Figure 6. Mice treated with metformin by tail vein injection showed better performance in the Morris water maze test. (A) Mice treated with metformin (n = 12) for 10 months showed a considerable disability rate compared with the control group (n = 12). (B) Twenty-month-old mice treated with metformin by tail vein injection (n = 4) showed a better performance in escape latency than mice treated by oral administration (n = 6). (C) Probe tests conducted at 24 h after the acquisition phase indicated that the first time-to-platform of 20-month-old mice treated with metformin by tail vein injection was shorter than in mice treated by oral administration. (D) No difference in swim speed was observed between control and metformin-treated groups (tail vein injection or oral administration). Ctrl: Control; Met: Metformin. The overall significance between two groups was determined by Student’s t-test, among three group was determined by one-way ANOVA. * p < 0.05, ** p < 0.01, *** p < 0.001, ns, not significant.