Stereological investigation of age-related changes of myelinated fibers in the rat cortex

Abstract

In the present study, the cortex volume, total volume, total length and mean diameter of the myelinated fibers in the cortices of young, middle-aged, and aged Long-Evans rats were quantitatively investigated by using stereological methods and electron microscopy techniques. There were no significant differences in the myelinated fibers between young and middle-aged rat cortex. The cortex volume and the total length of the myelinated fibers in the cortex of aged rats were significantly lower than those of young and middle-aged rats. However, no significant difference was found in the total volume of the myelinated fibers among three groups. The disproportional changes in the total length and total volume of the myelinated fibers in the cortex of aged rats and the absolute distribution of the total length of the myelinated fibers in the cortex of the three groups suggested that the age-induced decrease of the myelinated fibers might be due mainly to a loss of the myelinated fibers with smaller diameters. The present results together with our previous findings indicated that the age-related changes of the myelinated fibers occurred widely in the central nervous system and that the age-related changes of the myelinated fibers in cortex occurred later than those in white matter.