0076 The Role of Preoptic Area GABAergic Axonal Projections to Tuberomammillary Nucleus in Sleep Homeostasis

Abstract

Introduction Sleep deprivation has profound widespread physiological effects including cognitive impairment, compromised immune system function and increased risk of cardiovascular disease. The preoptic area (POA) of the hypothalamus contains sleep-active GABAergic neurons that respond to sleep homeostasis. We have shown that activation of POA GABAergic axons innervating the tuberomammillary nucleus (TMN, GABAergicPOA ->TMN) are critical for sleep regulation but it is unknown if these projections modulate sleep homeostasis. Methods To monitor in vivo neural activity of GABAergicPOA ->TMN projection neurons during sleep deprivation and rebound, fiber photometry was used. GAD2-Cre mice (n=6) were injected with AAV-DIO-GCaMP6S into the POA and an optic fiber was implanted into the TMN. An electroencephalogram (EEG) and electromyography (EMG) implant was mounted upon the skull to identify brain states. Calcium activity was measured for six hours starting at ZT4. Each mouse was recorded for three days to establish baseline sleep calcium activity with at least two days between sessions. During sleep deprivation sessions, an experimenter sleep deprived each mouse starting at ZT0 for six hours by gently brushing the animal with a small paintbrush to maintain wakefulness and minimize the stress to the animal. Results During baseline sleep recordings, GABAergicPOA ->TMN projection neurons are most active during sleep (NREM and REM) which is maintained until wake onset. As sleep pressure increases, GABAergicPOA ->TMN projection neurons display gradual increase in neural activity compared to time-matched points during baseline sleep recordings. Once mice were permitted to enter sleep rebound, GABAergicPOA ->TMN projection neurons gradually displayed decreased activity as sleep pressure eased. Conclusion GABAergicPOA ->TMN projection neurons show a strong increase in activity to drive homeostatic sleep need during periods of increased sleep pressure but subside once this pressure is reduced. Support This work is supported by NIH grant R01-NS-110865.