A role for the ventral pallidum in context-induced and primed reinstatement of alcohol seeking.

The ventral pallidum (VP) is a major target of projections from the nucleus accumbens, and has been implicated in the reinstatement of psychostimulant seeking as part of a cortical-striatal-pallidal 'final common pathway' for relapse. Here, we studied the role of the VP in context-induced and primed reinstatement of alcoholic beer seeking, using a combination of microinjections and tract tracing studies. In experiment 1, rats were trained to respond to alcoholic beer in one context (A), and then extinguished in a second context (B), prior to testing for reinstatement (ABA renewal) and extinction (ABB). VP microinjection of the μ-opioid receptor (MOR) antagonist CTAP prevented reinstatement. In experiment 2, VP microinjection of CTAP also prevented the primed reinstatement of alcoholic beer seeking after rats were trained, extinguished, and tested in the same context. In experiment 3, we employed retrograde neural tract tracing together with c-Fos immunohistochemistry to identify the VP afferents recruited during context-induced reinstatement of alcoholic beer seeking. There was evidence for the recruitment of accumbens core→VP, basolateral amygdala→VP and paraventricular thalamus→VP pathways during context-induced reinstatement. These results indicate that the VP MORs are critical for context-induced reinstatement, and that the VP receives inputs from a number of regions known to be important in reinstatement of drug seeking.