An examination of prefrontal lesion size and the effects of cortical grafts on performance of the Morris water task by rats

Abstract

We studied the effects of prefrontal cortex lesions and prefrontal cortical grafts on the performance of rats in the Morris water task. Adult male rats received cortical tissue grafts (E21) 2 weeks after aspiration of the medial prefrontal cortex. They were later studied in the Morris water maze, and their behavior was subsequently correlated with lesion size, graft presence, and graft size. The results showed that lesion size had a major effect on behavior: animals with lesions including the prelimbic cortex were unable to learn the location of the hidden platform, whereas those with lesions sparing this cortex eventually learned the task, although they were impaired relative to control animals. The presence of cortical grafts had no chronic effect upon behavior, and the size of the graft also did not predict behavior. True Blue injections into the host or graft in different animals showed that although the grafts invaded the hosts, the hosts did not invade the grafts themselves. These results are consistent with the growing body of evidence that suggests that cortical grafts do not allow the re-establishment of neural networks that replace the lost tissue, although there may be a general trophic effect of cortical grafts.