Gordon F. Buchanan - US grants

All mammals possess a circadian clock that governs daily oscillations with neural, hormonal, and metabolic functions for the organism with a near 24-h period. The suprachiasmatic nucleus (SCN) within the brain's hypothalamus houses this clock. The SCN has neural connections with various regions of the brain. Prominent among these connections are cholinergic projections from regions of the brain responsible for asleep and alerting, namely the basal forebrain (BF) and brainstem. A considerable body of work is available regarding intracellular signal transduction pathways within SCN. Pharmacological studies in vitro have implicated the M1-subtype of the muscarinic acetylcholine receptor (M1AChR) as the receptor mediating the effects of cholinergics on the circadian system. Recently, the International Union of Pharmacology Committee on Receptor Nomenclature and Drug Classification has questioned the specificity of the drugs used to implicate the M1AChR in the cholinergic signaling cascade. In lieu of specific pharmacology, other methods must be employed to confidently identify the receptor(s) mediating cholinergic circadian signaling. In this proposal, electrophysiological, behavioral and anatomical studies will be carried out in mice devoid of the M1AChR (M1KO). First, the B6129PF1/J mouse, a mouse of similar genetic background to the M1K0, will be tested for sensitivity to the cholinergic agonist, carbachol, both in vitro and in vivo. Second, the M1KO will be tested for decreased sensitivity to carbachol. Finally, double-label fluorescence confocal microscopy will be used to evaluate whether the cholinergic terminals within the SCN are juxtaposed to M1AChR-containing cells and to map their distribution.

DESCRIPTION (provided by applicant): This mentored clinical scientist research career development award is designed to advance the candidate toward a career as an independent scientist while investigating serotonergic mechanisms of cortical activation as they may pertain to sleep-wake regulation and epilepsy. Neurons in the medulla and midbrain of the brain that contain the neurotransmitter serotonin (5-HT) are central chemoreceptors that sense changes in blood carbon dioxide (CO2) concentration and pH. In the medulla, 5-HT neurons modulate breathing in response to changes in CO2 concentration, or pH. The reason for the chemosensitivity of midbrain 5-HT neurons was not known; however, we now have data to suggest it mediates an arousal response to elevated CO2 concentrations. 5-HT has also been implicated in epilepsy. Given the involvement with sleep-wake regulation, respiratory control and seizure susceptibility, 5-HT neuron dysfunction has been proposed to underlie the pathophysiology of sudden unexpected death in epilepsy (SUDEP), a devastating disease that results in premature death. To date there is a paucity of animal models to study SUDEP. This research proposal seeks to understand the role of 5-HT neurons, especially in their capacity as central chemoreceptors, in the regulation of sleep-wakefulness and breathing following a seizure. In doing this the specific 5-HT mechanisms in the arousal response to CO2 will also be elucidated. A variety of anatomical, surgical, electrophysiological and behavioral techniques will be employed in two different genetically altered mouse lines in which 5-HT neurons are either absent from birth or can be acutely silenced later in life. Completion of the proposed work will ideally lead to improved prophylactic measures in individuals at risk for SIDS and SUDEP and prevent untimely death. The candidate has recruited an outstanding group of mentors and advisors that will guide experimental design, execution of experiments, and analysis of results. For career development, this mentor and advisor team will continue to support the candidate as he develops an independent research program within the Department of Neurology at the Yale School of Medicine relevant to the regulation of sleep and wakefulness and the regulation of consciousness following seizures. Expertise gained in surgical, behavioral, and electrophysiological techniques through coursework, seminars and national conferences as part of this mentored award will carry the candidate into his career as an independent neuroscientist.

DESCRIPTION (provided by applicant): This mentored clinical scientist research career development award is designed to advance the candidate toward a career as an independent scientist while investigating serotonergic mechanisms of cortical activation as they may pertain to sleep-wake regulation and epilepsy. Neurons in the medulla and midbrain of the brain that contain the neurotransmitter serotonin (5-HT) are central chemoreceptors that sense changes in blood carbon dioxide (CO2) concentration and pH. In the medulla, 5-HT neurons modulate breathing in response to changes in CO2 concentration, or pH. The reason for the chemosensitivity of midbrain 5-HT neurons was not known; however, we now have data to suggest it mediates an arousal response to elevated CO2 concentrations. 5-HT has also been implicated in epilepsy. Given the involvement with sleep-wake regulation, respiratory control and seizure susceptibility, 5-HT neuron dysfunction has been proposed to underlie the pathophysiology of sudden unexpected death in epilepsy (SUDEP), a devastating disease that results in premature death. To date there is a paucity of animal models to study SUDEP. This research proposal seeks to understand the role of 5-HT neurons, especially in their capacity as central chemoreceptors, in the regulation of sleep-wakefulness and breathing following a seizure. In doing this the specific 5-HT mechanisms in the arousal response to CO2 will also be elucidated. A variety of anatomical, surgical, electrophysiological and behavioral techniques will be employed in two different genetically altered mouse lines in which 5-HT neurons are either absent from birth or can be acutely silenced later in life. Completion of the proposed work will ideally lead to improved prophylactic measures in individuals at risk for SIDS and SUDEP and prevent untimely death. The candidate has recruited an outstanding group of mentors and advisors that will guide experimental design, execution of experiments, and analysis of results. For career development, this mentor and advisor team will continue to support the candidate as he develops an independent research program within the Department of Neurology at the Yale School of Medicine relevant to the regulation of sleep and wakefulness and the regulation of consciousness following seizures. Expertise gained in surgical, behavioral, and electrophysiological techniques through coursework, seminars and national conferences as part of this mentored award will carry the candidate into his career as an independent neuroscientist.

? DESCRIPTION (provided by applicant): Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death in patients with refractory epilepsy. The majority of SUDEP cases occur at night, during sleep, but why this is the case in unclear. It has been proposed that a portion of these cases may be due to lack of adequate supervision during the nighttime and relayed resuscitation efforts following a seizure. Recent evidence suggests this is not the whole story. There are a number of physiologic changes that occur during sleep that may make sleep relatively intolerant to the additional physiologic insult of a seizure. Seizure-induced impairment of respiratory, cardiac and arousal mechanisms have all been implicated in SUDEP. All of these are subject to sleep state-dependent regulation. A large body of evidence suggests that abnormalities in signaling of the neurotransmitter serotonin are important in SUDEP. Serotonin is also regulated in a sleep state-dependent manner, and is involved in the regulation of breathing, cardiac activity, and sleep and wakefulness, and can modulate seizures. The primary goal of this proposal is to understand how seizures that occur during sleep become fatal. In pursuing this goal we will test the overarching hypothesis that serotonin is involved in regulating the state-dependence of seizure-induced death. In Aim 1 we will determine how seizures that occur during sleep dysregulate respiratory function. In Aim 2 we will determine how seizures that occur during sleep dysregulate arousal mechanisms. Finally, in Aim 3 we will determine how REM sleep is protective against seizures. Completion of these aims will provide an understanding of how seizures that occur during sleep could be fatal, and some of the findings could be directly translatable to the clinic to aid in identification of persons at risk for SUDEP and in implementation of novel prophylactic strategies. This work will additionally lay the groundwork for future projects delving deeper into these mechanisms.