Behavioral and electrophysiological effects of various types of peripheral nerve lesions in the rat: a comparison of possible models for chronic pain.

Three types of nerve lesions involving the brachial plexus were produced in rats: (1) multiple dorsal rhizotomy; (2) spinal nerve section just distal to the dorsal root ganglia (DRG); (3) section of the median, ulnar and radial nerves. The 3 types of lesion caused self-mutilation (autotomy) of the denervated forelimb. Significant differences were found in the time course and severity of this abnormal behavior among the 3 groups. Rats that had undergone spinal nerve lesion (group 2) performed significantly less severe autotomy than rats with dorsal rhizotomy (group 1) or peripheral nerve lesions (group 3). The latency to the onset of autotomy was significantly shorter for group 2 than for groups 1 and 3. Electrophysiological investigation of rats in group 2 revealed neural activity in the dorsal roots. The characteristics of the neural discharge were largely a function of postoperative survival times. The possible role of the various types of nerve lesion in producing chronic pain states is discussed.