Discriminative stimulus properties of naloxone in Long–Evans rats: assessment with the conditioned taste aversion baseline of drug discrimination learning
Psychopharmacology Online First 2 Julu 2008

The characterization of the discriminative stimulus properties of naloxone has focused primarily on its actions at the mu opioid receptor, although naloxone also displays an affinity for delta and kappa receptor subtypes.

The present study extends this characterization of the naloxone cue by investigating if relatively specific antagonists for the mu (naltrexone: 0.10–0.56 mg/kg), delta (naltrindole: 1–18 mg/kg), and kappa (MR2266: 1.8–10 mg/kg) opioid receptor subtypes will substitute for naloxone in animals trained to discriminate naloxone from its vehicle. The temporal nature of the naloxone cue was examined by varying pretreatment time points (15, 30, 45, 60 min). Finally, various doses of naltrexone methobromide (1–18 mg/kg) were assessed to determine peripheral mediation of the cue.

Only naloxone and naltrexone produced dose-dependent decreases in saccharin consumption. Naloxone administered at 15 and 30 min before saccharin produced decreases in consumption similar to that displayed on training days. Naltrexone methobromide substituted only at the highest dose tested (18 mg/kg).

Naloxone’s stimulus effects appear to be mediated centrally via activity at the mu opioid receptor.

Read Full Abstract

Request Reprint E-Mail: cd2994a@american.edu
___________________________________________________________