Comparison between the effect of gonadal hormones on nociceptive behavior of male rats in two neuropathic pain models

As sex differences have been observed repeatedly in chronic pain, it is likely that the gonadal hormones are responsible for these differences. To investigate the responsible mechanism for chronic pain different models have been created. This study is examining the effects of gonadal hormones on nociceptive responses of the rats in CCI (chronic constriction injury) and SNI (spread nerve injury) model. For this reason male rats were undertaken to gonadectomy or sham surgery two weeks before nerve injury. A plantar analgesic meter was used to measure gonadectomy-induced changes in paw withdrawal latency (PWL) values, and von Frey monofilaments and Randal selitto test were used to assess changes in paw withdrawal threshold (PWT) in response to mechanical stimuli. Animals were subjected to the behavioral tests before induction of nerve injury and then once a week starting from the first week after nerve injury for three weeks. t-test and Mann-Whitney were used for statistical analysis. The data revealed that PWL and PWT values were the same in these two nerve injury models and PWL was significantly lower in gonadectomized rats comparing to sham group. There were no gonadetomy-related differences in the development of mechanical allodynia. Also it seems that mechanical hyperalgesia is more affected by sexual hormones in SNI model during the first week after nerve injury. These findings demonstrate that CCI and SNI model induces similar nociceptive behaviors in rats and mechanical and thermal nociceptive responses are differentially affected by gonadal hormones in male rats.