Sleep disturbances are strongly associated with cardiovascular diseases. Baroreflex, a basic cardiovascular regulation mechanism, is modulated by sleep-wake states. Here, we show that neurons at key stages of baroreflex pathways also promote sleep. Using activity-dependent genetic labeling, we tagged neurons in the nucleus of the solitary tract (NST) activated by blood pressure elevation and confirmed their barosensitivity with optrode recording and calcium imaging. Chemogenetic or optogenetic activation of these neurons promoted non-REM sleep in addition to decreasing blood pressure and heart rate. GABAergic neurons in the caudal ventrolateral medulla (CVLM)-a downstream target of the NST for vasomotor baroreflex-also promote non-REM sleep, partly by inhibiting the sympathoexcitatory and wake-promoting adrenergic neurons in the rostral ventrolateral medulla (RVLM). Cholinergic neurons in the nucleus ambiguous-a target of the NST for cardiac baroreflex-promoted non-REM sleep as well. Thus, key components of the cardiovascular baroreflex circuit are also integral to sleep-wake brain-state regulation.

The nucleus basalis of the basal forebrain is an essential component of the neuromodulatory system controlling the behavioral state of an animal and it is thought to be important in regulating arousal and attention. However, the effect of nucleus basalis activation on sensory processing remains poorly understood. Using polytrode recording in rat visual cortex, we found that nucleus basalis stimulation caused prominent decorrelation between neurons and marked improvement in the reliability of neuronal responses to natural scenes. The decorrelation depended on local activation of cortical muscarinic acetylcholine receptors, whereas the increased reliability involved distributed neural circuits, as evidenced by nucleus basalis-induced changes in thalamic responses. Further analysis showed that the decorrelation and increased reliability improved cortical representation of natural stimuli in a complementary manner. Thus, the basal forebrain neuromodulatory circuit, which is known to be activated during aroused and attentive states, acts through both local and distributed mechanisms to improve sensory coding.

In humans and other mammalian species, lesions in the preoptic area of the hypothalamus cause profound sleep impairment, indicating a crucial role of the preoptic area in sleep generation. However, the underlying circuit mechanism remains poorly understood. Electrophysiological recordings and c-Fos immunohistochemistry have shown the existence of sleep-active neurons in the preoptic area, especially in the ventrolateral preoptic area and median preoptic nucleus. Pharmacogenetic activation of c-Fos-labelled sleep-active neurons has been shown to induce sleep. However, the sleep-active neurons are spatially intermingled with wake-active neurons, making it difficult to target the sleep neurons specifically for circuit analysis. Here we identify a population of preoptic area sleep neurons on the basis of their projection target and discover their molecular markers. Using a lentivirus expressing channelrhodopsin-2 or a light-activated chloride channel for retrograde labelling, bidirectional optogenetic manipulation, and optrode recording, we show that the preoptic area GABAergic neurons projecting to the tuberomammillary nucleus are both sleep active and sleep promoting. Furthermore, translating ribosome affinity purification and single-cell RNA sequencing identify candidate markers for these neurons, and optogenetic and pharmacogenetic manipulations demonstrate that several peptide markers (cholecystokinin, corticotropin-releasing hormone, and tachykinin 1) label sleep-promoting neurons. Together, these findings provide easy genetic access to sleep-promoting preoptic area neurons and a valuable entry point for dissecting the sleep control circuit.

The dorsal pons has long been implicated in the generation of rapid eye movement (REM) sleep, but the underlying circuit mechanisms remain poorly understood. Using cell-type-specific microendoscopic Ca(2+) imaging in and near the laterodorsal tegmental nucleus, we found that many glutamatergic neurons are maximally active during REM sleep (REM-max), while the majority of GABAergic neurons are maximally active during wakefulness (wake-max). Furthermore, the activity of glutamatergic neurons exhibits a medio-lateral spatial gradient, with medially located neurons more selectively active during REM sleep.

Top-down modulation of visual processing is mediated in part by direct prefrontal to visual cortical projections. Here, we show that the mouse cingulate cortex (Cg) regulates visual processing not only through corticocortical neurons projecting to the visual cortex but also through corticotectal neurons projecting subcortically. Bidirectional optogenetic manipulation demonstrated a prominent contribution of Cg corticotectal neurons to visually guided behavior, which is mediated by their collateral projections to both the motor-related layers of the superior colliculus (SC) and the lateral posterior nucleus of the thalamus (LP, analogous to the primate pulvinar). Whereas the Cg innervates the anterior LP (LPa), the SC innervates the posterior LP (LPp). Activating each stage of the Cg→SC→LPp or the Cg→LPa pathway strongly enhanced visual performance of the mouse and the sensory responses of visual cortical neurons. These results delineate two subcortical pathways by which a subtype of prefrontal pyramidal neurons exerts a powerful top-down influence on visual processing. VIDEO ABSTRACT.

A crucial step in understanding the sleep-control mechanism is to identify sleep neurons. Through systematic anatomical screening followed by functional testing, we identified two sleep-promoting neuronal populations along a thalamo-amygdala pathway, both expressing neurotensin (NTS). Rabies-mediated monosynaptic retrograde tracing identified the central nucleus of amygdala (CeA) as a major source of GABAergic inputs to multiple wake-promoting populations; gene profiling revealed NTS as a prominent marker for these CeA neurons. Optogenetic activation and inactivation of NTS-expressing CeA neurons promoted and suppressed non-REM (NREM) sleep, respectively, and optrode recording showed they are sleep active. Further tracing showed that CeA GABAergic NTS neurons are innervated by glutamatergic NTS neurons in a posterior thalamic region, which also promote NREM sleep. CRISPR/Cas9-mediated NTS knockdown in either the thalamic or CeA neurons greatly reduced their sleep-promoting effect. These results reveal a novel thalamo-amygdala circuit for sleep generation in which NTS signaling is essential for both the upstream glutamatergic and downstream GABAergic neurons.

Selective attention modulates neuronal activity in multiple brain regions, but the origins of attention signals remain unclear. We show that, during a visual task requiring spatial attention directed by an auditory cue, an inferior-superior colliculus circuit provides the key attention signal. In mice performing a task based on a visual stimulus in the cued hemifield while ignoring a conflicting stimulus on the uncued side, the visual cortex (V1) and superior colliculus (SC) showed strong attentional modulation, with a shorter latency in the SC. The nucleus of the brachium of the inferior colliculus (nBIC), which provides auditory inputs to the SC, was activated not only at auditory cue onset but also during the delay period before the visual stimulus. The delay activity, but not cue onset activity, was crucial for task performance and attentional modulation in the SC and V1. These results establish a new behavioral paradigm for studying visual attention in mice and identify a midbrain signal controlling auditory cue-directed spatial attention.