Circling behaviour induced by activation of GABAA receptors in the subthalamic nucleus

The behavioural effect of drugs acting on GABAA receptors in the subthalamic region and the entopeduncular nucleus was studied in freely moving cats. Microinjections of muscimol into the zona incerta-Forel's fields produced tilt of the head to the injected site, while injections of bicuculline or picrotoxin produced the same effect but to the opposite side. Microinjections of muscimol into the subthalamic nucleus elicited circling behaviour to the contralateral side, while bicuculline and picrotoxin produced ipsilateral turning. However, when high doses of the antagonists were injected, contralateral circling was observed. Activation or blockade of GABAA receptors into the entopeduncular nucleus was ineffective. These results imply that GABAergic mechanisms in the subthalamic nucleus and the zona incerta-fields of Forel are involved in circling behaviour and vertical head movements, respectively.