Dopaminergic and serotonergic mechanisms of thermoregulation: mediation of thermal effects of apomorphine and dopamine.

The effects of dopaminergic and serotonergic antagonists on apomorphine- and dopamine-induced changes in body temperature were studied in the rat. Intraperitoneal administration of apomorphine produced dose-dependent hypothermia. At a dose of 0.1 mg/kg, apomorphine caused either no significant effect or a slight decrease in body temperature. However, it caused hyperthermia in rats pretreated with the DA antagonist, haloperidol, and hypothermia in rats pretreated with the serotonin depletor, p-chlorophenylalanine or serotonin antagonists, cyproheptadine, metergoline or cinanserin. Intracerebroventricular injection of 100 micrograms/2 microliter of DA transiently decreased body temperature. Pretreatment with cyproheptadine potentiated and prolonged the responses. However, the same injection of DA produced hyperthermia in haloperidol-pretreated animals. These data suggest that both dopaminergic and serotonergic mechanisms in the brain mediate the effects of apomorphine on body temperature. We propose that apomorphine can simultaneously activate two opposing DA-related thermoregulatory mechanisms with different sensitivities to haloperidol: a haloperidol-sensitive hypothermia and a haloperidol-nonsensitive hyperthermia mechanisms. Furthermore, the action of the latter mechanism is mediated by a secondary activation of serotonergic mechanisms.