Seasonal differences in brain anatomy and cell proliferation in hibernating thirteen-lined ground squirrels (Ictidomys tridecemlineatus).

Abstract

Hibernation is characterized by cyclical periods of rest (torpor) and arousal (IBAs). During torpor, neurons in non-vital regions in the brain disconnect from one another and reconnect upon arousal into IBA. However, neurons in vital regions likely retain connections and activity throughout torpor, and therefore employ different protective mechanisms. The goal of this study was to examine potential neuroprotective strategies employed by non-vital and vital regions. We studied seasonal differences (torpor, summer, and IBA) in neuron number/size, average %area of astrocytes, and cell proliferation, in vital and non-vital regions of Thirteen-lined ground squirrels. We observed more neurons in the somatosensory cortex (SSC) during torpor compared to summer. We also observed a greater %area of astrocytes in torpor compared to summer for nearly all analyzed regions. Finally, we identified potential evidence of cell proliferation in both vital and non-vital regions using a known proliferation marker, finding a significant increase in the number of proliferating cells in the SSC during IBA compared to summer. Overall these results suggest that during hibernation, the ground squirrel brain is dynamic and likely utilizes several supportive and neuroprotective strategies for cell survival, including both increased neuronal support by astrocytes and neuron replacement strategies.