Disruption of latent inhibition in rats with postnatal hippocampal lesions.

Disruption of latent inhibition has been proposed as a possible model of cognitive abnormalities that underlie positive symptoms of a schizophrenia. We tested neonatal hippocampal lesioned rats in a latent inhibition paradigm. Lesions of the ventral hippocampus were induced by bilateral injections of ibotenic acid in 7 days old rats. The behavior of lesioned rats was tested postpubertally. We found a hyperresponsiveness to dopaminergic stimulation by apomorphine in locomotion tests. Latent inhibition was tested using the acquisition of a conditioned reaction in a two-way shuttle box. Sham operated control animals showed after preexposure of the to-be-conditioned stimulus (combined tone and light stimulus) a low acquisition. Ibotenic acid lesioned animals learned the conditioned reaction with and without preexposure in the same way, indicating disturbed latent inhibition. These results demonstrate disturbances in early postnatal hippocampal lesioned rats comparable with those seen in schizophrenic patients, thus further validating this procedure as a useful animal model of some aspects of schizophrenia.