Analgesic activity of catalpol in rodent models of neuropathic pain, and its spinal mechanism.

Neuropathic pain is a major health issue that represents considerable social and economic burden worldwidely. In this study, we investigated the potential of catalpol, an iridoid glucoside of Rehmannia glutinosa Steud, to alleviate neuropathic pain. The potential analgesic effects of catalpol were evaluated by chronic constriction injury (CCI) and lumbar 5 spinal nerve ligation (L5 SNL) model. In addition, we explored whether catalpol altered the degree of microglia activation and neuroinflammation in rat spinal cord after CCI induction. Repeated administration of catalpol (1, 5, 25, and 125 mg/kg) reversed mechanical allodynia induced by CCI and L5 SNL in a dose-dependent manner in rats. Levels of activated microglia, activated NF-κB, and proinflammatory cytokines (IL-1β, IL-6, TNF-α) in lumber spinal cord were elevated in rats following CCI induction, and catalpol significantly inhibited these effects. Our results demonstrated that catalpol produces significant antinociceptive action in rodent behavioral models of neuropathic pain and that this effect is associated with modulation of neuroinflammation in spinal cord.