Role of Piriform Cortex and Its Afferent Projections in Relapse to Fentanyl Seeking after Food Choice-Induced Voluntary Abstinence

We previously demonstrated a role of piriform cortex (Pir) in relapse to fentanyl seeking after food choice-induced voluntary absti-nence. Here, we used this model to further study the role of Pir and its afferent projections in fentanyl relapse. We trained male and female rats to self-administer palatable food pellets for 6 d (6 h/day) and fentanyl (2.5 mg/kg/infusion, i.v.) for 12 d (6 h/day). We assessed relapse to fentanyl seeking after 12 voluntary abstinence sessions, achieved through a discrete choice procedure between fen-tanyl and palatable food (20 trials/session). We determined projection-specific activation of Pir afferents during fentanyl relapse with Fos plus the retrograde tracer cholera toxin B (injected into Pir). Fentanyl relapse was associated with increased Fos expression in an-terior insular cortex (AI) and prelimbic cortex (PL) neurons projecting to Pir. We next used an anatomical disconnection procedure to determine the causal role of these two projections (AI-Pir and PL-Pir) in fentanyl relapse. Contralateral but not ipsilateral disconnection of AI-Pir projections decreased fentanyl relapse but not reacquisition of fentanyl self-administration. In contrast, con-tralateral but not ipsilateral disconnection of PL-Pir projections modestly decreased reacquisition but not relapse. Fluorescence -activated cell sorting and quantitative PCR data showed molecular changes within Pir Fos-expressing neurons associated with fentanyl relapse. Finally, we found minimal or no sex differences in fentanyl self-administration, fentanyl versus food choice, and fentanyl relapse. Our results indicate that AI-Pir and PL-Pir projections play dissociable roles in nonreinforced relapse to fentanyl seeking versus reacquisition of fentanyl self-administration after food choice-induced voluntary abstinence.