"Effects of the novel relatively short-acting kappa opioid receptor antagonist LY2444296 in behaviors observed after chronic extended-access cocaine self-administration in rats".

The recruitment of the stress circuitry contributes to a shift from positive to negative reinforcement mechanisms sustaining long-term cocaine addiction. The kappa opioid receptor (KOPr) signaling is upregulated by stress and chronic cocaine exposure. While KOPr agonists induce anhedonia and dysphoria, KOPr antagonists display antidepressant and anxiolytic properties. Most of the knowledge on KOPr antagonism is based on drugs with unusual pharmacokinetic and pharmacodynamic properties, complicating interpretation of results. Here we characterized in vivo behavioral and neuroendocrine effects of the novel relatively short-acting KOPr antagonist LY2444296. To date, no study has investigated whether systemic KOPr blockade reduced anxiety-like and depressive-like behaviors in animals previously exposed to chronic extended access cocaine self-administration. We tested the effect of LY2444296 in blocking KOPr-mediated aversive and neuroendocrine effects. Then, we tested acute systemic LY2444296 in reducing anxiety- and depression-like behaviors, as well as releasing the stress hormone corticosterone (CORT), observed after chronic extended access (18 h/day for 14 days) cocaine self-administration. LY2444296 blocked U69,593-induced place aversion and -reduced motor activity as well as U69,593-induced release of serum CORT, confirming its major site of action, without exerting an effect per se. Acute systemic administration of LY2444296 reduced anxiety-like and depressive-like behaviors, as well as CORT release, in rats tested after chronic extended access cocaine self-administration, but not in cocaine-naïve rats. Results suggest that acute blockade of KOPr by a relatively short-acting antagonist produces therapeutic-like effects selectively in rats with a history of chronic extended access cocaine self-administration.