Possible noradrenergic involvement in naloxone potentiation of apomorphine-induced stereotypic climbing in mice.

Apomorphine-induced stereotypic climbing behavior in mice was significantly potentiated by pretreatment with the opiate receptor blocker naloxone. In animals additionally pretreated with alpha-methyl-p-tyrosine, brain levels of norepinephrine (NE) and dopamine (DA) were markedly reduced and naloxone potentiation of apomorphine-induced stereotypic climbing was blocked. In mice pretreated with diethyldithiocarbamic acid, brain NE was slightly reduced, brain DA was slightly elevated but naloxone potentiation of apomorphine-induced stereotypic climbing was unaltered. In animals pretreated with reserpine, both brain NE and DA were significantly reduced by naloxone potentiation of apomorphine-induced stereotypic climbing was not affected. In other experiments, pretreatment with low doses of the alpha-adrenergic receptor blocker BE-2254 failed to suppress climbing activity induced by apomorphine alone but did successfully prevent naloxone potentiation of apomorphine-induced stereotypic climbing. These findings suggest the possibility that NE and alpha-adrenergic receptors might play a role in the potentiating influence of naloxone upon apomorphine-induced stereotypic climbing activity in mice.