Sex differences in the effects of haloperidol, morphine, and their combination on colonic temperature in rats

Previously it was found that during the loss of postural support induced by combined administration of haloperidol and morphine, rats became markedly hypothermic. The present work was a more detailed study of this hypothermia. Morphine alone (20 mg/kg) produced a slight hyperthermia (1 degrees C) in female rats and no effect in males. Haloperidol alone (5 mg/kg) elicited a hypothermia of about 3 degrees C in females and no effect in males. The combination of both elicited a greater decrease of temperature (about 5 degrees C) in female rats and, unexpectedly, a decrease of 3 degrees C in males. According to these data, increased endorphinic activity with a concomitant decrease in dopamine in some unidentified regions of the central nervous system causes hypothermia.