Sinomenine is a principal ingredient of
traditional Chinese medicine, Sinomenium Acutum, which has been reported to have various pharmacological effects including anti-
rheumatism and
immunomodulation. This study examined the effects of
sinomenine in rats that received chronic constriction injury (CCI), a model of peripheral
neuropathic pain. CCI injury on the right sciatic nerve led to long-lasting
mechanical hyperalgesia. Acute
sinomenine treatment (10-40 mg/kg, i.p.) significantly and dose-dependently reversed
mechanical hyperalgesia. In addition, the antinociceptive effects of
sinomenine remained stable during repeated daily treatment for up to 2 weeks. Although
sinomenine did not alter the duration of immobility in the forced swimming test in healthy animals, it dose-dependently reversed the increased immobility time in rats receiving CCI, suggesting that
sinomenine attenuated
chronic pain-induced depressive-like behavior. The antinociceptive effects of
sinomenine were blocked by the GABAa receptor antagonist bicuculine. The doses of
sinomenine studied here did not significantly alter the spontaneous locomotor activity. Together, these results suggested that
sinomenine exerts significant antinociceptive effects for
neuropathic pain via GABAa-mediated mechanism, which suggests that
sinomenine may be useful for the management of chronic painful conditions such as
neuropathic pain.