INFLUENCE OF PARTIAL NERVE INJURY IN THE RAT ON EFFERENT FUNCTION OF SYMPATHETIC AND ANTIDROMICALLY ACTING SENSORY NERVE-FIBERS

Objective: To investigate how partial injury of a large peripheral ner ve affects efferent (vasomotor) function of sympathetic and antidromic ally acting sensory nerve fibers, Design: Randomized animal study, Mat erials and Methods: We assessed, by laser Doppler flowmetry, skin bloo d flow (SBF) in the hindpaw of male Lewis rats before partial injury o f the ipsilateral sciatic nerve (through loose ligation) as well as at an early stage (day 4) and at a later stage (day 21) after this proce dure, This procedure has been reported to induce signs and symptoms li ke those observed in patients with causalgia, At the two time points a fter nerve injury, SBF was assessed before and after (chemical) blocka de of sensory and nonsensory (sympathetic) sciatic nerve fibers, Furth ermore, at day 21 we measured the density of sympathetic nerve fibers in footpad arteries, Measurements and Main Results: At day 4, compared with preligation values, we observed an increase in SBF that was redu ced by blockade of sensory nerve fibers, Subsequent blockade of nonsen sory nerve fibers further reduced SBF, At day 21, SBF was decreased co mpared with preligation values, Blockade of sensory nerve fibers furth er reduced SBF, and subsequent blockade of nonsensory nerve fibers did so as well, The density of sympathetic nerve fibers was lower on the ligated side than on the nonligated side, Conclusions: Partial injury of the rat sciatic nerve causes an ipsilateral increase in SBF at an e arly stage, which is followed by a decrease at a later stage, At both stages, antidromically acting sensory and orthodromically acting nonse nsory (sympathetic) nerve fibers are involved in the vasodilator respo nse, At a later stage, however, neurogenic vasodilator mechanisms are overruled by a nonneurogenic vasoconstrictor mechanism, The latter may consist of supersensitivity of skin microvessels to catecholamines co nsequent to reduced neurogenic disposition of catecholamines.