Abstract
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.
Highlights
Pressure (PaO2) as compared to non-hibernator rat brains (Ma et al, 2005), but Arctic Ground Squirrel (AGS) brain tissue oxygen
Hibernation is a well regulated adaptive response partial pressure (PtO2) is low (Ma and Wu, 2008). to environmental conditions of low ambient When aroused from hibernation, AGS experiences a temperature (Ta) and food shortage during winter drop in PaO2 to ~ 9 mm Hg, but while hypoxic there is (Ortmann and Heldmaier, 2000; Jinka et al, 2011). no evidence of cellular stress, inflammatory response, Body temperature, metabolic rate, heart rate, blood neuronal pathology, or oxidative modification in brain pressure and cerebral blood flow are greatly reduced following the period of high metabolic demand relative to resting euthermic state in natural hibernation necessary for arousal (Ma et al, 2005)
A regulated body temperature drops close to, or even below zero degree, whole body metabolism falls to only 1-2% of basal values during hibernation of Arctic Ground Squirrels euthermic state, AGS have shown low PaO2 and low hemoglobin oxygen saturation which was not observed in rats (Ma et al, 2005)
Summary
Pressure (PaO2) as compared to non-hibernator rat brains (Ma et al, 2005), but AGS brain tissue oxygen. Because brain temperature varies at any given time, PtO2 measurement had to be corrected to obtain the real physiological effect. The details of the principle mm; L±3.25 mm; D, -4.0 mm) for AGS and another and the procedures of temperature correction for PtO2 four holes were made with a steel burr (0.5-mm measurement was described in Ma and Wu (2008). (mm Hg) = (Patm- PH2O)*FO2, electrode, the calibrated and sterilized PO2 electrode and needle micro-thermocouple for Tbrain were inserted through the pre-implanted guide cannulae into the left and right striatum, respectively and secured by medical tape. Temperature in Celsius (t)-were used to derive a temperature correction factor (f = A e−kt, where the values of A and k are determined by each electrode calibration) to calculate the actual PO2 of tissues measured at various temperatures: were transferred into an experimental chamber with a normal swivel set-up for active animals.
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