Cardiorespiratory responses to hypercarbia in tambaqui<i>Colossoma macropomum</i>: chemoreceptor orientation and specificity
Bibliographic record
Abstract
Experiments were carried out to test the hypothesis that ventilatory and cardiovascular responses to hypercarbia (elevated water P(CO2)) in the tambaqui Colossoma macropomum are stimulated by externally oriented receptors that are sensitive to water CO(2) tension as opposed to water pH. Cardiorespiratory responses to acute hypercarbia were evaluated in both the absence and presence of internal hypercarbia (elevated blood P(CO2)), achieved by treating fish with the carbonic anhydrase inhibitor acetazolamide. Exposure to acute hypercarbia (15 min at each level, final water CO(2) tensions of 7.2, 15.5 and 26.3 mmHg) elicited significant increases in ventilation frequency (at 26.3 mmHg, a 42% increase over the normocarbic value) and amplitude (128%), together with a fall in heart rate (35%) and an increase in cardiac stroke volume (62%). Rapid washout of CO(2) from the water reversed these effects, and the timing of the changes in cardiorespiratory variables corresponded more closely to the fall in water P(CO2) (Pw(CO2)) than to that in blood P(CO2) (Pa(CO2)). Similar responses to acute hypercarbia (15 min, final Pw(CO2) of 13.6 mmHg) were observed in acetazolamide-treated (30 mg kg(-1)) tambaqui. Acetazolamide treatment itself, however, increased Pa(CO2) (from 4.81+/-0.58 to 13.83+/-0.91 mmHg, mean +/-S.E.M.; N=8) in the absence of significant change in ventilation, heart rate or cardiac stroke volume. The lack of response to changes in blood P(CO2) and/or pH were confirmed by comparing responses to the bolus injection of hypercarbic saline (5% or 10% CO(2); 2 ml kg(-1)) into the caudal vein with those to the injection of CO(2)-enriched water (1%, 3%, 5% or 10% CO(2); 50 ml kg(-1)) into the buccal cavity. Whereas injections of hypercarbic saline were ineffective in eliciting cardiorespiratory responses, changes in ventilation and cardiovascular parameters accompanied injection of CO(2)-laden water into the mouth. Similar injections of CO(2)-free water acidified to the corresponding pH of the hypercarbic water (pH 6.3, 5.6, 5.3 or 4.9, respectively) generally did not stimulate cardiorespiratory responses. These results are in agreement with the hypothesis that in tambaqui, externally oriented chemoreceptors that are predominantly activated by increases in water P(CO2), rather than by accompanying decreases in water pH, are linked to the initiation of cardiorespiratory responses to hypercarbia.
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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) | 0.001 | 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 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".