Eyeblink conditioning performance and brain-wide C-fos expression in male and female mice

Abstract

The functional and molecular sources of behavioral variability in mice are not fully understood. As a consequence, the predominant use of male mice has become a standard in animal reseach, under the assumption that males are less variable than females. Similarly, to homogenize genetic background, neuroscience studies have almost exclusively used the C57BL/6 (B6) strain. Here, we examined individual differences in performance in the context of associative learning. We performed delayed eyeblink conditioning while recording locomotor activity in mice from both sexes in two strains (B6 and B6CBAF1). Further, we used a C-FOS immunostaining approach to explore brain areas involved in eyeblink conditioning across subjects, and correlate them with behavioral performance. We found that B6 male and female mice show comparable variability in this task and that females reach higher learning scores. We found a strong positive correlation across sexes between learning scores and voluntary locomotion. C-FOS immunostainings revealed positive correlations between C-FOS positive cell density and learning in the cerebellar cortex as well as multiple, previously unreported extra-cerebellar areas. We found consistent and comparable correlations in eyeblink performance and C-fos expression in B6 and B6CBAF1 females and males. Taken together, we show that differences in motor behavior and activity across brain areas correlate with learning scores during eyeblink conditioning across strains and sexes.

Deficits in Cerebellum-Dependent Learning and Cerebellar Morphology in Male and Female BTBR Autism Model Mice

“…Previously regarded as a potential source of variation in measurements in female mice, a widely cited meta-analysis shows that female mice, when tested irrespective of their estrous cycle, showed no significant increase in variation compared to male mice [106]. This lack of difference in variability has recently been confirmed for delay eyeblink conditioning, motor behavior, and other aspects of cerebellar function in study [87]. It is possible that other factors that vary with sex that are cited in the Oyaga study, like wheel running [107] and response to stressful and anxiogenic situations [108], may account for the differences noted in our study as well as in the literature.…”

“…How might a sex difference in delay eyeblink conditioning arise? Differences in the speed of eyeblink acquisition have been ascribed to the role of the hormonal stress response in learning in female mice [86] or differences in the activity of neurons in the motor areas of the cerebellum [87]. It is possible that sex differences in stress processing [88] or sex differences in the electrophysiology of Purkinje cells [89] in the BTBR mice might account for this difference.…”