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. Anatomical evidence and our data indicate that mesopontine cholinergic neurons are important targets of these peptides. This proposal focuses on identifying the mechanisms by which Hcrt/Orx acts upon mesopontine cholinergic neurons and associated sleep-related neurons. We will investigate the general hypothesis that Hcrt/Orx peptides regulate both the short-term and long-term excitability of sleep-related neurons. To do so we will use whole-cell recording and calcium imaging methods in brain slices obtained from control mice and mice lacking the two known orexin receptors. We will address this hypothesis by 1) characterizing the ionic currents responsible for the post-synaptic excitatory actions of Hcrt/Orx peptides; 2) Identifying the sources and consequences of intracellular [Ca2+] changes produced by Hcrt/Orx peptides; 3) Identifying the specific roles of each orexin receptor by utilizing single and double receptor knockout mice and 4) Investigating possible alterations in neuron excitability in the mouse double orexin receptor knockout model of narcolepsy. Collectively, these results will advance the understanding of the molecular and cellular mechanisms underlying sleep regulation and its pathology.
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