Role of ventral subiculum neuronal ensembles in incubation of oxycodone craving after electric barrier-induced voluntary abstinence

We recently developed a rat model of incubation of oxycodone craving after electric barrier-induced voluntary abstinence, and showed time-dependent increases in drug seeking on abstinence days 15 and 30 compared to day 1. Here, we studied the role of ventral subiculum (vSub) neuronal ensembles in incubation of oxycodone seeking after electric barrier-induced abstinence using the activity marker Fos, and inactivation of vSub neurons using muscimol+baclofen (GABAA+B receptor agonists) or the Daun02 chemogenetic inactivation procedure. We trained Sprague Dawley or Fos-lacZ transgenic rats to self-administer oxycodone (0.1 mg/kg/infusion, 6-h/d) for 14 days. We then introduced an electric barrier of increasing shock intensity (0.1 to 0.4 mA) near the drug-paired lever that led to cessation of oxycodone self-administration. We tested Sprague Dawley rats (n=6-7/group) for relapse to oxycodone seeking (extinction tests) in the absence of shock and drug on abstinence day 15, and extracted the brains for Fos immunohistochemistry or tested the rats (n=10-12/group) after vSub injections of vehicle or muscimol+baclofen. We then tested Fos-lacZ transgenic rats (n=10-11/group) for relapse to oxycodone seeking on abstinence day 18 after selective Daun02 induced chemogenetic inactivation of relapse-activated Fos neurons in vSub on abstinence day 15. Relapse after electric barrier-induced abstinence was associated with increased Fos expression in vSub, and both local and selective inactivation of vSub Fos-expressing neuronal ensembles decreased “incubated” oxycodone seeking. Together, these data demonstrate a role of vSub neuronal ensembles in incubation of oxycodone craving after cessation of drug taking due to adverse consequences of drug seeking.