Studies on rectal temperature of rats in relation to seasonal air temperature and morphine administration

Abstract

The present findings demonstrate that seasonal air temperature does not only influence the basal core temperature of rats, but also modifies the physiological/pharmacological actions of drugs. Thus, at low ambient temperature, intracerebroventricular or intraperitoneal administration of morphine produces mainly hypothermia followed by a secondary rise in rectal temperature. On the other hand, at high ambient temperature, the drug produces hyperthermia only. The hypothermic response at low ambient temperature is abolished by pretreatment of rats with 6-hydroxydopamine but not with phenoxybenzamine administration. This suggests that the catecholamine pathway in the central nervous system is involved in the morphine induced hypothermic response. Further, the role of cholinergic neurons in this response is also indicated.