Involvement of histaminergic mechanisms in the antagonistic effect of morphine on methamphetamine stereotypy in mice

: Pretreatmentwith morphine was found to decrease the intensity of methamphetaminc stereotypy in mice.This inhibitory effect of morphine on methamphetamine stereotypy was significantly increased by prior treatment with L-histidine, a precursor of brain histamine, in a dose which per se had no significant effect on methamphetamine stereotypy. Further, pretreatment with chlorcyclizine, a H1 receptor antagonist, not only increased the intensity of methamphetamine stereotypy but also prevented morphine from exerting an inhibitory effect on methamphetamine stereotypy.The results with L-histidine and chlorcyclizine suggest an involvement of central histaminergic mechanisms in the inhibitory effect of morphine on methamphetamine stereotypy in mice.