Pontine circuitry regulating REM sleep and atonia

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Description (provided by applicant): Rapid eye movement (REM) sleep is a behavioral state characterized by activation of the cortical and hippocampal EEG, rapid eye movements and muscle atonia. While some progress has been made in recent years in the effort to delineate 1) the locus of the pontine switching circuitry for REM sleep, 2) the neurotransmitters regulating REM phenomenon, i.e., muscle atonia, activation of the cortical and hippocampal EEG, and 3) how dysfunction of this circuitry may form the neuropathologic basis of REM sleep behavior disorder, major gaps remain in our knowledge. Recent work by our laboratory has revealed the presence of mutually inhibitory REM-off and REM-on areas in the mesopontine tegmentum that may form the neuroanatomical basis of the switching circuitry for REM sleep. These findings, which form the basis of the present research plan, posit a REM switching circuitry model that is analogous to an electronic 'flip-flop' switch. In this flip-flop switch arrangement, GABAergic REM-on neurons (located in the sublateraldorsal tegmental nucleus (SLD)) inhibit GABAergic REM-off neurons (located in the ventrolateral periaqueductal gray matter (vlPAG) and lateral pontine tegmentum (LPT)) and vice versa. Inside this pontine brainstem "switch" the REM-on area contains two populations of glutamatergic neurons, the first of which projects to the basal forebrain and regulates EEG components of REM sleep and the second which projects to the ventromedial medulla and spinal cord and regulates atonia during REM sleep. To demonstrate the critical role of glutamatergic SLD neurons in producing REM without atonia, we will selectively eliminate glutamatergic neurotransmission in the SLD by stereotaxically injecting an adeno-associated virus containing the gene for Cre recombinase (AAV-Cre) into the SLD of conditional knock-out mice with lox-P modified alleles of the vesicular glutamate transporter 2 (VGLUT2) genes. We will similarly eliminate GABAergic neurotransmission in the SLD and LPT by stereotaxically injecting AAV-Cre into mice with lox-P modified alleles of the vesicular GABA transporter (VGAT). Finally, we will examine the role of the ventromedial medulla in REM atonia by combining injections of orexin-saporin into rats and AAV-Cre injections into VGAT and VGLUT2 mice. Findings from the present proposal will provide a context for understanding the pathophysiologic mechanisms and etiological bases for a variety of sleep disorders, including REM sleep behavior disorder.