The effect of tenotomy and immobilization on muscle spindles and tendon organs of the rat calf muscles. A histochemical and morphometrical study.

The morphological and histochemical alterations in the muscle spindles and Golgi tendon organs of tenotomized or immobilized calf muscles of rats (m. soleus, m. gastrocnemius) were studied in 54 animals. The intact contralateral feet served as controls. There was no change in the number of mechanoreceptors in either the tenotomized or the immobilized muscles. The diameter of the intrafusal fibers was increased somewhat after 1 week, but decreased by 14% to 40% in 3 weeks. The periaxial space of muscle spindle had diminished or disappeared by 2 weeks from the beginning of the procedures. The thickness of the outer capsule of the spindles had markedly increased, especially in the polar region. In the Golgi tendon organs the capsule had also thickened significantly and the internal space diminished. The alterations were similar following tenotomy or immobilization, but more marked after tenotomy than after immobilization.