In our daily life, we are exposed to uncontrollable and stressful events that disrupt our sleep. However, the underlying neural mechanisms deteriorating the quality of non-rapid eye movement sleep (NREMs) and REM sleep are largely unknown. Here, we show in mice that acute psychosocial stress disrupts sleep by increasing brief arousals (microarousals [MAs]), reducing sleep spindles, and impairing infraslow oscillations in the spindle band of the electroencephalogram during NREMs, while reducing REMs. This poor sleep quality was reflected in an increased number of calcium transients in the activity of noradrenergic (NE) neurons in the locus coeruleus (LC) during NREMs. Opto- and chemogenetic LC-NE activation in naïve mice is sufficient to change the sleep microarchitecture similar to stress. Conversely, chemogenetically inhibiting LC-NE neurons reduced MAs during NREMs and normalized their number after stress. Specifically inhibiting LC-NE neurons projecting to the preoptic area of the hypothalamus (POA) decreased MAs and enhanced spindles and REMs after stress. Optrode recordings revealed that stimulating LC-NE fibers in the POA indeed suppressed the spiking activity of POA neurons that are activated during sleep spindles and REMs and inactivated during MAs. Our findings reveal that changes in the dynamics of the stress-regulatory LC-NE neurons during sleep negatively affect sleep quality, partially through their interaction with the POA.

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.

Introduction Locus coeruleus (LC) is a noradrenergic nucleus in the brainstem involved in the regulation of attention, arousal, mood and sensory gating. LC projects to multiple brain regions and recent development of novel systems neuroscience tools allows the dissection of projection-specific LC function in more detail. One of the regions with noradrenergic projection is the preoptic area of the hypothalamus (POA). POA has been shown to contain neurons that are important for regulating sleep, and we have examined the function of the LC projection to the POA in sleep and arousal. Methods We used optogenetics, chemogenetics, fiber photometry and in vivo electrophysiology to study the function of LC noradrenergic projection to the POA. Results Norepinephrine release in the POA fluctuates with brain state changes indicating that the LC to POA projection may be involved in regulating sleep and arousal. Optogenetic stimulation of LC fibers in the POA promotes wakefulness. Furthermore, optogenetic stimulation of the LC fibers in the POA modulates the activity of sleep- and wake-active neurons. Conclusion We have identified the role of the LC noradrenergic projection to the POA in the regulation of brain states. Stimulation of the LC fibers in the POA promotes wakefulness and modulates the activity dynamics of sleep- and wake-active neurons in the POA. Our results provide more detailed information about the role of this specific projection, which has been known to exist for a long time, but with insufficient in vivo evidence of its precise function. Support Sigrid Juselius foundation, Alfred P. Sloan Research Fellowship in Neuroscience, The Whitehall foundation grant, McCabe Fund Award, NARSAD Young Investigator Award.