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

Abstract

Arctic Ground Squirrels (AGS) are classic hibernators known for their tolerance to hypoxia. AGS have been studied as a model of hypoxia with potential as a medical research model. Problem statement: Their unique resistance to the stressors of low oxygen led us to hypothesize that AGS might also be adaptable to hyperoxia. Approach: This study examined the physiological pattern associated with hyperoxia in response to brain tissue oxygen partial pressure (P t O 2 ), brain temperature (T brain ), global oxygen consumption (V O2 ) and respiratory frequency (f R ) using non-sedated and nonanesthetized Arctic Ground Squirrels (AGS) and rats. Results: We found that 1) 100% inspired oxygen (F i O 2 ) increased the baseline values of brain P t O 2 significantly in both summer euthermic AGS (24.4 ± 3.6-87.3 ± 3.6 mmHg, n=6) and in rats (18.2 ± 5.2-73.3 ± 5.2 mmHg, n = 3); P t O 2 was significantly higher in AGS than in rats during hyperoxic exposure; 2) hyperoxic exposure had no effect on brain temperature in either AGS or rats, with the brain temperatures maintaining constancy before, during and after 100% O 2 exposure; 3) systemic metabolic rates increased significantly during hyperoxic exposure in both euthermic AGS and rats; moreover, V O2 were significantly lower in AGS than in rats during hyperoxic exposure; 4) the respiratory rates for rats were maintained before, during and after 100% O 2 exposure, while the respiratory responding patterns to hyperoxic exposure changed after exposure in AGS. AGS f R was significantly lower after hyperoxic exposure than before the exposure. Conclusion: These results suggest that hyperoxic ventilation induced P t O 2 and V O2 differences between AGS and rats and led to altered respiratory patterns between these species. AGS and the rat serves as an excellent comparative model for hypoxic and hyperoxic stress studies of the brain.

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

“…Because brain temperature varies at any given time, P t O 2 measurement had to be corrected to obtain the real physiological effect. The details of the principle and the procedures of temperature correction for P t O 2 measurement was described in Ma and Wu (2008) Ma et al (2009) and Ma et al (2011). Briefly, to perform such a temperature correction, the following steps were taken:…”

“…29 cm, height 32 cm) previously described (Ma and Wu, 2008;Ma et al, 2009;Ma et al, 2011). Air was drawn into a distribution tube through a vertical cylindrical-shaped Plexiglas metabolic chamber at a flow rate of 3 L min −1 by a membrane pump and measured by a mass flow meter (model AFSC-10 K, Teldyne Hastings-Raydist, Hampton, VA).…”