LATENT INHIBITION OF THE CLASSICALLY-CONDITIONED RABBIT NICTITATING-MEMBRANE RESPONSE IS UNAFFECTED BY THE NMDA ANTAGONIST MK801

Induction of long-term potentiation, a putative substrate for behavioral plasticity, appears to be dependent on NMDA receptor activation. Blockade of NMDA receptor activity has been shown to impair both classical conditioning and spatial cognition. The present study evaluated the effects of NMDA-receptor blockade by MK801 on latent inhibition of the classically conditioned nictitating membrane response in rabbits. Nonreinforced preexposure to a tone conditioned stimulus retarded acquisition rates in subjects pretreated with either saline or MK801. Thus, latent inhibition does not appear to be mediated by or dependent on NMDA activity or related NMDA-dependent long-term potentiation. Findings are discussed in relation to potential substrates for latent inhibition.