Key result
Immunohistochemical analysis of 232 human muscle spindles provided anatomical evidence for direct sympathetic innervation of intrafusal fibers via NPY and NPY receptors.
This study provides the first morphological evidence of direct sympathetic innervation of human muscle spindles, which may help explain motor and proprioceptive dysfunction under stress conditions.
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May suggest sympathetic modulation of proprioception; leaves open physiological relevance and clinical implications.
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.
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Radovanovic et al. (2015) studied this question. Immunohistochemical examination for NPY, NPY receptors, and TH was evaluated on Presence and localization of sympathetic innervation. Immunohistochemical analysis of 232 human muscle spindles provided anatomical evidence for direct sympathetic innervation of intrafusal fibers via NPY and NPY receptors.
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