A drug discrimination analysis of ethanol-induced behavioral excitation and sedation: the role of endogenous opiate pathways.

The drug discrimination technique was used to characterize the biphasic behavioral effects of ethanol (ETOH) and examine the role of opiate pathways in mediating ETOH's excitatory (EX) and sedative (SED) phase effects. Forty Sprague-Dawley rats were trained to perform ETOH vs. saline discriminations during either ETOH's EX (6 min post-dose) or SED (30 min post-dose) phase of action in a double-lever food reinforced operant paradigm. After animals had achieved the required performance criterion, dose-response and phase-generalization tests were conducted in each group. In addition, preliminary studies were conducted to examine the effect of naloxone (NLX) pretreatment on discrimination of ETOH's EX and SED phase stimulus effects. Results of generalization testing demonstrate that discrimination of ETOH was dose-dependent and there was no generalization between phases regardless of the initial training condition. NLX pretreatment significantly attenuated discrimination of ETOH's EX phase effects but was ineffective in antagonizing ETOH's SED effects. These data demonstrate that the stimulus properties of ETOH are phase-dependent and suggest that opiate pathways are critical for the expression of ETOH's EX phase behavioral effects.