Oxycodone withdrawal induces HDAC1/2-dependent transcriptional maladaptations in the reward pathway in a murine model of peripheral nerve injury

The development of physical dependence and addiction disorders due to misuse of opioid analgesics is a major concern with pain therapeutics. In this study, we developed a mouse model of oxycodone exposure to gain insight into genes and molecular pathways in reward-related brain regions that are affected by prolonged exposure to oxycodone and subsequent withdrawal in the presence or absence of chronic neuropathic pain. RNA-Sequencing (RNA-Seq) and bioinformatic analyses revealed that oxycodone withdrawal alone triggers robust gene expression adaptations in the nucleus accumbens (NAc), medial prefrontal cortex (mPFC), and ventral tegmental area (VTA), with numerous genes and pathways selectively affected by oxycodone withdrawal under peripheral nerve injury states. Our pathway analysis predicted that histone deacetylase 1 (HDAC1), an epigenetic modifier with a prominent role in striatal plasticity, is a top upstream regulator in opioid withdrawal in both the NAc and mPFC. Indeed, treatment with the novel HDAC1/2 inhibitor RBC1HI (Regenacy Brain Class 1 HDAC Inhibitor) attenuated behavioral manifestations of oxycodone withdrawal, with the drug being more efficacious under states of neuropathic pain. Since RBC1HI displays antiallodynic actions in models of neuropathic pain, inhibition of HDAC1/2 may provide an avenue for chronic pain patients dependent on opioids to transition to non-opioid analgesics. Overall, our study highlights transcriptomic events in components of the reward circuitry associated with oxycodone withdrawal under pain-free and prolonged neuropathic pain states, thereby providing information on possible new targets for the treatment of physical dependence to opioids and transitioning individuals to non-opioid medications for chronic pain management. Male C57BL6/J animals underwent sham or tibial spared nerve injury 2.5 months prior to oxycodone administration. Animals were then given daily subcutaneous injections of either saline or oxycodone (30 mg/kg) for 14 days. Animals then underwent spontaneous withdrawal for 21 days prior to sacrifice.