We next examined whether the unimpaired cognitive functions in enriched aged mice could be attributed to reductions in PPs

Aged EE mice also had lower escape latencies in the 1st 5 days than aged SH mice (p < 0.05 Fig 2D). In fact, aged EE mice performed equivalent to young EE mice and even better than young SH mice across days 1 to 5 ( < 0.05), but across days 6 to 9, there was no difference with young SH and they fared worse than young EE mice (p < 0.05 Fig 2D). Although swim speed was a factor 76822-21-4 between aged and young (ANOVA, effect of `group’, p < 0.001 S4D and S4E Fig), aged EE mice acquired the platform as well as young EE mice throughout training despite the handicap. Interestingly, young EE mice had significantly faster acquisition times across days 1 to 5 ( p < 0.01) and overall in the 9 days (p < 0.05) than young SH mice, whose learning was more linear (Fig 2D). In the probe trial, both young and aged mice spent more time in the target quadrant than by chance alone (ANOVA, effect of `quadrant', p < 0.001), however, young mice spent significantly longer time (p < 0.01 Fig 2E) and had a higher number of average platform crossings in the target quadrant than aged mice (p < 0.05 S4F Fig). There was no difference in time spent in the target quadrant and the average number of platform crossings when separated by housing (ANOVA, effect of `group', Fig 2E and S4G Fig).We tested another cohort of aged and young mice in a single, displaced and novel object recognition memory (DNOR) task (Fig 3A). Aged and young mice had similar preferences for three pre-determined objects (S5A Fig). 24 hours after training, one object was displaced to an adjacent corner and mice were allowed to explore for 5 minutes. All mice spent equivalent time with all three objects except standard-housed aged mice, which spent more time with familiar object 2 (6.46 1.21 s) than with the displaced object (2.51 0.69 s p <0.01 S5B Fig). 7792930There was no difference in the discrimination ratio between groups (Fig 3B). Following 5 minutes ITI, the mice were then allowed to explore another 5 minutes but with object 2 replaced by a novel object. Aged EE, young EE and young SH mice spent significantly more time with the novel object than with the other two familiar objects, compared to aged SH mice (S5C Fig). Aged EE mice (65.57 7.64%) preferred the novel object 58.5% more than aged SH mice (41.38 6.05% ANOVA, effect of `group’, p < 0.05 Fig 3C). This agrees with previous studies of recognition memory impairment in aged mice [34].We next examined whether the unimpaired cognitive functions in enriched aged mice could be attributed to reductions in PPs. We performed calcineurin and PP1 activity assays in the hippocampus of mice that were tested on DNOR memory tasks following 6 weeks of EE or SH (Fig 3A). Combined PP1 and PP2A activity levels in aged EE (0.13 0.03 nmol) and young EE (0.16 0.04 nmol) mice were significantly lower than in aged SH (0.44 0.09 nmol p < 0.01) and young SH (0.34 0.05 nmol p < 0.05) mice (ANOVA, effect of `group', p < 0.01 Fig 4A).Fig 3. Recognition memory in aged and young mice following respective housing conditions. (A) Experimental design of the displaced and novel object recognition memory (DNOR) tasks over two days in 5 min blocks with 5 min ITI (n = 9, 8, 9, 8 for Aged EE (solid red), Aged SH (red stripes), Young EE (solid blue), Young SH (blue stripes), respectively).