Evidence for an endogenous dopamine-mediated hypothermia in the rat.

1 Unilateral intrahypothalamic injection of either dopamine (10 mug) or amphetamine (10 mug) caused a fall in core temperature in the rat. Pimozide (0.5 mg/kg, i.p.) significantly reduced the hypothermic response, whereas pretreatment with phentolamine (1 mg/kg, i.p.) or methysergide (5 mg/kg, i.p.) was ineffective.2 Systemic pretreatment with cocaine (20 mg/kg) abolished the hypothermic effect of amphetamine, but slightly enhanced the hypothermic response to dopamine.3 Systemic pretreatment with tranylcypromine (10 mg/kg) had no significant effect on the fall in core temperature induced by either amphetamine or dopamine.4 Intraperitoneal injection of cocaine and tranylcypromine, on their own, caused a fall in core temperature in the rat, which was significantly antagonized by either systemic or central pretreatment with pimozide. Phentolamine and methysergide failed to block the hypothermia.5 Unilateral intrahypothalamic injection of cocaine (20 mug) or tranylcypromine (10 mug) also caused a significant fall in core temperature, which was reduced by intrahypothalamic pretreatment with pimozide (0.5 mug), but not significantly changed by pretreatment with phentolamine (25 mug) or methysergide (5 mug).6 These results provide evidence for the presence of a dopaminergic system within the preoptic region, which mediates a lowering of core temperature in the rat.