Role of gonadectomy in development of hyperalgesia induced by partial sciatic nerve ligation in male mice

Neuropathic pain arising from sciatic nerve ligation (SNL) injury can result in increased sensitivity to both noxious (hyperalgesia) and non-noxious stimuli (allodynia). Some research studies have been shown that the mechanisms underlying neuropathic pain processing differed as a function of gender and gonadal hormone status. In this study, we try to show the effects of nerve injury after gonadectomy in time-course of hyperalgesia that has not been extensively studied. Methods and Materials: 45 albino male mice weighting 25-35 gr were subjected to Intact, Sham-operated, Sciatic Nerve Ligated, Gonadectomized, and Sciatic Nerve Ligated+Gonadectomized groups. The tail flick latency was measured at set intervals 10th-20th days for 11 days after surgical operation (peripheral nerve injury by left sciatic nerve ligation and gonadectomy) in all groups by tail flick analgesiometer. The gonadectomized mice responded (7.15±1.8 sec) significantly faster than intact ones (10.78±1.43 sec) to a thermal nociceptive stimulus (P<0.05). In ligated mice, hyperalgesia developed significantly within 11-17 days after sciatic nerve ligation (6.35±1.33 sec; P<0.05). In sciatic nerve ligated+gonadectomized group, tail flick latency time (5.45±1.14 sec) decreased significantly within 11 and 13-16 days after surgical operations in comparison with sham-operated mice (9.99 ± 1.64 sec; P<0.05) and as compared with tail flick latency in sciatic nerve ligated mice (6.62 ± 1.75 sec) within 13th-14th (P<0.05) and 15th (P<0.01) days after surgical operations. It was concluded that testosterone might play a role in the pain modulation. In addition, we suggest that testosterone also affects neuropathic pain that is accompanied by a number of neuroplastic alternations at the level of spinal cord including up- and down-regulation of neurotransmitters during sciatic nerve ligation-induced hyperalgesia.