Effects on eye movements of a GABA agonist and antagonist injected into monkey superior colliculus.

Injection of muscimol, a GABA agonist, into the superior colliculus of awake monkeys produces saccades to visual targets in the movement field of colliculus cells near the injection site that have longer latency and shortened amplitude. Bicuculline, a GABA antagonist, leads to irrepressible saccades towards the movement field. These results are consistent with a tonic inhibition by the substantia nigra on the superior colliculus mediated by GABA which is reduced at the time of saccade initiation.