Adaptive response of brain tissue oxygenation to environmental hypoxia in non-sedated, non-anesthetized arctic ground squirrels

Abstract

The present study examined the physiological mechanisms of the responses of brain tissue oxygen partial pressure (P tO 2), brain temperature ( T brain), global oxygen consumption (V̇ O2), and respiratory frequency ( f R) to hypoxia in non-sedated and non-anesthetized arctic ground squirrels ( Spermophilus parryii, AGS) and rats. We found that (1) in contrast to oxygen partial pressure in blood (P aO 2), the baseline value of P tO 2 in summer euthermic AGS is significantly higher than in rats; (2) both P tO 2 and P aO 2 are dramatically reduced by inspired 8% O 2 in AGS and rats, but AGS have a greater capacity in P tO 2 to cope with environmental hypoxia; (3) metabolic rate before, during, and after hypoxic exposure is consistently lower in AGS than in rats; (4) the respiratory responding patterns to hypoxia in the two species differ in that f R decreases in AGS but increases in rats. These results suggest that (1) AGS have special mechanisms to maintain higher P tO 2 and lower P aO 2, and these levels in AGS represent a typical pattern of adaptation of heterothermic species to and a brain protection from hypoxia; (2) AGS brain responds to hypoxia through greater decreases in P tO 2 and decreased f R and ventilation. In contrast, rat brain responds to hypoxia by less reduction in P tO 2 and increased f R and ventilation.