Abstract
During the torpor phase of mammalian hibernation when core body temperature is near 4 degrees C, the autonomic system continues to maintain respiration, blood pressure and heartbeat despite drastic reductions in brain activity. In addition, the hibernator's neuronal tissues enter into a protected state in which the potential for ischemia-reperfusion injury is markedly minimized. Evolutionary adaptations for continued function and neuroprotection throughout cycles of torpor and euthermia in winter are predicted to manifest themselves partly in changes in the brainstem proteome. Here, we compare the soluble brainstem protein complement from six summer active ground squirrels and six in the early torpor (ET) phase of hibernation. Thirteen percent of the approximately 1,500 quantifiable 2D gel spots alter significantly from summer to ET; the proteins identified in these differing spots are known to play roles in energy homeostasis via the tricarboxylic acid cycle (8 proteins), cytoarchitecture and cell motility (14 proteins), anabolic protein processes (13 proteins), redox control (11 proteins) and numerous other categories including protein catabolism, oxidative phosphorylation, signal transduction, glycolysis, intracellular protein trafficking and antiapoptotic function. These protein changes represent, at least in part, the molecular bases for restructuring of cells in the brainstem, a shift away from glucose as the primary fuel source for brain in the winter, and the generation of a streamlined mechanism capable of efficient and rapid energy production and utilization during the torpor and arousal cycles of hibernation.