Fermented Dendrobium officinale Ameliorates Sleep Deprivation-Induced Depressive-like Behaviors by Attenuating Neuroinflammation and Restoring 5-HT Synthesis via the Gut–Brain Axis

Chronic sleep deprivation (SD) disrupts gut–brain axis (GBA) homeostasis and is closely associated with gut microbiota dysbiosis, neuroinflammation, and depression-like behaviors. This study investigated whether fermentation enhances the antidepressant-like effects of Dendrobium officinale by comparing fermented Dendrobium officinale (FDO) with unfermented Dendrobium officinale (DO) in a chronic SD mouse model. FDO significantly ameliorated anxiety and depressive-like behaviors in SD mice. It reshaped gut microbial structures, enriched beneficial bacteria taxa such as Dubosiella, [Eubacterium]_coprostanoligenes_group, and Allobaculum, and increased SCFA levels. FDO also enhanced colonic ZO-1 and Occludin expression and reduced serum levels of LPS and the pro-inflammatory cytokines. At the central nervous system level, FDO inhibited the activation of hippocampal microglia and astrocytes; alleviated neuroinflammation; restored hippocampal TPH2, 5-hydroxytryptamine (5-HT), and 5-HIAA levels; and modulated the 5-HT1A/5-HT2A receptor balance. In addition, FDO upregulated BDNF, PSD-95, and SYN expression and reduced corticosterone (CORT) levels. Compared with DO, FDO showed more pronounced regulatory effects. Correlation analysis suggested that 5-HT may link gut microbial metabolites, inflammation, and synaptic plasticity. In summary, these findings support FDO as a potential GBA-targeted functional food for SD-related depressive-like behaviors.