Neuropharmacology and AnalgesiaThe antinociceptive effect of intrathecal escin in the rat formalin test

This study investigated the antinociceptive effect of intrathecal escin and examined its effect on the formalin-induced activation of c-Fos and phosphorylated p38 mitogen-activated protein kinase (p-p38 MAPK) in the rat spinal cord. Rats were chronically implanted with lumbar intrathecal catheters, and the ability of intrathecal escin to alter nociceptive behaviours in the rat formalin test was examined. The expression of c-Fos and p-p38 MAPK in the dorsal horn of the spinal cord was detected in the control and escin (40 μg) groups using immunohistochemical techniques. Intrathecal escin produced a dose-dependent reduction in formalin-evoked flinching behaviour in rats during the second phase; however, no effect was observed in the first phase. In addition, immunohistochemical experiments showed that the expression of c-Fos and p-p38 MAPK in the spinal cord dorsal horn increased after an injection of formalin into the paw. Interestingly, the 40 μg dose of intrathecal escin, which was the larger of the two doses that blocked formalin-induced hyperalgaesia, attenuated the formalin-induced increases in c-Fos and p-p38 MAPK in the dorsal horn of the spinal cord. The decrease in pain-related behaviours and c-Fos expression indicated that escin produced antinociceptive effects in the rat formalin test. Although the specific mechanisms of these effects were not investigated, the reduction in p-p38 MAPK in the dorsal horn of the spinal cord may be involved.