Attenuation of the discriminative stimulus properties of cocaine by delta-opioid receptor antagonists.

The effects of selective delta-opioid receptor antagonists on the discriminative stimulus properties of cocaine were examined in rats trained to discriminate between cocaine (10 mg/kg) and saline. Pretreatment with naltrindole (a non-selective delta-opioid receptor antagonist) and naltriben (a selective delta 2-opioid receptor antagonist), but not 7-benzylidenenaltrexone (a selective delta 1-opioid receptor antagonist), significantly attenuated the discriminative stimulus properties of cocaine. Naltrindole and naltriben attenuated the discriminative stimulus properties of doses of cocaine lower than the training dose. Although the effects produced by the training dose were not changed, our finding may have some bearing on the relative importance of the role of delta-opioid (especially delta 2-opioid) receptors in the discriminative stimulus properties of cocaine.