1. The effects of ipsilateral removal of the superior cervical ganglion on the subsequent responsiveness of C-fiber polymodal nociceptors (
CPMs) of the ear to close-arterial
injections of
norepinephrine (NE) were evaluated in adult, anesthetized rabbits. 2. In normal unanesthetized rabbits, the two ears were usually at the same temperature. Immediately after the
ganglionectomy, the ipsilateral ear was warmer; however, at the time of electrophysiological recordings (4-23 days) the majority of animals had the ipsilateral ear cooler by > or = 1 degree 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 (50 ng). The responses varied considerably but typically consisted of 2-4 impulses in the 60 s after the NE injection. In some instances, repetitive activity continued for many minutes. Such prolonged discharge differs from the
adrenergic responses seen after partial nerve damage. 5. The induction of
adrenergic excitability in
CPMs by
sympathectomy is suggested to be a counterpart to postsympathectomy
neuralgia in human beings and a possible part of the mechanism leading to sympathetically related
pain states.