Competitive NMDA receptor antagonist, CGP 40116, substitutes for the discriminative stimulus effects of ethanol

A drug discrimination procedure was used to compare the ability of competitive (CGP 37849, D,L-(E)-2-amino-4-methyl-5-phosphono-3-pentanoate; CGP 40116, D-(E)-2-amino-4-methyl-5-phosphono-3-pentanoate) and non-competitive (dizocilpine) NMDA receptor antagonists to substitute for ethanol in rats trained to discriminate between a 1.0 g/kg dose of ethanol (i.p.) and saline. Dizocilpine (0.1-0.3 mg/kg) substituted partially for ethanol at doses that markedly reduced the rate of responding. CGP 37849 (1.25-5.0 mg/kg) substituted partially for ethanol and suppressed the response rate. CGP 40116 (0.5-2.5 mg/kg), an active D-stereoisomer of CGP 37849, completely substituted (88%) for ethanol, and caused only moderate suppression of the response rate.