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 behavior al plasticity, appears to be dependent on NMDA receptor activation. Bl ockade of NMDA receptor activity has been shown to impair both classic al conditioning and spatial cognition. The present study evaluated the effects of NMDA-receptor blockade by MK801 on latent inhibition of th e classically conditioned nictitating membrane response in rabbits. No nreinforced preexposure to a tone conditioned stimulus retarded acquis ition rates in subjects pretreated with either saline or MK801. Thus, latent inhibition does not appear to be mediated by or dependent on NM DA activity or related NMDA-dependent long-term potentiation. Findings are discussed in relation to potential substrates for latent inhibiti on.