EFFECTS OF BRAIN MONO-AMINE DEPLETION ON CHLORPROMAZINE-INDUCED HYPOTHERMIA IN RABBITS

The thermal responses of three groups of control, 6-hydroxydopamine (6-OHDA) treated and 5,7-dihydroxytryptamine (5,7-DHT)treated rabbits to the administration of chlorpromazine (CPZ)were assessed at three different ambient temperatures (T(a): 2, 22, and 32°C). Depleting catecholamines (CA) in brain with 6-OHDA produced a decrease in metabolic rate, in respiratory evaporative heat loss, and in ear blood flow at both T(a)'s of 2 and 22°C, while depleting 5-hydroxytryptamine (5-HT)contents in brain with 5,7-DHT produced the opposite responses at the same T(a)'s. However, these amine-depleted animals maintained their rectal temperatures within normal limits over a wide range of T(a)'s tested. Furthermore, intraperitoneal administration of CPZ produced hypothermia at both T(a)'s of 2 and 22°C. The major cause of the CPZ-induced hypothermia was an inhibition of metabolic heat production at T(a) of 2°C. At T(a) of 22°C, the CPZ-induced hypothermia was due to both a decrease in heat production and an increase in ear blood flow. However, CPZ hypothermia was attenuated in the CA-depleted animals, but was potentiated in the 5-HT-depleted animals. The data indicate that brain monoamines are involved in the central mechanisms of CPZ-induced hypothermia.