Impingement of plical synovial tissue in a facet joint could cause pain. Plical tissue was removed during surgery for recurrent disc herniation or spinal stenosis. The presence of nerves was studied with silver impregnation, immunofluorescence, and avidin-biotin-peroxidase complex (ABC) immunostaining. Heterologous antisera to protein gene product (PGP) 9.5, substance P, calcitonin gene-related peptide (CGRP), and galanin were used to stain nerves. After silver impregnation, nerve-like structures were observed perivascularly. Such nerves located close to blood vessels were also immunoreactive for PGP 9.5, a more general cytoplasmic neural marker, whereas only few perivascular small varicosities were seen with antisera to substance P and galanin and none with antiserum to CGRP. In addition, PGP-9.5-, substance-P-, and galanin-immunoreactive nerves were occasionally seen very near to fat globules. Very few peptide-immunoreactive nerve varicosities were seen with immunofluorescence, and none of the PGP-9.5-immunoreactive nerves that were observed with ABC immunostaining were immunoreactive for neuropeptides as well. One mechanism for pain production could be mechanical compression of fatty tissue, but it is considered more likely that nerves in this particular tissue are mainly involved in local vasoregulation and that they are not sensory nociceptive nerves.
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