PO <sub>2</sub> Profiles in the Retina of the Hemoglobin‐less Icefishes
Bibliographic record
Abstract
The retina of vertebrates has one of the highest O 2 demands and requires a constant O 2 supply. Four general types of retinal circulations have been described for O 2 delivery in extant vertebrates: 1) sole reliance on the choriocapillaris; 2) capillaries penetrating the retina; 3) capillarization of the inner side of the retina; and 4) O 2 secretion. Oxygen secretion is based on acid secretion into the blood resulting in a potent unloading of O 2 from so‐called Root effect hemoglobins (Hb), which is augmented by venous to arterial O 2 diffusion in a vascular rete lining the back side of the retina. This choroid rete mirabile (CRM) allows O 2 delivery at super‐atmospheric pressure in the avascular retina of some fishes that have the thickest retinae and some of the largest eyes (relative to body size) of all extant vertebrates. The suborder Notothenioidei, which consists of Antarctic and sub‐Antarctic fishes, provides a model system to unravel how the interactions between Hb function and retinal vascularity evolved to produce modern fish eyes. While several phyletically basal notothenioids have been shown to display similar ocular arrangements as in other Perciform species containing a CRM, more phyletically derived notothenioids have highly reduced CRM or have lost it completely. Of particular interest are the species of the family Channichthyidae, icefishes, that are unique among adult vertebrates in possessing pale white blood containing only few vestigial immature erythrocytes and no Hb. Without Hb, O 2 secretion is not functional, and icefishes have been demonstrated to possess heavily increased pre‐retinal capillarization most probably to maintain retinal oxygenation and preserve large eyes and thick retinae. However, whether available O 2 at different retinal levels actually follows the degree of vascularization has not been tested. Using thin O 2 sensors, we measured profiles of partial pressure of O 2 (PO 2 ) in the retina of six species of icefishes, two species of related, but red‐blooded dragonfishes (Bathydraconidae), and four species of more distantly related notothens (Nototheniidae). Arterial PO 2 was statistically significantly higher in icefishes than in notothens [t‐test; p = 0.0066 (n = 3); P a O 2 = 16.64 ± 3.84 kPa in Chaenocephalus aceratus ; P a O 2 = 4.42 ± 1.40 kPa in Notothenia coriiceps ]. In general, pre‐retinal PO 2 was high in icefishes (19.20 ± 6.35 kPa in C. aceratus ), approaching the theoretical O 2 solubility limit without O 2 secretion. The PO 2 level decreased towards the outer portion of the retina, but with a small peak on the choroid side of the retina, possibly due to a vestigial choriocapillaris. In notothens displaying Root effect, pre‐retinal PO 2 was slightly lower (12.07 ± 5.12 kPa in N. coriiceps ) but increased to a super‐atmospheric level on the outer portion of the retina (52.25 ± 32.46 kPa in N. coriiceps ). Our results demonstrate that retinal PO 2 is dictated by vascularization in the Hb‐deprived icefishes, leading to a unique reversal in the retinal oxygen profile. Support or Funding Information US National Science Foundation grant PLR‐1444167 Carlsberg Foundation Velux Foundations This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .
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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 | 0.001 | 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 | 0.001 | 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".