Different strains and substrains of rats show different levels of neuropathic pain behaviors

This study compared and contrasted the manifestation of neuropathic pain behaviors in several strains of rats. These included ACI, Brown-Norway, Fischer 344, Lewis, Long-Evans, Sprague-Dawley, and Wistar-Furth, all obtained from Harlan Sprague-Dawley Inc. Comparison was also made between two substrains of Sprague-Dawley rats: one from Harlan and the other from Sasco. Neuropathic injury was produced by tightly ligating the left L5 and L6 spinal nerves with the animals under halothane anesthesia. Tests were conducted for 2 weeks to examine behavioral signs representing mechanical allodynia, cold allodynia, and spontaneous pain. There was no difference between strains in any of the tested behaviors before surgery. After neuropathic injury, rats in most groups developed high levels of behavioral signs of various components of neuropathic pain; however, some strains of rats showed weak behavioral signs of neuropathic pain. When a comparison was made between two substrains of Sprague-Dawley rats from two different sources, the ones from Sasco showed weaker behavioral signs than those from Harlan. When comparisons were made between different strains of rats from the same source (Harlan), Brown-Norway and Long-Evans rats showed the smallest magnitude of neuropathic pain behaviors. The data indicate that different strains and substrains of rats display different degrees of pain behaviors, suggesting that strains and substrains are important variables in the development of neuropathic pain after peripheral nerve injury.