Honors & Awards

  • Philip Wrightson Postdoctoral Fellowship, New Zealand Neurological Foundation (2017/2018)
  • Giract Ph.D. Flavor Research Bursary, Giract (2014)
  • University of Otago Postgraduate Publishing Bursary, University of Otago (2012)
  • University of Otago Summer Research Scholarship, University of Otago (2010)
  • University of Otago Alumni Scholarship, University of Otago Alumni Association (2008)

Professional Education

  • Doctor of Philosophy, University of Potsdam (2017)
  • Master of Science, University Of Otago (2013)
  • Bachelor of Arts, University Of Otago (2011)


All Publications

  • Tastant-evoked Arc expression in the nucleus of the solitary tract and nodose/petrosal ganglion of the mouse is specific for bitter compounds. Chemical senses Töle, J., Stolzenburg, A., Tyree, S. M., Stähler, F., Meyerhof, W. 2018


    Despite long and intense research, some fundamental questions regarding representation of taste information in the brain still remain unanswered. This might in part be due to shortcomings of the established methods that limit the researcher either to thorough characterization of few elements or analyze the response of the entirety of neurons to only one stimulus. To overcome these restrictions, we evaluate the use of the immediate early gene Arc as a neuronal activity marker in the early neural structures of the taste pathway, the nodose/petrosal ganglion (NPG) and the nucleus of the solitary tract (NTS). Responses of NPG and NTS neurons were limited to substances that taste bitter to humans and are avoided by mice. Arc expressing cells were concentrated in the rostromedial part of the dorsal NTS suggesting a role in gustatory processing. The use of Arc as a neuronal activity marker has several advantages, primarily the possibility to analyze the response of large numbers of neurons while using more than one stimulus makes Arc an interesting new tool for research in the early stages of taste processing.

    View details for DOI 10.1093/chemse/bjy017

    View details for PubMedID 29514200

  • Optogenetic Investigation of Arousal Circuits. International journal of molecular sciences Tyree, S. M., de Lecea, L. 2017; 18 (8)


    Modulation between sleep and wake states is controlled by a number of heterogeneous neuron populations. Due to the topological proximity and genetic co-localization of the neurons underlying sleep-wake state modulation optogenetic methods offer a significant improvement in the ability to benefit from both the precision of genetic targeting and millisecond temporal control. Beginning with an overview of the neuron populations mediating arousal, this review outlines the progress that has been made in the investigation of arousal circuits since the incorporation of optogenetic techniques and the first in vivo application of optogenetic stimulation in hypocretin neurons in the lateral hypothalamus. This overview is followed by a discussion of the future progress that can be made by incorporating more recent technological developments into the research of neural circuits.

    View details for PubMedID 28809797

  • Lateral Hypothalamic Control of the Ventral Tegmental Area: Reward Evaluation and the Driving of Motivated Behavior. Frontiers in systems neuroscience Tyree, S. M., de Lecea, L. 2017; 11: 50


    The lateral hypothalamus (LH) plays an important role in many motivated behaviors, sleep-wake states, food intake, drug-seeking, energy balance, etc. It is also home to a heterogeneous population of neurons that express and co-express multiple neuropeptides including hypocretin (Hcrt), melanin-concentrating hormone (MCH), cocaine- and amphetamine-regulated transcript (CART) and neurotensin (NT). These neurons project widely throughout the brain to areas such as the locus coeruleus, the bed nucleus of the stria terminalis, the amygdala and the ventral tegmental area (VTA). Lateral hypothalamic projections to the VTA are believed to be important for driving behavior due to the involvement of dopaminergic reward circuitry. The purpose of this article is to review current knowledge regarding the lateral hypothalamic connections to the VTA and the role they play in driving these behaviors.

    View details for DOI 10.3389/fnsys.2017.00050

    View details for PubMedID 28729827

    View details for PubMedCentralID PMC5498520

  • Anxiolytic-like effects of leptin on fixed interval responding PHARMACOLOGY BIOCHEMISTRY AND BEHAVIOR Tyree, S. M., Munn, R. G., McNaughton, N. 2016; 148: 15-20


    Leptin has been shown to affect energy homeostasis, learning and memory, and some models of anxiolytic action. However, leptin has produced inconsistent results in previous non-operant behavioural tests of anxiety. Here, we test the anxiolytic potential of leptin in an operant paradigm that has produced positive results across all classes of anxiolytic so far tested. Rats were tested in the Fixed Interval 60 Seconds (FI60) task following administration of 0/0.5/1.0mg/kg (i.p.) leptin or an active anxiolytic control of 5 mg/kg (i.p.) chlordiazepoxide (CDP). By the end of the 14 days of testing in the FI60 task, 0.5mg/kg leptin released suppressed responding in a manner similar to CDP, and 1.0mg/kg leptin produced a relative depression in responding, a similar outcome pattern to previously tested 5HT-agonist anxiolytics. This suggests that leptin behaves similarly to established serotonergic anxiolytics such as buspirone and fluoxetine; with the delay in development of effect during testing, and the inverted-U dose-response curve explaining the inconsistent behaviour of leptin in behavioural tests of anxiety, as this type of pattern is common to serotonergic anxiolytics.

    View details for DOI 10.1016/j.pbb.2016.05.005

    View details for Web of Science ID 000382347800003

    View details for PubMedID 27180106

  • The frequency of hippocampal theta rhythm is modulated on a circadian period and is entrained by food availability FRONTIERS IN BEHAVIORAL NEUROSCIENCE Munn, R. G., Tyree, S. M., McNaughton, N., Bilkey, D. K. 2015; 9


    The hippocampal formation plays a critical role in the generation of episodic memory. While the encoding of the spatial and contextual components of memory have been extensively studied, how the hippocampus encodes temporal information, especially at long time intervals, is less well understood. The activity of place cells in hippocampus has previously been shown to be modulated at a circadian time-scale, entrained by a behavioral stimulus, but not entrained by light. The experimental procedures used in the previous study of this phenomenon, however, necessarily conflated two alternative entraining stimuli, the exposure to the recording environment and the availability of food, making it impossible to distinguish between these possibilities. Here we demonstrate that the frequency of theta-band hippocampal EEG varies with a circadian period in freely moving animals and that this periodicity mirrors changes in the firing rate of hippocampal neurons. Theta activity serves, therefore, as a proxy of circadian-modulated hippocampal neuronal activity. We then demonstrate that the frequency of hippocampal theta driven by stimulation of the reticular formation also varies with a circadian period. Because this effect can be observed without having to feed the animal to encourage movement we were able to identify what stimulus entrains the circadian oscillation. We show that with reticular-activated recordings started at various times of the day the frequency of theta varies quasi-sinusoidally with a 25 h period and phase-aligned when referenced to the animal's regular feeding time, but not the recording start time. Furthermore, we show that theta frequency consistently varied with a circadian period when the data obtained from repeated recordings started at various times of the day were referenced to the start of food availability in the recording chamber. This pattern did not occur when data were referenced to the start of the recording session or to the actual time of day when this was not also related to feeding time. This double dissociation demonstrates that hippocampal theta is modulated with a circadian timescale, and that this modulation is strongly entrained by food. One interpretation of this finding is that the hippocampus is responsive to a food entrainable oscillator (FEO) that might modulate foraging behavior over circadian periods.

    View details for DOI 10.3389/fnbeh.2015.00061

    View details for Web of Science ID 000352270900001

    View details for PubMedID 25814943

    View details for PubMedCentralID PMC4356069