Effects of Probiotic Bacteria on Central Neuronal Activation in Experimental Colitis

Abstract

Background: Brain-gut axis dysregulation is observed in inflammatory bowel disease. However, the effect of altered gut flora on neuro- immunomodulation and its role in the pathogenesis of inflammatory bowel disease are unknown. The aims of this study are to determine (i) whether colitis modifies the expression of c-fos, a marker of general neuronal activation in the brain and (ii) whether this activation could be modulated by probiotic bacteria.

Methods: In this study, 28 Sprague-Dawley rats were divided into 4 groups: colitis-probiotic group, non-colitis-fed-control group receiv- ing probiotic Lactobacillus delbrueckii subsp. Bulgaricus B3 strain for 7 days, colitis group, and sham group receiving only sodium chlo- ride. Colitis was induced by intracolonic administration of trinitrobenzene sulfonic acid-ethanol. The expression of c-fos was detected by immunohistochemistry in the brain tissue. Cytokines and inflammatory mediators were analyzed in the plasma. Histological scores and oxidative status were analyzed in the colon samples.

Results: The inflammatory response was accompanied by increased levels of cytokines, lipid peroxidation activities, c-fos expression in the medial nucleus of the amygdala, and decreased levels of antioxidant enzymes in the colitis (P < .001). Probiotic treatment reversed those effects. Also, histopathologic scores were significantly lower in the probiotic-treated groups compared to the colitis group (P = .035). In contrast, the expression of c-fos was significantly increased in the paraventricular nucleus of hypothalamus in the probiotic- treated rats (P < .001).

Conclusion: Colitis and intestinal inflammation are associated with the activation of neurons in the limbic system creating stress-like effects in the brain. Probiotics diversely modulate limbic response and hypothalamic axis activity in addition to protective effects in inflammation.

Figure 1.

The graph of body weight percentage changes at the beginning and at the end of the study. The weight loss in the model colitis group was significantly higher than the other groups throughout the whole experiment (P < .016).

Figure 2.

(A) The graph representing the histopathological scores of colonic damages in the groups. Histopathological colitis score was significantly higher in the colitis group compared to the probiotic groups (^*colitis vs probiotic: P = .035; colitis vs fed probiotic: P = .007); (B) MDA levels of tissue in experimental groups. Results are expressed in mean ± SEM; n = 7. MDA levels were significantly higher in colitis group when compared to the other groups (^* P < .0003) which prevented by probiotic treatment; (C) light micrographs of rat colonic mucosa (H&E, 10 × 10) in colitis group. Epithelial cell loss marked cell infiltration, edema, and dilated vessels; (D) light micrographs of rat colonic mucosa (H&E, 10 × 10) in the probiotic groups. Probiotic treatment prevents inflammation. H&E, hematoxylin and eosin; MDA, malondialdehyde.

Figure 3.

(A) Graphical representation of the mast cell counts in the groups. Colitis significantly decreased the total number of mast cells compared to the sham and the fed groups (^*colitis vs sham: P = .032, colitis vs fed probiotic: P = .048); (B) percent of degranulated mast cells significantly increased colitis group, probiotic treatment prevented degranulation (^* P < .02); (C) photomicrographs showing degranulated mast cells in the colitis group (toluidine blue, 20 × 10); (D) photomicrographs showing mostly granulated mast cells in the probiotic group (toluidine blue, 20 × 10).

Figure 4.

C-fos expression in the experimental groups. (A) The number of c-fos positive cells in MNA. Colitis significantly increased the expression of c-fos in this area as compared to the sham group (^* P < .001). Probiotic treatment significantly reduced the c-fos expression in the MNA in comparison with the sham and colitis groups; (B) the number of c-fos positive cells in the PVN of the hypothalamus. The c-fos expression is significantly increased in this nucleus in the probiotic-treated groups with respect to the other groups (*P < .001); (C) photomicrographs showing c-fos positive cells (black) in the MNA of the colitis group (10 × 10); (D) photomicrographs showing c-fos positive cells (black) in the PVN of the probiotic group (10 × 10). MNA, medial nucleus amygdala; PVN, paraventricular nucleus.