The world is full of microorganisms. Up to 40,000 species make their home in the human gut alone. Most, like the lactobacillus found in yogurt, live harmoniously with us.
Such probiotics are thought essential for protecting against invasion by disease-causing organisms. Others are necessary for stimulating development of the immune system and maintaining its integrity; still others enable the process of digestion. But the biggest news of all is that some probiotic strains influence the brain, and behavior, as well.
Scientists are exploring how variations in the composition of gut microbes affect the functioning of the nervous system. The link may be the parasympathetic nervous system, which, via the vagus nerve, connects the brain to many internal organs, providing agents with a pathway for communicating with the brain.
Although it’s premature to recommend agents and dosages, some specific organisms may have value in alleviating depression, pain, and psychosomatic disorders such as irritable bowel disease.
Axis of Irritability
Psychiatric illness seldom stands alone. Gastrointestinal disease, for example, and especially dyspepsia and irritable bowel syndrome, are commonly accompanied by impaired mood. More than half of patients with IBS also meet the criteria for diagnosis of mood disorders. Korean researchers now point to a common cause–disturbance in gut probiotics. Scientists suspect that gut microbes play a key role in balancing both intestinal and neural function.
A New Prozac?
Maybe the best way to treat the brain is through the gut. Mood dysregulation has long been linked to inflammation, suggesting there’s immune dysfunction in depression. Researchers report that treating animals with gut probiotic Bifidobacterium infantis leads to positive changes in neurochemical function.
The microbe raised levels of the serotonin precursor tryptophan in the frontal lobe and the amygdala, two brain areas associated with mood and emotion.
Bye-Bye Valium
Depression isn’t the only psychiatric condition that accompanies gastrointestinal disorders. Anxiety does, too. Animals experimentally infected with a gut parasite developed not only gut inflammation but anxiety-like behavior as well. What’s more, infection reduced levels of the brain growth factor BDNF in the hippocampus, a structure associated with mood and memory. Treatment with the probiotic B. longum normalized both behavior and BDNF levels.
Perish the Pain
The probiotic B. infantis 35624 may be especially useful for treating the pain of IBS. Scientists know that IBS is accompanied by changes in the number and species of gut microbes. Those changes may lower the visceral pain threshold in IBS patients, as microbes play a role in pain signaling. Scientists in Ireland find that treating stressed animals with B. infantis reduces pain behaviors, indicating that the microbes alleviate visceral hypersensitivity.
A Hairy Hypothesis
The gut-brain link may be just the half of it. Sure, scientists are busy testing the value of specific probiotics in treating psychiatric disorders. But some suggest there’s a much wider gut-brain-skin axis, with gut bugs influencing immune and nerve pathways in all three organs. A team of international researchers finds that use of specific probiotics not only greatly reduces stress-related skin inflammation but transforms hair follicles to regrow hair.
-Tarah Knaresboro, Psychology Today Magazine
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