Effects of galacto-oligosaccharide prebiotics in the flinders sensitive line rat model of depression on behavioural outcomes

Introduction: The gut may play an important role in Major Depressive Disorder and interventions targeting gut microbiota- may serve as potential treatments. Prebiotics have been reported to reduce anxiety and depressive-like phenotypes in mice, rats, and humans. Bimuno®, a commercially available beta-galactooligasaccharide, has been shown to increase gut microbiota diversity. Aim: To investigate the effect of Bimuno® on rat anxiety- and depressive-like behaviour in the Flinders Sensitive (FSL) and Resistant Line (FRL) rats. Methods: Guided by our published protocol, 64 8-14 week old male rats, (32 FSL and 32 FRL), were randomised to receive Bimuno® or control (4g/kg) daily for 4 weeks. We assessed despair (using the Forced Swim Test) and anxiety-like (Elevated Plus Maze) behaviours, and locomotion using the open field test. All behavioural tests were conducted and assessed blinded to rat line and treatment allocation. We recorded animals’ weight and food and water intake weekly. We used two-way ANOVA to investigate the effect of treatment (control or prebiotic) and strain (FSL or FRL) on despair and anxiety-like behaviours. Results: Treatment with Bimuno® had no effect on performance in the Forced Swim Test or the Elevated Plus Maze. We observed the expected behavioural differences between the FSL and FRL rats. Discussion: We only used male animals and our sample size calculation was informed by published data. While confirmatory studies are needed, the present study questions the role of the microbiome reported in the literature.