Pth4 neurons define a novel hypothalamic circuit that promotes sleep via brainstem monoaminergic neurons.

Classical studies identified a critical role for the hypothalamus in regulating sleep and wake states, but few such hypothalamic neuronal populations have been identified. Here we describe a sleep-promoting population of hypothalamic neurons that expresses the neuropeptides QRFP and parathyroid hormone 4 (Pth4) in zebrafish. Optogenetic stimulation of these neurons results in a large increase in sleep that requires but not . Noradrenergic locus coeruleus (LC) neurons and serotonergic raphe neurons (RN) in the hindbrain express distinct , and genetic epistasis and cell ablation experiments revealed that Pth4 neuron-induced sleep is suppressed in mutants that lack noradrenaline in the LC or lack the serotonergic RN. Pth4 neuron-induced sleep is also suppressed in ( ) mutants, possibly via -expressing neurons in the prethalamus that express . These results identify QRFP/Pth4 neurons as a novel hypothalamic sleep-promoting population and support a model in which distinct sleep- and wake-promoting hypothalamic populations act via monoaminergic neurons in the hindbrain to control vigilance state.