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Keywords:

  • amygdala;
  • glucose utilization;
  • hippocampus;
  • substance abuse

Abstract

Previous studies utilizing a nonhuman primate model have shown that cocaine self-administration in its initial stages is accompanied by alterations in functional activity largely within the prefrontal cortex and ventral striatum. Continued cocaine exposure may considerably change this response. The purpose of the present investigation was to characterize the effects of reinforcing doses of cocaine on cerebral metabolism in a nonhuman primate model of cocaine self-administration, following an extended history of cocaine exposure, using the quantitative 2-[14C]deoxyglucose (2-DG) method. Rhesus monkeys were trained to self-administer 0.03 mg/kg/injection (n = 4) or 0.3 mg/kg/injection (n = 4) cocaine and compared to monkeys trained to respond under an identical schedule of food reinforcement (n = 6). Monkeys received 30 reinforcers per session for a total of 100 sessions. Metabolic mapping was conducted at the end of the final session. After this extended history, cocaine self-administration dose-dependently reduced glucose utilization throughout the striatum and prefrontal cortex similarly to the initial stages of self-administration. However, glucose utilization was also decreased in a dose-independent manner in large portions of the temporal lobe including the amygdala, hippocampus and surrounding neocortex. The recruitment of temporal structures indicates that the pattern of changes in functional activity has undergone significant expansion beyond limbic regions into association areas that mediate higher order cognitive and emotional processing. These data strongly contribute to converging evidence from human studies demonstrating structural and functional abnormalities in temporal and prefrontal areas of cocaine abusers, and suggest that substance abusers may undergo progressive cognitive decline with continued exposure to cocaine.