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 P_tO₂ during arousal has not been studied, we hypothesized that P_tO₂ is Interdependent of Tbrain and a key component in the arousal process. Approach: Simultaneous in vivo measurements of P_tO₂ and brain temperature (T_brain) 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 (P_tO₂) is associated with the complex phenomena of spontaneous arousal. In this study, we observed that: (1) a P_tO₂ elevation precedes changes in T_brain and V₀₂; (2) P_tO₂ 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 P_tO₂ appearing at different T_brain during arousal suggest that changes in P_tO₂ are Tbrain interdependent and support the concept that arousal from hibernation is complex process invoking different feedbacks.