Circling behaviour induced by apomorphine after lesions of the habenula.

Apomorphine, 2 mg/kg (s.c.) produced significant contralateral turning in rats with unilateral radiofrequency lesions of the habenula nucleus over a test period of 60 min when tested at post-surgery days 3, 7, and 14. Levels of contralateral circling were not significantly increased when the animals were tested on days 21 and 28, although a contralateral bias was still observed. Rotation induced by apomorphine was completely blocked by the administration of haloperidol (0.3 mg/kg i.p.), and there was no behavioural asymmetry in lesioned animals following administration of saline or a high dose of haloperidol (2 mg/kg i.p.). These results indicate that unilateral habenula lesions lead to imbalance of dopaminergic activity, which is expressed as contralateral circling when the animal is challenged with apomorphine.