Thermoregulatory roles of preoptic area histamine H ₁ receptor-expressing neurons

The preoptic area (POA) is a key regulator of body temperature, orchestrating behavioral and physiological thermoregulatory functions, including fever, torpor, and homeostatic responses to ambient temperature. Histamine regulates body temperature across animal taxa, including mammals, lower vertebrates, and invertebrates. Hrh1 , which encodes the histamine H ₁ receptor, is expressed in several neuronal populations in the POA with limited overlap with other POA thermoregulatory neurons. Acute activation of POA ^Hrh1 neurons increased body temperature and physical activity. Acute inhibition attenuated the dark phase increase in body temperature without affecting physical activity. There was no effect of inhibition on body temperature during the light phase, fever, cold exposure, or warm exposure. Assessing behavioral thermoregulation, we found that POA ^Hrh1 neurons stimulated nest building in both sexes, possibly contributing to cold-induced nesting behavior. Through projections to the arcuate, dorsomedial hypothalamic and tuberomammillary nuclei, POA ^Hrh1 neurons can increase body temperature and physical activity. Overall, POA ^Hrh1 neurons participate in several thermoregulatory functions, including daily body temperature rhythm regulation, physical activity, and nest building behavior.