An infusion of bupivacaine into the nucleus accumbens disrupts the acquisition but not the expression of contextual fear conditioning.

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Abstract
An infusion of the local anesthetic bupivacaine into the nucleus accumbens (Acb) impaired the acquisition but not the expression of fear responses (freezing) to a shocked context but spared both the acquisition and expression of these responses to an auditory conditioned stimulus (CS) paired with the shock. In contrast, an infusion of bupivacaine into the amygdala impaired the acquisition and the expression of fear responses to both the CS and the context. The results demonstrate a critical role for the Acb in the acquisition but not the expression of contextual fear conditioning and are consistent with the view that this structure is involved in the processes by which rats represent a context.