Effects of hypothalamic noradrenaline depletion with 6-hydroxydopamine on the body temperature regulation of the rat.

Rats which had been pretreated with 3 intrahypothalamic doses of 10 micrograms of 6-hydroxydopamine (6-OHDA) to cause a selective depletion of hypothalamic noradrenaline to 26.7% of control hypothalamic noradrenaline maintained rectal temperature within the normal limits displayed by the control group. However, noradrenaline-depleted rats displayed a decrease in both cutaneous temperature and metabolic heat production in the cold (8 degrees C). Intrahypothalamic injections of 6-OHDA in normal rats at room temperature (22 degrees C) caused an acute hyperthermia of up to 1.1 degree C which lasted for about 6 h. The acute hyperthermia in response to 6-OHDA was due to both cutaneous vasoconstriction and increased metabolism in the rat. Selective depletion of hypothalamic noradrenaline without affecting hypothalamic dopamine by prior treatment with 6-OHDA markedly reduced the hyperthermic responses to a subsequent dose of 6-OHDA. Therefore, the acute hyperthermic responses to 6-OHDA may be related to a release of noradrenaline in the hypothalamus. The data indicate that activation of noradrenergic pathways in the hypothalamus facilities heat production and inhibits heat loss mechanisms in the rat.