Chronic or intermittent sleep disorders such as narcolepsy, sleep apnea, and insomnia afflict nearly 40 million people in the United States. Yet the neural mechanisms controlling both normal sleep and its pathologies remain poorly understood. Considerable evidence indicates that mesopontine cholinergic neurons are critical for this control and that their disregulation is involved in narcolepsy, Parkinson's disease, supranuclear palsy and depression. The long term goal of this project is to understand the synaptic and non- synaptic mechanisms regulating activity of mesopontine cholinergic neurons. Recent compelling evidence indicates that disruption of the novel Hypocretin/Orexin (Hcrt/Orx) peptide system results in narcolepsy - a sleep disorder characterized by excessive daytime sleepiness, sleep fragmentation and the intrusion of rapid eye movement sleep behaviors into wakefulness. Building on the finding from the last funding period, which showed that mesopontine cholinergic neurons are important targets of these peptides, we will continue to investigate the general hypothesis that Hcrt/Orx peptides regulate both the short-term and long-term excitability of these neurons and that loss of Hcrt/Orx signaling upregulates the cholinergic phenotype of MPCh neurons and thereby contributes to the expression of cataplexy. To do so we will 1) continue to identify the ion channels activated by Hcrt/Orx and investigate their impact on the excitability of MPCh neurons;2) investigate the microsircuitry within the LOT to determine if functionaly related subsets of cholinergic neurons are differentially modulated by Hcrt/Orx and 3) determine if the upregulation of the enzymes responsible for cholinergic transmission following the loss of Hcrt/Orx signalling contributes to cataplexy. These experiments will use whole-cell patch clamp recording and calcium imaging methods in brain slices, tract tracing, tissue biochemistry, a novel extracellular probe to measure Ach release and behavioral pharmacology in control mice and mice lacking the two known orexin receptors to investigate these issues. Collectively, these results will advance the understanding of the molecular and cellular mechanisms underlying sleep regulation and its pathology.
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