Recovery of C-fiber-induced extravasation following peripheral nerve injury in the rat

Peripheral nerve injury leads to substantial alterations in injured sensory neurons. These include cell death, phenotypic modifications, and regenerat ion. Primary sensory neurons have recently been shown not to die until a ti me beyond 4 months following a nerve crush or ligation and this loss is, mo reover, limited to cells with unmyelinated axons, the C-fibers, The late lo ss of C-fibers may be due to a lack of target reinnervation during the rege nerative phase. In order to investigate this, we have used a particular per ipheral function, unique to C-fibers, as a measure of peripheral reinnervat ion: an increase in capillary permeability on antidromic activation of C-fi bers, i.e., neurogenic extravasation, This was investigated in rats that ha d received a nerve crush injury 1 to 50 weeks earlier. Some recovery of the capacity of C-fibers to generate extravasation was detected at 8-10 weeks, which increased further at 12-14 weeks, and then plateaued at this level w ith no further recovery at 30 or 50 weeks. In intact and damaged sciatic ne rves, A beta-fibers never induced extravasation. These findings are compati ble with the hypothesis that those C-fibers which make it back to their per ipheral targets do not subsequently die and those that do not, may die, (C) 1998 Academic Press.