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 amygdala of rats self-administering cocaine (1.5 mg/kg per injection i.v.) under a progressive ratio schedule of reinforcement. Post-lesion access 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 biochemical results show a significant reduction in dopamine and DOPAC levels within the amygdala and an increase in dopamine within the NACC. In contrast, noradrenaline and serotonin (5-HT) levels were unaffected by the lesion in any of the dissected areas. These results demonstrate that no specific effect on cocaine reinforcement was produced by 6-OHDA lesions of the amygdala. The possibility that the lesion may have attenuated the anxiogenic qualities of the high dose of cocaine is discussed.