Dietary prebiotics promote anxiolytic-like behavior in the open field test and reduce relative adrenal and spleen weight in Fischer 344 rats

It is becoming increasingly clear that the community of microorganisms living in the mammalian gut (the gut microbiota) exerts a significant influence on brain function. Evidence suggests that the microbiota plays a role in anxiety and anxiety-like behavior in animal models. Several studies have demonstrated reduced anxiety-like behavior with administration of probiotics (live bacteria with known health benefits), but less work has been done to investigate the potential anxiolytic effects of prebiotics (dietary substances that promote probiotics already residing in the gut). Prebiotics have several advantages over probiotics as an intervention against anxiety. We tested the effects of a diet containing prebiotics on anxiety-like symptoms in male Fischer 344 rats, including behavior in the open field test, corticosterone levels, and the weights of the adrenals, spleen, and thymus. One group of animals consumed the prebiotic diet for approximately 4 weeks and underwent behavioral testing during adolescence; another group consumed the diet for 6 weeks and underwent testing during adulthood. Animals who consumed the prebiotic diet displayed anxiolytic-like behavior in the open field test regardless of age, spending more time in the aversive open center of the field compared to controls. These animals also exhibited reduced relative adrenal and spleen weight. Interestingly, relative adrenal weight was inversely correlated with time spent in the center of the field during the open field test in adult rats. These results suggest an anxiolytic effect of dietary prebiotics. Further investigation is required to determine what changes in the microbiota, metabolome, and brain may have accompanied this anxiolytic effect.