Experimental hemichorea/hemiballismus in the monkey. Studies on the intracerebral site of action in a drug-induced dyskinesia.

Antagonists of the neurotransmitter gamma aminobutyric acid (GABA) were injected at seventy intracerebral sites in the conscious monkey. Injections located in or near to the subthalamic nucleus provoked involuntary movements of the contralateral limbs. These movements had the characteristics of chorea and, when severe, resembled hemiballismus as seen following subthalamic nucleus lesions in man and monkey. Localized injections of GABA antagonists into the medial segment of the globus pallidus were without observable effect on motor activity. These observations are discussed with regard to the role of GABA in subthalamopallidal relations. Injection of GABA antagonists at some other sites provoked different forms of dyskinesia. Injections in or near the zona incerta adjacent to the subthalamic nucleus induced torticollis and circling behaviour either in isolation or in addition to contralateral limb dyskinesia. Injections at some sites located in the lateral segment of the globus pallidus or in the putamen induced choreoathetoid or myoclonic movements, respectively.