HISTOLOGICAL STUDY OF AGE-RELATED CHANGES IN THE SKELETAL MUSCLES OF MALE ALBINO RATS

SummaryThis work was performed to study the possible histological changes that may occur in the skeletal muscles of male albino rats from birth till aging. For this purpose, thirty healthy male albino rats were utilized. The animals were classified into three age groups (ten rats each); Group A: Neonatal animals (1 day-1 month old rats), Group B: Adult animals (5-8 months old rats), and Group C: Senile animals (12-18 old rats).The animals were anaesthetized; diaphragm and rectus abdominis were dissected out. Paraffin sections were prepared, stained with H & E stains, Mallory’s trichrome stain, orcein stain and immunostained for detection of desmin, and examined by light microscope. Also, minute specimens were rapidly taken and processed to obtain ultra thin sections stained with uranyl acetate, to be examined by TEM.The results of light microscope examination of diaphragm and rectus abdominis muscles of all age groups of rats revealed muscle fibers parallel to each others. Muscle fascicles were separated by the connective tissue of the perimysium.The individual muscle fibers were covered by the connective tissue of the endomysium.The muscle fibers showed eosinophilic sarcoplasm and cross striations in the form of alternating dark and light bands. The nuclei were oval and peripheral. The intercellular spaces showed blood capillaries and collagen fibers. Examination of immunostained sections showed that the desmin was highly concentrated in the newborn rat muscles, moderately concentrated in the adult rat muscles and minimally concentrated in the senile group.Ultrastructurally, longitudinally-sectioned myocytes demonstrated long, parallel, and striated myofibrils. The myofibrils showed A, I and H bands as well as Z and M lines.Examination of the newborn rat muscles showed myocytes with large euchromatic nuclei. Blood capillaries and fat cells were seen in the intercellular spaces.The myocytes of adult rats revealed elongated euchromatic nuclei. Numerous mitochondria appeared around the nucleus and between the myofibrils. Glycogen granules were seen in the sarcoplasm. Collagen fibers were observed in the intercellular spaces and around blood vessels.Examination of senile rat muscles revealed some myocytes with irregularly-out lined nuclei. There were some cells showed myofibrils with areas of disorganized or lost microfilaments. Mitochondria appeared between the myofibrils and around the nucleus. Some of them were large, deformed. T-tubules were seen in the sarcoplasm at the level of A-I junction. There was a marked increase in collagen fibers in the intercellular spaces. Also, the sarcoplasm showed membrane whorl vacuole and some electron dense bodies.It is concluded that several age-related changes occur in the skeletal muscles that may lead to weakness in the muscle and reduce its viscoelastic properties that could affect the maximum total strength in old age.