Sex‐Specific Long‐Term Effects of Perinatal Limosilactobacillus reuteri on Social Cognition, Gene Expression, and Gut Microbiota

ABSTRACT Recent research highlights the potential of early‐life probiotic interventions to promote brain health later in life. In this study, we investigated the long‐term effects of Limosilactobacillus reuteri ( L. reuteri ) supplementation during a critical perinatal window (gestational Day 6 to postnatal Day 7) on behavioral, molecular, and gut microbiota outcomes in adult male and female BALB/c mice. Perinatal L. reuteri supplementation led to significant and lasting improvements in sociability, social recognition, and gut microbiota composition in male offspring. These changes were accompanied by increased gene expression of the anti‐inflammatory cytokine Il10 in both the striatum and colon of male offspring. Notably, expression of the oxytocin receptor ( Oxtr ), a key regulator of social and anxiety‐like behaviors, was significantly increased in both the prefrontal cortex and striatum in males and females. However, probiotic‐exposed females exhibited a distinct behavioral profile, showing a trend toward reduced anxiety‐like behavior but impaired social recognition. They also displayed increased gene expression of the peptidoglycan transporters Slc46a2 and Slc46a3 in the striatum, whereas only Slc46a2 was elevated in males, suggesting a potential mechanistic pathway underlying the observed sex‐dependent effects. These findings indicate that perinatal L. reuteri supplementation modulates the microbiota–gut–brain axis in a sex‐specific manner, influencing behavior, neuroimmune signaling, and gut microbiota composition. Our results underscore the importance of accounting for sex differences when developing early‐life microbiota‐based interventions for neurodevelopmental disorders and long‐term brain health. image