INVOLVEMENT OF ALPHA(2)-ADRENOCEPTORS IN MEDIATING SYMPATHETIC EXCITATION OF INJURED DORSAL-ROOT GANGLION NEURONS IN RATS WITH SPINAL NERVELIGATION

The present study examined the effects of sympathetic stimulation on t he activity of primary afferent neurons that had peripheral axons bein g injured previously by a spinal nerve ligation. About 22% of afferent s with injured fibers that showed spontaneous discharge were excited b y sympathetic stimulation or systemic injection of adrenaline. Most sy mpathetically-excited afferent neurons had axons that conducted in the A-fiber range. This sympathetically-evoked afferent excitation was no t affected by cutting the spinal nerve at a place close to the dorsal root ganglion (DRG). Yohimbine, alpha(2)-antagonist, suppressed sympat hetically-evoked afferent excitation which was not affected by alpha(i )-antagonist prazosin. Clonidine, alpha(2)-agonist, exerted an excitat ory effect, whereas oil-agonist phenylephrine had no effect on the act ivity of afferents with injured fibers. No afferent fibers in control preparations responded to sympathetic stimulation. The results suggest that after a spinal nerve ligation, injured DRG neurons with fast-con ducting fibers become sensitive to sympathetic activity via activation of alpha(2)-adrenoceptors. (C) 1997 Elsevier Science Ireland Ltd.