title: Sympathetic innervation of human muscle spindles.
abstract: The aim of the present study was to investigate the presence of sympathetic innervation in human muscle spindles, using antibodies against neuropeptide Y (NPY), NPY receptors and tyrosine hydroxylase (TH). A total of 232 muscle spindles were immunohistochemically examined. NPY and NPY receptors were found on the intrafusal fibers, on the blood vessels supplying muscle spindles and on free nerve endings in the periaxial space. TH-immunoreactivity was present mainly in the spindle nerve and vessel. This is, to our knowledge, the first morphological study concerning the sympathetic innervation of the human muscle spindles. The results provide anatomical evidence for direct sympathetic innervation of the intrafusal fibers and show that sympathetic innervation is not restricted to the blood vessels supplying spindles. Knowledge about direct sympathetic innervation of the muscle spindle might expand our understanding of motor and proprioceptive dysfunction under stress conditions, for example, chronic muscle pain syndromes.
authors.affiliation: Department of Integrative Medical Biology, Section of Anatomy, Umeå University, Umeå, Sweden.
authors.forename: Dina
authors.initials: D
authors.lastname: Radovanovic
authors.affiliation: Department of Anatomy, Medical Faculty Carl Gustav Carus, TU Dresden, Dresden, Germany.
authors.forename: Kevin
authors.initials: K
authors.lastname: Peikert
authors.affiliation: Department of Integrative Medical Biology, Section of Anatomy, Umeå University, Umeå, Sweden.
authors.forename: Mona
authors.initials: M
authors.lastname: Lindström
authors.affiliation: Department of Integrative Medical Biology, Section of Anatomy, Umeå University, Umeå, Sweden.|Department of Clinical Sciences, Ophthalmology, Umeå University, Umeå, Sweden.
authors.forename: Fatima Pedrosa
authors.initials: FP
authors.lastname: Domellöf
mesh_terms: D006801:Humans; D007150:Immunohistochemistry; D009046:Motor Neurons / Q000502:physiology; D009470:Muscle Spindles / Q000294:innervation*; D018482:Muscle, Skeletal / Q000294:innervation*; D009478:Neuropeptide Y / Q000032:analysis; D017476:Receptors, Neuropeptide Y / Q000032:analysis; D013564:Sympathetic Nervous System / Q000033:anatomy & histology*; D014446:Tyrosine 3-Monooxygenase / Q000032:analysis
chemical_list: D009478:Neuropeptide Y; D017476:Receptors, Neuropeptide Y; D014446:Tyrosine 3-Monooxygenase
keywords: chronic muscle pain; human skeletal muscles; muscle spindle; neuropeptide Y; neuropeptide Y receptors; sympathetic innervation; tyrosine hydroxylase