Fig. 1.

Reduced expression of dopamine signaling-associated genes and dopamine levels in large intestine of aged mice. A Venn plot of detected genes in large intestinal epithelial cells analyzed by RNA-seq in 2-month-old (2M) and 18-month-old (18M) mice. B A volcano plot showing the up- and down-regulated genes in 2M and 18M mice. C A heatmap showing downregulated expression of genes associated with DA signaling in large intestinal epithelial cells of 2M or 18M mice. D, E Expression of Arrb2 and Cryab in RNA-seq analysis is significantly decreased in 18M mice. Data are presented as the mean ± SEM, n = 3. Unpaired t-test. *P <0.05. F Concentrations of free active DA in the colonic lumen measured by HPLC. Data are presented as the mean ± SEM, 3-month-old (3M), n = 3; 12-month-old (12M), n = 5, 18-month-old (18M), n = 7. One-way ANOVA followed by post-hoc test. *P <0.05. G–I Expression of DRD2 in large intestinal cells assessed in 3M, 12M, and 18M mice. The intestinal epithelial DRD2 levels are assessed by western blotting (G), and quantitative data are shown in (H). Data are presented as the mean ± SEM, 3M, n = 3; 12M, n = 4, 18M, n = 3. One-way ANOVA followed by post-hoc test. *P <0.05. I Levels of Drd2 mRNA in the intestinal epithelium of mice assessed by quantitative PCR at various ages. Data are presented as the mean ± SEM, 3M, n = 4, 12M, n = 4, 18M, n = 2. Unpaired t-test. *P <0.05.