Functional and molecular partitioning of the brain provides neuroprotection to cardiorespiratory nuclei in ground squirrels during hibernation

Abstract

Torpor and hibernation are among the most extreme examples of energy conservation and CNS plasticity in endotherms. In torpor the respiratory rate of the 13‐lined ground squirrel (Spermophilus tridecemlineatus) decreases 98%, and heart rate drops to 1% of the aroused state. While dendrites of cortical neurons retract during torpor, corresponding to a cessation of neuronal activity, cardiorespiratory function is maintained. We are investigating molecular and electrophysiological properties of neurons in the cortex and brainstem of ground squirrels during the annual cycle that may underlie this partitioning. Data indicate that cortex is significantly remodeled upon entrance into and arousal from torpor, whereas the brainstem, which contains cardiorespiratory nuclei, remains static. qRT‐PCR showed significant increases in mRNA for several GABA‐A receptor subunits as well as synaptophysin in cortex during interbout arousals. No such changes were seen in brainstem. Ongoing experiments using intracellular recordings and dye injection will determine functional components of this partitioning at a cellular level. We speculate that cardiorespiratory nuclei remain active during torpor and are protected from the morphological and functional remodeling associated with hibernation by modulation of GABA receptors. DARPA W81XWH‐05‐02‐0016 (HC), NIH AG18760 (MB) and NIH T32 GM007507.