CIRCLING BEHAVIOR INDUCED BY ACTIVATION OF GABA(A) RECEPTORS IN THE SUBTHALAMIC NUCLEUS

THE behavioural effect of drugs acting on GABA(A) receptors in the sub thalamic region and the entopeduncular nucleus was studied in freely m oving cats. Microinjections of muscimol into the zona incerta-Forel's fields produced tilt of the head to the injected site, while injection s of bicuculline or picrotoxin produced the same effect but to the opp osite side. Microinjections of muscimol into the subthalamic nucleus e licited circling behaviour to the contralateral side, while bicucullin e and picrotoxin produced ipsilateral turning. However, when high dose s of the antagonists were injected, contralateral circling was observe d. Activation or blockade of GABA(A) receptors into the entopeduncular nucleus was ineffective. These results imply that GABAergic mechanism s in the subthalamic nucleus and the zona incerta-fields of Forel are involved in circling behaviour and vertical head movements, respective ly.