An immunohistochemical study of nerve structures in the anulus fibrosus ofhuman normal lumbar intervertebral discs

Study Design. The innervation of the anulus fibrosus of human macroscopical ly normal intervertebral discs from five patients was investigated immunohi stochemically. Objectives. Immunoreactivity to general nerve markers synaptophysin and pro tein gene product 9.51 and to neuropeptides (substance P and C-flanking pep tide of neuropeptide V) was studied. Summary of Background Data. In the lumbar disc of a newborn, free nerve end ings have been demonstrated in the outer layers of anulus fibrosus. In dege nerated and herniated discs, nerve structures have been shown to penetrate deeper into the anulus fibrosus. There are only a few studies on the innerv ation of normal adult intervertebral disc tissue. Methods. Thin frozen sections of human normal lumbar intervertebral disc ti ssue were immunostained for general nerve markers and neuropeptides. Results. Synaptophysin and protein gene product 9.5 immunoreactive nerve st ructures were observed penetrating 3.5 mm and 1.1 mm into the anulus, respe ctively. Immunoreactivity to C-flanking peptide of neuropeptide Y and subst ance P were observed at: a maximum depth of 0.9 and 0.5 mm in the anulus, r espectively. Antibodies to the former have been used to study sympathetic n erves, whereas substance P is a transmitter present in sensory nerves. Conclusions. In anulus fibrosus samples from macroscopically normal discs, a general marker for nerve endings can be found at a depth of a few millime ters, whereas neuropeptide markers show nerves only in the outermost layers of the anulus fibrosus, This absence of demonstrable nerves in deeper anul us fibrosus in normal discs is probably not a methodologic artifact, becaus e blood vessels have also been demonstrated only at the disc surface. It is , however, possible that neuropeptide nerves also penetrate to a depth of a few millimeters, but that methodologic limitations permit the visualizatio n of only the neuropeptide nerves closest to the disc surface. The results of the present study lend support to previous suggestions that, except at t he surface, a normal intervertebral disc is almost without innervation.