EFFECT OF 6-HYDROXYDOPAMINE LESIONS OF THE AMYGDALA ON INTRAVENOUS COCAINE SELF-ADMINISTRATION UNDER A PROGRESSIVE RATIO SCHEDULE OF REINFORCEMENT

Bilateral six-hydroxydopamine (6-OHDA) lesions were placed in the amyg dala of rats self-administering cocaine (1.5 mg/kg per injection i.v.) under a progressive ratio schedule of reinforcement. Post-lesion acce ss to three doses of cocaine (1.5, 0.75 and 0.37 mg/kg per injection i .v.) revealed a lesion effect only at the highest dose. At this dose, the lesion caused a significant increase in breaking point. No change in the breaking point was produced at the lower two doses. The biochem ical results show a significant reduction in dopamine and DOPAC levels within the amygdala and an increase in dopamine within the NACC. In c ontrast, noradrenaline and serotonin (5-HT) levels were unaffected by the lesion in any of the dissected areas. These results demonstrate th at no specific effect on cocaine reinforcement was produced by 6-OHDA lesions of the amygdala. The possibility that the lesion may have atte nuated the anxiogenic qualities of the high dose of cocaine is discuss ed.