Importantly, the mice did not associate the novel context with the original context and both young and aged mice could be fear conditioned a second time

Pre-determined novel contexts ended up utilized for secondary behavioral evaluations in the two dread conditioning and MWM jobs to stay away from generalization to the authentic behavioral paradigms (see Resources and Approaches). 36396-99-3 Middle-aged mice, now innovative in age and addressed hereafter as aged, reduced their weight differential (40.seventy four one.51 g) and weighed only 24.7% much more than youthful mice (32.65 .forty two g p < 0.001 S3C and S3D Fig). There was no effect of EE on the weight of young mice, but enriched aged mice weighed 16.1% less than standard-housed aged mice (Aged EE, 37.17 0.91 g Aged SH, 44.31 2.39 g p < 0.001 S3E Fig). Aged EE mice now reached a weight indistinguishable from that of standard-housed young mice (Young SH, 33.54 0.58 g), but not that of enriched young (Young EE, 31.68 0.46 g S3E Fig). The effect of long-term EE and SH in a different cohort of mice show nearly identical changes in weight (S5D5G Fig). There was no difference in time spent in center in the open field test following several weeks of housing (OF2), suggesting no improvement or impairment in exploratory behavior or anxiety with age and housing (S3F Fig). In the re-assessment of the fear conditioning task (FC2),Fig 2. Assessment of aged and young mice after several weeks of undisturbed housing in EE or SH. (A) Fear conditioning in a novel context (FC2) and (B) memory test 24 hours later in the same context (n = 8, 6, 7, 7 for Aged EE (solid red), Aged SH (red stripes), Young EE (solid blue), Young SH (blue stripes), respectively F3,24 = 3.646). Escape latency to a hidden platform in an alternate Morris water maze and room (MWM2), different than that of MWM1, (C) by age and (D) separated by age and housing conditions (n = 11, 11, 11, 10 for Aged EE (red line), Aged SH (red dashes), Young EE (blue line), Young SH (blue dashes), respectively days 1, F3,39 = 5.524, p < 0.01 days 6, F3,39 = 4.307, p < 0.05 days 1, F3,39 = 4.652, p < 0.01 p values shown with respect to aged (red) and young (blue)  < 0.05 (Aged EE to Young SH) p < 0.01 (Young EE to Aged SH) p < 0.05 (Young EE to Aged EE). Probe trial on day 10 9745358with the hidden platform removed, (E) separated by age and housing conditions (O, opposite R, right L, left T, target). p < 0.05, p < 0.01, p < 0.001. Shown as mean s.e.m baseline freezing (Before Shock 0 to 3 minutes) remained similar to FC1 following the unconditioned stimulus (After Shock 3 to 6 minutes Fig 2A). Importantly, the mice did not associate the novel context with the original context and both young and aged mice could be fear conditioned a second time. After adjusting to baseline freezing levels, aged EE mice (37.13 3.38%) exhibited freezing which was significantly higher than aged SH (15.03 6.18% ANOVA, effect of `group', p < 0.05) and was equivalent to levels in young mice (Fig 2B). To re-evaluate spatial memory performance following several weeks of housing, mice were re-trained and tested in a second novel Morris water maze (MWM2). Aged mice acquired the target in the same amount of time as young mice in the first five days (ANOVA, effect of `days', p < 0.001), however, young mice continued to improve with additional training (days 5 to 9 ANOVA, effect of `group', p < 0.01 Fig 2C).