Grooming, body extension, and vasomotor responses induced by hypothalamic warming at different ambient temperatures in rats.

During heat stress, rats extend their body and spread saliva onto their body surfaces (grooming) for evaporative heat loss in addition to tail vasodilation. We investigated the effects of changing hypothalamic (Thy) and ambient (Ta) temperatures on these thermoregulatory responses. The higher the Ta, the lower the Thy at which grooming started when Ta was changed from the thermoneutral zone (24 degrees C) to 28-40 degrees C. At any Ta grooming was induced only when the posterior hypothalamic region (PH) was warmed by implanted diathermy. Grooming was more strongly induced at a Ta of 28 degrees C than at 24 degrees C. At a Ta of 32 degrees C, PH warming evoked body extension as well, decreasing the duration of grooming as compared to that at 28 degrees C. Warming the preoptic area and anterior hypothalamus induced body extension and tail vasodilation regardless of Ta. The data suggest that grooming was induced by integrated temperature signals from the PH and from the peripheral skin.