Modification of the behavioural effects of amphetamine by a GABA agonist in a primate species.

Acute administration of d-amphetamine in the marmoset results in a dose dependent increase in small head movements (checking), and an almost total suppression of purposeful activities and social interaction. It has little effect on locomotion and does not induce stereotyped gnawing. The GABA-agonist, muscimol, decreases checking, locomotion, activities and social interaction when given alone, but induces jerking movements at large doses. When administered in combination with amphetamine, muscimol induces persistent stereotyped gnawing. On the basis of the present findings and those of experiments in rodents it is suggested that compulsive gnawing results from overactivity in the striatal efferent pathway, while checking is probably mediated by extra-striatal sites. Since the behavioural effects of muscimol resemble those of the typical neuroleptics with the exception of the induction of gnawing, it is suggested that muscimol, though sedative, may counteract certain extrapyramidal effects of neuroleptic treatment while facilitating their other behavioural effects.