Currently, when research on mental disorders is conducted in animal experiments, genetically manipulated mice are often used to produce these disorders, which is very invasive and, of course, harmful to these animals.

However, a recent discovery related to a curious fish opens the door to the possibility of investigating mental disorders without altering the genes of domestic species.

The case of the cave fish without eyes

In nature we can find beings that fascinate the most curious and become the object of study by researchers who want to unravel all their secrets. A very specific case is the fish known as Mexican tetra (Astyanax mexicanus) .

This rare aquatic species has a special characteristic: it exists in two distinct forms, one with eyes and the other without. The first form lives in rivers, while the other, besides being an albino, lives in aquatic areas inside certain caves and its eye cells have been degraded over time by living in the dark, to save energy, so its study may reveal more data about which genes are involved in the formation of the eyes.

And so it was that Masato Yoshizawa (a biologist from the University of Hawaii) along with his team, chose this animal for testing. The most surprising thing is that this animal could have more secrets, not only being a case about organ loss, but also becoming a good model for the study of mental illness in humans, such as autism or schizophrenia. Let’s see how this happened.

The Comparative Study for Understanding Mental Disorders

Thanks to the existence of these two populations within the same species, it has been possible to study their genetic code , making crosses between the two at a laboratory level, since reproduction between both is possible. In this process it is possible to quantify a characteristic and how it is distributed in its descendants, a technique used by Gregor Mendel, the father of genetics, in his study of peas. To give an example, thanks to this it has been known that a mutation in a gene known as “cbsa” is responsible for a population not developing eyes.

During their research, Yoshikawa and his collaborators saw that the two tetra populations were not only differentiated by their physical appearance, but that there was also a great difference in their social behavior. Those living in the surface waters are sociable and even have a social structure between them. In contrast, cave dwellers are solitary, in fact, they reject company. In addition, they show symptoms of anxiety and hyperactivity and never sleep.

Bearing these data in mind, in a first experiment, Yoshikawa crossed populations again to see to what extent this difference in social behaviour is genetically rooted or based on behaviours learned in a specific context.

Medicating cave fish

The results of their trials were presented at the 23rd International Underground Biology Conference in Fayeteville, Arkansas. Yoshikawa claims that 90% of the 101 classic genes that are related to the risk of developing mental illness in humans are present in the Mexican tetra genome. Data that could turn this animal into a new model for the study of these diseases.

But it doesn’t end there, as another trial treated the lonely fish with the psychoactive anti-depressant Fluoxetine (also known by its brand name Prozac) in combination with the antipsychotic Clozapine, causing the fish to become sociable, lower their anxiety levels, swim less frequently, and be able to sleep. With this, Yoshikawa’s team wanted to demonstrate that these fish react similarly to a human patient.

Conclusions

The importance he wants to give with this finding is to have an animal that has “symptoms” that are present in autism or schizophrenia, such as the absence of sleep, hyperactivity or anxiety, and all naturally.

There is still much to be done and more tests to be performed, but for the moment the evidence indicates that the Mexican tetra fish can become a new tool to follow studies of psychic disorders, both at the genetic base level and in the research of new drugs. Even so, some experts stress that there is a limitation in this model, as it is a fish, since humans and fish are separated by 400 million years of evolution and the results cannot be extrapolated so lightly.