Neonatal damage of the ventral hippocampus impairs working memory in the rat.

We investigated if a developmental lesion of the ventral hippocampus, studied previously as an animal model of schizophrenia, impairs performance in working memory tests related to the prefrontal cortex. Adult rats with a neonatal or adult excitotoxic lesion of the ventral hippocampus were tested in a continuous delayed alternation and a discrete paired-trial variable-delay alternation task. Performance of rats with the neonatal lesion was impaired as compared with control rats on both tasks, whereas performance of rats with the adult lesion was not altered in either task. The pattern of impaired performance, that worsened with increasing delays in neonatally lesioned rats, resembled that reported previously in animals with adult lesions of the medial prefrontal cortex. These results indicate that an early developmental, but not adult hippocampal, insult impairs performance in tasks sensitive to the integrity of the prefrontal cortex, and suggest that working memory may be compromised by neonatal damage of the ventral hippocampus.