Guidelines for best practice in placebo-controlled experimental studies on probiotics in rodent animal models

Neurobiological effects of a probiotic-supplemented diet in chronically stressed male Long-Evans rats: Evidence of enhanced resilience

Probiotics that regulate the microbiome-gut-brain axis and provide mental health benefits to the host are referred to as psychobiotics. Preclinical studies have demonstrated psychobiotic effects on early life stress-induced anxiety- and depression-related behavior in rodents; however, the specific mechanisms remain ill-defined. In the current study, we investigated the effects of probiotic supplementation on neurobiological responses to chronic stress in adult male Long-Evans rats. Twenty-four rats were randomly assigned to probiotic (PB) or vehicle control (VEH) groups, then to either chronic unpredictable stress (CUS) or no-stress control (CON) conditions within each group (n = 6/subgroup). We hypothesized that PB supplementation would reduce markers of anxiety and enhance emotional resilience, especially in the CUS animals. In the cognitive uncertainty task, a nonsignificant trend was observed indicating that the PB-supplemented animals spent more time oriented toward the food reward than VEH animals. In the open-field task, CUS-PB animals spent more time in the center of the arena than CUS-VEH animals, an effect not observed between the two CON groups. In the swim task, the PB animals, regardless of stress assignment, exhibited increased floating, suggesting a conserved response in a challenging context. Focusing on the endocrine measures, higher dehydroepiandrosterone (DHEA)-to-corticosterone fecal metabolite ratios, a correlate of emotional resilience, were observed in PB animals. Further, PB animals exhibited reduced microglia immunoreactivity in the basolateral amygdala, possibly indicating a neuroprotective effect of PB supplements in this rodent model. These results provide evidence that PB supplementation interacts with stress exposure to influence adaptive responses associated with endocrine, neural, and behavioral indices of anxiety.

Ingestion of probiotic (Lactobacillus helveticus and Bifidobacterium longum) alters intestinal microbial structure and behavioral expression following social defeat stress

Social stress exacerbates anxious and depressive behaviors in humans. Similarly, anxiety- and depressive-like behaviors are triggered by social stress in a variety of non-human animals. Here, we tested whether oral administration of the putative anxiolytic probiotic strains Lactobacillus helveticus R0052 and Bifidobacterium longum R0175 reduces the striking increase in anxiety-like behavior and changes in gut microbiota observed following social defeat stress in Syrian hamsters. We administered the probiotic at two different doses for 21 days, and 16S rRNA gene amplicon sequencing revealed a shift in microbial structure following probiotic administration at both doses, independently of stress. Probiotic administration at either dose increased anti-inflammatory cytokines IL-4, IL-5, and IL-10 compared to placebo. Surprisingly, probiotic administration at the low dose, equivalent to the one used in humans, significantly increased social avoidance and decreased social interaction. This behavioral change was associated with a reduction in microbial richness in this group. Together, these results demonstrate that probiotic administration alters gut microbial composition and may promote an anti-inflammatory profile but that these changes may not promote reductions in behavioral responses to social stress.

Neuroprotective effects of probiotics bacteria on animal model of Parkinson's disease induced by 6-hydroxydopamine: A behavioral, biochemical, and histological study

Parkinson's disease (PD) is an age-associated, progressive, and common neurodegenerative disorder. It is characterized by dopaminergic neuron degeneration in the substantia nigra pars compacta. The involvement of oxidative stress, inflammation, and dysbiosis in PD has been confirmed and probiotics also have the ability to regulate the mentioned mechanisms. Here, we assessed probiotics supplementation effects on experimental model of PD. Thirty Male Wistar rats were divided into three groups for a 14-day treatment. It was shown that a mixture of probiotics containing Lactobacillus acidophilus, Bifidobacterium bifidum, Lactobacillus reuteri, and Lactobacillus fermentum could improve rotational behavior, cognitive function, lipid peroxidation, and neuronal damage in the group received probiotic supplementation compared to the other groups (P < 0001, P < .001, and P = .026, respectively). Taken together, these findings revealed that probiotics supplementation could be an appropriate complementary treatment for PD.

Supplementation with Combined Lactobacillus helveticus R0052 and Bifidobacterium longum R0175 Across Development Reveals Sex Differences in Physiological and Behavioural Effects of Western Diet in Long-Evans Rats

The gut microbiome affects various physiological and psychological processes in animals and humans, and environmental influences profoundly impact its composition. Disorders such as anxiety, obesity, and inflammation have been associated with certain microbiome compositions, which may be modulated in early life. In 62 Long–Evans rats, we characterised the effects of lifelong Bifidobacterium longum R0175 and Lactobacillus helveticus R0052 administration—along with Western diet exposure—on later anxiety, metabolic consequences, and inflammation. We found that the probiotic formulation altered specific anxiety-like behaviours in adulthood. We further show distinct sex differences in metabolic measures. In females, probiotic treatment increased calorie intake and leptin levels without affecting body weight. In males, the probiotic seemed to mitigate the effects of Western diet on adult weight gain and calorie intake, without altering leptin levels. The greatest inflammatory response was seen in male, Western-diet-exposed, and probiotic-treated rats, which may be related to levels of specific steroid hormones in these groups. These results suggest that early-life probiotic supplementation and diet exposure can have particular implications on adult health in a sex-dependent manner, and highlight the need for further studies to examine the health outcomes of probiotic treatment in both sexes.