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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.)

Lack of Effective Treatments

With wide variability in the causes and symptoms of IBS, various treatments address motility and discomfort with limited success. Some drugs target gut neural receptors, including psychiatric drugs that address comorbid anxiety or depression. However, these drugs may have side effects ranging from headaches or constipation to cardiovascular events or diarrhea. While dietary approaches may provide some benefit, certain types of safe probiotics have demonstrated effects on the microbiota-gut-brain axis and reduced pain or improved motility in IBS.


Intestinal serotonin affects the motility of the gut and is a target for treatment in IBS. PS128 is able to raise serotonin in the brain as well as lower stress hormone levels [2] [3]. 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 rats received either a saline placebo or probiotic strain PS128 each day for two weeks. Researchers then simulated IBS and GI hypersensitivity by injecting the rats with 5-HTP (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 rat in order to assess PS128’s potential to alleviate pain and symptoms of GI hypersensitivity. After the experiment, 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 5-HTP 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 rats' 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 rats 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 rats, only the placebo-treated, 5-HTP group demonstrated visceral hypersensitivity and three times the level of stress experienced by the other rats. Those treated with psychobiotic PS128 showed no increase in stress, despite injection with 5-HTP. Their corticosterone levels were even lower than in the control group that had not received 5-HTP at all.


Physiological pain response was alleviated.

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


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