Hypothermic action of chlorpromazine in monkeys

1 In the conscious monkey (Macaca cyclopis) intravenous administration of chlorpromazine 0.1-8.0 mg/kg produced a fall of rectal temperature of 0.3 to 3.5 degrees C after a latency of 3.5 to 10.8 minutes. The course of hypothermia lasted from 125 to 600 min or more. 2 Direct injection of chlorpromazine 100-800 mug into the lateral or fourth cerebral ventricle produced a similar fall of 0.3 to 2.0 degrees C but with shorter latency (2 to 3.5 min) and with a duration of 94 to 375 minutes. 3 Two distinct structures in the brain stem, namely, the preoptic anterior hypothalamus (POAH) and medulla oblongata, responded to direct injection of chlorpromazine 200 mug. The sensitivity was slightly higher in the POAH than in the medulla. Structures in between were not sensitive. 4 The results suggest that chlorpromazine works principally through the central nervous system, i.e. the POAH and medulla oblongata, to mediate its hypothermic effect.