[Ultrastructural alterations of Golgi tendon organs in disuse atrophy induced by muscle immobilization in rats].

In order to investigate changes in the ultrastructure of Golgi tendon organs (GTOs), the leg muscles of Wistar strain rats were immobilized over various periods. The immobilized triceps surae muscles were divided into three categories: a stretched-position group, a relaxed-position group, and Achilles tendon tenotomy group. After 1, 2, 3, 4, 6 and 8 weeks the muscle preparations dissected from the muscle belly and from the muscle-tendon junction were processed for classification of the fiber type histochemically and to find GTOs in plastic embedded-preparations. In the Achilles tenotomy group, an early fiber transformation from type I to type II fiber was observed, but in the other two groups a low rate of transition of fiber type occurred. At the end of 8 weeks, similar tendencies were observed in all groups. The ultrastructures of GTOs were not significantly different among three groups in basic and general structure when compared with the control group. However, swollen mitochondria in axons and axon terminals and damage in the lamina structure of the myelin sheath were seen in the capsule, axon terminal, and myelinated nerve fiber of GTOs. Although some differences were observed with shorter periods of immobilization, several structural changes were observed over longer periods, indicating the more profound effect of the length of the period rather than the type of immobilization.