Postnatal growth and development of skeletal muscle fibers in albino rat. A histological and histochemical study

ABSTRACT

This work was done to study the postnatal development of the skeletal muscle fibers, which have received little attention in the few last decades, regarding their morphological and histochemical features. The gastocnemius muscle of fifty albino rats of different ages were examined histologically using H and E and Van Gieson's stain to study the morphological features of the developing skeletal muscle. This reveals that the skeletal muscle fibers, since birth, were enclosed by three levels of connective tissue containing blood vessels and nerves, which increase in amount with the advance of age. The nuclei were distributed irregularly throughout the skeletal muscle fiber during the first week of life, and then they take a peripheral position. The transverse striations of the skeletal muscle fibers couldn't be seen until 14[th] days of age of albino rat. The histochemistry of the developing skeletal muscle was investigated using Periodic acid Schiff reagent, Nitroblue tetrazolium technique for the detection of succinic dehydrogenage activity and Tetrazolium reductase linked staining technique for the detection of alpha-glycerophosphate dehydrogenase activity. This revealed that the gastrocnemius muscle displayed increasingly glycolytic fast fibers profile with the advance of age. According to succinic dehydrogenase activity the muscle could be differentiated since birth into 2 types of fibers Type 1 [slow oxidative fibers] and Type II [fast glycolytic fibers]. From 14[th] days postnatally a third type of fibers, Type III [fast oxidative glycolytic fibers] could be recognized. Differentiation of both types of skeletal muscle fibers [slow and fast twitch] according to alpha-glycorophosphate dehydrogenase enzyme activity could be made from the beginning of the first week of life, whereas the appearance of the third type of fibers[fast oxidative glycolytic fibers] was delayed till the third week of life. As regard the glycogen content, the skeletal muscle fibers in younger age groups contained more glycogen than in adults and differentiation between fast and slow twitch fibers based on this point could be made at the end of the first week postnatally. It is concluded that the skeletal muscle in albino rat was undeveloped at birth and its growth and differentiation was a gradual process including major changes in both morphological and histochemical features