Vagal afferent activation induces a NREM-sleep-like state with brain-body cooling, but locus coeruleus activation

Parasympathetic nervous system activity, vital for restorative sleep, is influenced by vagal sensory afferents, but how these shape brain-body correlates of sleep remains open. We investigated this by combining vagal sensory neuron (VSN) stimulation with EEG/EMG, heart rate, brain-body temperature, and noradrenergic locus coeruleus (LC) neuron population activity measures. Opto-/chemogenetic VSN manipulations in Vglut2-Cre mice were validated via in vitro synaptic physiology, cFos expression, and heart rate measures. Chemogenetic VSN stimulation during the resting phase induced a non-rapid-eye-movement sleep (NREMS)-like state with enriched, but homeostatically regulated, low-frequency (0.75-4 Hz) EEG activity, yet suppressed REMS. Simultaneously, brain-body temperatures dropped while LC activity increased. Recovery was gradual towards normal NREMS-REMS-cycles but accelerated by external warming, identifying cooling as key factor. We conclude that VSN activation can promote brain-body correlates as a continuum of normal NREM sleep while engaging forebrain neuromodulation, offering insights into mechanisms of sleep disruptions linked to autonomic dysregulation.