RESUMO
BACKGROUND: Denervation substantially impairs healing of the medial collateral ligament (MCL). Because normal ligaments are sparsely innervated, we hypothesized that neuropeptide-containing neurons would sprout or proliferate after ligament transection, followed by later regression with healing, in a manner analogous to blood vessels. METHODS: We transected the right MCL in 9 mature female New Zealand white rabbits and killed 3 rabbits at 2, 6 or 14 weeks. Alternate sets of 12-mm serial sections of healing MCL scars were examined by fluorescent immunohistochemistry for substance P (SP), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY) and pan-neuronal marker PGP9.5. RESULTS: Normal MCLs had few peptidergic fibres located in the epiligament in a perivascular pattern. At 2 weeks, PGP9.5-, SP-and CGRP-positive fibres had increased in the epiligament adjacent to the injury. By 6 weeks, there were increases in CGRP-and PGP9.5-positive fibres in epiligament and scar, with similar but less marked increases in SP-positive fibres. At 14 weeks, there was notable regression of immunostained peptidergic nerve fibres in the scar. CONCLUSION: This experiment shows evidence for a remarkable plasticity of ligament innervation after injury, supporting the idea that neuronal factors play a fundamental role in wound healing.