Increased incidence and severity of neuroleptic-induced movement disorder in pinealectomized rats.

The effects of prior pinealectomy on neuroleptic-induced perioral movements were examined in male Sprague-Dawley rats. Treatment with haloperidol resulted in significantly more severe movement disorder in pinealectomized rats than in unoperated control rats. Subsequent administration of melatonin (4 mg, i.p.) was associated with a nonsignificant reduction of the severity of movements in the pinealectomized rats within one hour. We conclude that pinealectomy facilitates the onset of neuroleptic-induced perioral movements, and suggest that impaired melatonin secretion may be implicated in the pathophysiology of tardive dyskinesia in humans.