Abstract
One of the main functions of the sensory system in our body is to maintain somatosensory homeostasis. Recent reports have led to a significant advance in our understanding of pain signaling mechanisms; however, the exact mechanisms of pain transmission have remained unclear. There is an urgent need to reveal the precise signaling mediators of pain to provide alternative therapeutic agents with more efficacy and fewer side effects. Accordingly, although the anti-inflammatory, antioxidative and anti-neuropathic effects of astaxanthin (AST) have been previously highlighted, its peripheral antinociceptive mechanisms are not fully understood. In this line, considering the engagement of L-arginine/nitric oxide (NO)/cyclic GMP (cGMP)/potassium channel (KATP) signaling pathway in the antinociceptive responses, the present study evaluated its associated role in the antinociceptive activity of AST. Male mice were intraperitoneally (i.p.) injected with L-arginine (100 mg/kg), SNAP (1 mg/kg), L-NAME (30 mg/kg), sildenafil (5 mg/kg), and glibenclamide (10 mg/kg) alone and prior to the most effective dose of AST. Following AST administration, intraplantarly (i.pl) injection of formalin was done, and pain responses were evaluated in mice during the primary (acute) and secondary (inflammatory) phases of formalin test. The results highlighted that 10 mg/kg i.p. dose of AST showed the greatest antinociceptive effect. Besides, while L-NAME and glibenclamide reduced the antinociceptive effect of AST, it was significantly increased by L-arginine, SNAP and sildenafil during both the primary and secondary phases of formalin test. These data suggest that the antinociceptive activity of AST is passing through the L-arginine/NO/cGMP/KATP pathway.
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