Evidence for consistent individual differences in rat sensitivity to carbon dioxide
Bibliographic record
Abstract
Carbon dioxide (CO2) gradual-fill is commonly used to kill laboratory rats, but this use remains controversial due to a lack of agreement between studies. Inconsistencies may arise from differences in behaviors measured (e.g. active versus passive behaviors), in how rats cope with threats, or in rat sensitivity to CO2. The aims of the current study were to 1) describe active and passive responses during CO2 forced exposure, 2) determine if these responses are consistent within individuals and across aversive stimuli, 3) assess individual differences in aversion to CO2 in aversion-avoidance and approach-avoidance tests and 4) determine how responses in aversion tests relate to individual differences in behavior during forced exposure. Twelve Sprague Dawley female rats were exposed twice to three treatments: CO2, oxygen (O2), and fox scent, and were exposed to CO2 twice in each aversion test. The change in behavior from baseline was higher for rearing and locomotion when rats were exposed to CO2 than when exposed to O2 and fox scent. Responses varied among rats but were consistent across multiple tests within rats. For example, rearing was consistent within individuals between two exposures to CO2. Similarly, the strength of aversion was consistent within individuals across multiple exposures to CO2 in aversion-avoidance and approach-avoidance testing. Latency to avoid CO2 in aversion-avoidance tests was negatively correlated with rearing during CO2 forced exposure. Collectively, these results indicate that rat responses to CO2 vary between (but are consistent within) individuals, suggesting that rats vary in CO2 sensitivity. However, even the less responsive rats avoided CO2 concentrations far below those necessary to achieve unconsciousness, indicating that all rats likely experience negative states when euthanized with CO2.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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 source (direct Gemma or distilled Codex), 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".