Do central dopamine receptors have a physiological role in thermoregulation?

1 Core and tail skin temperature was measured in rats which had guide cannulae implanted into their brains to allow drug injections directly into the preoptic anterior hypothalamus. 2 Apomorphine and dopamine (10 microgram in 1 microliter) injected into the area of the preoptic anterior hypothalamus caused a fall in core temperature which was preceded by a rise in tail skin temperature. 3 The decrease in core temperature following central injection of either apomorphine or dopamine was significantly reduced by pretreating rats for 2 h with pikozide 0.5 mg/kg i.p.). 4 Bilateral intrahypothalamic injection of pimozide (0.5 microgram in 1 microliter) significantly reduced the hypothermic effect of systemic apomorphine (1.25 mg/kg i.p.). 5 Control rats placed 65 cm below a 250 W infrared lamp responded with vasodilation of tail skin blood vessels as indicated by an increase in tail skin temperature. Pimozide pretreatment (0.5 mg/kg i.p.) significantly reduced this response. 6 These results suggest that the preoptic anterior hypothalamus contains dopamine receptors which mediate hypothermia in rodents and raise the possibility that endogenous dopamine has a physiological role in thermoregulation.