Figure 4

Spermidine treatment does not rescue the age-dependent decrease in SV density at CA3-CA1 synapses. (a–d) Ultrastructural analysis of presynaptic CA3-CA1 terminals, whose visible area is here highlighted in light blue. (a) Representative electron micrographs of CA3-CA1 synapses. Note the reduction in SV density in an aged Spd− bouton (black asterisk). (b) Synaptic vesicle (SV) density (young: 175 ± 5, n = 180 boutons, 6 mice analyzed; aged Spd−: 136 ± 4, n = 210, 7 mice; aged Spd+: 130 ± 4, n = 180, 6 mice; young versus aged Spd−: p < 0.0001; young versus aged Spd+: p < 0.0001, two samples Kolmogorov-Smirnov test Bonferroni corrected with α set to 0.016667). (c) Visible bouton profile indicating the synaptic bouton area visible within each image (young: 0.135 ± 0.006, aged Spd−: 0.166 ± 0.008, aged Spd+: 0.173 ± 0.008; young versus aged Spd+: p = 0.000106, Kruskal-Wallis test followed by Mann Whitney U test Bonferroni corrected with α set to 0.016667). (d) Active zone (AZ) length (young: 260 ± 7, aged Spd−: 280 ± 7, aged Spd+: 287 ± 7; young versus aged Spd+: p = 0.002623, Kruskal-Wallis test followed by Mann Whitney U test Bonferroni corrected with α set to 0.016667). **p < 0.01, ***p < 0.001. Arrowheads indicate active zones, note an active zone with drastically reduced neighboring SVs in the representative electron micrograph of an aged control mouse. Values represent mean ± SEM. Graphs show medians, interquartile ranges and min/max values. Circles are outliers and pentagons are extremes.