Neurotrophins and other growth factors in the regenerative milieu of proximal nerve stump tips

Classic ideas on mechanisms for axon sprouting and nerve regeneration from peripheral nerves suggest that there is a prominent role for neurotrophin support. There has been comparatively less attention towards features of the regenerative process that develop from the proximal nerve trunk without the support of target tissues or the denervated trunk of a peripheral nerve. We studied early (2–14 d) expression of local growth factors in proximal nerve stump tips of transected sciatic nerves in rats. Immunohistochemical labelling was used to address specific deposition of BDNF, NGF, NT-3, bFGF, CNTF and IGF-1. We observed a unique localisation of BDNF, and to a much lesser extent, NGF in mast cells of injured nerve trunks but they were also observed in intact uninjured nerves. Macrophages did not express either BDNF or NGF. CNTF and IGF-1 were expressed in Schwann cells of intact nerves and stumps. We did not observe bFGF or NT-3 expression in any of the samples we studied. Mast cells may represent an important reservoir of BDNF in peripheral nerves.