[The discriminative stimulus properties of naloxone during dissociative learning in a Y maze in morphine-dependent rats].

The study was dedicated to evaluation of discriminative stimulus properties of opiate withdrawal syndrome precipitated by naloxon. The possibility of naloxon-appropriate reaction significantly increased in a dose-dependent manner (0-1.0 mg/kg, ED50 = 0.03 mg/kg) and was observed during the period of morphine withdrawal (8-96 h, peak at 24 h). Naloxone stimulus effects were antagonized by morphine (10-100.mg/kg), thus providing the experimental evidence for competitive and saturatable nature of interaction with opiate receptors. The probability of naloxone-appropriate reaction decreased during administration of the conditioned stimulus associated with morphine injection. Ligands of peripheral opiate receptors failed to either substitute for naloxone (methylnaloxon, 0.1-3.0 mg/kg) or attenuate naloxone stimulus effects (loperamide, 1-30 mg/kg).