Correlation of morphine-induced locomotor activity with changes in core temperature of the rat

A marked temporal correlation was discovered between the pattern of changes in core temperature (CT) and that of locomotor activity induced by the i.p. injection of morphine in both the Sprague-Dawley and Wistar male rat. Although CT and locomotor activity increased following the intracerebral microinjection of morphine, the time course of the changes in each measure were not as closely related as after the i.p. injections. Since restraining the rat attenuates morphine-induced hyperthermia, the data suggest that the prevention of locomotor activity by restraint may contribute to the diminution in the morphine-induced rise in CT. Further work will be required to determine whether the most sensitive intracerebral sites for morphine-induced increases in CT and locomotor activity are distinct.