Neuropeptide- and tyrosine hydroxylase-immunoreactive nerve fibers in painful Morton's neuromas

We examined the expression of three neuropeptides that have been implicated in nociceptive transmission, and the sympathetic nerve fiber marker tyrosi ne hydroxylase, in 11 painful human Morton's neuromas, using immunohistoche mistry. Antibodies against the neural markers RT97 and PGP 9.5 were used to map the general nerve fiber organization of the neuromas. Four specimens o f normal human peripheral nerves were used as controls. Substance P, calcit onin gene-related peptide, and neuropeptide Y immunoreactivities were more pronounced in neuroma tissue than in control nerves. Neuropeptide immunoflu orescence was seen both in larger nerve fiber trunks and in masses of disor ganized axon profiles dispersed in loose connective tissue, Tyrosine hydrox ylase immunoreactivity was present at varying levels of expression in neuro ma nerve fiber trunks, in connective tissue nerve fiber bundles, and around some blood vessels, Our findings suggest that neuropeptides are involved i n the response to injury in Morton's neuromas and that they could play a ro le in initiation or modulation of pain. In addition, pain from Morton's neu romas could be influenced by sympathetic nerve fibers. (C) 2000 John Wiley & Sons, Inc.