Degeneration and alteration of axons and intrafusal muscle fibers in spindles following tenotomy.
The effect of tenotomy (cutting of distal and proximal tendons) on the spindles in soleus muscle of adult rats was examined by light and electron microscopy in tissue obtained 1, 2, 3, 4, 5, 6, 7, and 14 days after surgery. Degenerative changes in the spindles progressed with time; also, the degree of alteration observed in a spindle varied with its position in the muscle, i.e., the earliest and most extensive changes occurred in spindles situated near the tendons. The disorganization and breakdown of myofibrils in the intrafusal muscle fibers were observed 3 days after tenotomy and continued with longer periods after surgery. The progression of morphological changes included alteration in fiber outline and the external lamina of the intrafusal muscle fibers and changes in the extracellular environment within the spindle capsule. The intrafusal muscle fibers of some spindles were shortened, apparently due to the loss of their polar ends, and degenerated axons which apparently supplied the intrafusal muscle fibers were also observed. Completely necrotic intrafusal fibers were absent. A possible relationship between the observed morphologic alterations and an adjustment of the spindle to muscle shortening is discussed.
D000818:Animals; D001369:Axons / Q000648:ultrastructure*; D005260:Female; D008465:Mechanoreceptors / Q000648:ultrastructure*; D009132:Muscles / Q000648:ultrastructure*; D009410:Nerve Degeneration; D051381:Rats; D011919:Rats, Inbred Strains; D013710:Tendons / Q000502:physiology*