Meeting Abstract
Brain anatomy is not static throughout the lifetime of an individual; both sex and reproductive status can alter the anatomy of brain regions and neurons within them. However, the extent to which sex and season affect neuron size and morphology in wild mammals is poorly understood. Richardson’s ground squirrel exhibits seasonal variation and sex differences in behavior and seasonal neuroplasticity in brain region volumes, but whether that variation extends to neuron morphology was unknown. Using virtual microscopy, we imaged Golgi stained hippocampal pyramidal neurons from wild male and female ground squirrels caught during breeding and non-breeding seasons. From these images, we measured neuronal morphology and dendritic spine density of over 130 neurons. Within the CA1 region, females had larger cell bodies than males and non-breeding females had longer basal dendrites than breeding females. Dendritic spine density of basal and apical dendrites of CA1 neurons was also higher in non-breeding than breeding animals of both sexes. Within CA3, non-breeding males had larger neuronal volumes than breeding males and non-breeding animals of both sexes had higher basal spine densities than breeding animals. The seasonal differences likely reflect synaptic pruning during hibernation combined with high cortisol levels in the breeding season and parallels a similar pattern in hippocampal neurogenesis. The larger CA3 neurons with more spines in non-breeding males might also support food caching, a male-specific behavior in this species. We conclude that sex and season do interact to affect neuron morphology in ground squirrels, but that these effects are likely to vary across mammalian species.
