Uninjured C-Fiber Nociceptors Develop Spontaneous Activity and Alpha- Adrenergic Sensitivity Following L-6 Spinal Nerve Ligation in Monkey
Resource
JOURNAL OF NEUROPHYSIOLOGY v.81 n.2 pp.455-466
Journal
JOURNAL OF NEUROPHYSIOLOGY
Journal Volume
v.81
Journal Issue
n.2
Pages
455-466
Date Issued
1999
Date
1999
Author(s)
CHIEN, HSIUNG-FEI
Abstract
We investigated whether uninjured cutaneous C-fiber nociceptors in primates develop abnormal responses after partial denervation of the skin. Partial denervation was induced by tightly ligating spinal nerve L-6 that innervates the dorsum of the foot. Using an in vitro skin-nerve preparation, we recorded from uninjured single afferent nerve fibers in the superficial peroneal nerve. Recordings were made from 32 C-fiber nociceptors 2-3 wk after ligation and from 29 C-fiber nociceptors in control animals. Phenylephrine, a selective alpha(1)-adrenergic agonist, and UK14304 (UK), a selective alpha(2)-adrenergic agonist, were applied to the receptive field for 5 min in increasing concentrations from 0.1 to 100 mu M. Nociceptors from in vitro control experiments were not significantly different from nociceptors recorded by us previously in in vivo experiments. In comparison to in vitro control animals, the afferents found in lesioned animals had 1) a significantly higher incidence of spontaneous activity, 2) a significantly higher incidence of response to phenylephrine, and 3) a higher incidence of response to UK. In lesioned animals, the peak response to phenylephrine was significantly greater than to UK, and the mechanical threshold of phenylephrine- sensitive afferents was significantly lower than for phenylephrine-insensitive afferents. Staining with protein gene product 9.5 revealed an similar to 55% reduction in the number of unmyelinated terminals in the epidermis of the lesioned limb compared with the contralateral limb. Thus uninjured cutaneous C-fiber nociceptors that innervate skin partially denervated by ligation of a spinal nerve acquire two abnormal properties: spontaneous activity and alpha- adrenergic sensitivity. These abnormalities in nociceptor function may contribute to neuropathic pain.
Subjects
SYMPATHETICALLY MAINTAINED PAIN
ROOT GANGLION NEURONS
RAT DORSAL-ROOT
PERIPHERAL-NERVE
NEUROPATHIC PAIN
POLYMODAL NOCICEPTORS
Type
journal article