Development of tolerance to the muscular rigidity produced by morphine and replacement by stereotypic behaviour

After chronic treatment with morphine, the muscular rigidity mediated by opioid receptors in the striatum, was gradually replaced by stereotypic behaviour indicating an increased nigrostriatal dopaminergic activity. These results suggest that one behavioural pattern, originating in the striatum, was replaced by another one, which is antagonistic to the first one.