Fig. 4

Transplantation of nitrate-supplemented oral microbiota improves cognitive function. A Schematic diagram showing the study design for OMT. B The composition of the oral microbiota of two groups at the genus level (n = 9–10). C The changes in body weight during two weeks (n = 9–10). D and E Differences in the relative abundance of Neisseria and Haemophilus (n = 9–10). F and G Behavioral tests showed that spontaneous alternation in the Y-maze test were significantly higher in the rPI group compared with the rBL group, while novelty preference in the NOR test did not differ with statistically significant difference (n = 9–10). H Representative images of Iba1 immunofluorescence in the CA1, CA3, DG (hippocampus) and dmPFC and vmPFC (mPFC). Scale bar = 100 μm. Higher definition picture was shown in Supplementary Fig. 8. I–M Quantification of the number of Iba1-positive microglia in the CA1, CA3, DG, vmPFC and dmPFC. The rPI group exhibited significant decreases in the number of Iba1-positive cells compared with the rBL group (n = 9–10). N–Q Significant decreases in the proinflammatory cytokines IL-1β and IL-6 were found in brain tissue in group rPI compared with group rBL. TNF-α and IL-10 in brain tissue showed no significant differences between the two groups (n = 9–10). R S100β in the serum showed no significant difference between the two groups (n = 9–10). The data are expressed as the mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001