Papers of the Week

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 misuse in order 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 RCY1305 attenuated behavioral manifestations of oxycodone withdrawal, with the drug being more efficacious under states of neuropathic pain. Our studies also suggest that RCY1305 treated mice did not develop conditional place preference. Since RCY1305 displays antiallodynic actions with no rewarding effects 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-naïve 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.