Capsaicin impairs preoptic serotonin-sensitive structures mediating hypothermia in rats.

In an attempt to elucidate the possible mechanisms involved in the development of the thermoregulatory disturbances induced by systemic capsaicin treatment, the effects of 5-HT injected into the preoptic region or into the cisterna magna on the body temperature and on tail skin vasodilation were studied in control and capsaicin-treated rats. Intracisternal 5-HT elicited a comparable decrease in body temperature in both groups of animals. In contrast, intrapreoptic injection of different doses of 5-HT-induced tail skin vasodilation and hypothermia in the controls, but not in the capsaicin-treated rats. It is suggested that changes in the sensitivity of preoptic warm-responsive structures to 5-HT may contribute essentially to the specific thermoregulatory impairment brought about by systemic capsaicin treatment.