EFFECTS OF DOPAMINE DEPLETIONS IN THE MEDIAL PREFRONTAL CORTEX ON DRLPERFORMANCE AND MOTOR-ACTIVITY IN THE RAT

Two experiments assessed the behavioral effects of dopamine depletions in the medial prefrontal cortex that were produced by injection of th e neurotoxic agent 6-hydroxydopamine. In the first experiment, rats we re trained to respond on a differential reinforcement of low rates of responding-30 second (DRL30) schedule. On this schedule, rats were onl y reinforced if they withheld responding for 30 s. Rats with prefronta l dopamine depletions were found to be impaired in the DRL task. These animals responded more than controls, received fewer reinforcers, and were less efficient in their responses. Moreover, an analysis of inte rresponse times (IRTs) revealed that rats with medial prefrontal dopam ine depletions made more responses with short-duration IRTs, and fewer responses with long-duration IRTs. In the second experiment, rats wer e tested on open field activity, amphetamine-induced locomotor activit y and stereotypy. No increase in spontaneous locomotor activity was fo und following surgery; however, increases in amphetamine-induced locom otor activity and stereotypy were observed. These results are consiste nt with hypothesized role for the prefrontal cortex in behavioral inhi bition, and indicates that prefrontal cortical dopamine is an integral part of the system.