Sex Differences in Age-related Impairments Vary across Cognitive and Physical Assessments in Rats

Inclusion of female subjects in biomedical research is imperative for understanding the mechanisms of age-related cognitive decline, as more than half of individuals older than 65 are female. Few behavioral and physical assays, however, have been conducted in both sexes within the same study. In the current experiments young and aged male and female rats underwent a battery of cognitive and physical assessments to examine for potential sex and age differences. Physical performance was measured with a rotarod test of motor coordination, assessment of maximum grip strength and swim speed. While there were differences between males and females in rotarod and grip strength, there was also a clear age-dependent decline in physical performance in both sexes. Cognitive assessment included the Morris watermaze test of hippocampal dependent spatial navigation and a biconditional association task (BAT) with a working memory (WM) component. Notably, a similar BAT has previously been validated as a more sensitive assay of age-related cognitive decline than the watermaze in male rats, which is replicated here in both female and male rats. Furthermore, young and aged female rats both spent a similar percent of time in each estrus cycle phase and phase did not influence WM/BAT performance. In conclusion, robust age differences in biconditional association task performance are observed in both sexes with no need for increased cohort size. Thus, future studies utilizing similar behavioral paradigms should be representative of the human population they intend to model through the inclusion of female subjects.