Different hypothalamic receptors mediate 5-hydroxytryptamine- and tryptamine-induced core temperature changes in the rat.

1 Unilateral intrahypothalamic injection of 5-hydroxytryptamine (5-HT) caused a dose-related fall in core temperature in rats, whereas injection of tryptamine into the same site caused a dose-related rise in core temperature. 2 The core temperature changes induced by 5-HT or tryptamine were inhibited by intrahypothalamic pretreatment with indoleamine receptor antagonists in a dose-related manner. 3 Other neurotransmitter antagonists, haloperidol, atropine, phentolamine and (-)-propranolol, had no significant effect on core temperature changes induced by 5-HT or tryptamine. 4 A differential antagonism was observed for the indoleamine receptor antagonists against 5-HT and tryptamine-induced core temperature changes. Methergoline and triflupromazine were more selective against tryptamine-induced hyperthermia, while cyproheptadine was more selective against 5-HT-induced hypothermia. 5 Intrahypothalamic pretreatment with 5,-7-dihydroxytryptamine (5,7-DHT) 42 nmol in 2 microliter inhibited tryptamine-induced hyperthermia, but was without effect on 5-HT-induced hypothermia. 6 These results suggest the possible existence of two different receptor populations within the preoptic anterior hypothalamus in rats; one specific for 5-HT and the other for tryptamine.