Glass frogs hide their red blood cells to make themselves invisible.

This is demonstrated by a team of biologists and biomedical engineers in a paper published in the journalism. Sciencenot only helps to better understand the physiology and behavior of the glass frog, but also can be used to optimize diagnostic imaging tools used in biomedicine. In the future, it may even help improve the treatment of cardio and cerebrovascular diseases.

The transparency of glass frogs is considered something rare in the animal kingdom. And the thing is, while many marine animals are known to be able to change their skin color, this ability is much less common on land. Glass frogs do this by controlling their red blood cells to act in a way that is most beneficial to them.

Red blood cells can absorb green light, the color that plants and other plants usually reflect. In turn, these oxygen-rich cells reflect red light, making the blood and thus the circulatory system highly visible, especially against a bright green leaf. Again, frogs manage to get rid of this obstacle.

To find the mechanism by which they achieved this, Carlos Taboada, postdoctoral researcher at Duke and co-author of the paper, decided to explore them in the lab. The first thing the research group did was look at them under a microscope, and that’s what animals do. they were able to achieve transparency as they expel the red blood cells from the blood vessels. He suspected that the cells were stored in one of the frog’s internal organs, but he did not know which.

a complex investigation

He then decided to join forces with the American Museum of Natural History, Stanford University, and the University of South Carolina to solve this complex puzzle. However, shortly after starting the investigations, they realized that they were not moving forward. “Whether these frogs are awake, stressed, or under anesthesia, their circulatory systems are filled with red blood cells and are opaque,” insists Jesse Delia, a postdoctoral researcher at the American Museum of Natural History. “The only way to study transparency was to do it while the animals were sleeping happily.It’s a difficult thing to achieve in a research lab.”

After much thought, they decided to change the method. Taboada applied photoacoustic microscopy (PAM), a technique consisting of: shoot a harmless laser beam into the animal’s tissues. This beam is absorbed by the molecules and converted into ultrasonic waves, which are then used to create detailed images of the molecules.

“It was an ideal tool for non-invasive imaging of red blood cells because it didn’t require the injection of contrast agents,” says Junjie Yao, assistant professor of biomedical engineering at Duke who specializes in such technologies.

Frogs sleeping happily on a petri dish had no idea what was going on in the lab. There, researchers had enthusiastically unraveled the mystery of these amphibians’ ‘invisibility power’. The scientists came to the following conclusion: When frogs fall asleep, they remove 90% of their circulating red blood cells and store them in their liver. In additional testing, the team also saw that red blood cells leave and circulate through the liver while the frogs are active, then return to the liver as the frogs recover.

“When glass frogs want to be transparent, that is, when they are at rest and are vulnerable to predation, they filter almost all red blood cells and store them in a liver covered with a tissue that functions like a mirror,” explains Sönke Johnsen. , a professor of biology at Duke and lead author of the paper. But again, something surprised them. The frogs were able to perform this mechanism without forming a large blood clot.

Therefore, the next step in this research has a good chance of leading to a more comprehensive study of this mechanism that could one day be applied to vascular diseases in the human population.

Reference work: https://www.science.org/doi/10.1126/science.abl6620

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