5-Hydroxytryptamine-induced hypothermia in rats as an in vivo model for the quantitative study of 5-hydroxytryptamine receptors.

Intrahypothalamic injection of 5-hydroxytryptamine (5-HT) caused a fall in core temperature in lightly restrained rats maintained at an ambient temperature of 17 degrees C. The hypothermia was blocked by 5-HT antagonists with a relative potency of methiothepin greater than methergoline greater than methysergide greater than cinanserin greater than cyproheptadine. The peripheral 5-HT antagonist, xylamidine, was not an antagonist, suggesting the hypothermia was of central origin. Other neurotransmitter antagonists, haloperidol, atropine, phentolamine, and propranolol failed to prevent 5-HT-induced hypothermia. This suggests that the hypothermic response to 5-HT can be used for a quantitative study of drug action at central 5-HT receptors.