It is indicated the intestinal environment affects anxiety and emotions directly in recent years. For example, improvement of intestinal environment is known to suppresses the anxiety-like behavior in mice model of depression and schizophrenia. Such gut-brain relationships, called “gut-brain axis”, are suggested to involve both endocrine and neuronal system via the vagus nerve. However, previous studies have mainly used psychiatric disease models, therefore how intestinal environment will affect on emotion in normal animals remains unclear. In the present study, we verified psychological and physiological effect of food-induced intestinal environment modification.
First, we divided mice into two groups and fed either MF (Standard diet: contains various dietary fibers) or AIN-93M (contains cellulose alone) for 16 weeks. As reported, AIN-93M reduced the level of short-chain fatty acids in the cecum. Further, we found the significant decrease in peristalsis and the change in intestinal inflammation in AIN-93M-fed animals, suggesting the exacerbation of intestinal environment in those animals comparing to MF-fed control group. Interestingly, AIN-93M-fed animals also displayed the significant increase of marble-burying behavior compared to MF-fed group, indicating the enhancement of anxiety by that 16-week exposure to AIN-93M. These effects were abolished by vagotomy, suggesting that enhanced anxiety is caused by the AIN-93M-induced intestinal disturbance through gut-brain axis. We further measured brain monoamine levels in these animals, and found the dopamine level in amygdala was significantly increased in the AIN-93M-fed group. 
These results suggest that the cellulose-induced intestinal disturbance and decreased intestinal function caused overactivation of dopaminergic system, which may enhance the anxiety level.