Anxiolytic-like effects of baicalein and baicalin in the Vogel conflict test in mice.

A previous receptor binding assay indicated that baicalein, one of the active principles of the Chinese herbal drug, Huangqin (Scutellariae Radix), interacts with the benzodiazepine binding site of GABA(A) receptors in mouse cortex membrane preparations with a K(i) value of 13.1 microM. Therefore, the present study examined whether baicalein and its 7-glucuronide, baicalin, have anxiolytic-like effects in a Vogel conflict test adapted for ICR mice. The results showed that both baicalein (10 mg/kg, i.p.) and baicalin (20 mg/kg, i.p.) significantly increased the number of shocks accepted in the Vogel lick-shock conflict paradigm over 9 min, as did a benzodiazepine receptor agonist, chlordiazepoxide (5.0 mg/kg, i.p.) and a 5-HT(1A) receptor agonist, 8-hydroxy-2(di-n-propylamino)tetralin (0.5 mg/kg, i.p.). Since the total volume of water intake and the shock sensitivity of mice were not significantly changed after drug treatment, the effect of baicalein or baicalin was not due to an enhancement of thirst or shock tolerance. Furthermore, this anxiolytic-like effect of baicalein or baicalin was antagonized by co-administration with a benzodiazepine receptor antagonist, flumazenil (2 mg/kg, i.p.), but not with a 5-HT(1A) receptor antagonist, pindolol (10 mg/kg, i.p.). It is concluded that the anxiolytic-like effect of baicalein or baicalin may be mediated through activation of the benzodiazepine binding site of GABA(A) receptors.