CORTICAL-LESIONS ATTENUATE THE OPPOSING EFFECTS OF AMPHETAMINE AND HALOPERIDOL ON NEOSTRIATAL NEURONS IN FREELY MOVING RATS

Neuronal activity was recorded from the neostriatum of freely moving r ats at least 1 week following either sham or bilateral ablations of fr ontal and somatosensory cortex. In both groups of animals, the majorit y of neurons increased firing rate in close temporal association with spontaneous movement. No group differences emerged either with respect to baseline firing rates or open-field behavior. Following amphetamin e administration, however, the excitatory response of motor-related ne urons was suppressed in cortical-lesioned rats. A behavioral clamping procedure, which assessed neuronal activity during matched pre- and po st-amphetamine behaviors, confirmed these results, suggesting that the amphetamine-induced changes in neuronal activity reflect a direct dru g effect independent of behavioral feedback. In animals that received a subsequent injection of 1.0 mg/kg haloperidol, cortical lesions atte nuated the ability of this neuroleptic to block both the behavioral an d neuronal effects of amphetamine. Collectively, these results support mounting evidence for an important modulatory influence of cortical a fferents on the amphetamine-induced excitation of neostriatal neurons and the reversal of this effect by haloperidol.