A team of scientists has found that a network of nerves connecting the human eyes and brain was already present in ancient fish.
Study of animal models—an invaluable way for researchers to learn more about health and disease, but making connections to the human condition from these models can be challenging. Zebrafish, for example, are popular model organisms, but their wiring "between the eye and brain is very different from human.
Cayman fish brain.In this microscope image, the left hemisphere of the brain is green and the right hemisphere is magenta. However, at the bottom of the image, nerves of both colors can be seen connecting to both hemispheres. This shows that both her eyes are connected to both sides of his brain, like the eyes of a human. Credit: RJ Vigouroux et al. Science 372: eabe7790 (2021)
Modern fish do not have this type of connection between the eye and the brain. This is one of the reasons why people thought that such a network was something new for four-legged animals.
Carapace, or carapace pike, or caymanfish, - a family of ray-finned fishes, the only modern one in the order of carapace-like. The group includes seven living species of fish that live in fresh, brackish, and occasionally even in sea waters.
Such fish evolved more slowly than fishzebrafish This means that armored fish are more similar to the last common ancestor between fish and humans. These similarities may make caiman fish a useful animal model for human health research. Therefore, scientists are working to better understand their biology and genetics.
To conduct the study, scientists usedan innovative technique to see the nerves that connect the eyes and the brain in different types of fish. Among them are the well-studied zebrafish, as well as more rare specimens - carapace and Australian lungfish.
In zebrafish, each eye has one nerve,connecting it to the opposite side of the fish's brain. That is, one nerve connects the left eye to the right hemisphere of the brain, and the other connects the right eye to the left hemisphere of the brain. Other, more “ancient” fish function differently. Armored pikes have what are called ipsilateral or bilateral visual projections. Here, each eye has two nerve connections, one on each side of the brain, just like in humans.
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Model organisms are organisms used as models for studying certain properties, processes or phenomena of living nature.