Pairing extinction training with vagus nerve stimulation (VNS) reduces drug-seeking by altering activity in afferents...

Relapse triggered by drug-associated cues or stress remains a major challenge in treating substance use disorders (SUDs), as re-exposure reliably provokes craving and reinstatement of drug seeking. Extinction-based interventions can reduce cue reactivity, yet extinction learning is often weak or context-dependent, limiting its clinical impact. Vagus nerve stimulation (VNS) enhances learning-related plasticity via widespread engagement of neuromodulatory systems and cortical circuits. Recent preclinical work shows that pairing extinction with VNS facilitates extinction learning and reduces cue-induced reinstatement of cocaine seeking, suggesting translational potential as an adjunct to exposure-based therapies. However, the circuit-level mechanisms underlying these effects remain unclear. To address this gap, we examined how VNS paired with extinction alters activity in medial prefrontal cortex (mPFC) networks that regulate drug seeking, focusing specifically on afferent projections from the basolateral amygdala (BLA) and ventral hippocampus (vHPC). Male rats received retrograde AAV-eGFP infusions into either the prelimbic (PL) or infralimbic (IL) cortex to label upstream projections, followed by cocaine self-administration, extinction training with VNS or sham stimulation, and cue-induced reinstatement. cFos immunolabeling in the BLA and vHPC revealed pathway-specific modulation: VNS decreased overall BLA activity and reduced activation of BLA to IL projections, but increased activation of BLA to PL projections. In the vHPC, VNS selectively decreased activation of vHPC to IL projections without affecting PL-projecting neurons. Because these pathways synapse onto parvalbumin interneurons (PVIs) in the mPFC, we quantified PVI activation and found that VNS decreased overall prefrontal cFos expression, but increased PVI activity in the PL, and decreased PVI activity in the IL. Together, these results demonstrate that VNS paired with extinction reshapes prefrontal-amygdala-hippocampal circuits in a pathway-specific manner, potentially modulating feed-forward inhibition to reduce relapse-like behavior. These findings support VNS as a promising strategy to strengthen extinction learning and improve treatment outcomes in SUD.