Abstract: Objective To investigate the effects of short-term enriched environment on the white matter and the myelinated fibers in the white matter of aged male rats. Methods Twenty 24-month old male SD rats were reared in enriched environment (EE) or standard environment (SE) for 4 months, respectively. Four rats were randomly selected from each group. The white matter and the myelinated fibers in the rat white matter were quantitatively investigated with transmission electronic microscopy and stereological techniques. Results The white matter volume, the total length and total volume of the myelinated fibers in the white matter and the total volume of axons in the white matter of EE rats were all significantly larger than those of SE rats. The mean inner diameter and outer diameter of myelinated fibers, the total volume of myelin sheaths, the mean thickness of myelin sheaths, the mean inner perimeter and outer perimeter of myelin sheaths and the cross-sectional areas of the myelinated fibers, myelin sheaths and axons were not significantly different between EE and SE rats. Conclusion Short-term enriched environment has positive effects on the white matter and myelinated fibers in the white matter in 24-month male rats. These results suggest that short-term enriched environment might induce the remyelination of the demyelinated fibers in the white matter of aged male rats.

Key words: White matter, Myelinated fiber, Enriched environment, Stereology, Aged male rat