SYMPATHECTOMY INDUCES ADRENERGIC EXCITABILITY OF CUTANEOUS C-FIBER NOCICEPTORS

1. The effects of ipsilateral removal of the superior cervical ganglio n on the subsequent responsiveness of C-fiber polymodal nociceptors (C PMs) of the ear to close-arterial injections of norepinephrine (NE) we re evaluated in adult, anesthetized rabbits. 2. In normal unanesthetiz ed rabbits, the two ears were usually at the same temperature. Immedia tely after the ganglionectomy, the ipsilateral ear was warmer; however , at the time of electrophysiological recordings (4-23 days) the major ity of animals had the ipsilateral ear cooler by greater than or equal to 1 degrees C, suggestive of denervation supersensitivity. 3. NE (50 ng) did not activate any CPMs (n = 28) from intact animals. 4. Seven of 22 CPMs recorded from sympathectomized ears were activated by NE (5 0 ng). The responses varied considerably but typically consisted of 2- 4 impulses in the 60 s after the NE injection. In some instances, repe titive activity continued for many minutes. Such prolonged discharge d iffers from the adrenergic responses seen after partial nerve damage. 5. The induction of adrenergic excitability in CPMs by sympathectomy i s suggested to be a counterpart to postsympathectomy neuralgia in huma n beings and a possible part of the mechanism leading to sympathetical ly related pain states.