Effects of hypoxia on the respiratory and metabolic responses to progressive cooling in newborn rodents that range in heterothermic expression
Bibliographic record
Abstract
New Findings What is the central question of this study? Adult homeotherms and heterotherms differ in cold and hypoxia tolerance and in how they match O 2 supply and demand in response to these stressors. It has never been ascertained whether these differences reflect different developmental trajectories or whether they are already present at birth. What is the main finding and its importance? When exposed to cold and hypoxia, newborn rodents differed in how they matched O 2 supply and demand, with responses reflecting the degree of heterothermic expression and tolerance. Our findings indicate that elements of the adult phenotype are already present at birth. Abstract There are physiological differences in how adult rodents regulate O 2 supply and O 2 demand when exposed to hypoxia in the cold. We examined whether these differences reflect divergent developmental trajectories of homeotherms and heterotherms or whether the differences are already present at birth. We exposed newborn rodents (0–4 days old) that ranged in heterothermic expression [a homeotherm, the rat ( Rattus norvegicus ); two facultative heterotherms, the mouse ( Mus musculus ) and the hamster ( Mesocricetus auratus ); and an obligate heterotherm, the ground squirrel ( Ictidomys tridecemlineatus )] to either normoxia (21% O 2 ) or hypoxia (7% O 2 ) and measured their metabolic, thermoregulatory and ventilatory responses while progressively reducing the ambient temperature from 33 to 15°C. All newborns reduced their body temperature, O 2 consumption rate and ventilation during progressive cooling, both in normoxia and in hypoxia. When progressively cooled in hypoxia, however, the homeothermic rats exhibited the greatest thermogenic response, depressed their O 2 consumption rate the least and increased ventilation the most. In contrast, the obligate heterotherm, the ground squirrel, did not mount a thermogenic response, exhibited the greatest reduction in O 2 consumption rate and increased O 2 uptake not by increasing ventilation like the rat, but by extracting ≤80% of the O 2 from each breath. Facultative heterotherms (mice and hamsters) exhibited responses in between these two extreme phenotypes. We conclude that even as newborns, homeotherms and heterotherms diverge in how they match O 2 supply and O 2 demand when progressively cooled in hypoxia, with responses reflecting the degree of heterothermic expression, in addition to reported hypoxia and cold tolerance.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".