Effect on core temperature of restraint after peripherally and centrally injected morphine in the Sprague-Dawley rat

The changes in core temperature (Tc) evoked by morphine in the Sprague-Dawley rate were altered by restraining the rat. The Tc of the free-moving rat rose after the IP (5, 15, 30, 60 mg/kg) or intracerebral injections (10, 20, 50 micrograms) of morphine. In the restrained rate, however, identical doses of morphine evoked either a hyperthermia of lesser magnitude than in the free-moving rat or a drop in Tc. These findings reemphasize the importance of restraint in determinating the action of morphine on Tc and extend the finding to the Sprague-Dawley rat.