Early nerve regeneration after Achilles tendon rupture — a prerequisite for healing? A study in the rat

Abstract

Nerve regeneration during healing of Achilles tendon rupture in the rat was studied by immunohistocheinistry including semiquantitative assessment. Neuronal markers for regenerating and mature fibers, ie., growth associated protein 43 (GAP-43) and protein gene product 9.5 (PGP 9.5), respectively, were analyzed at different time points (1-16 weeks) post-rupture. In the paratenon, both thc ruptured and intact contralateral tendon (control) consistently exhibited immunoreactivity to the two neuronal markers. However, in the proper tendinous tissue only the ruptured tendon showed immunoreactivity to GAP-43 and PGP 9.5. This expression was seen already at week 1 post-rupture to reach a peak at week 6 followed by a successive drop till week 16. Also the occurrence of sensory and autonomic fibers according to immunorcactivity for calcitonin gene-related peptide (CGRP) and neuropeptide Y (NPY), respectively, was analyzed. CGRP-positivity was abundantly seen from weeks 2-6 in both perivascular and sprouting free nerve endings in the proper tendon tissue undergoing healing. NPY appeared later, at weeks 6-8 post-rupture around blood vessels mainly located in the surrounding loose connective tissue. Apart from a role in vasoaction (CGRP, vasodilatory; NPY. vasoconstrictory), both neuropeptides have been implicated in fibroblast and endothelial cell proliferation required for angiogenesis. The present study shows that early healing of ruptured tendons is characterized by an orchestrated, temporal appearance of nerve fibers expressing peptides with different actions. The observed pattern of neuronal regeneration and neuropeptide expression may prove to be important for normal connective tissue healing.

Physical activity modulates nerve plasticity and stimulates repair after achilles tendon rupture

“…This approach, which offers a fair and reproducible estimation of nerve fiber occurrence, has previously been utilized in several studies on neuropeptides. 10,11,28 In the present study, only the semiquantitative results on PGP and CGRP were considered, because the SP immunoreactivity was too low to permit meaningful quantification.…”

“…This was done according to a method developed at our laboratory and described in detail previously. 10 Two pictures of each section were taken of the area exhibiting the highest occurrence of immunoreactive nerve fibers and analyzed using the software Easy Image Analysis 2000 (Tekno Optik AB, Sweden). The program takes into account the intensity, within a defined interval, and the area of the immunostaining.…”

“…Throughout weeks 2-4, that is, the proliferative phase, the amount of newly organized collagen at the rupture site increased up to 130%, while the tendon diameter was unchanged. During the remaining weeks (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16), that is, the remodeling phase, the amount of newly organized collagen slowly increased to almost reach the total diameter of the tendon. of the wheel-running group (RUN) compared to that of the plaster-treated group (IMMOB) (Fig.…”

“…10,21,26 Recently, we reported that ruptured tendons during the early regenerative phase of healing (weeks 1-4) exhibit intense new nerve fiber ingrowth into the proper tendon, otherwise devoid of nerves fibers. 10 We also noted that nerve ingrowth was characterized by a specific temporal occurrence of sensory neuropeptides.…”

“…10,21,26 Recently, we reported that ruptured tendons during the early regenerative phase of healing (weeks 1-4) exhibit intense new nerve fiber ingrowth into the proper tendon, otherwise devoid of nerves fibers. 10 We also noted that nerve ingrowth was characterized by a specific temporal occurrence of sensory neuropeptides. 11 The two sensory neuropeptides analyzed, that is, substance P (SP) and calcitonine gene related peptide (CGRP), have previously been reported to promote angiogenesis and tissue regeneration, 12,13,15,16,23,26 partly by stimulating proliferation of endothelial cells and fibroblasts.…”