Modification of d-amphetamine- or chlorpromazine-induced hypothermia by beta-endorphin, MIF-I, and alpha-MSH: mediation by the dopaminergic system.

The effects of beta-endorphin, MIF-I, and alpha-MSH on d-amphetamine- a CPZ-induced hypothermias in rats kept at 4 degrees C were tested in three experimental groups: (a) intact; (b) rats with lesions of the olfactory tubercle; and (c) rats in which the link between the DA mesolimbic pathway and the striatum was disconnected. All drugs tested alone (except MIF-I) caused significant hypothermia. Pretreatment with CPZ, MIF-I, and alpha-MSH potentiated d-amphetamine-induced hypothermia in intact rats. Pretreatment with alpha-MSH potentiated CPZ-induced hypothermia. beta-Endorphin partially blocked d-amphetamine-induced hypothermia, but did not interact with CPZ, MIF-I, or alpha-MSH. All potentiations were either reduced or disappeared in the incisioned rats. CPZ and alpha-MSH caused hypothermia in olfactory tubercle-lesioned rats. The results indicate that: (a) the DA mesolimbic pathway is involved in the hypothermic response of all drugs tested; (b) an intact feedback loop is required for the potentiation of the hypothermic response of CPZ on d-amphetamine, MIF-I on d-amphetamine, and alpha-MSH on d-amphetamine and CPZ; (c) beta-endorphin acts as a partial blocker of d-amphetamine; MIF-I is a weak potentiator of d-amphetamine, alpha-MSH acts as a negative modulator of the DA system, most probably in the striatum.