Gender differences in rat neuropathic pain sensitivity is dependent on strain.

It is well recognized that gender differences play a major role in pain sensitivity, pain report, analgesic efficacy and prevalence of certain chronic pain disorders. In the present study we sought to determine whether male or female rats of two different outbred strains (Sprague-Dawley and Holtzman) experienced differential pain sensitivity after the same mononeuropathy lesion. Following baseline mechanical allodynia testing, rats of each sex and strain underwent an L5 spinal nerve transection. Mechanical allodynia using 2 and 12 g von Frey filaments was assessed at days 1, 3, 5, 7, and 10 post surgery. There were no statistically significant differences in allodynia between gender in the Holtzman strain or between strains. However, mechanical allodynia was significantly greater in female Sprague-Dawley rats as compared with males following a spinal nerve transection. These data suggest that the choice of rat gender and strain should be considered in experimental neuropathic pain studies, especially in the assessment of potential analgesics.