Inactivation of the Prelimbic Cortex Attenuates Context-Dependent Operant Responding.

ABSTRACT

Operant responding in rats provides an analog to voluntary behavior in humans and is used to study maladaptive behaviors, such as overeating, drug taking, or relapse. In renewal paradigms, extinguished behavior recovers when tested outside the context where extinction was learned. Inactivation of the prelimbic (PL) region of the medial prefrontal cortex by baclofen/muscimol (B/M) during testing attenuates renewal when tested in the original acquisition context after extinction in another context (ABA renewal). Two experiments tested the hypothesis that the PL is important in context-dependent responding learned during conditioning. In the first, rats learned to lever-press for a sucrose-pellet reward. Following acquisition, animals were infused with either B/M or vehicle in the PL and tested in the acquisition context (A) and in a different context (B). All rats showed a decrement in responding when switched from Context A to Context B, but PL inactivation decreased responding only in Context A. Experiment 2a examined the effects of PL inactivation on ABC renewal in the same rats. Here, following reacquisition of the response, responding was extinguished in a new context (C). Following infusions of B/M or vehicle in the PL, responding was tested in Context C and another new context (D). The rats exhibited ACD renewal regardless of PL inactivation. Experiment 2b demonstrated that PL inactivation attenuated the ABA renewal effect in the same animals, replicating earlier results and demonstrating that cannulae were still functional. The results suggest that, rather than attenuating renewal generally, PL inactivation specifically affects ABA renewal by reducing responding in the conditioning context.SIGNIFICANCE STATEMENT Extinguished operant behavior can recover ("renew") when tested outside the extinction context. This suggests that behaviors, such as overeating or drug taking, might be especially prone to relapse following treatment. In rats, inactivation of the prelimbic cortex (PL) attenuates renewal. However, we report that PL inactivation after training attenuates responding in the context in which responding was acquired, but not in another one. A similar inactivation has no impact on renewal when testing occurs in a new, rather than the original, context following extinction. The PL thus has a more specific role in controlling contextually dependent operant behavior than has been previously reported.