Early-life, limited bedding stress induces anxiety-like and repetitive behavior, early microbiome maturation and blood brain barrier robustness

Over 50% of anxiety patients do not respond to current treatments, highlighting the need for new therapeutic targets. The gut microbiome is increasingly implicated in behavioral disorders, yet how early-life stress (ELS) alters microbiome development and host function remains unknown. Here, we used a limited bedding and nesting mouse model of ELS to link microbiome-driven mechanisms with anxiety-like behavior. ELS induced robust, sex-specific increases in anxiety-like, fear, and repetitive behaviors without impairing learning or memory. ELS exposure significantly increased short-chain fatty acid producers and induced earlier microbiome maturation. Antibiotic modulation improved anxiety-like behavior in a sex-dependent manner. Interestingly, ELS serum led to a protective effect on the blood-brain barrier ex vivo, and we observed no evidence of overt gastrointestinal damage in vivo. Together, these findings support a mechanistic framework in which ELS chronically decreases permeability and disrupts gut-brain axis communication through early microbiome shifts rather than barrier breakdown (as seen in the maternal separation model). These results underscore the importance of microbiome-inclusive biobehavioral research for the future implementation of personalized anxiety treatments.