Role of benzodiazepine-GABAA receptor complex in attenuation of U-50,488H-induced analgesia and inhibition of tolerance to its analgesia by ginseng total saponin in mice.

In the present study, the role of benzodiazepine-GABAA receptor complex in the attenuation of U-50,488H (U50), a selective kappa opioid agonist-induced analgesia and inhibition of tolerance to its analgesia by ginseng total saponin (GTS) was investigated using the mice tail-flick test. The intraperitoneal (i.p.) treatment of GTS (100 and 200 mg/kg) and diazepam (0.1-1 mg/kg) dose-dependently attenuated the U50 (40 mg/kg, i.p.)-induced analgesia. GTS (0.001-10 microg/ml) did not alter binding of [3H]naloxone to mice whole brain membrane. The attenuation effect of GTS (100 mg/ kg) and diazepam (0.5 mg/kg) on U50-induced analgesia was blocked by flumazenil (0.1 mg/kg, i.p.), a benzodiazepine receptor antagonist, and picrotoxin (1 mg/kg, i.p.), a GABAA-gated chloride channel blocker. However, bicuculline (1 mg/kg, i.p.), a GABAA receptor antagonist blocked the attenuation effect of diazepam (0.5 mg/kg) but not GTS (100 mg/kg) on U50-induced analgesia. Chronic treatment (day 4-day 6) of GTS (50-200 mg/kg) and diazepam (0.1-1 mg/kg) dose-dependently inhibited the tolerance to U50-induced analgesia. Flumazenil (0.1 mg/kg) and picrotoxin (1 mg/kg) on chronic treatment blocked the inhibitory effect of GTS (100 mg/kg) and diazepam (0.5 mg/kg) on tolerance to U50-induced analgesia. On the other hand, chronic treatment of bicuculline (1 mg/kg) blocked the inhibitory effect of diazepam (0.5 mg/kg) but not GTS (100 mg/kg) on tolerance to U50-induced analgesia. In conclusion, the findings suggest that GTS attenuates U50-induced analgesia and inhibits tolerance to its analgesia and this action involves benzodiazepine receptors and GABAA-gated chloride channels.