| The present study was designed to investigate the contributions of the peripheral5-HT2A receptor on the matainence of carrageenan-evoked hyperalgesia.This study was conducted with behavioral and immunohistochemical techniques.Intraplantar (i.pl) post-treatment with ketanserin, a selective antagonist of 5-HT2Areceptor, in the hindpaw produced dose-dependent inhibition (2, 6 and 20μg) on thecarageenan-evoked hyperalgesia but not edema. Ketanserin at a dose of 20μg alsoinhibited formalin-induced pain response and expression of c-fos-like immunoreactivityin the spinal dorsal horn of segments L4～5. The study further investigated the mechanismof hyporalgesia induced by the blockade of 5-HT2A receptor and found that subcutaneousadministered naloxone, an nonselective opioid antagonist, can reverse the hyporalgesia.Exogenous 5-HT inhibited the express of opioid receptor in the DRG neurons.The present study provided evidence that peripheral 5-HT plays an important role inthe matainence of inflammatory hyperalgesia induced by carrageenan, and this effect ismediated by 5-HT2A receptor. It is proposed that endogenous opioids may be involved tocompromise inflammatory hyperalgesia.
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