Hypothalamic and striatal dopamine receptor activation inhibits heat production in the rat

Direct injection of dopaminergic agonist apomorphine into the lateral cerebral ventricle, the preoptic anterior hypothalamus, the caudate-putamen complex, or the globus pallidus caused hypothermia, decreased metabolism and cutaneous vasoconstriction at ambient temperature (Ta) 8 and 22 degrees C, and hyperthermia and cutaneous vasoconstriction in the rat at Ta 30 degrees C. On the other hand, local injection of dopaminergic antagonists such as haloperidol and pimozide into the preoptic anterior hypothalamus and the striatal nuclei caused hyperthermia, increased metabolism and cutaneous vasoconstriction at Ta 8, 22, and 30 degrees C. However, there was no change in respiratory evaporative heat loss in response to administration of either dopaminergic agonist or antagonists in the rat at all Ta studied. The data indicate that hypothalamic and striatal dopaminergic receptor activation inhibits metabolic heat production in rats. In addition, intrahypothalamic injection of 5-hydroxytryptamine caused hypothermia, decreased metabolism and cutaneous vasodilatation in the rat at Ta 8 and 22 degrees C, whereas at Ta 30 degrees C caused an insignificant change in the thermoregulatory responses. Furthermore, the thermal responses induced by intrahypothalamic injection of apomorphine were not altered by depletion of hypothalamic 5-hydroxytryptamine. These observations do not support the contention that there is a dopamineserotonin link in the hypothalamic pathways that mediate heat loss mechanisms in the rat.