BACKGROUND: The circadian system influences many different biological processes across the lifespan, including memory performance and daily activity patterns. The biological process of aging causes decreased control of the circadian system that is accompanied by a decline in memory performance, suggesting that these two processes may be linked. Indeed, our previous work has shown that in male mice, the clock genefunctions within the dorsal hippocampus to exert diurnal control over memory and repression ofin the old hippocampus contributes to age-related impairments in spatial memory. Although it is clear thatmay be a key molecular link between memory and the circadian rhythm, next to nothing is known about how sex impacts this role in the young or old brain. Here, we are interested in understanding how the factors of sex and age impact memory performance, circadian activity patterns, sleep behavior, and hippocampalexpression. Per1Per1Per1Per1
METHODS: We used a combination of spatial memory (Object Location Memory (OLM)) and circadian activity monitoring to determine how male and female mice change across the lifespan. In addition, we used RT-qPCR to quantify the change inlevels in response to learning in young and old, male and female mice. Per1
RESULTS: Young female mice resist diurnal oscillations in memory, showing robust spatial memory across the diurnal cycle. In contrast, old female mice show an emergence of diurnal memory oscillations, with better memory during the day than at night (similar to what we observed previously in young male mice). In contrast, old male mice showed better memory performance during the night than the day, suggesting that their peak memory performance is drastically shifted compared to young males. We also measured activity patterns and sleep behavior across the diurnal cycle and found that sex was more of an influence than age in multiple analyses, but age did have an impact, with old male mice showing stronger circadian rhythm disruptions than any other cohort. Finally, we investigated whether the circadian clock geneplays a role in these sex- and age-dependent effects in diurnal memory performance. We found that, in general, learning-inducedand memory performance peaked at similar times of day in each group, consistent with our hypothesis thatexerts diurnal control over memory performance. Per1Per1Per1
CONCLUSIONS: This work supports a role forin exerting diurnal control over memory and suggests thatmay be an appealing therapeutic target to improve memory and circadian dysfunction in old age. Per1Per1
