Effect of apomorphine and nigrostriatal lesions on aggression and striatal dopamine turnover during morphine withdrawal: Evidence for dopaminergic supersensitivity in protracted abstinence

Reliable aggression was seen in rats which were grouped 30 days after undergoing continuous withdrawal from morphine. This withdrawal aggression, associated with long-lasting effects of morphine dependence, was blocked by morphine or lesions of the nigrostriatal bundle, but not by lesions of the median forebrain bundle. When the nigrostriatal lesioned rats were treated with a small dose of apomorphine, the aggression was reinstated. Apomorphine reduced the turnover of dopamine in the 30-day withdrawn rats at doses which were ineffective in similarly housed non-dependent rats. These results suggest that animals undergoing protracted morphine abstinence show aggression due to a latent dopaminergic supersensitivity, similar to that previously reported during acute narcotic withdrawal.