Ultrastructural Changes in the Skeletal Muscle of Senile Rats with Significant Age-Dependent Motor Deficits

The anterior tibial (AT) muscle of 6 female Wistar rats aged 35-44 months, was examined by an electron microscopy. Previously, significant age-dependent functional and morphological deficits were found in these rats including [1] a strongly decreased muscle mass and force, [2] muscle stiffness, [3] spontaneous, tonic electromyographic activity, and [4] light-microscopic features of chronic denervation atrophy. In the present study diverse ultrastructural changes were found in muscle which correspond to chronic denervation atrophy. A number of already described abnormalities could be demonstrated in our material. However, sarcoplasmic reticulum (SR) tubular formations and extensive muscle fiber fragmentation have not been previously associated with senile changes in muscle. This can be explained by a very advanced age of our experimental animals and, in consequence, a more advanced denervation atrophy. Therefore it would appear that no single abnormality or set of morphological changes are characteristic of senile skeletal muscle.