title: Ultrastructural and molecular biologic comparison of classic proprioceptors and palisade endings in sheep extraocular muscles.
abstract: OBJECTIVE
  To analyze and compare the structural and molecular features of classic proprioceptors like muscle spindles and Golgi tendon organs (GTOs) and putative proprioceptors (palisade endings) in sheep extraocular muscle (EOMs).
  
  
  METHODS
  The EOMs of four sheep were analyzed. Frozen sections or wholemount preparations of the samples were immunohistochemically labeled and analyzed by confocal laser scanning microscopy. Triple labeling with different combinations of antibodies against neurofilament, synaptophysin, and choline acetyltransferase (ChAT), as well as alpha-bungarotoxin and phalloidin, was performed. Microscopic anatomy of the nerve end organs was analyzed by transmission electron microscopy.
  
  
  RESULTS
  The microscopic anatomy demonstrated that muscle spindles and GTOs had a perineural capsule and palisade endings a connective tissue capsule. Sensory nerve terminals in muscle spindles and GTOs contained only a few vesicles, whereas palisade nerve terminals were full of clear vesicles. Likewise, motor terminals in the muscle spindles' polar regions were full of clear vesicles. Immunohistochemistry showed that sensory nerve fibers as well as their sensory nerve terminals in muscle spindles and GTOs were ChAT-negative. Palisade endings were supplied by ChAT-positive nerve fibers, and the palisade complexes including palisade nerve terminals were also ChAT-immunoreactive. Motor terminals in muscle spindles were ChAT and alpha-bungarotoxin positive.
  
  
  CONCLUSIONS
  The present study demonstrated in sheep EOMs that palisade endings are innervated by cholinergic axons exhibiting characteristics typical of motoneurons, whereas muscle spindles (except the polar regions) and GTOs are supplied by noncholinergic axons. These results raise the question of whether palisade endings are candidates for proprioceptors in EOMs.
authors: Center of Anatomy and Cell Biology, Integrative Morphology Group, Medical University Vienna, Vienna, Austria.
authors: Stefanie
authors: S
authors: Rungaldier
authors: Stefan
authors: S
authors: Heiligenbrunner
authors: Regina
authors: R
authors: Mayer
authors: Christiane
authors: C
authors: Hanefl-Krivanek
authors: Marietta
authors: M
authors: Lipowec
authors: Johannes
authors: J
authors: Streicher
authors: Roland
authors: R
authors: Blumer
mesh_terms: D000818:Animals; D002038:Bungarotoxins / Q000378:metabolism; D002795:Choline O-Acetyltransferase / Q000378:metabolism; D002799:Cholinergic Fibers; D008465:Mechanoreceptors / Q000378:metabolism / Q000648:ultrastructure*; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D009470:Muscle Spindles / Q000378:metabolism / Q000648:ultrastructure*; D009411:Nerve Endings / Q000378:metabolism / Q000648:ultrastructure*; D009801:Oculomotor Muscles / Q000294:innervation*; D009802:Oculomotor Nerve / Q000648:ultrastructure*; D012756:Sheep; D016708:Synaptophysin / Q000378:metabolism
chemical_list: D002038:Bungarotoxins; D016708:Synaptophysin; D002795:Choline O-Acetyltransferase