Site-dependent difference in the density of sympathetic nerve fibers in muscle-innervating nerves: a histologic study using human cadavers

ABSTRACT

The autonomic nerve supply of skeletal muscle has become a focus of interest because it is closely related to the adaptation of energy metabolism with aging. However, there is no comprehensive information concerning the sympathetic nerves present in muscle-innervating nerves (muscle-nerve). At the point of entry of muscle-nerves into 8 striated muscles (the soleus, extensor carpi radialis, infraspinatus, genioglossus, extra- ocular medial rectus, temporalis, lateral pterygoid, and digastricus anterior belly) in 15 cadavers of elderly people, we counted both tyrosine hydroxylasepositive nerve fibers (TH- fibers) and motor nerve fibers to estimate the ratio of THfiber/ motor fibers. The 3 limb muscles were found to have a high ratio (soleus, 58%; infraspinatus; 45%; extensor, 36%), whereas the 4 head muscles (digastricus, 23%; genioglossus, 15%; temporalis, 10%; lateral pterygoid, 6%; medial rectus, 1%) had relatively low ratios. The site- dependent characteristics of the THfibers seemed to reflect their commitment to muscle activity. However, some discrepant characteristics were noted 1) In spite of the tonic and continuous activity required for both the genioglossus and infraspinatus, the proportions of TH-fibers were quite different between the tongue and the shoulder muscles; 2) Likewise, the soleus and extra-ocular rectus showed a considerable difference, even though rapid and phasic contraction is essential for both muscles. Rather than reflecting the influence of postnatal functional demand, these site- dependent characteristics might develop as a result of differences in sympathetic innervation of the striated muscles during fetal development, i.e., a short course along the arteries feeding the head muscles, or a long course along the muscle-nerves to the limb muscles (AU)

RESUMEN

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