Involvement of the nucleus accumbens and medial prefrontal cortex in the expression of conditioned hyperactivity to a cocaine-associated environment in rats

This study examined the roles of the nucleus accumbens (NAc), medial prefro ntal cortex, basolateral amygdala, and ventral subiculum of the hippocampus in the expression of Pavlovian conditioned hyperactivity responses to coca ine-related stimuli. This was accomplished by pharmacologically inhibiting these regions prior to drug-free tests for conditioned hyperactivity in an environment previously associated with cocaine. The results indicate that c onditioned hyperactivity could be disrupted by infusions of the GABA-B agon ist, baclofen (0.2 nmol/0.5 mul/side) into the NAc, or completely blocked b y infusions of the GABA-A agonist, muscimol (0.1 and 0.2 nmol/0.5 mul/side) into the medial prefrontal cortex. In contrast, conditioned hyperactivity was unaffected by pharmacological inhibition of the basolateral amygdala, t he ventral subiculum, or sites dorsal to the NAc or prefrontal cortex. Thes e findings suggest that the NAc and the prefrontal cortex are crucial eleme nts of the neural circuitry underlying the expression of Pavlovian conditio ned responses to cocaine-related stimuli. (C) 2000 American College of Neur opsychopharmacology. Published by Elsevier Science Inc.