Intact female rats are more susceptible to the development of tactile allodynia than ovariectomized female rats following partial sciatic nerve ligation (PSNL)

As previously reported, this laboratory has determined that female rats are more prone to develop tactile allodynia, an indicator of neuropathic pain, than male rats using the partial sciatic nerve ligation (PSNL) model. In order to further characterize this gender difference, the role of ovarian hormones in predisposing female rats to the development of tactile allodynia was investigated. In a double blind randomized trial, 12 intact and 12 ovariectomized (ovx) female rats underwent PSNL of the right rear leg. Sham 1 operated (exposure of the nerve without ligation; 2 intact, 2 ovx) and sham 2 operated (incision through skin only; 1 intact, 2 ovx) controls were also included in the study groups. Animals were evaluated on 3 consecutive days for withdrawal from touch with von Frey filaments on post-injury days 13-15, 20-22 and 27-29. A significant difference was observed at post-injury days 20-22 and 27-29 between the two groups. The intact group resulted in 12/12 animals that were statistically more sensitive than sham groups, compared to 6/12 for the ovx group. At post-injury days 13-15 no statistical difference was seen between the two groups (8/12 for intact versus 10/12 for ovx). This study indicates that ovarian hormones, via some unknown mechanism, predispose female rats to develop tactile allodynia following injury.