Irritable bowel syndrome (IBS)Trusted Source is a functional gastrointestinal disorder that does not have a physical cause and affects around 11%Trusted Source of the global population.
Currently, there is a dearth of animal models that accurately recapitulate the features of this disorder observed in humans.
A recent study published in Frontiers of Neuroscience shows that mice subjected to psychological stress showed IBS-like symptoms without causing inflammation or structural changes in the gut.
The study’s author Akiyoshi Saitoh, Ph.D., a professor at Tokyo University of Science, told Medical News Today:
“IBS is a disease whose pathophysiology has not been elucidated due to the lack of useful animal models for research, and no fundamental treatment has been established. In this study, we found that ‘chronic vicarious social defeat stress model mice’ subjected to repetitive mental stress alone showed diarrhea-type IBS-like symptoms of increased bowel hypermobility and increased visceral pain-related behaviors, even though there were no histological abnormalities in the intestines.”
Dr. Saitoh added that no animal model has ever shown diarrheal IBS-like symptoms due to mental stress alone.
“This mouse model is expected to play an important role in elucidating the pathophysiology and developing therapeutic agents as an IBS model animal,” Dr. Saitoh said.
What are the symptoms of IBS?
IBS is a chronic gastrointestinal disorder characterized by co-occurring symptoms, such as abdominal pain or discomfort, and disturbances in bowel movements, including constipation and diarrhea.
Depending on the prevalence of symptoms of diarrhea, constipation, or both, IBS can be categorized into four main subtypes:
- IBS with diarrhea (IBS-D)
- IBS with constipation (IBS-C)
- undefined IBS (IBS-U)
- IBS-mixed (IBS-M)
IBS-mixed is characterized by symptoms of both constipation and diarrhea, whereas the symptoms associated with IBS-U tend to vary.
Despite the uncomfortable symptoms, individuals with IBS do not show signs of structural damage to the digestive tract, such as ulcers.
Some of the potential mechanisms contributing to these symptoms include altered gut motility and heightened pain sensitivity of internal organs.
Animal models explore the link between IBS and stress
Several lines of evidence suggest that gut and brain health are intertwined.
Consistent with this, studiesTrusted Source suggest that the dysregulation of the gut-brain axis, involving bidirectional communication between the brain and the intestine, may also contribute to the development of IBS.
Psychological stress plays a role in the development of IBS and may exacerbate its symptoms. In addition, people with IBS also often have co-occurring psychiatric conditions, such as depression and anxiety.
Scientists have used animal models exposed to stress to study the effects of IBS. But these models either rely on physical stress or are associated with structural changes in the intestine. In contrast, stress experienced by humans often only involves an emotional component.
Chronic social defeat stress (cSDS) is a model of depression which involves subjecting rodents to repeated instances of defeat during aggressive encounters with a larger, dominant conspecific (i.e., member of the same species).
After experiencing repeated bouts of social defeat, rodents show depression-like symptoms, including social withdrawal and reduced ability to experience pleasure. However, rodents subjected to chronic social defeat experience both physical and emotional stress during an aggressive encounter with another animal.
Scientists have previously shown that rodents witnessing another animal of the same species subjected to cSDS also show depressive-like symptoms.
This model, known as chronic vicarious social defeat stress (cVSDS)Trusted Source, can help isolate the effects of emotional stress while eliminating the potential effects of physical stress associated with direct social defeat stress.
How emotional stress impacts gastrointestinal function
In the present study, scientists in Japan examined the potential of the cVSDS model to serve as a model for IBS.
The study consisted of adolescent mice ages 5 to 6 weeks old that were subjected to either cSDS or cVSDS for 10 minutes per day for 10 days.
On the day following the completion of the 10-day social stress exposure, animals subjected to both cVSDS and cSDS showed elevated levels of the stress hormone corticosterone, suggesting an increase in stress levels.
IBS is also associated with abnormal intestinal peristalsis, which describes the rhythmic contractions of intestinal muscles that facilitate food movement through the gut.
On the day after the completion of social stress exposure, the animals exposed to cVSDS, but not cSDS, also showed increased intestinal peristalsis than control mice that were not exposed to social stress.
These changes in intestinal motility in the animals exposed to emotional stress due to cVSDS were accompanied by an increase in IBS with diarrhea(IBS-D)-like symptoms, including an increase in the frequency of defecation, stool weight, and stool water content.