Electrophysiological study on primary afferent properties of a chronic constriction nerve injury model in spinal rats

A chronic constriction nerve injury (CCI) model of the rat sciatic nerve is known to exhibit neuropathic pain behavior. The authors conducted electrophysiological analysis for the primary afferent properties of this model in a decerebrate spinal preparation. In the CCI model, electrical transcutaneous stimulation for A-delta and C-fibers showed a low current threshold to elicit the flexion withdrawal reflex. The antidromic ectopic firing activity recorded from the sural nerve showed abnormal firing patterns, which were not seen in normal rats, as follows: (1) an increase of spontaneous firing frequency, (2) development of an on-off pattern that consisted of cyclic burst spikes, and (3) increased firing number under the hypoxic condition. The amplitude of the A-delta component in the antidromic sensory nerve-evoked potential was lower than that in normal rats. The current study clarified the electrophysiological parameters reflecting pathological hypersensivity and excitability of primary afferents in the CCI model, which could not found by behavioral analysis. These results may be useful in future studies evaluating possible treatments of neuropathic pain.