MODULATION OF THE GUT-BRAIN AXIS BY PROBIOTICS: STUDY OF THE INFLAMMATORY PROFILE IN ANIMALS FROM THE MODEL OF SPONTANEOUS AGGRESSION (MSA)

Stress is a biological response to threatening situations. When chronic, particularly in  social contexts, it can promote behavioral, neuroinflammatory, and intestinal  alterations through the gut-brain axis. Communication between the gut microbiota and  the central nervous system occurs through neural, endocrine, and immune pathways. Changes in the intestinal microbiota may increase gut permeability, favoring the  release of pro-inflammatory cytokines into the systemic circulation. These mediators  can reach the brain, increase blood-brain barrier permeability, and contribute to  neuroinflammation and behavioral changes. This study aims to investigate the  influence of the gut-brain axis before and after probiotic treatment by evaluating the  inflammatory profile of animals subjected to chronic social stress. In the chronic social  stress model (MSA), animals underwent social regrouping at 10 weeks of age and  were classified from the 12th week onward as non-regrouped (NR), harmonious (Har),  defeated (AgD), or aggressors (AgR). Animals were treated with Bacillus clausii by gavage for six weeks. Intravital microscopy was performed following intravenous  administration of rhodamine to evaluate cerebral leukocyte rolling and adhesion. Cytokine levels in the brain, intestine, and plasma were quantified by flow  cytometry.Preliminary results from the control group showed a significant increase in  IL-10 in the amygdala and IL-2 in the jejunum of AgD animals. In the prefrontal cortex,  IFN-γ levels were increased in NR animals compared with AgR animals. In plasma,  IL-10 levels were elevated in AgR animals, whereas IL-17A levels were increased in  the NR and Har groups. Additionally, TNF-α, IFN-γ, and IL-6 levels were mainly  increased in the Har and AgD groups, suggesting a systemic pro-inflammatory profile.  No significant differences were observed in the hippocampus or colon, indicating the  absence of a relevant inflammatory response in these regions. Cerebral leukocyte analysis revealed significantly increased leukocyte rolling and adhesion in AgD  animals compared with the other groups, demonstrating enhanced cerebral  inflammatory activation.These findings suggest that chronic social stress induces  distinct systemic and cerebral inflammatory alterations according to behavioral  phenotype, reinforcing the role of the gut-brain axis in the inflammatory response  associated with chronic social stress.