Fluctuation of Brain Tissue Oxygen Partial Pressure: A Biochemical Landmark in the Arctic Ground Squirrel's Spontaneous Arousal

Hibernation in the Arctic Ground Squirrel (AGS) is a regulated, adaptive response to arctic environmental conditions. Problem statement: Regional brain Blood Flow (rCBF) has been observed to increase dramatically during arousal in hibernators. However, the real time dynamic change in PtO2 during arousal has not been studied, we hypothesized that PtO2 is Interdependent of Tbrain and a key component in the arousal process. Approach: Simultaneous in vivo measurements of PtO2 and brain temperature (Tbrain) in conjunction with oxygen consumption (V02) were conducted in the striatum of non-sedated, non-anesthetized Arctic ground squirrels during spontaneous arousal from hibernation. Results: A dramatic fluctuation of brain tissue oxygen partial pressure (PtO2) is associated with the complex phenomena of spontaneous arousal. In this study, we observed that: (1) a PtO2 elevation precedes changes in Tbrain and V02; (2) PtO2 changes do not correlate with changes in V02 during arousal and (3), endogenous O2 shift from O2 enriched blood to brain in hibernating AGS induces an arousal with the pharmaceutical chemical, efaproxiral (RSR-13). Conclusion: The four turning points of PtO2 appearing at different Tbrain during arousal suggest that changes in PtO2 are Tbrain interdependent and support the concept that arousal from hibernation is complex process invoking different feedbacks.