Memory-based learning in preweanling and adult rats after infantile x-irradiation-induced hippocampal granule cell hypoplasia.

Infantile exposure to x-irradiation induced severe hippocampal granule cell hypoplasia in preweanling and young adult rats. Hippocampally damaged pups, tested at 16 days of age, showed deficits in a memory-based discrimination based on single alternations of reward and nonreward when training was conducted at a 60-s intertrial interval (ITI) but not when conducted at a 30-s ITI. This deficit was still present at the 60-s ITI in animals x-irradiated in infancy and tested at 60-65 days of age. These data provide further support for the role of the hippocampus in intermediate-term memory and demonstrate, in a developmental context, the importance of an intact hippocampus in learning that depends on nonspatial memory.