Recovery from GABA-mediated hemiplegia in young and aged rats: effects of catecholaminergic manipulations.

We investigated the participation of catecholaminergic mechanisms in the functional recovery from motor cortex lesions in young (9 months) and aged (26 months) rats. The animals were studied during the recovery period from an hemiplegic syndrome secondary to small motor cortex lesions potentiated by the localized, chronic (7 days) infusion of GABA into the lesion site. Acute administration of haloperidol (0.1 mg/kg IP) to these recovered animals induced a re-emergence of the contralateral motor syndrome in both groups. In the young group, the haloperidol-induced hemiplegia lasted one day whereas in the aged animals the deficit was significantly prolonged lasting three days. Apomorphine administration (0.5 mg/kg IP) prior to or immediately after haloperidol injection failed to prevent or reverse the reappearance of the motor deficit. Adult animals recovered from motor cortex aspirations performed 7 to 12 months prior were refractory to haloperidol effects. Amphetamine administration to young rats treated chronically with saline or GABA infusion into the somatomotor region also failed to alter the clinical evolution of the motor deficit. The evidence suggests that dopaminergic mechanisms are involved in the functional recovery from brain lesions and that these mechanisms are most susceptible to neuroleptic blockade during the early post-lesional period. The deleterious effects of dopaminergic blockade are heightened in aged populations. The use of dopaminergic antagonists in brain-lesioned subjects, and particularly in geriatric populations, is considered potentially harmful, particularly in the early stages of the recovery process.