ABSTRACTBackground:Prescription opioid addiction is a significant health problem characterized by compulsive drug seeking, withdrawal and chronic relapse. We investigated the neurobiological consequences of escalation of prescription opioid use using extended access to intravenous oxycodone self-administration in rats.Methods:Male Wistar rats acquired oxycodone self-administration (0.15 mg/kg/infusion, i.v.) in 1h or 12h access sessions. Electrophysiological and immunohistochemical studies investigated the effects of oxycodone self-administration on kappa opioid receptor (KOR) regulation of GABAergic signaling and dynorphin expression in the central nucleus of the amygdala (CeA).Results:Rats given 12h access to oxycodone for 5 sessions/week (LgA) escalated their responding more than rats given 1h oxycodone (ShA) or 12h saline access. Slowed escalation of responding was found in rats given 12h access for 7 sessions/week (LgA-7day) or rats pretreated with the KOR antagonist nor-binaltorphamine dihydrochloride (norBNI) before LgA (norBNI+LgA). The KOR agonist U-50488 decreased GABA release in CeA neurons of all groups except LgA. norBNI increased GABA release in control group neurons, suggesting tonic KOR activity. This activity was abolished in ShA, norBNI+LgA, and LgA-7day rat neurons, consistent with decreased CeA dynorphin immunoreactivity observed in LgA-7day rats. However, norBNI effects were reversed (decreased CeA GABA release) in LgA rat neurons.Conclusions:The experience of intermittent extended withdrawal periods accelerates the escalation of oxycodone self-administration and causes greater dysregulation of CeA KOR-mediated GABAergic signaling. A KOR agonist/antagonist switch effect seen with other drugs of abuse was absent, which suggests that oxycodone-induced neuroadaptations may be distinct from those resulting from other drugs of abuse.
Withdrawal-induced escalated oxycodone self-administration is mediated by kappa opioid receptor function
