Grant: Discovery Grants Program - Individual

Sleep is critical for good health, cognitive performance, and well-being, and much is known about how the brain, in particular its principal cells called neurons control sleep and wake states. However, the brain contains other cells and recent research indicates that astrocytes, formerly considered "housekeeping" cells, are in fact important partners of neurons for various brain functions and behaviours. Yet, little is known about how astrocytes contribute to sleep/wake regulation. One key role of astrocytes is to modulate the "synapse", the site of communication between neurons. We recently found that sleep deprivation (SD, 6h; mimics prolonged wake) affects the way astrocytes modulate, in a cell type-specific matter, signal transmission at synapses to two major neuronal groups: wake-promoting orexin (ORX) and sleep-promoting melanin-concentrating hormone neurons. This occurs through modulation of astrocytic transporters that clear synaptically-released glutamate or GABA. In the case of ORX neurons, this plasticity would inhibit ORX neurons, which would promote the transition to sleep. We further found that this plasticity is a result of physical withdrawal of astrocytic processes from synapses. We posit that structural remodeling of astrocytic processes at synapses may be a cellular mechanism for sleep regulation according to sleep need. To advance further on these exciting recent findings, we will investigate the following three key questions in the next five years, using electron microscopy (Q1), confocal microscopy (Q1,3), electrophysiology (Q2) and sleep/wake EEG/EMG recordings (Q3) in rodents: 1)Does the sleep history-dependent astrocytic structural remodeling occur at both excitatory (glutamatergic) and inhibitory (GABAergic) synapses to ORX neurons? While sleep history-dependent structural remodeling of perisynaptic astrocytes is intriguing, it is important to know whether this remodeling occurs at both excitatory and inhibitory synapses to ORX neurons. 2)Does the reduction in GABA transporter apposition with ORX neurons observed after SD enhance inhibitory transmission to ORX neurons? Greater inhibitory transmission to ORX neurons (wake-active) would promote transition to sleep. We will use patch-clamp recordings from ORX neurons in slices from animals after SD or Rest. 3)Does deletion of connexin 30 (Cx30) compromise astrocytic transporter apposition plasticity in ORX and other key sleep/wake-neurons, and impair sleep and the ability to recover lost sleep after SD? Cx30 is known to regulate astrocytic synapse invasion and its levels are decreased in chronic insomnia. We will use Cx30 KO and WT mice to investigate these questions. Collectively, we expect that our research program will generate unique, original and important information on the role of astrocytes in modulating neuronal communications in the brain to regulate sleep according to sleep need. This will advance sleep neurobiology and neuroscience in general.