Presence and morphological variability of Golgi tendon organs in the distal portion of sheep extraocular muscle

This study was undertaken to demonstrate the presence of Golgi tendon organ s (GTOs) in the distal portion of sheep extraocular muscle (EOM) and to des cribe the morphological variability of these receptors. Extraocular muscles of a young and an old sheep were perfusion fixed and/or immersion fixed. T issue was prepared for light microscopy and transmission electron microscop y. Immunohistochemistry was done to demonstrate the myosin pattern of the i ntracapsular muscle fibers of the GTOs. All GTOs in the distal portions of the sheep EOMs were located in a distinct muscle layer which was designated in a former investigation as the so-called peripheral patch layer. Each EO M of the young sheep contained GTOs; between four and 15 GTOs were counted in the rectus EOMs. Eight GTOs were found in the superior rectus of the old sheep. Golgi tendon organs in EOMs of the young and the old sheep did not differ in their morphology. In the young sheep the mean length of the GTOs was 447 +/- 132 mu m (n = 60) and their mean width 101 +/- 26 mu m (n = 60) . In the old sheep values were 576 +/- 188 mu m (mean length, n = 8) and 10 3 +/- 18 mu m (mean width, n = 8). The GTOs were encapsulated by perineuria l cells. In 12 GTOs, only collagen bundles were inside. In the remaining GT Os (56), intracapsular muscle fibers were present. Muscle fibers entered th e proximal poles of the GTOs and either terminated inside the receptors or muscle fibers left the GTOs at their distal poles. These intracapsular musc le fibers were of the multiply-innervated type. In the GTOs variably shaped nerve terminals were found which contained a high number of mitochondria. In two GTOs, additionally, nerve terminals with aggregates of densely packe d vesicles were present. Anat Rec 258:359-868, 2000. (C) 2000 Wiley-Liss, I nc.