Acamprosate does not antagonise the discriminative stimulus properties of amphetamine and morphine in rats

Acamprosate (calcium acetylhomotaurinate) is a GABA derivative that prevents drinking relapses in a significant number of alcoholics. Since little is known about the interaction of acamprosate with other addictive drugs, we studied the effects of this agent (as sodium salt) in two groups of rats trained to discriminate, respectively, morphine (1.7 mg kg(-1)i.p.) or amphetamine (0.5 mg kg(-1)i.p.) from solvent in a two-lever fixed ratio 30 operant behaviour reinforced by water access. Accordingly to the finding that acamprosate inhibits the action of excitatory aminoacids, its effects were compared with those of dizocilpine (MK-801), an NMDA antagonist. Results show that acamprosate (170 and 320 mg kg(-1)i.p. ) produced a slight, and not significant, shift to the left of generalization curves of both morphine and amphetamine without affecting response rates. In contrast, MK-801 potentiated response rate effects of both morphine and amphetamine without affecting their generalization curves. As far as discriminative stimuli participate in the relapsing process of addiction, our results do not predict a role of acamprosate in the prevention of amphetamine or morphine abuse relapsing.