Doctor of Philosophy, University of Calgary (2017)
Bachelor of Science, University of Waterloo (2011)
I aim to better understand hippocampal network function in both physiology and epilepsy using in vivo imaging, optogenetics, and electrophysiology. I am currently addressing two main research questions: (1) what is the neurobiological basis of postictal amnesia? and (2) why do certain seizures spread to cause convulsions and others remain focal?
Seizures are often followed by sensory, cognitive or motor impairments during the postictal phase that show striking similarity to transient hypoxic/ischemic attacks. Here we show that seizures result in a severe hypoxic attack confined to the postictal period. We measured brain oxygenation in localized areas from freely-moving rodents and discovered a severe hypoxic event (pO2 < 10 mmHg) after the termination of seizures. This event lasted over an hour, is mediated by hypoperfusion, generalizes to people with epilepsy, and is attenuated by inhibiting cyclooxygenase-2 or L-type calcium channels. Using inhibitors of these targets we separated the seizure from the resulting severe hypoxia and show that structure specific postictal memory and behavioral impairments are the consequence of this severe hypoperfusion/hypoxic event. Thus, epilepsy is much more than a disease hallmarked by seizures, since the occurrence of postictal hypoperfusion/hypoxia results in a separate set of neurological consequences that are currently not being treated and are preventable.
View details for DOI 10.7554/eLife.19352
View details for Web of Science ID 000390850800001
View details for PubMedID 27874832
View details for PubMedCentralID PMC5154758
The present study tested whether HCN channels contribute to the organization of motor cortex and to skilled motor behaviour during a forelimb reaching task. Experimental reductions in HCN channel signalling increase the representation of complex multiple forelimb movements in motor cortex as assessed by intracortical microstimulation. Global HCN1KO mice exhibit reduced reaching accuracy and atypical movements during a single-pellet reaching task relative to wild-type controls. Acute pharmacological inhibition of HCN channels in forelimb motor cortex decreases reaching accuracy and increases atypical movements during forelimb reaching.The mechanisms by which distinct movements of a forelimb are generated from the same area of motor cortex have remained elusive. Here we examined a role for HCN channels, given their ability to alter synaptic integration, in the expression of forelimb movement responses during intracortical microstimulation (ICMS) and movements of the forelimb on a skilled reaching task. We used short-duration high-resolution ICMS to evoke forelimb movements following pharmacological (ZD7288), experimental (electrically induced cortical seizures) or genetic approaches that we confirmed with whole-cell patch clamp to substantially reduce Ih current. We observed significant increases in the number of multiple movement responses evoked at single sites in motor maps to all three experimental manipulations in rats or mice. Global HCN1 knockout mice were less successful and exhibited atypical movements on a skilled-motor learning task relative to wild-type controls. Furthermore, in reaching-proficient rats, reaching accuracy was reduced and forelimb movements were altered during infusion of ZD7288 within motor cortex. Thus, HCN channels play a critical role in the separation of overlapping movement responses and allow for successful reaching behaviours. These data provide a novel mechanism for the encoding of multiple movement responses within shared networks of motor cortex. This mechanism supports a viewpoint of primary motor cortex as a site of dynamic integration for behavioural output.
View details for DOI 10.1113/JP273068
View details for Web of Science ID 000392021800020
View details for PubMedID 27568501
View details for PubMedCentralID PMC5199725
Epilepsy is commonly associated with a number of neurodegenerative and pathological alterations in those areas of the brain that are involved in repeated electrographic seizures. These most prominently include neuron loss and an increase in astrocyte number and size but may also include enhanced blood-brain barrier permeability, the formation of new capillaries, axonal sprouting, and central inflammation. In animal models in which seizures are either repeatedly elicited or are self-generated, a similar set of neurodegenerative and pathological alterations in brain anatomy are observed. The primary causal agent responsible for these alterations may be the cascade of events that follow a seizure and lead to an hypoperfusion/hypoxic episode. While epilepsy has long and correctly been considered an electrical disorder, the vascular system likely plays an important causal role in the neurodegeneration and pathology that occur as a consequence of repeated seizures.
View details for DOI 10.1007/978-3-319-57193-5_12
View details for PubMedID 28674987
A recent article by Farrell et al. characterizes the phenomenon, mechanisms, and treatment of a local and severe hypoperfusion/hypoxia event that occurs in brain regions following a focal seizure. Given the well-established role of cerebral ischemia/hypoxia in brain damage and behavioral dysfunction in other clinical settings (e.g., stroke, cerebral vasospasm), we put forward a new theory: postictal hypoperfusion/hypoxia is responsible for the negative consequences associated with seizures. Fortunately, inhibition of two separate molecular targets, cyclooxygenase-2 (COX-2) and l-type calcium channels, can prevent the expression of postictal hypoperfusion/hypoxia. These inhibitors are important experimental tools used to separate the seizure from the resulting hypoperfusion/hypoxia and can allow researchers to address the contribution of this phenomenon to negative outcomes associated with seizures. Herein we address the implications of this postictal stroke-like event in acute behavioral dysfunction (e.g., Todd's paresis) and sudden unexpected death in epilepsy (SUDEP). Moreover, anatomic alterations such as increased blood-brain barrier permeability, glial activation, central inflammation, and neuronal loss could also be a consequence of repeated hypoperfusion/hypoxic events and, in turn, underlie chronic interictal cognitive and behavioral comorbidities (e.g., memory deficits, anxiety, depression, and psychosis) and exacerbate epileptogenesis. Thus these seemingly disparate and clinically important observations may share a common point of origin: postictal hypoperfusion/hypoxia.
View details for DOI 10.1111/epi.13827
View details for PubMedID 28632329