Structural changes in locust leg muscle fibres in response to tenotomy and joint immobilization

Tenotomy and immobilization at minimum physiological length resulted in degenerative changes in the ultrastructure of the locust metathoracic flexor tibiae muscle.Degeneration was observed in some muscle fibres 9 days after tenolomy and was progressive, affecting an increasing proportion of fibres at longer times after operation. Changes included disruption and loss of myofilaments, Z-disk streaming, degeneration of sarcoplasmic reticulum, formation of large membranous complexes and changes in number and appearance of mitochondria. Different muscle fibres followed different degenerative pathways. By 73 days very few intact muscle fibres remained.Joint immobilization resulted in similar but much less severe progressive degeneration. Degenerate fibres were largely localized in the distal and medial parts of the muscle. Both immobilized and tenotomized muscles were invaded by large numbers of fat body cells in the later stages of degeneration.Nerve terminals on degenerate tenotomized and immobilized muscle fibres were ultrastructurally normal. Tendinous cells attaching degenerate muscle fibres to the cuticle themselves degenerated.