Effects of a 4 month enriched environment on the hippocampus and the myelinated fibers in the hippocampus of middle-aged rats

Abstract

An enriched environment has been shown to enhance learning and memory and to induce morphological changes in the hippocampus. In the present study, 14-month (middle-aged) female and male Sprague–Dawley rats were randomly divided into enriched environment (EE) rats and standard environment (SE) rats. EE rats were reared in an enriched environment and SE rats were reared in a standard environment for 4months. The spatial learning capacity was assessed with Morris water maze. The hippocampus and the myelinated fibers in the rat hippocampus were quantitatively investigated with a transmission electronic microscope technique and stereological methods. The female rats housed in an enriched environment showed improved performance in the Morris water maze. There was no significant difference in the total volume of hippocampus between SE rats and EE rats. The total length and total volume of the myelinated fibers in the hippocampus of the female and male EE rats were significantly increased, respectively, when compared to the female and male SE rats. The increase of the total length of the myelinated nerve fibers in the hippocampus was mainly due to the increase of the myelinated fibers with diameters from 0.5 to 0.9μm. Our results showed that a 4month enriched environment had significant effects on the spatial learning capacity and the myelinated fibers in the hippocampus of middle-aged rats. The present study might provide an important theoretical basis for searching for an ethological strategy to delay the progress of brain aging in the future.