Probiotics reduce risk-taking behavior in the Elevated Plus Maze in the Flinders Sensitive Line rat model of depression.

Several studies have reported beneficial effects of probiotics on behavior and stress in humans and animals. The multi-strain probiotic product Ecologic® Barrier has shown antidepressant-like effects in rats when given in combination with high-fat diet. To circumvent the need for high-fat diet for future clinical use, the present study aimed to potentiate the behavioral effects of Ecologic® Barrier by developing a customized product that includes four additional bacterial species known to be associated with depression. Flinders Sensitive Line (FSL) rats, an animal model of depression, were randomized to receive vehicle, Ecologic® Barrier, or the customized product Ecologic® Barrier + 4. The control strain, Flinders Resistant Line rats, received vehicle to ascertain the depressive-like phenotype of FSL rats. Behavior was tested in the Elevated Plus Maze, Y-Maze, Novel Object Recognition Test, Open Field, and Forced Swim Test; HPA-axis reactivity was assessed by the Dexamethasone Suppression Test. Our results indicate that both probiotic products reduced open arm exploration in the Elevated Plus Maze, suggesting a reduction in risk-taking behavior. There were no intervention effects on cognition, locomotion, or depressive-like behavior. Moreover, all intervention groups had similar plasma corticosterone concentrations following the Dexamethasone Suppression Test. There was no difference between the two probiotic products, suggesting that the addition of four bacterial strains to Ecologic® Barrier did not potentiate its effect. Future studies should further investigate the effects of probiotics on risk-taking behavior and gain more mechanistic insights by studying individual strains and their cumulative contributions to the overall effect of a multi-strain product.