Hyperthermic and hypothermic effects of morphine in mice: interactions with apomorphine and pilocarpine and changes in sensitivity after caudate nucleus lesions.

In mice, both apomorphine and pilocarpine either potentiated a hypothermic effect of a high dose of morphine or reversed a hyperthermic effect of a low dose of morphine to a hypothermic effect. Haloperidol paritally blocked the hypothermic effect but not the hyperthermic effect of morphine. Scopolamine partially blocked the hyperthermic but not the hypothermic effect of morphine. Bilateral lesions of the caudate nuclei produced no changes in sensitivity to either the acute hyperthermic or hypothermic effect of morphine but did selectively facilitate the developement of tolerance to morphine-induced hypothermia. The results suggest that morphine's temperature effects are determined by the interaction of several mechanisms and that the caudate nucleus may have a specific role in drug tolerance.