Neuroinflammation related to the blood–brain barrier and sphingosine‐1‐phosphate in a pre‐clinical model of periodontal diseases and depression in rats

Abstract Aim To explore the potential mechanisms of neuroinflammation (microglia, blood–brain barrier [BBB] permeability, and the sphingosine‐1‐phosphate [S1P] pathways) resulting from the association between periodontitis and depression in rats. Materials and Methods This pre‐clinical in vivo experimental study used Wistar rats, in which experimental periodontitis (P) was induced by using oral gavages with Porphyromonas gingivalis and Fusobacterium nucleatum. Then, a chronic mild stress (CMS) model was implemented to induce a depressive‐like behaviour, resulting in four groups: P with CMS (P+CMS+), P without CMS (P+CMS−), CMS without P (P−CMS+), and control (P−CMS−). After harvesting brain samples, protein/mRNA expression analyses and fluorescence immunohistochemistry were performed in the frontal cortex (FC). Results were analysed by ANOVA. Results CMS exposure increased the number of microglia (an indicator of neuroinflammation) in the FC. In the combined model (P+CMS+), there was a decrease in the expression of tight junction proteins (zonula occludens‐1 [ZO‐1], occludin) and an increase in intercellular and vascular cell adhesion molecules (ICAM‐1, VCAM‐1) and matrix metalloproteinase 9 (MMP9), suggesting a more severe disruption of the BBB. The enzymes and receptors of S1P were also differentially regulated. Conclusions Microglia, BBB permeability, and S1P pathways could be relevant mechanisms explaining the association between periodontitis and depression.