PACAP Signaling Network in the Nucleus Accumbens Core Regulates Reinstatement Behavior in Rat.

Cocaine use disorder (CUD) lacks FDA-approved treatments, partly due to the difficulty of creating therapeutics that target behavior-related neural circuits without disrupting signaling throughout the brain. Recent evidence highlights the therapeutic potential of targeting gut-brain axis components, such as GLP-1 receptors, to modulate neural circuits with minimal central nervous system disruption. Like GLP-1, pituitary adenylate cyclase polypeptide (PACAP) is a component of the gut-brain axis that regulates behavior through a network spanning the gut and brain. Here, we investigated the potential existence and function of an endogenous PACAP signaling network within the nucleus accumbens core (NAcc), which is a structure that integrates emotional, cognitive, and reward processes underlying behavior. We found that PACAP and its receptor, PAC1R, are endogenously expressed in the rat NAcc and that PACAP mRNA is present in medial prefrontal cortical projections to the NAcc. Behaviorally, intra-NAcc infusions of PACAP (100 pm) did not induce seeking behavior but blocked cocaine-primed reinstatement (10 mg/kg, IP). Intra-NAcc PACAP also inhibited reinstatement driven by co-infusion of the D1 receptor agonist (SKF 81297, 3 µg) but not the D2 receptor agonist (sumanirole, 10 ng). These findings are significant since D1 and D2 receptor activities in the NAcc govern distinct behavioral mechanisms indicating precise actions of PACAP even within the NAcc. Future research should examine whether NAcc PACAP signaling can be selectively engaged by peripheral gut-brain axis mechanisms, potentially unveiling novel therapeutic approaches for CUD and related disorders.