Enriched environment increases the myelinated nerve fibers of aged rat corpus callosum.

In this study, the effect of enriched environment (EE) on the spatial learning of aged rats was examined, and then the effects of EE on the aged corpus callosum (CC) were investigated by means of the modern stereological methods. We found that EE significantly improved the spatial learning of aged rats. The CC volume, the total volume of the myelinated fibers and total volume of the myelin sheaths in the CC, the total length of the myelinated fibers in the CC of enriched rats were significantly increased when compared to standard rats. The increase of the myelinated fibers in enriched rat CC might provide one of the structural bases for the enrichment-related improvement of the spatial learning. This study provided, to the best of our knowledge, the first evidence of environmental enrichment-induced increases of the CC and the myelinated fibers in the CC of aged rats.