Simultaneous measurement of brain tissue oxygen partial pressure, temperature, and global oxygen consumption during hibernation, arousal, and euthermy in non-sedated and non-anesthetized Arctic ground squirrels

Abstract

This study reports an online temperature correction method for determining tissue oxygen partial pressure (P t O 2 ) in the striatum and a novel simultaneous measurement of brain P t O 2 and temperature (T brain ) in conjunction with global oxygen consumption (VO 2 ) in non-sedated and non-anesthetized freely moving Arctic ground squirrels (AGS, Spermophilus parryii). This method fills an important research gap-the lack of a suitable method for physiologic studies of tissue P O2 in hibernating or other cool-blooded species. P t O 2 in AGS brain during euthermy (21.22 ± 2.06 mm Hg) is significantly higher (P=0.016) than during hibernation (13.21 ± 0.46 mm Hg) suggests brain oxygenation in the striatum is normoxic during euthermy and hypoxic during hibernation. These results in P t O 2 are different from blood oxygen partial pressure (PaO 2 ) in AGS, which are significantly lower during euthermy than during hibernation and are actually hypoxic during euthermy and normoxic during hibernation in our previous study. This intriguing difference between the P O2 of brain tissue and blood during these two physiological states suggests that regional mechanisms in the brain play a role in maintaining tissue oxygenation and protect against hypoxia during hibernation.

Effects of Hyperoxia on Brain Tissue Oxygen Tension in Non-Sedated, Non- Anesthetized Arctic Ground Squirrels: An Animal Model of Hyperoxic Stress

“…After completing the drilling process, four anchor stainless steel bone screws (BAS, West Lafayette, IN) were driven into the skull through the screw holes. Two guide cannulae (CMA11, Acton, MA) were stereotaxically positioned above the right and left striatum (AP, 13.5 or 14 mm; L, ±3.25 mm; D, -4.0 mm), as previously described in detail (Osborne et al, 1999;Zou et al, 2002;Ma and Wu, 2008) and were slowly lowered 4 mm from the cortical surface. The surgical procedures for rats were similar to those for AGS.…”

“…The details of the principle and the procedures of temperature correction for P t O 2 measurement was described in Ma and Wu, 2008. Briefly, to perform such a temperature correction, the following steps were taken:…”

“…While in the euthermic state, AGS have low P a O 2 and low hemoglobin oxygen saturation (sO 2 ) in contrast to non-hibernating rats, indicating a natural mild, chronic hypoxia in AGS blood (Ma et al, 2005). However, the P t O 2 in the euthermic state is higher than in the hibernating state (Ma and Wu, 2008;Ma et al, 2009).…”

“…Its unique metabolism during hibernation is a topic that is just beginning to be understood and has implications for neuroscience (Frerichs, 1999;Ma and Wu, 2008) and disease processes. Hypoxia in the AGS has been the focus of most studies because of its potential to answer questions related to reperfusion injury and neurodegeneration in Alzheimer's Disease, Parkinson's Disease and brain tumors.…”

“…During hibernation, AGS blood is well oxygenated with similar blood oxygen partial pressure (P a O 2 ) as compared to rat brains (Ma et al, 2005), but AGS brain tissue oxygen partial pressure (P t O 2 ) is hypoxic (Ma and Wu, 2008). When aroused from hibernation, AGS experiences extreme blood hypoxia (~ 9 mm Hg), but there is no evidence of cellular stress, inflammatory response, neuronal pathology, or oxidative modification in brain following the period of high metabolic demand necessary for arousal (Ma et al, 2005).…”