S8 and S10 mice exhibit accelerated-senescence phenotypes. (a) Proportion of surviving S8 mice (blue squares, n = 237), S10 mice (purple diamonds, n = 169), SR1 mice (green triangles, n = 189) and B6 mice (black crosses, n = 75, data from Pugh et al. ). Using a Kaplan-Meier survival analysis, the S8 and S10 survival profiles are significantly different from SR1 (p < 0.0001 and p < 0.0015, respectively) by the Mantel-Cox log rank test. Arrows and lines indicate the two ages (3 months and 16 months) at which mice were dissected and used for the gene expression experiments in the SAM strains. An arrow also indicates the age at which the old B6J mice were sacrificed for gene expression analysis. (b) Retention of foot shock is indicated as latency to entry into the dark chamber (day 2-day 1) in a passive avoidance paradigm. Difference in latency to entry is shown on the y-axis and age on the x-axis at a young time point and an old time point for S8 (blue: young n = 43, old n = 8), S10 (purple: young n = 31, old n = 7) and SR1 (green: young n = 41, old n = 27) mice. Error bars indicate standard error. S8 and S10 mice show decreased latency to entry relative to SR1 at both young (two-tailed Student's t-test: p < 0.003 and p < 0.002, respectively) and old (p < 0.05, S8) time points.