Latent inhibition in rats is abolished by NMDA-induced neuronal loss in the retrohippocampal region, but this lesion effect can be prevented by systemic haloperidol treatment.

Latent inhibition (LI) refers to the retardation in learning about the significance of a neutral stimulus that results from its nonreinforced preexposure. There is evidence that electrolytic or aspiration lesions of the hippocampal formation can disrupt LI (see I. Weiner, 1990). It has been suggested that this effect may stem from the interruption of a projection from the retrohippocampal region to the nucleus accumbens (A. J. M. Clark et al., 1992). The present experiment assessed this possibility by comparing LI in rats with retrohippocampal N-methyl-D-aspartate (NMDA) lesions extending from the entorhinal cortex to the ventral subiculum to that seen in vehicle controls and unoperated controls. LI was abolished by the retrohippocampal lesion. The effect of the lesion on LI was prevented by treatment with systemic haloperidol (0.2 mg/kg). The results are discussed with respect to an animal model of schizophrenia.