Anti-nociceptive mechanisms of Testosterone in unilateral sciatic nerve ligated male rat: role of opioidergic, GABAergic and dopaminergic receptors

BACKGROUND: Neuropathic pain is a chronic condition which mediates by complex mechanisms via nerve neurotransmitter re‌lease. A correlation exists between sex hormones and neuropathic pain, but many aspects of this phenomenon still unclear.OBJECTIVE: So, the aim of the current study was to determine anti-nociceptive activity of the testosterone and its interaction with opioidergic, GABAergic and dopaminergic receptors in sciatic nerve ligated male rat.METHODS: In this study 170 adult male following sciatic nerve ligature randomly allocated into 4 experimental group. In experiment 1, animals were injected (i.p) with saline, testosterone (10 and 15mg/kg), morphine (5mg/kg), and 30 minutes later injected with formalin into the plantar surface of the right paw. In experiment 2, animals were injected with saline, testosterone (15mg/kg), naloxone (2mg/kg) and testosterone (15mg/kg)+naloxone (2mg/kg). In experiments 3 and 4 flumazenil (5mg/kg) and yohimbine (2mg/kg) were injected instead of naloxone. Then, the time spent for paw licking was determined the in first and second phase after formalin injection.RESULTS: According to the results, injection of the testosterone in a dose dependent manner decreased time of the licking and biting in injected paw compared to the control group(p <0.05). Pre-treatment with naloxone or flumazenil significantly decreased anti-nociceptive effect of the testosterone(p <0.05). Pre-treatment with yohimbine significantly increased anti-nociceptive effect of the testosterone(p <0.05).CONCLUSIONS: These results suggested, testosterone has anti-nociceptive activity and this effects mediates via opioidergic, GABAergic and dopaminergic receptors in sciatic nerve ligated male rat.