INFLUENCE OF PRELIMBIC AND SENSORIMOTOR CORTICES ON STRIATAL NEURONS IN THE RAT - ELECTROPHYSIOLOGICAL EVIDENCE FOR CONVERGING INPUTS AND THE EFFECTS OF 6-OHDA-INDUCED DEGENERATION OF THE SUBSTANTIA-NIGRA

These studies were designed to investigate whether there are convergen t prelimbic and sensorimotor cortical inputs onto striatal neurons in the rat and whether dopaminergic (DA) nigrostriatal fibers regulate th ese inputs. The influence of the nigrostriatal DA system was assessed in rats with either small or large 6-hydroxydopamine-induced lesions o f the substantia nigra. In normal rats 39 out of 74 neurons (52.7%) we re excited by stimulation of both the prelimbic and the sensorimotor c ortex. No marked change in corticostriatal transmission was evident in rats with small 6-OHDA-induced lesions (defined as 10-35% decrease in H-3!DA uptake in striatal synaptosomes). In rats with large lesions (75-85% decrease in striatal H-3!DA uptake), however, a complete rear rangement of the corticostriatal transmission occurred. This was evide nt in a decrease of thresholds to obtain cortical responses, by modifi cations of the discharge properties of striatal neurons receiving inpu t from cortices and by an increase in the number of neurons responding to cortical stimulation. In addition, a significantly higher percenta ge of striatal neurons responded to stimulation of both prelimbic and sensorimotor cortices in rats with large lesions than in rats with sma ll lesions or in control rats. This data suggests that: (1) no functio nal separation of prelimbic and sensorimotor cortical inputs occurs in the rat striatum, (2) the nigrostriatal DA system exerts a focusing e ffect on these inputs, (3) the striatum is actively involved in the in tegrative processing of descending cortical information.