A Coumarin‐ and Phthalide‐Rich Fraction From Baichuan Baile Formula Alleviates Reserpine‐Induced Depression‐Like Behaviors by Modulating the Monoaminergic System and Gut Microbiota

Baichuan Baile (BCBL) is a novel herbal formula composed of three herbs and a food additive with proven antidepressant-like effects. However, its unclear bioactive constituents hinder quality control. This study evaluated BCBL-CP, a fraction extracted via ethanol precipitation and macroporous resin chromatography, mainly comprising coumarins (5-hydroxyxanthotoxin, oxypeucedanin hydrate, byakangelicin) and phthalides (senkyunolides H and I). We rapidly assessed BCBL-CP's efficacy using behavioral despair and 5-hydroxytryptophan-induced head-twitch tests. Subsequently, therapeutic effects on a reserpine-induced depression-like mouse model were evaluated through behavioral assessments. Its effects on the monoaminergic system, cerebral pathology, brain-derived neurotrophic factor (BDNF), and gut microbiota were detected through enzyme-linked immunosorbent assay, hematoxylin and eosin staining, immunofluorescence, and 16S rDNA sequencing. Results showed BCBL-CP exhibited significant antidepressant-like activity in both acute behavioral screening and chronic reserpine-induced depression studies. Mechanistically, BCBL-CP selectively increased prefrontal norepinephrine (p < 0.05), attenuated neuronal damage (p < 0.001), and showed a trend toward BDNF upregulation (p = 0.083). Uniquely, it restored gut microbiota α-diversity (p < 0.01), normalized β-diversity, and modulated eight key bacterial taxa (p < 0.01 or p < 0.05). These findings confirm that these five compounds constitute the major characteristic bioactive constituents of BCBL, providing quality-control markers for developing this prospective antidepressant.