Suppressive Effects of Intrathecal Paeoniflorin on Bee Venom-Induced Pain-Related Behaviors and Spinal Neuronal Activation

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Recently, paeoniflorin (PF) administered systemically was found to have analgesic effects against inflammatory pain and hypersensitivity in a naloxone-reversible manner. In the present study, we adopted intrathecal administration to evaluate whether PF has direct antinociceptive actions at the spinal level. Pain-related behaviors and spinal c-Fos expression were induced by subcutaneous injection of bee venom (BV) into one hind paw of a rat. Intrathecal pretreatment of PF resulted in an inhibition of the BV-induced persistent spontaneous nociception and partially suppressed the occurrence of both thermal and mechanical hypersensitivity. Moreover, the PF-produced antinociception was completely reversed by naloxone. We further evaluated the intrathecal effects of the drug on the BV-induced c-Fos expression. The result showed that intrathecal PF preconditioning was effective to suppress spinal c-Fos expression in both superficial (lamina I-II) and deep (lamina IV-VI) layers of the L(4-5) dorsal spine. This result showed that PF has a direct pharmacological action in the spinal cord dorsal horn via activation of opioid receptors.