Abstract
Morphine dependence has been reported to cause supersensititive dopamine receptors in rodent's brain. Male mice (25-30g) were rendered dependent to morphine. Changes in locomtor activity of groups of morphine dependent mice were compared with groups of non-dependent mice. The spontaneous activity of morphine-dependent mice was significantly lower than that of non-dependent animals. Methamphetamine (2.5 mg/kg, i.p.) induced activity was less in morphine dependent than in non-dependent animals. More inhibitory effects of various doses of apomorphine, sulpiride and L-dopa were observed in morphine-dependent animals. These results indicate a depressant effect of chronic morphine use on central dopaminergic activity.