Gut microbiota-derived trimethylamine N-oxide (TMAO) has been implicated in both intestinal and renal diseases; however, its specific role in modulating gut–kidney interactions remains unclear. This study aimed to investigate the effects of TMAO on gut–kidney crosstalk using a mouse model of diarrhea. Mice were divided into four groups: normal, model, TMAO, and TMAO + model. The normal group received sterile water, while the other groups were administered adenine + Folium sennae, TMAO, or a combination of TMAO and adenine + Folium sennae. Samples were collected to assess morphological changes in the colon and kidney, evaluate the colonic mucosal barrier and renal function, and measure NLRP3 inflammasome activity and inflammatory cytokine levels in colonic and renal tissues. TMAO levels and the gut microbiota composition were analyzed using 16S rRNA sequencing. The model group exhibited altered stool morphology, which was further aggravated by TMAO intervention. Both the model and TMAO + model groups exhibited significant damage to intestinal and renal tissues, along with compromised intestinal mucosal barriers and impaired renal function compared to controls. Inflammatory markers were elevated in these groups, with the TMAO + model group showing the most pronounced increases. Correlation analysis indicated significant relationships among TMAO levels, inflammasome activation, and inflammatory cytokines. The genera Mucispirillum and Anaerotruncus negatively correlated with TMAO, whereas Parabacteroides and Parasutterella genera positively correlated with TMAO. In conclusion, TMAO plays a critical role in modulating gut–kidney crosstalk by promoting inflammation, disrupting mucosal and renal integrity, and altering the gut microbial ecosystem.

Background: Areca catechu L. is an evergreen tree belonging to the Arecaceae family. As an important traditional Chinese medicine, it has wide applications in the field of herbal medicine. Arecoline is the main active component responsible for its medicinal effects and plays a key role in its central nervous system (CNS) stimulant properties. Methods: This study investigated the excitatory effects of arecoline by analyzing behavioral changes in mice, neurotransmitter levels, the intestinal microbiota composition, and enzymatic activities. We further explored the bidirectional interactions between the intestinal microbial ecosystem and the nervous system following arecoline exposure. Results: Arecoline administration significantly increased the activity time ratio in mice (p < 0.05). It also elevated fecal lactase and amylase activities (p < 0.05), suggesting enhanced carbohydrate metabolism that may be one of the reasons for the increased activity time of mice. Serum analysis showed decreased 5-hydroxytryptamine (5-HT, p < 0.05), increased dopamine (DA) and brain-derived neurotrophic factor (BDNF) levels (p < 0.001), and no significant change in γ-aminobutyric acid (GABA). These findings suggest that arecoline may also play a role in modulating neurotransmitter balance. At the genus level, Escherichia was significantly enriched and positively correlated with DA, BDNF, and GABA, while Clostridium abundance decreased and was positively correlated with 5-HT. Conclusions: Arecoline administration altered multiple enzymatic activities and the microbial composition abundance in the mouse intestine, eliciting psychostimulant effects while maintaining neurotransmitter homeostasis. This study provides an experimental foundation for further pharmacological exploitation of arecoline.