard, J. R., Prince, D. A. 2006; 96 (2): 834-845

    Abstract

    Classification of inhibitory interneurons is critical in determining their role in normal information processing and pathophysiological conditions such as epilepsy. Classification schemes have relied on morphological, physiological, biochemical, and molecular criteria; and clear correlations have been demonstrated between firing patterns and cellular markers such as neuropeptides and calcium-binding proteins. This molecular diversity has allowed generation of transgenic mouse strains in which GFP expression is linked to the expression of one of these markers and presumably a single subtype of neuron. In the GIN mouse (EGFP-expressing Inhibitory Neurons), a subpopulation of somatostatin-containing interneurons in the hippocampus and neocortex is labeled with enhanced green fluorescent protein (EGFP). To optimize the use of the GIN mouse, it is critical to know whether the population of somatostatin-EGFP-expressing interneurons is homogeneous. We performed unsupervised cluster analysis on 46 EGFP-expressing interneurons, based on data obtained from whole cell patch-clamp recordings. Cells were classified according to a number of electrophysiological variables related to spontaneous excitatory postsynaptic currents (sEPSCs), firing behavior, and intrinsic membrane properties. EGFP-expressing interneurons were heterogeneous and at least four subgroups could be distinguished. In addition, multiple discriminant analysis was applied to data collected during whole cell recordings to develop an algorithm for predicting the group membership of newly encountered EGFP-expressing interneurons. Our data are consistent with a heterogeneous population of neurons based on electrophysiological properties and indicate that EGFP expression in the GIN mouse is not restricted to a single class of somatostatin-positive interneuron.

    View details for DOI 10.1152/jn.01079.2005

    View details for Web of Science ID 000238974700033

    View details for PubMedID 16707715

  • Enhanced excitatory synaptic connectivity in layer V pyramidal neurons of chronically injured epileptogenic neocortex in rats JOURNAL OF NEUROSCIENCE Jin, X. M., Prince, D. A., Huguenard, J. R. 2006; 26 (18): 4891-4900

    Abstract

    Formation of new recurrent excitatory circuits after brain injuries has been hypothesized as a major factor contributing to epileptogenesis. Increases in total axonal length and the density of synaptic boutons are present in layer V pyramidal neurons of chronic partial isolations of rat neocortex, a model of posttraumatic epileptogenesis. To explore the functional consequences of these changes, we used laser-scanning photostimulation combined with whole-cell patch-clamp recording from neurons in layer V of somatosensory cortex to map changes in excitatory synaptic connectivity after injury. Coronal slices were submerged in artificial CSF (23 degrees C) containing 100 microM caged glutamate, APV (2-amino-5-phosphonovaleric acid), and high divalent cation concentration to block polysynaptic responses. Focal uncaging of glutamate, accomplished by switching a pulsed UV laser to give a 200-400 micros light stimulus, evoked single- or multiple-component composite EPSCs. In neurons of the partially isolated cortex, there were significant increases in the fraction of uncaging sites from which EPSCs could be evoked ("hot spots") and a decrease in the mean amplitude of individual elements in the composite EPSC. When plotted along the cortical depth, the changes in EPSCs took place mainly between 150 and 200 microm above and below the somata, suggesting a specific enhancement of recurrent excitatory connectivity among layer V pyramidal neurons of the undercut neocortex. These changes may shift the balance within cortical circuits toward increased synaptic excitation and contribute to epileptogenesis.

    View details for DOI 10.1523/JNEUROSCI.4361-05.2006

    View details for Web of Science ID 000237271700020

    View details for PubMedID 16672663

  • Barrel cortex microcircuits: Thalamocortical feedforward inhibition in spiny stellate cells is mediated by a small number of fast-spiking interneurons JOURNAL OF NEUROSCIENCE Sun, Q. Q., Huguenard, J. R., Prince, D. A. 2006; 26 (4): 1219-1230

    Abstract

    Inhibitory and excitatory neurons located in rodent barrel cortex are known to form functional circuits mediating vibrissal sensation. Excitatory neurons located in a single barrel greatly outnumber interneurons, and form extensive reciprocal excitatory synaptic contacts. Inhibitory and excitatory networks must interact to shape information ascending to cortex. The details of these interactions, however, have not been completely explored. Using paired intracellular recordings, we studied the properties of synaptic connections between spiny neurons (i.e., spiny stellate and pyramidal cells) and interneurons, as well as integration of thalamocortical (TC) input, in layer IV barrels of rat thalamocortical slices. Results show the following: (1) the strength of unitary excitatory connections of spiny neurons is similar among different targets; (2) although inhibition from regular-spiking nonpyramidal interneurons to spiny neurons is comparable in strength to excitatory connections, inhibition mediated by fast-spiking (FS) interneurons is 10 times more powerful; (3) TC EPSPs elicit reliable and precisely timed action potentials in FS neurons; and (4) a small number of FS neurons mediate thalamocortical feedforward inhibition in each spiny neuron and can powerfully shunt TC-mediated excitation. The ready activation of FS cells by TC inputs, coupled with powerful feedforward inhibition from these neurons, would profoundly influence sensory processing and constrain runaway excitation in vivo.

    View details for DOI 10.1523/JNEUROSCI.4727-04.2006

    View details for Web of Science ID 000234896200020

    View details for PubMedID 16436609

  • REORGANIZATION OF BARREL CIRCUITS LEADS TO THALAMICALLY-EVOKED CORTICAL EPILEPTIFORM ACTIVITY. Thalamus & related systems Sun, Q., Huguenard, J. R., Prince, D. A. 2005; 3 (4): 261-273

    Abstract

    We studied circuit activities in layer IV of rat somatosensory barrel cortex containing microgyri induced by neonatal freeze lesions. Structural abnormalities in GABAergic interneurons are present in the epileptogenic paramicrogyral area (PMG) and we therefore tested the hypothesis that decreased postsynaptic inhibition within barrel microcircuits occurs in the PMG and contributes to epileptogenesis when thalamocortical afferents are activated. In thalamocortical (TC) slices from naïve animals, single electrical stimuli within the thalamic ventrobasal (VB) nucleus evoked transient cortical multi-unit activity lasting 65±42 ms. Similar stimuli in TC slices from lesioned barrel cortex elicited prolonged 850 ±100 ms paroxysmal discharges that originated in the PMG and propagated laterally over several mm. Paroxysmal discharges were shortened in duration by ~70 % when APV was applied, and were totally abolished by CNQX. The cortical paroxysmal discharges did not evoke thalamic oscillations. Whole cell patch clamp recordings showed that there was a shift in the balance of TC evoked responses in the PMG that favored excitation over inhibition. Dual whole-cell recordings in layer IV of the PMG indicated that there was selective loss of inhibition from fast-spiking interneurons to spiny neurons in the barrel circuits that likely contributed to unconstrained cortical recurrent excitation with generation and spread of paroxysmal discharges.

    View details for PubMedID 18185849

  • Modulation of neocortical interneurons: extrinsic influences and exercises in self-control TRENDS IN NEUROSCIENCES Bacci, A., Huguenard, J. R., Prince, D. A. 2005; 28 (11): 602-610

    Abstract

    Neocortical GABAergic interneurons are a highly heterogeneous cell population that forms complex functional networks and has key roles in information processing within the cerebral cortex. Mechanisms that control the output of these cells are therefore crucial in regulating excitability within the neocortex during normal and pathophysiological activities. In addition to subtype-specific modulation of GABAergic cells by neurotransmitters released by afferents from subcortical nuclei, interneurons belonging to different classes are controlled by distinct self-modulatory mechanisms, each unique and powerful. In this article, we review the diverse responses of neocortical interneurons to extrinsic and intrinsic neuromodulators. We discuss how specificity of responses might differentially influence inhibition in somatodendritic compartments of pyramidal neurons and affect the balance of activities in neocortical circuits.

    View details for DOI 10.1016/j.tins.2005.08.007

    View details for Web of Science ID 000233213700006

    View details for PubMedID 16139371

  • Impaired Cl- extrusion in layer V pyramidal neurons of chronically injured epileptogenic neocortex JOURNAL OF NEUROPHYSIOLOGY Jin, X. M., Huguenard, J. R., Prince, D. A. 2005; 93 (4): 2117-2126

    Abstract

    In the mature brain, the K(+)/Cl- cotransporter KCC2 is important in maintaining low [Cl-]i, resulting in hyperpolarizing GABA responses. Decreases in KCC2 after neuronal injuries result in increases in [Cl-]i and enhanced neuronal excitability due to depolarizing GABA responses. We used the gramicidin perforated-patch technique to measure E(Cl) ( approximately E(GABA)) in layer V pyramidal neurons in slices of partially isolated sensorimotor cortex of adult rats to explore the potential functional consequence of KCC2 downregulation in chronically injured cortex. E(GABA) was measured by recording currents evoked with brief GABA puffs at various membrane potentials. There was no significant difference in E(Cl) between neurons in control and undercut animals (-71.2 +/- 2.6 and -71.8 +/- 2.8 mV, respectively). However, when loaded with Cl- by applying muscimol puffs at 0.2 Hz for 60 s, neurons in the undercut cortex had a significantly shorter time constant for the positive shift in E(Cl) during the Cl- loading phase (4.3 +/- 0.5 s for control and 2.2 +/- 0.4 s for undercut, P < 0.01). The positive shift in E(Cl) 3 s after the beginning of Cl- loading was also significantly larger in the undercut group than in the control, indicating that neurons in undercut cortex were less effective in maintaining low [Cl-]i during repetitive activation of GABA(A) receptors. Application of furosemide eliminated the difference between the control and undercut groups for both of these measures of [Cl-]i regulation. The results suggest an impairment in Cl- extrusion resulting from decreased KCC2 expression that may reduce the strength of GABAergic inhibition and contribute to epileptogenesis.

    View details for DOI 10.1152/jn.00728.2004

    View details for Web of Science ID 000227701600029

    View details for PubMedID 15774713

  • Excitatory and inhibitory postsynaptic currents in a rat model of epileptogenic microgyria JOURNAL OF NEUROPHYSIOLOGY Jacobs, K. M., Prince, D. A. 2005; 93 (2): 687-696

    Abstract

    Developmental cortical malformations are common in patients with intractable epilepsy; however, mechanisms contributing to this epileptogenesis are currently poorly understood. We previously characterized hyperexcitability in a rat model that mimics the histopathology of human 4-layered microgyria. Here we examined inhibitory and excitatory postsynaptic currents in this model to identify functional alterations that might contribute to epileptogenesis associated with microgyria. We recorded isolated whole cell excitatory postsynaptic currents and GABA(A) receptor-mediated inhibitory currents (EPSCs and IPSCs) from layer V pyramidal neurons in the region previously shown to be epileptogenic (paramicrogyral area) and in homotopic control cortex. Epileptiform-like activity could be evoked in 60% of paramicrogyral (PMG) cells by local stimulation. The peak conductance of both spontaneous and evoked IPSCs was significantly larger in all PMG cells compared with controls. This difference in amplitude was not present after blockade of ionotropic glutamatergic currents or for miniature (m)IPSCs, suggesting that it was due to the excitatory afferent activity driving inhibitory neurons. This conclusion was supported by the finding that glutamate receptor antagonist application resulted in a significantly greater reduction in spontaneous IPSC frequency in one PMG cell group (PMG(E)) compared with control cells. The frequency of both spontaneous and miniature EPSCs was significantly greater in all PMG cells, suggesting that pyramidal neurons adjacent to a microgyrus receive more excitatory input than do those in control cortex. These findings suggest that there is an increase in numbers of functional excitatory synapses on both interneurons and pyramidal cells in the PMG cortex perhaps due to hyperinnervation by cortical afferents originally destined for the microgyrus proper.

    View details for DOI 10.1152/jn.00288.2004

    View details for Web of Science ID 000226342000005

    View details for PubMedID 15385597

  • Cortical injury affects short-term plasticity of evoked excitatory synaptic currents JOURNAL OF NEUROPHYSIOLOGY Li, H. F., Bandrowski, A. E., Prince, D. A. 2005; 93 (1): 146-156

    Abstract

    The hypothesis that plastic changes in the efficacy of excitatory neurotransmission occur in areas of chronic cortical injury was tested by assessing short-term plasticity of evoked excitatory synaptic currents (EPSCs) in neurons of partially isolated neocortical islands (undercut cortex). Whole cell recordings were obtained from layer V pyramidal neurons of sensorimotor cortical slices prepared from P36-P43 control and undercut rats. AMPA/kainate receptor-mediated EPSCs elicited by stimuli delivered at 40 to 66.7 Hz exhibited more paired-pulse depression (PPD) in undercut cortex than control, the time constant of depression evoked by trains of 20- to 66.7-Hz stimuli was faster, and the steady-state amplitude of EPSCs reached after five to seven EPSCs was lower. An antagonist of the glutamate autoreceptor, group II mGluR, increased the steady-state amplitude of EPSCs from undercut but not control cortex, suggesting that activation of presynaptic receptors by released glutamate is more prominent in undercut cortex. In contrast, the GABA(B) receptor antagonist (2S)-3-[[(1S)-1-(3,4-dichlorophenyl)ethyl]amino-2-hydroxypropyl](phenylmethyl)phosphinic acid had no effect. Increasing [Ca(2+)](o) from 2 to 4 mM increased PPD, with a smaller effect in neurons of the undercut. The I-V relationship of AMPA/kainate receptor-mediated EPSCs was close to linear in both control and undercut neurons, and spermine had no significant effect on the EPSCs, suggesting that decreases in postsynaptic glutamate receptors containing the GluR2 subunit were not involved in the alterations in short-term plasticity. Results are compatible with an increase in the probability of transmitter release at excitatory synapses in undercut cortex due to functional changes in presynaptic terminals.

    View details for DOI 10.1152/jn.00665.2004

    View details for Web of Science ID 000225777900015

    View details for PubMedID 15342719

  • Antiepileptogenic treatment of undercut neocortex reduces expression of neuritin 59th Annual Meeting of the American-Epilepsy-Society/American-Clinical-Neurophysiology-Society Graber, K. D., Fontoura, P. P., Ho, P. P., Steinman, L., Prince, D. A. WILEY-BLACKWELL. 2005: 105–105
  • Increased layer vexcitatory connectivity in the neocortical undercut model of post-traumatic epilepsy 59th Annual Meeting of the American-Epilepsy-Society/American-Clinical-Neurophysiology-Society Jin, X. M., Huguenard, J. R., Prince, D. A. WILEY-BLACKWELL. 2005: 109–109
  • Long-lasting self-inhibition of neocortical interneurons mediated by endocannabinoids NATURE Bacci, A., Huguenard, J. R., Prince, D. A. 2004; 431 (7006): 312-316

    Abstract

    Neocortical GABA-containing interneurons form complex functional networks responsible for feedforward and feedback inhibition and for the generation of cortical oscillations associated with several behavioural functions. We previously reported that fast-spiking (FS), but not low-threshold-spiking (LTS), neocortical interneurons from rats generate a fast and precise self-inhibition mediated by inhibitory autaptic transmission. Here we show that LTS cells possess a different form of self-inhibition. LTS, but not FS, interneurons undergo a prominent hyperpolarization mediated by an increased K+-channel conductance. This self-induced inhibition lasts for many minutes, is dependent on an increase in intracellular [Ca2+] and is blocked by the cannabinoid receptor antagonist AM251, indicating that it is mediated by the autocrine release of endogenous cannabinoids. Endocannabinoid-mediated slow self-inhibition represents a powerful and long-lasting mechanism that alters the intrinsic excitability of LTS neurons, which selectively target the major site of excitatory connections onto pyramidal neurons; that is, their dendrites. Thus, modulation of LTS networks after their sustained firing will lead to long-lasting changes of glutamate-mediated synaptic strength in pyramidal neurons, with consequences during normal and pathophysiological cortical network activities.

    View details for DOI 10.1038/nature02913

    View details for Web of Science ID 000223864000042

    View details for PubMedID 15372034

  • A critical period for prevention of posttraumatic neocortical hyperexcitability in rats ANNALS OF NEUROLOGY Graber, K. D., Prince, D. A. 2004; 55 (6): 860-870

    Abstract

    Penetrating cortical trauma frequently results in delayed development of epilepsy. In the rat undercut model of neocortical posttraumatic hyperexcitability, suppression of neuronal activity by exposing the injured cortex to tetrodotoxin (TTX) in vivo for approximately 2 weeks prevents the expression of abnormal hypersynchronous discharges in neocortical slices. We examined the relationship between neuronal activity during the latent period after trauma and subsequent expression of hyperexcitability by varying the timing of TTX treatment. Partially isolated islands of rat sensorimotor cortex were treated with Elvax polymer containing TTX to suppress cortical activity and slices obtained for in vitro experiments 10 to 15 days later. TTX treatment was either started immediately after injury and discontinued after a variable number of days or delayed for a variable time after the lesion was placed. Immediate treatment lasting only 2 to 3 days and treatment delayed up to 3 days prevented hyperexcitability. Thus, there is a critical period for development of hyperexcitability in this model that depends on cortical activity. We propose that the hyperexcitability caused by partial cortical isolation may represent an early stage of posttraumatic epileptogenesis. A hypothetical cascade of events leading to subsequent pathophysiological activity is likely initiated at the time of injury but remains plastic during this critical period.

    View details for DOI 10.1002/ana.20124

    View details for Web of Science ID 000221716300013

    View details for PubMedID 15174021

  • Effects of preventive treatment on NARP expression in posttraumatic epileptogenesis 58th Annual Meeting of the American-Epilepsy-Society Graber, K. D., Fontoura, P. P., Ho, P. P., Steinman, L., Prince, D. A. WILEY-BLACKWELL. 2004: 18–18
  • Target-specific neuropeptide Y-ergic synaptic inhibition and its network consequences within the mammalian thalamus JOURNAL OF NEUROSCIENCE Sun, Q. Q., Baraban, S. C., Prince, D. A., Huguenard, J. R. 2003; 23 (29): 9639-9649

    Abstract

    Neuropeptides are commonly colocalized with classical neurotransmitters, yet there is little evidence for peptidergic neurotransmission in the mammalian CNS. We performed whole-cell patch-clamp recording from rodent thalamic brain slices and repetitively stimulated corticothalamic fibers to strongly activate NPY-containing GABAergic reticular thalamic (RT) neurons. This resulted in long-lasting (approximately 10 sec) feedforward slow IPSPs (sIPSPs) in RT cells, which were mimicked and blocked by NPY1 (Y1) receptor agonists and antagonists, respectively, and were present in wild-type mice but absent in NPY-/- mice. NPYergic sIPSPs were mediated via G-proteins and G-protein-activated, inwardly rectifying potassium channels, as evidenced by sensitivity to GDP-beta-S and 0.1 mm Ba2+. In rat RT neurons, NPYergic sIPSPs were also present but were surprisingly absent in the major synaptic targets of RT, thalamic relay neurons, where instead robust GABA(B) IPSPs occurred. In vitro oscillatory network responses in rat thalamus were suppressed and augmented by Y1 agonists and antagonists, respectively. These findings provide evidence for segregation of postsynaptic actions between two targets of RT cells and support a role for endogenously released NPY within RT in the regulation of oscillatory thalamic responses relevant to sleep and epilepsy.

    View details for Web of Science ID 000186107100018

    View details for PubMedID 14573544

  • Major differences in inhibitory synaptic transmission onto two neocortical interneuron subclasses JOURNAL OF NEUROSCIENCE Bacci, A., Rudolph, U., Huguenard, J. R., Prince, D. A. 2003; 23 (29): 9664-9674

    Abstract

    Locally projecting GABAergic interneurons are the major providers of inhibition in the neocortex and play a crucial role in several brain functions. Neocortical interneurons are connected via electrical and chemical synapses that may be crucial in modulating complex network oscillations. We investigated the properties of spontaneous and evoked IPSCs in two morphologically and physiologically identified interneuron subtypes, the fast-spiking (FS) and low threshold-spiking (LTS) cells in layer V of rodent sensorimotor cortex. We found that IPSCs recorded in FS cells were several orders of magnitude more frequent, larger in amplitude, and had faster kinetics than IPSCs recorded in LTS cells. GABA(A) receptor alpha- and beta-subunit selective modulators, zolpidem and loreclezole, had different effects on IPSCs in FS and LTS interneurons, suggesting differential expression of GABA(A) receptor subunit subtypes. These pharmacological data indicated that the alpha1 subunit subtype is poorly expressed by LTS cells but makes a large contribution to GABA(A) receptors on FS cells. This was confirmed by experiments performed in genetically modified mice in which the alpha1 subunit had been made insensitive to benzodiazepine-like agonists. These results suggest that differences in IPSC waveform are likely attributable to distinctive expression of GABA(A) receptor subunits in FS and LTS cells. The particular properties of GABAergic input on different interneuronal subtypes might have important consequences for generation and pacing of cortical rhythms underlying several brain functions. Moreover, selective pharmacological manipulation of distinct inhibitory circuits might allow regulation of pyramidal cell activities under specific physiological and pathophysiological conditions.

    View details for Web of Science ID 000186107100020

    View details for PubMedID 14573546

  • Vasoactive intestinal polypeptide and pituitary adenylate cyclase-activating polypeptide activate hyperpolarization activated cationic current and depolarize thalamocortical neurons in vitro JOURNAL OF NEUROSCIENCE Sun, Q. Q., Prince, D. A., Huguenard, J. R. 2003; 23 (7): 2751-2758

    Abstract

    Ascending pathways mediated by monoamine neurotransmitters regulate the firing mode of thalamocortical neurons and modulate the state of brain activity. We hypothesized that specific neuropeptides might have similar actions. The effects of vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) were tested on thalamocortical neurons using whole-cell patch-clamp techniques applied to visualized neurons in rat brain slices. VIP (2 microm) and PACAP (100 nm) reversibly depolarized thalamocortical neurons (7.8 +/- 0.6 mV; n = 16), reduced the membrane resistance by 33 +/- 3%, and could convert the firing mode from bursting to tonic. These effects on resting membrane potential and membrane resistance persisted in the presence of TTX. Morphologically diverse thalamocortical neurons located in widespread regions of thalamus were all depolarized by VIP and PACAP38. In voltage-clamp mode, we found that VIP and PACAP38 reversibly activated a hyperpolarization-activated cationic current (I(H)) in thalamocortical neurons and altered voltage- and time-dependent activation properties of the current. The effects of VIP on membrane conductance were abolished by the hyperpolarization-activated cyclic-nucleotide-gated channel (HCN)-specific antagonist ZD7288, showing that HCN channels are the major target of VIP modulation. The effects of VIP and PACAP38 on HCN channels were mediated by PAC(1) receptors and cAMP. The actions of PACAP-related peptides on thalamocortical neurons suggest an additional and novel endogenous neurophysiological pathway that may influence both normal and pathophysiological thalamocortical rhythm generation and have important behavioral effects on sensory processing and sleep-wake cycles.

    View details for Web of Science ID 000182107200028

    View details for PubMedID 12684461

  • Baseline glutamate levels affect group I and II mGluRs in layer V pyramidal neurons of rat sensorimotor cortex JOURNAL OF NEUROPHYSIOLOGY Bandrowski, A. E., Huguenard, J. R., Prince, D. A. 2003; 89 (3): 1308-1316

    Abstract

    Possible functional roles for glutamate that is detectable at low concentrations in the extracellular space of intact brain and brain slices have not been explored. To determine whether this endogenous glutamate acts on metabotropic glutamate receptors (mGluRs), we obtained whole cell recordings from layer V pyramidal neurons of rat sensorimotor cortical slices. Blockade of mGluRs with (+)-alpha-amino-4-carboxy-alpha-methyl-benzeacetic acid (MCPG, a general mGluR antagonist) increased the mean amplitude of spontaneous excitatory postsynaptic currents (sEPSCs), an effect attributable to a selective increase in the occurrence of large amplitude sEPSCs. 2S-2-amino-2-(1S,2S-2-carboxycyclopropyl-1-yl)-3-(xanth-9-yl)propanoic acid (LY341495, a group II antagonist) increased, but R(-)-1-amino-2,3-dihydro-1H-indene-1,5-dicarboxylic acid (AIDA) and (RS)-hexyl-HIBO (group I antagonists) decreased sEPSC amplitude, and (R,S)-alpha-cyclopropyl-4-phosphonophenylglycine (CPPG, a group III antagonist) did not change it. The change in sEPSCs elicited by MCPG, AIDA, and LY341495 was absent in tetrodotoxin, suggesting that it was action potential-dependent. The increase in sEPSCs persisted in GABA receptor antagonists, indicating that it was not due to effects on inhibitory interneurons. AIDA and (S)-3,5-dihydroxyphenylglycine (DHPG, a group I agonist) elicited positive and negative shifts in holding current, respectively. LY341495 and (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG-IV, a group II agonist) elicited negative and positive shifts in holding current, respectively. The AIDA and LY341495 elicited currents persisted in TTX. Finally, in current clamp, LY341495 depolarized cells by approximately 2 mV and increased the number of action potentials to a given depolarizing current pulse. Thus ambient levels of glutamate tonically activate mGluRs and regulate cortical excitability.

    View details for DOI 10.1152/jn.00644.2002

    View details for Web of Science ID 000181426400014

    View details for PubMedID 12626613

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