Anti-nociceptive Mechanisms of Testosterone in Unilateral Sciatic Nerve Ligated Male Rat

BACKGROUND: Neuropathic pain is a chronic condition which is mediated by complex mechanisms exerted by the release of nerve neurotransmitter. A correlation exists between the sex hormones and neuropathic pain, however many aspects of this correlation still remain unclear. OBJECTIVES: The aim of the current study was to determine the anti-nociceptive activity of testosterone and its interaction with the opioidergic, GABAergic, and dopaminergic receptors in sciatic nerve-ligated male rats. METHODS: In this study, 170 adult male rats were randomly allocated into the 4 experimental groups following the sciatic nerve ligation. In the experimental group 1, the animals were injected intraperitoneally (i.p.) with saline, testosterone (10 and 15 mg/kg), and morphine (5 mg/kg), and 30 minutes later with formalin into the plantar surface of the right paw. In the experimental group 2, the animals were injected with saline, testosterone (15 mg/kg), nalox-one (2 mg/kg), and testosterone (15 mg/kg)+naloxone (2 mg/kg). In the groups 3 and 4, flumazenil (5 mg/kg) and yohimbine (2 mg/kg) were injected instead of naloxone. Then, the time spent for paw licking was monitored for the first and second phases after the formalin injection. RESULTS: According to the results, the injection of testosterone in a dose dependent manner decreased the time of licking and biting in the injected paw compared to the control group (P<0.05). Likewise, pretreatment with na-loxone or flumazenil significantly decreased the anti-nociceptive effect of testosterone (P<0.05). While pretreatment with yohimbine significantly increased the anti-nociceptive effect of testosterone (P<0.05). CONCLUSIONS: These results suggested testosterone has an anti-nociceptive activity and this effect is mediated by the opioidergic, GABAergic, and dopaminergic receptors in the sciatic nerve-ligated male rat.