Project Summary/Abstract
In this proposal, we make use of optogenetic and chemogenetic tools, in vivo calcium
imaging, RNA-seq, viral-based circuit tracing, and genetic targeting techniques to dissect the
neural circuits that control sleep behavior in the mammalian brain. At a fundamental level, the
work presented in this research proposal may provide valuable information for developing
new treatments for various human sleep disorders, such as insomnia.
Decades of studies have revealed neuromodulatory circuits as key regulators of sleep and
wakefulness. However, most of these studies focus on the arousal system. Sleep-promoting
neurons are theoretically required for the initiation and maintenance of sleep states based on
the flip-flop model of wake-sleep switching, in which sleep-promoting neurons are mutually
inhibitory with wake-promoting neurons. Previous studies have identified several brain
structures that promote non-rapid eye movement (or NREM) sleep, but whether these
structures are involved in the initiation or the maintenance remains largely unknown. In this
research project, we will primarily focus on neural control of sleep initiation, i.e. the transition
from wakefulness to sleep – under physiological conditions, always to NREM sleep. We
aim to decipher the circuit mechanisms underlying the wake-sleep transition.
In pilot studies, we have identified a novel population of glutamatergic neurons in
the ventrolateral medulla (VLM) that project to the preoptic area (POA), a prominent sleep
center. We present preliminary data showing that these VLM neurons are activated during
wake-sleep transitions and optogenetic activation of these neurons induces long-lasting
NREM sleep in awake mice. These results lead to our working hypothesis: VLM
glutamatergic neurons induce the transition from wakefulness to NREM sleep, which
subsequently activate their downstream targets to maintain NREM sleep. In Aim 1, we will
activate and inactivate VLM glutamatergic neurons and examine the sufficiency and necessity
of their activity in the wake-sleep transition. In Aim2, we will perform microendoscopic calcium
imaging in VLM glutamatergic neurons and examine their activity during sleep. Then, we will
use single-cell RNA-seq to identify genetic markers of sleep-active VLM glutamatergic
neurons for further in vivo experiments. In Aim 3, we will use viral-based circuit tracing to
characterize the inputs and outputs of VLM neurons and examine their function in sleep
regulation. Together, the results obtained from this proposal will expand our understanding of
the neural basis of sleep behavior.