Neuronal Circuit Controlling Sleep-Promoting Ventrolateral Preoptic Neurons

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Project Summary/Abstract Sleep is an active process requiring the participation of delimited nodes of sleep-promoting cell populations. Work over the last twenty years has demonstrated that galanin expressing neurons in the ventrolateral preoptic (VLPOGal) neurons are necessary for normal sleep and cortical slow wave activity. There remain however several fundamental gaps in our understanding of the cellular and synaptic basis by which VLPOGal neurons are regulated. One highly influential circuit model for behavioral sleep-wake control is the `flip-flop' model of sleep-state switching, which proposes that sleep-wake transitions are regulated by a reciprocal inhibition between sleep-promoting VLPOGal neurons and monoaminergic and cholinergic wake-promoting nodes of the forebrain and brainstem. The findings that reciprocal anatomical connections exist between the VLPO and monoamine and cholinergic neurons and that these cell groups exhibit, respectively, sleep- and wake-active firing profiles have provided general support for the model. However, the VLPO receives afferent inputs from many other sources including non-cholinergic and non-monoaminergic neurons directly involved in sleep and wake regulation. We have recently found that activation of GABAergic neurons of the lateral hypothalamus potently promotes arousal by directly inhibiting VLPOGal neurons. Here we seek to extend this finding by identifying other potential synaptic drives that control arousal levels, including both long-range and local synaptic drives. To this end, while it has been appreciated for some time that VLPOGal neurons are under local synaptic control, the details of this intra-VLPO circuit remains largely uncharacterized. We have found that VLPOGal neurons are directly inhibited by a group of local GABAergic neurons. We propose that this local GABAergic circuit serves as common entry node through which afferent wake- and sleep-promoting pathways control VLPOGal neurons, with the specific hypotheses that this occurs by 1) direct and feedforward inhibition to produce arousal and 2) disinhibition of VLPOGal neurons to produce sleep. The current proposal thus seeks to identify, first in vitro and then in vivo, the long-range afferent inputs that directly or indirectly regulate VLPOGal neurons to drive behavioral and cortical arousal via the local GABAergic network. To do so, we will first employ in Specific Aims 1 in vitro circuit mapping and focal deletion of GABAergic transmission in VLPO neurons to determine the necessity of the local GABAergic circuit for the control of VLPOGal neurons. In Specific Aim 2 we will identify with in vitro recordings the postsynaptic neurons in VLPO that are targeted by wake- and sleep-promoting inputs. Finally, in Specific Aim 3 we will use in vivo optogenetics to test whether the afferent inputs to the VLPO first identified in vitro slices are necessary to produce sleep and wake behavioral changes and fiber photometry to examine the state-dependent activity of these afferents to VLPO. Given the large knowledge gap this proposal seeks to fill, we expect results from this collaborative work to provide important and novel insights into the brain circuitry supporting sleep and wake regulation.