Interaction of the Basolateral Amygdala and Orbitofrontal Cortex is Critical for Drug Context-Induced Reinstatement of Cocaine-Seeking Behavior in Rats

Abstract

The basolateral amygdala (BLA) and lateral orbitofrontal cortex (OFC) are critical elements of the neural circuitry that regulates drug context-induced reinstatement of cocaine-seeking behavior. Given the existence of dense reciprocal anatomical connections between these brain regions, this study tested the hypothesis that serial information processing by the BLA and OFC is necessary for drug context-induced cocaine-seeking behavior. Male Sprague-Dawley rats were trained to lever press for un-signaled cocaine infusions (0.15 mg/infusion, i.v.) in a distinct environment (cocaine-paired context) then underwent extinction training in a different environment (extinction context). During four subsequent test sessions, rats were re-exposed to the cocaine-paired and extinction contexts in order to assess cocaine-seeking behavior (non-reinforced active lever responding). Immediately before each test session, rats received microinfusions of the GABA(A)/GABA(B) agonist cocktail, baclofen+muscimol (BM: 1.0/.01 mM), or vehicle unilaterally into the BLA plus the contralateral or ipsilateral OFC, or unilaterally into the OFC alone. Exposure to the previously cocaine-paired context, but not the extinction context, reinstated extinguished cocaine-seeking behavior. BM-induced unilateral OFC inactivation failed to alter this behavior, similar to the effect of unilateral BLA inactivation in our previous study (Fuchs et al, 2007). Conversely, neural inactivation of the BLA plus the contralateral or ipsilateral OFC equally attenuated drug context-induced cocaine seeking without altering food-reinforced instrumental responding, relative to vehicle pretreatment. These findings suggest that the BLA and OFC co-regulate drug context-induced motivation for cocaine either through sequential information processing via intra- and interhemispheric connections or by providing converging input to a downstream brain region.