Recent studies have suggested that gut microbacteria communicate with the central nervous system via endocrine, neural and immune pathways.
Furthermore, probiotic bacteria may protect against tissue damage by diminishing the production of inflammatory cytokines and / or free radicals, possibly due to the inhibition of tumour necrosis factor alpha (TNF-α) synthesis and the oxidative stress pathway.
These studies have verified probiotics' potential to alter brain function and mood, meaning that probiotic supplementation may also help in the management of anxiety, depression, cognitive impairment, chronic pain, and inflammatory diseases.
Bacteria versus brain damage
Researchers at Iran's Semnan University of Medical Sciences and Shahid Beheshti University of Medical Sciences therefore conducted two trials to assess the impact of the probiotic strains Bifidobacterium breve, Lactobacillus casei, Lactobacillus bulgaricus, and Lactobacillus acidophilus on preventing or minimising brain damage in an experimental murine model of stroke.
For the first trial, they randomly divided 15 male mice equally into three groups, two of which they induced with focal cerebral ischaemia, to determine probiotics' impact on infarct size and neurological outcome.
Placebo surgery (i.e., surgery without the therapeutic steps) was performed on the group without induced focal cerebral ischaemia, while the second was orally administered saline daily for 14 days, and the third was pre-treated with 107CFU/ml of probiotics daily for 14 days.
Then, 24 hours after brain ischaemia, they measured neurological outcome, biochemical markers, and infarct size.
They reported that pre-treatment with probiotics reduced infarct size by 54% compared to the saline group, though it did not manage to improve neurological function.
For the second trial, they randomly divided another 15 male mice into three groups to determine probiotics' effect on malondialdehyde (an oxidative stress marker) and TNF-α.
Once again, two of the groups were induced with focal cerebral ischaemia, and all three groups were subjected to the same methods employed in the first trial.
They then observed that the group pre-treated with probiotics saw lowered malondialdehyde content and TNF-α level in ischaemic brain tissue.
'Not completely understood'
However, they also said the "mechanisms by which probiotics can reduce the risk of brain damage are not completely understood".
They hypothesised that the probiotics' may have activated the innate immune system, which could have led to changes in the circulating levels of anti-inflammatory and pro-inflammatory cytokines and in turn, directly affected brain function.
In conclusion, they wrote: "The findings of the present study showed that probiotic supplements might be useful in the prevention or attenuation of brain ischaemic injury in patients at risk of cerebral stroke.
"Probiotics may open new therapeutic alternatives for the prevention of stroke. More pre-clinical and clinical studies are, however, needed to clarify their efficacy in cerebral stroke and to consider their possible therapeutic effects in stroke patients."
Source: Iranian Journal of Medical Sciences
Vol. 43, no. 1
"Effects of the Oral Ingestion of Probiotics on Brain Damage in a Transient Model of Focal Cerebral Ischemia in Mice"
Authors: Kobra Akhoundzadeh, et al.