The flavonoid baicalin, isolated from the dried root of Scutellaria baicalensis G. (Labiatae), is widely used in traditional Chinese herbal medicine. In the present study, baicalin, at doses of 20, 40, and 80 mg=kg (p.o.), reduced immobility time in tail suspension test (TST) and the forced swimming test (FST) in mice. Baicalin also decreased immobility time at 12.5, 25, and 50 mg=kg (p.o.) in FST in rats. Furthermore, baicalin (25 mg=kg), as well as fluoxetine (FLU; 20 mg=kg), showed a significant recovery in sucrose intake compared with the vehicle-treated stressed animals for 5 weeks treatment in a chronic mild stress (CMS) model in rats. The effect of baicalin at the dose of 25 mg was as potent as that of reference antidepressant FLU (20 mg=kg) in the CMS model. With the monoamine oxidase (MAO A and B) assay, oral administration of baicalin at the doses of 12.5, 25, and 50 mg=kg significantly inhibited MAO A activity in a dose-dependent manner in rats. However, only baicalin at the doses of 25 and 50 mg=kg markedly inhibited MAO B activity. Neither baicalin nor FLU, at the doses tested, produced a significant effect on locomotor activity in mice. These results suggest that baicalin had a specific antidepressant-like effect in vivo. The antidepressant activity of baicalin may be mediated in part through MAO A and B inhibition in rat brain.
The current study investigated the putative antidepressant-like effect of paeonol, a phenolic component from the root bark of Paeonia suffruticosa Andr. (Ranunculaceae), in mice or rats using the tail suspension test (TST) and forced swimming test (FST), two widely accepted pharmacological models for detecting antidepressant activity in modern medicinal researchers. It was found that paeonol, at doses of 20, 40, and 80 mg=kg (p.o.), reduced immobility time in TST and FST in mice. Paeonol also decreased immobility time at 25 and 50 mg=kg (p.o.) in the FST in rats. Furthermore, paeonol as well as fluoxetine (FLU), at the doses tested, did not produce significant effects on locomotor activity. With 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and lactic dehydrogenase (LDH) assay, 5, 10, and 20 mM paeonol or a classical antidepressant, 10 mM FLU, protected PC12 cells from the lesion induced by 10 mM corticosterone (Cort) treatment for 48 h. In the fura-2=AM (acetoxymethyl ester) labeling assay, 10 and 20 mM paeonol, 10 mM FLU attenuated the intracellular Ca 2 þ overloading induced by 200 mM Cort treatment for 48 h in PC12 cells. In summary, we first demonstrated that paeonol possessed an antidepressant-like action through the protection of PC12 cells as well as reversal intracellular Ca 2 þ overloading.
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