Fig. 6

Periodontitis impairs spatial memory and affects cell functions in the brain. a, b Performances in the Barnes maze of the 3 M and 5 M model mice groups, respectively, were assessed by measuring the time taken to reach the goal and the number of incorrect turns made (n = 4). Periodontitis caused poorer performance. c Graph showing the correlation between serum IL-1β, TNF-α, and IFN-γ levels and Barnes maze performance in the 5 M groups. Poor performance is positively correlated with higher levels of these inflammatory cytokines (n = 3). d A graph quantifying Iba1-positive microglia in bilateral hippocampi of both the 3 M and 5 M groups (n = 5). The number of microglia significantly increased with disease severity in the 5-month disease model. e Representative micrographs of anti-Iba stained microglia in the hippocampus, shown together with magnified images. Scale bar: 50 μm. f Graphs and matching pie charts, quantifying the number of reactive microglia and amoeboid microglia in bilateral hippocampi and the proportion of microglia by morphology in the 5 M groups (n = 4). Periodontitis increased the number of reactive microglia. g Clusters of microglia in the hippocampus were observed only in the 5MP_PG group (n = 5). Anti-Iba stained tissue section; Scale bar: 50 μm. h, i Anti-DCX stained cells, indicative of newborn neurons, in the hippocampal dentate gyrus of 3 M and 5 M groups, respectively. Periodontitis decreased the number of DCX-positive cells. Scale bar: 100 μm. Data are presented as mean ± SD. Statistical significance was determined using an unpaired two-tailed Student’s t-test. One-way ANOVA followed by the Tukey–Kramer test, *p < 0.05, **p < 0.01, ns: not significant