COMPARISON OF IMMUNOHISTOCHEMICAL AND FUNCTIONAL REINNERVATION OF SKIN AND MUSCLE AFTER PERIPHERAL-NERVE INJURY

In order to investigate the usefulness of immunohistochemical detectio n of regenerating axons as a correlate of functional recovery, reinner vation of mouse foot pads, hairy skin, and muscle were studied at seve ral intervals along 3 months after sciatic nerve crush using immunohis tochemical markers PGP 9.5 and CGRP. These histological results were c ompared with functional recovery of sweat glands (SGs), plantar muscle s, and pain sensibility. One week after nerve injury all neural functi ons were abolished in the operated hindpaw of all mice, no CGRP-immuno reactive (-ir) fibers were seen in the samples studied, while PGP 9.5 immunofluorescence remained at dim levels within nerve trunks, but dis appeared from terminal innervation. The first PGP 9.5- and CGRP-ir reg enerating fibers were seen at 15-16 days postoperation (dpo) in dermal nerve trunks of dorsal hairy skin and some days later in dermal trunk s of foot pads. Regenerating nerve fibers progressed along the periphe ry of the dermis reinnervating the different dermal appendages, At 25 dpo all target organs were reinnervated. The first SGs activated by pi locarpine reappeared by 16 dpo and increased in number to 88% of contr ol counts. Nociceptive responses reappeared at 17 dpo and reached 100% of control values. The first PGP immunofluorescence in neuromuscular junctions was seen at 16 dpo, while the first muscle action potentials were recorded at 19 dpo, and the potentials amplitude increased to 66 % of controls. Good correlations were found between morphological and functional results of reinnervation. However, the density and distribu tion of nerve profiles in the tissues studied did not reach normal lev els, while neural functions conveyed by small fibers reached levels si milar to controls. (C) 1997 Academic Press.