Hibernating Golden-Mantled Ground Squirrels (Spermophilus [Callospermophilus] lateralis) have High Inter-individual Variability in Oxygen Consumption Rates with Warmer Ambient Temperatures

Ambient temperature (T a ) is a prominent part of mammalian hibernation. An excellent example of this can be found in the ground squirrels, which hibernate relatively well in cold T a s of <4°C, where extremely low body temperatures (T b ) of -2.9°C and profound metabolic depression (1% of active oxygen consumption rates [VȮ 2 ]) have been reported. These characteristics highlight the importance of initiating and maintaining a decreased T b to effectively shut down key homeostatic processes. Resumption of such processes occurs during interbout arousals (IBAs), where VȮ 2 and T b return to active (‘euthermic’) values. An important question then is whether these torpor characteristics would continue at warmer T a s, and if so, up to which T a ? Previous research demonstrated an acute uncoupling of translational initiation from elongation precisely at T b = 18°C in squirrels entering torpor. Given that protein synthesis often accounts for ~30% of VȮ 2, one might expect a large change in VȮ 2 at ~18-20°C. Further, we hypothesized that squirrels hibernating at warmer temperatures would be more variable as their ability to depress energetically expensive processes was compromised. We hibernated golden-mantled ground squirrels ( Spermophilus [Callospermophilus] lateralis) at T a s of 4, 8, 12, 16, 20, 24, 28, and 30°C and measured VȮ 2 , carbon dioxide production (V̇CO 2 ), and core T b . We found hibernation at T a >20°C caused VȮ 2 to become less predictable and more variable. Further, animals had a larger difference between T b and T a at higher T a s. We interpret the results to suggest an inability to effectively depress homeostatic processes. These data have profound implications for the engineering of torpor use in humans as it relates to spaceflight. The data suggests that humans will either 1) have to be very cold wherein homeostatic processes are depressed and the person is arrested in a quasi-homeostatic state or 2) be at a higher temperature that provides for adequate homeostasis. NASA-Translational Research Institute for Space Health (TRISH) grant. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.