Microinjection of muscimol (406 pmol) into the rat entopeduncular nucleus, the analogue of the primate globus pallidus pars interna, significantly suppressed pilocarpine but not maximal electroshock seizures in a spatially specific manner. In contrast to its lack of efficacy in the entopeduncular nucleus, microinjection of muscimol into the substantia nigra suppressed maximal electroshock seizures. These findings suggest that the neural networks and/or the neurotransmitters that subserve the propagation of pilocarpine and maximal electroshock seizures differ with regard to the entopeduncular nucleus. The data also underscore the powerful regulatory role of the substantia nigra in diverse models of seizures.