Early morphological changes in the rat soleus muscle induced by tenotomy and denervation

Early morphological changes of the rat soleus muscle induced by tenotomy were examined by scanning and thin-section electron microscopy. The potassium hydroxide (KOH) and collagenase treatment was successfully used to remove extracellular materials and to examine the surface of muscle fibres with a scanning electron microscope. Morphological changes in the fibre surface appeared as early as 12 h after tenotomy, showing wrinkling of the sarcolemma in localized areas. At 24 h post-operative, transverse folds and grooves were conspicuous along the entire length of muscle fibres. Tenotomized muscles which were denervated simultaneously or within 24 h of tenotomy did not show any appreciable changes in the fibre surface. Thin-section electron microscopy revealed that the earliest change inside muscle fibres was the occurrence of focal or segmental areas of an irregular alignment of myofibrils representing myofibril disorganization with occasional disintegrated Z lines at 24 h after tenotomy. Segmental myofibril breakdown was occasionally found to extend obliquely from the fibre periphery to the central area. Such myofibril disorganization became more conspicuous along muscle fibres, especially in the central area, at 2 days after tenotomy, showing the loss of thick filaments within myofibrils and the disintegration of Z lines. Such myofibrillar disorganization can be correlated with the morphological changes in the fibre surface in view of the clinical implication.