Studies on the role of ammonia in the control of breathing in the Pacific hagfish (Eptatretus stoutii) and rainbow trout (Oncorhynchus mykiss)
Bibliographic record
Abstract
Ammonia, which is excreted across the gills, is the major nitrogenous waste of fish. It is also a toxicant. My thesis focuses on how and why ammonia influences breathing in fish, using the phylogenetically ancient Pacific hagfish (an agnathan) and the rainbow trout (a teleost) as models. I first characterized the unique breathing mechanism of hagfish, demonstrating a two-phase unidirectional system with a fast suction velar pump for inhalation through the nostril and a much slower force pump for exhalation through gill pouches. High environmental ammonia (HEA) causes an initial hypoventilation, sometimes apnea, and a later sustained hyperventilation. The hypoventilation is independent from responses to O₂ and CO₂ and is mediated by external receptors. The hyperventilation is mediated by increased blood ammonia, detected internally, similar to previous findings on teleosts. In trout, I confirmed an assumption in the literature that ventilation would not affect ammonia excretion. However, I then used chronic internal ammonia loading to upregulate the ammonia transport system (rhesus glycoproteins) in the gills. This removed diffusion limitation so that ammonia excretion became sensitive to ventilation. Hyperventilating trout, therefore, excrete more ammonia. After developing a new less invasive system for the direct measurement of ventilation, I used it to show that HEA hyperventilation is not immediate, but develops gradually, mediated by internal receptors. Indeed, specific application of HEA to the external surface of the gills causes a transient acute hypoventilation, again as in hagfish. Direct application of ammonia to the hindbrain causes hyperventilation by the stimulation of central chemoreceptors, while peripheral chemoreceptors in the gills (neuroepithelial cells) sense increased plasma ammonia. In humans, ammonia buildup in the brain similarly stimulates breathing. I conclude that a role for ammonia in ventilatory control is probably ubiquitous in vertebrates, including the oldest extant representatives (hagfish). Initial hypoventilation is protective against the uptake of a toxicant, while sustained hyperventilation is beneficial at times of internal ammonia loading such post-exercise recovery, and after feeding. This hyperventilation will facilitate not only greater ammonia excretion, but also the greater O₂ uptake needed to recover from exercise and to metabolically process food.
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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 | 0.000 |
| 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) | 0.001 | 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".