Adapter protein 2-modulated μ -opioid receptor trafficking in paraventricular thalamus contributes to fentanyl contextual addiction memory in mice.

Fentanyl and its analogues are the most commonly used synthetic opioid analgesics in clinical practice, but their abuse is a significant concern. Drug-paired environmental cues often trigger memory retrieval, leading to relapse, complicating treatment and overdose prevention. In this study we investigated μ-opioid receptor-related molecular mechanisms underlying the retrieval of fentanyl contextual addiction memory in mice. A conditional place preference (CPP) model was established in mice by citrate injections of fentanyl (0.1 mg/kg) for 4 days. By performing whole-brain screening using c-Fos immunofluorescence staining, we found that the paraventricular thalamus (PVT) was dramatically activated. We conducted Western blotting, co-immunoprecipitation and proteomics to evaluate the proteins interacting with μ-opioid receptors on the membrane, and found marked externalization of μ-opioid receptors on the membrane in PVT neurons. We revealed that μ-opioid receptors trafficking in PVT was regulated by the extent of binding of Ap2a1 to the membrane μ-opioid receptors. By conditional knockdown and chemogenetic manipulation, we demonstrated the contribution of μ-opioid receptors to the retrieval of fentanyl contextual memory via modulating the neuronal activity in PVT. In conclusion, this study suggests that Ap2a1-mediated trafficking of μ-opioid receptors underlies the retrieval of fentanyl contextual addiction memory through regulating the neuronal activity in PVT.