The effects of cortical ablation on multiple unit activity in the striatum following dexamphetamine

Bilateral removal of the fronto-parietal cortex of the rat resulted in decreased spontaneous multiple-unit activity recorded in the striatum of freely-moving rats. Cortical ablations changed the neuronal response in the striatum to systemic administration of dexamphetamine (2.5 mg kg i.p.) from excitation in control animals (88%) to inhibition in ablated animals (61%). Furthermore, catalepsy, induced by haloperidol, but not by morphine, was markedly attenuated after cortical ablation. These changes were accompanied by a 23% decrease in the specific binding of [³H]spiperone in the striatum. The binding of [³H]met-enkephalin was unaffected by the cortical lesions. Levels of glutamate in the striatum decreased from 8.88 ± 0.5 μmols g in control animals to 6.93 ± 0.37 μmols g after bilateral cortical ablation. On the other hand, cortical ablations did not alter the content of either the γ-aminobutyric acid or glutamine of the striatum. It is concluded that the excitatory response, observed in striatal neurons in freely-moving animals, is dependent upon an intact cerebral cortex and requires intact cortico-striatal afferents. The results further suggest that neurons in the striatum are under the tonic influence of glutamate, released from cortico-striatal afferents. Lastly, some dopamine D₂ binding sites in the striatum are located on cortico-striatal afferent terminals and blockade of these striatal D₂ sites may be involved in the induction of catalepsy by neuroleptic drugs.