Saphenous nerve injury and regeneration on one side of a rat suppresses the ability of the contralateral nerve to evoke plasma extravasation.

Leakage of Evans blue dye from the circulation into the skin has been used to measure plasma extravasation evoked by antidromic nerve stimulation of the saphenous nerves in anaesthetised rats. Normal animals and ones in which one saphenous nerve had been cut and left to regenerate some time before were studied. Saphenous nerve injury on one side of a rat significantly reduced the ability of the contralateral, uninjured nerve to evoke plasma extravasation compared with the response measured in totally uninjured control animals. This suppression of plasma extravasation was not dependent on activation of nerve fibres in the regenerated nerve. The effect was evident by 6 weeks after injury and persisted for at least another 20 weeks. At the moment the mechanism underlying this suppression of neurogenic plasma extravasation is unknown.