Combined Administration of Lactobacillus or Bifidobacterium Offers Enhanced Antidepressant and Anxiolytic Activity in a Dose Dependent Manner

Abstract

Purpose: Gut microbiota is strongly linked to the activity of the bidirectional gut-brain axis, which influences neuropsychological processes at multiple levels. Changes in the gut microbiota have been implicated in mood disorders, and probiotics have been explored for their ability to mitigate the effects of stress on mental health. Here, we investigated the therapeutic benefits of different concentrations and combinations of Lactobacillus and Bifidobacterium in a mouse model of stress induced depression and anxiety.

Methods: Sixty-three male ICR mice (6-8 weeks old; 20-25g) divided into nine groups were used for this study. The test groups underwent chronic unpredictable mild stress protocols for two weeks before receiving low (10⁴ CFU/ml) or high (10⁸ CFU/ml) doses of either monotherapy (Lactobacillus or Bifidobacterium) or a combination therapy (Lactobacillus and Bifidobacterium) for four weeks. The antidepressant, fluoxetine, served as the positive control. Measurements of weight and sucrose preference were performed at four time points in addition to a battery of behavioral tests (open field tests, forced swim test, tail suspension test, and hot plate test) at the endpoint to assess depression and anxiety-like behavior.

Results: Low doses of the probiotic formulation (mono- or combined therapy) reversed weight loss but not anhedonia. In contrast, high doses of probiotic formulations (mono- or combined therapy), along with fluoxetine, were effective in reversing the weight loss and anhedonia caused by chronic unpredictable mild stress. Probiotics ameliorated stress-induced immobility as measured by both the forced swim and tail suspension tests, while also reducing anxiety-like behavior (increased peripheral activity) in the open field test. High doses of mono- or combined therapy increased curling behavior in the tail suspension test, whereas fluoxetine failed to do so.

Conclusion: This study indicates the species- and dose-dependent beneficial effects of probiotics on behavioral outcomes associated with depression while also reversing weight loss. Evidence suggests that probiotics and fluoxetine may exert antidepressant activity via different mechanisms.

Keywords: gut microbiome; lactic acid bacteria; mental health; probiotics.

FIGURE 1

(A) Chronic unpredictable mild stress (UCMS) study scheme and timeline in days. SPT‐sucrose preference test, FST‐force swim test, TST‐tail suspension test, OPT‐open field test, PBT‐pain‐like behavior test. The numbers in circles represent days. (B) Effect of formulations on weight or (D) sucrose preference test over the six week experimental period. (C) Animal weights and (E) sucrose preference ratio at week 6 showing concentration‐dependent benefits of Lactobacillus (H.Lacto, L.Lacto) and Bifidobacterium (H.Bifido, L.Bifido) similar to benefits conferred by fluoxetine (Flx). Data are represented as mean ± SEM. (B and D) (two‐way ANOVA followed by Bonferroni post hoc test); (C and E) (one‐way ANOVA followed by Tukey's multiple comparison test). #P < 0.05, ### P < 0.001 when compared to control group and * P < 0.05, *** P < 0.001 when compared to the stress group.

FIGURE 2

Effect of probiotic administration on behavioral measures of depression, helplessness, and anxiety. (A)–(C) Force swim test: probiotics decreased stress induced immobility (A) Immobility time (s), (B) swimming time (s), and (C) climbing time (s). (D)–(F) Tail suspension test: probiotics reversed stress induced behavioral deficits but not to the same degree as fluoxetine (D); Immobility time (s), (E) curling time (s), and (F) swinging time (s). (G)–(I) Open field test: probiotics protected against stress‐induced deficits in exploratory behavior. (G) Number of crossings, (H) periphery time (s), (I) c time (s). Data are presented as mean ± SEM. One‐way ANOVA followed by Tukey's multiple comparison test) # P < 0.05, ## P < 0.01, ### P < 0.001, when compared to the control group (Veh‐NS); *P < 0.05, ** P < 0.01, *** P < 0.001 when compared to the stress group (Veh‐S).

FIGURE 3

Effect of probiotic administration on pain response time (s). Probiotics protected against stress‐induced increased pain sensitivity to levels similar those two of fluoxetine (flx). Data are presented as mean ± SEM. **P < 0.01, *** P < 0.001 when compared to the vehicle stress group (Veh‐S) and ### P < 0.001when compared to the vehicle control group (Veh‐NS) (one‐way ANOVA followed by Tukey's multiple comparison test).