Many studies have highlighted the significance of the “gut-brain axis” in establishing our mental and metabolic health, and this axis has been linked to our emotional states. Major depressive disorder (MDD) and post-traumatic stress disorder (PTSD) have recently been modeled after chronic social defeat stress (cSDS) and chronic vicarious social defeat stress (cVSDS). Is it possible that cVSDS animal models could aid in our comprehension of IBS? Professor Akiyoshi Saitoh of the Faculty of Pharmaceutical Sciences at Tokyo University of Science (TUS) and his team of researchers used cVSDS mouse models to find out. The researchers wanted to know how long-term emotional stress affected gastrointestinal health.
The study
Higher intestinal transit ratios and visceral pain-related behaviors were observed in the mice that were subjected to psychological stress. The researchers stressed out mice by putting them through or watching them experience physical aggression for 10 minutes a day for 10 days.
In order to gauge the level of stress experienced by the animals in the experiment, a social interaction test was carried out on day 11. In addition to the charcoal meal experiment and the capsaicin-induced hyperalgesia test, the levels of plasma corticosterone and the duration of the animals’ resting periods after the tests were used to approximate the animals’ levels of stress. Intestinal permeability, intestinal pathology, frequency of defecation, as well as stool content were also assessed in the mice.
They discovered that mice exposed to emotional stress had a significantly higher charcoal transit ratio, an indicator of intestinal passage, in comparison to mice in the controlgroup. Physically stressed mice, however, showed only minor effects. Mice that were put under psychological duress also had an increase in the frequency and volume of their bowel movements.
After a month without stress loading, the effects persisted. Intestinal permeability and pathological status did not differ between unstressed and emotionally-stressed mice, either, indicating that there were no changes at the cellular or tissue level as a result of the stress.
This research provides the first evidence that mice can develop IBS-D-like symptoms after experiencing only the psychological stress associated with cVSDS. To better understand the pathophysiological conditions that contribute to IBS and to develop effective treatments, future studies may use the cSDS and cVSDS paradigms.
