Modification of apomorphine hypothermia by drugs affecting brain 5-hydroxytryptamine function.

Intraperitoneal administration of apomorphine caused hypothermia in mice. Pretreatment with the serotonin (5-HT) receptor antagonists methysergide (3 mg/kg), cinanserin (10 mg/kg) or brom-LSD (3 mg/kg) potentiated this response of apomorphine. Brain 5-HT depletion by p-chlorophenylalanine caused similar modification. On the contrary, the 5-HT receptor agonists quipazine (3 mg/kg) and MK-212 (3 mg/kg), significantly blocked apomorphine hypothermia. It was concluded that 5-HT modulates the dopamine (DA)-mediated body temperature changes and that drug-induced alterations in the brain 5-HT function modify apomorphine-induced hypothermia in a predictable manner. One mg/kg dose of lysergic acid diethylamide (LSD) blocked apomorphine hypothermia. The apomorphine-blocking effect of both quipazine and LSD developed tolerance. Moreover, LSD showed cross tolerance with quipazine. It was concluded that the hypothermia-blocking property of LSD resides on its ability to activate the hypothalamic 5-HT receptors.