High activity of the endogenous opioid system and acute but not chronic stress influence experimental colitis...

Exposition to environmental factors is one of the major underlying causes in inflammatory bowel diseases (IBD), with several endogenous systems involved. Our aim was to characterize the impact of stress on the colitis development in relation to the endogenous opioid system (EOS) activity in mice. A unique mouse model of high and low activity of EOS (namely high (HA)/low (LA) stress-induced analgesia) was employed. Mice were bred using bidirectional selection and classified as HA or LA line based on the measurement of analgesia. Colitis was induced by instillation of trinitrobenzenesulfonic acid in 30% EtOH/0.9% NaCl. After 4 days, the macroscopic score was assessed and samples for molecular and histological studies were collected. To evaluate the influence of stress on colitis development, chronic mild stress (exposure to stress stimuli for 2 and 5 weeks) and acute stress (short restraint over 3 days) were applied before colitis induction. We observed a difference in the colitis development between non-stressed HA and LA mice, as indicated by macroscopic and ulcer scores. Acute stress improved colitis in HA mice but did not change the inflammation score in LA line as compared to respective non-stressed mice. Chronic mild stress had no influence on colitis in either of mouse lines. Our study supports the hypothesis that the activity of EOS may be crucial in IBD development. We also evidence that acute, but not chronic stress influenced IBD exacerbation, depending on EOS function.