Fibrillin and elastin networks in extrafusal tissue and muscle spindles of bovine extraocular muscles.

PURPOSE Bovine extraocular rectus muscles were examined to map the distribution of elastin and fibrillin in extrafusal tissue and muscle spindles. METHODS Immunohistochemical techniques and immunolocalization were employed to pin-point the placement of molecules relative to muscle fibers. RESULTS Strands containing elastin and fibrillin surrounded all extrafusal fibers. They also covered the external surface of intrafusal fibers, more extensively at the equator than at the pole. Within strands elastin was placed in the center, whereas fibrillin was located in microfibrils on the periphery. CONCLUSIONS The wide distribution in extrafusal tissue of elastin and fibrillin suggests that they are factors in determining the mechanical properties of extraocular muscles. Their placement in proximity to individual intrafusal fibers should affect the viscoelastic properties of these fibers and, thus, influence the dimensions of the afferent discharge.