Studies on the mechanism of action of tetrabenazine as a morphine antagonist II. A participation of catecholamine in the antagonism.

Ealier observations in this laboratory have demonstrated that tetrabenazine, a brain monoamine releaser, antagonizes morphine analgesia in mice (1) and that it antagonizes the depressive effects of morphine on the several afferent pathways in the central nervous system in cat (2). More recently it has also been demonstrated that the change of brain noradrenaline (NA) plays more important role than that of serotonin (5-HT) in the antagonism of morphine analgesia by tetrabenazine or reserpine (3) and that morphine decreases the content of dopamine (DA) as well as that of NA in the brain (4). The purpose of this study was to investigate the mechanism of tetrabenazine antago nism of morphine analgesia in relation to DA and NA content in the brain.