Ethanol effects of pigeons trained to discriminate MK-801, PCP or CGS-19755

The non-competitive N-methyl-D-aspartate (NMDA) antagonists MK-801, PCP and ketamine have recently been found to produce full drug-appropriate responding in pigeons trained to ethanol (1.5 g/kg) in a two-key operant drug discrimination procedure. In the present study, ethanol (0.56-3.2 g/kg i.g.) was administered to pigeons trained to discriminate MK-801 (0.18 mg/kg, n = 5), PCP (1.0 mg/kg, n = 4) or the competitive NMDA antagonist CGS-19755 (1.8 mg/kg, n = 4) from vehicle. Up to doses that caused large reductions in response rates, ethanol produced only vehicle-appropriate responding in the pigeons trained to PCP and only low levels of drug-appropriate responding in pigeons trained to MK-801 and CGS-19755. The present results suggest there could be asymmetric generalization between the discriminative stimulus effects of i.g. ethanol and NMDA antagonists.