Fig. 1.

Home-cage locomotor activity (mean number of beam breaks) and baseline corticosterone concentrations in adult versus aged mice. Adult mice exhibit three distinct peaks in activity (A), whereas aged mice have a flattened rhythm (B). During the 2 to 3 h before lights on, the time which would correspond with late afternoon sundowning symptoms in diurnal humans, aged mice are significantly more active than adult mice (C). Arrows in C indicate the time anxiety tests and blood/brain collections were performed. Total activity counts were equivalent for adult and aged mice (D). Adult and aged mice had equivalent baseline plasma corticosterone concentrations regardless of time point (E). n = 10–13 mice per group for activity; n = 4–6 mice per group for hormone assay. Activity graphs depict mean ± SD and bar graph depicts mean ± SEM. In A and B, dotted lines connect datapoints and solid lines represent smooth curves added for purposes of visualizing the general pattern of activity. *P < 0.05.