Sex differences have been repeatedly observed in chronic pain, therefore it is likely that the gonadal hormones are involved in nociception. On the other hand, different experimental models have been created to investigate the responsible mechanisms of chronic pain. This study examines the effects of gonadal hormones on nociceptive responses of rats in the CCI (chronic constriction injury) and SNI (spread nerve injury) models. Methods: Male rats underwent gonadectomy or sham surgery 2 weeks

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... re 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 the paw withdrawal threshold (PWT) in response to mechanical stimuli. Animals were subjected to the behavioral tests before induction of nerve injury. Behavioral tests were also performed 1 week after nerve injury and were then repeated once a week for 3 weeks. t-Test and Mann-Whitney were used for statistical analysis. Results: 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 compared to sham group. There were no gonadectomy-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. Conclusion: These findings demonstrate that CCI and SNI models induce similar nociceptive behaviors in rats and mechanical and thermal nociceptive responses are differentially affected by gonadal hormones in male rats.