Figure 6

The expression of zif268 in the suprapyramidal DG is attenuated with age during exploration but not rest. (a) Compartmental expression of zif268 is depicted for adult (red) and aged (blue) animals that explored a novel environment and those that remained within the home cage (hatched). When zif268 expression in adult and aged animals is compared during each epoch (b) a dramatic decline is apparent in the number of granule cells transcribing zif268 during exploration in aged animals. During the resting period immediately prior to sacrifice, however, no significant difference is seen in the number of zif268+ granule cells. Note that zif268 expression in caged control animals is depicted solely in the “rest” category since these animals were never removed from the home cage and thus their only experience was comparable to the rest period of both adult and aged delay animals. When the percentage of granule cells expressing zif268 during both epochs (exploration + rest) is analyzed relative to probability of co-expression based on chance (c) a significantly higher than chance proportion of cells show zif268 labeling during both epochs in both the adult and aged DG. The comparable number and pattern of zif268 expression during rest is particularly striking given the profound decrease in the number of cells transcribing zif268 during exploration in the aged DG (All data are mean ± SEM; *p < 0.05, **p < 0.01 relative to age-matched caged controls, †p < 0.05, adult vs. aged animals within the same behavioral group; ‡‡ p < 0.01 vs. random chance).