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"Just because I’m used to it doesn’t mean it doesn’t hurt anymore."

 - Unknown

Irritable bowel syndrome (IBS) is a common disorder of the digestive tract, affecting anywhere from 10-20% of the population globally [1]. Key symptoms are chronic abdominal pain or discomfort paired with changes in bowel movement (frequency, form, etc.) Notably, no physical damage of gastrointestinal (GI) organs is present.


Neurologic Bowel Disorder

The etiology of IBS is unknown, but its cause may be related to a hypersensitive enteric nervous system and an imbalanced microbiota-gut-brain axis. Contributing to this theory, stress and emotions seem to affect IBS directly. Clinical patients often report excruciating abdominal pain or other symptoms being triggered by stressful events (an exam, a speaking presentation, etc.)

Treatment Complications

Currently, IBS is commonly treated with a class of drug called that blocks neural receptors within the gut. This reduces GI motility and pain associated with IBS, but by slowing GI activity, constipation can easily occur. Psychiatric drugs are prescribed to IBS patients, as many suffer anxiety or even depression because of the disorder, but these often further complicate GI symptoms. More recently, research on the microbiota-gut-brain axis has emerged showing probiotics as an effective treatment option for IBS.


PS128 is able to raise serotonin and lower stress hormone levels [2][3], changes that could potentially benefit sufferers of IBS. Scientists in Taiwan conducted an experiment to test whether or not the psychobiotic is able to alleviate symptoms of this seemingly neurological disorder [4].

Study on Rats with IBS-like Symptoms

Research Methods

A group of lab mice received either a saline placebo or probiotic strain PS128 each day for two weeks. Researchers then simulated IBS and GI hypersensitivity by injecting the mice with 5HTP (which induces visceral pain) and inserting a small balloon into their rectum. Inflating the balloon would cause particular pain. A control group was injected with only saline.


Muscle spasm count was analyzed for each mouse in order to assess PS128’s potential to alleviate pain and symptoms of GI hypersensitivity. After the experiment, the animals were sacrificed. Their serum corticosterone along with brain amygdala glucocorticoid receptors (GRs) and mineralocorticoid receptors (MRs) were measured to assess their physiological response to and mechanisms that might relieve pain.


The study confirmed that compared to the placebo cohort, mice receiving PS128 for two weeks showed less visceral hypersensitivity to 5HTP and decreased pain response from the rectal balloon. The probiotic treatment regulated both corticosterone in the hypothalamic-pituitary-adrenal axis as well as GRs and MRs in the amygdala. PS128 reduced the mice’s IBS-like symptoms, affected their brains’ emotional center, relieved pain, and enhanced their ability to calmly face stress.


Visceral hypersensitivity was relieved.

Electromyogram analysis showed internal motor reflex accompanying each rectal balloon expansion. Greater balloon expansion caused an increased visceral motor response to pain only in mice who were treated with the saline placebo; those that received the probiotic showed no additional pain response as the balloon was further expanded. PS128 relieved symptoms of gut hypersensitivity.



Serum stress hormone and stress response were reduced.

Comparing the corticosterone of each group of mice, only the placebo-treated, 5HTP group demonstrated visceral hypersensitivity and three times the level of stress experienced by the other mice. Those treated with psychobiotic PS128 showed no increase in stress, despite injection with 5HTP. Their corticosterone levels were even lower than in the control group that had not received 5HTP at all.


Physiological pain response was alleviated.

In the amygdala, GRs and MRs play a unique role in pain regulation. When perceiving pain, GR concentration is decreased while MR concentration increases. When the levels are reversed, pain is relieved.


Only the placebo 5HTP group of mice showed pain response, as well as GR and MR concentrations that were decreased and increased, respectively, nearly three times that of normal mice. The PS128 5HTP cohort showed no clear response to pain, and their GR and MR concentrations paralleled those of normal mice.


[1] Endo, Y., Shoji, T., & Fukudo, S. (2015). Epidemiology of irritable bowel syndrome. Annals of gastroenterology, 28(2), 158–159.

[2] Liu, Y. W., Liu, W. H., Wu, C. C., Juan, Y. C., Wu, Y. C., Tsai, H. P., Wang, S., & Tsai, Y. C. (2016). Psychotropic effects of Lactobacillus plantarum PS128 in early life-stressed and naïve adult mice. Brain research, 1631, 1–12.

[3] Liu, W. H., Chuang, H. L., Huang, Y. T., Wu, C. C., Chou, G. T., Wang, S., & Tsai, Y. C. (2016). Alteration of behavior and monoamine levels attributable to Lactobacillus plantarum PS128 in germ-free mice. Behavioural brain research, 298(Pt B), 202–209.

[4] Liu YW, Wang YP, Yen HF, Liu PY, Tzeng WJ, Tsai CF, Lin HC, Lee FY, Jeng OJ, Lu CL, Tsai YC. Lactobacillus plantarum PS128 Ameliorated Visceral Hypersensitivity in Rats Through the Gut-Brain Axis. Probiotics Antimicrob Proteins. 2020 Sep;12(3):980-993.

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