Morphological and Histochemical Adaptation on Different Compartments in the Rat Medial Gastrocnemius Muscle ―Examination in the Early Phase of Skeletal Muscle Atrophy Caused by Cast-immobilization―

Rat medial gastrocnemius (MG) muscle is a compartmentalized muscle: two extramuscular nerve branches innervate proximal or distal compartments. The purpose of this study was to investigate adaptive responses of different compartments on the rat MG muscle in the early phase of skeletal muscle atrophy caused by one-week cast-immobilization. Cross sectional area (CSA) of each typed fiber in individual compartments were determined. CSA of each typed fiber in both compartments were decreased by cast-immobilization. CSA of type IIa and IId fibers in the proximal compartment were more atrophied in the distal compartment. These results suggested that the degree of atrophy for each typed muscle fiber between different compartments was not similar in the early phase of atrophy caused by cast-immobilization