The zebra fish, a distant cousin of the common carp that is found in Quebec, is a small fish about 5 cm in length, originally from South Asia. He does not use his brain to plan the meals of the week or the annual holidays of his family, to find the balance between his personal life and his professional obligations, to interpret a work on the piano or to solve complex problems requiring an elaborate abstract thought. And yet, the brain of this humble fish could reveal things to us about the functioning of our own brain. Scientists from the Faculty of Science and Engineering of Laval University and the Cervo Research Center have demonstrated it in a series of experiences whose results have just appeared in the journal Science Advances.
At first glance, the brain of the Zebroker is pale compared to that of humans: the first would count between 1 and 2 million neurons while the second would have 86 billion. But, recalls Professor Paul de Koninck, specialist in molecular neuroscience and co -responsible for the study, “our understanding of the brain has been built thanks to studies on various animal species, from the tiny green C. elegans up to non -human primates. Even if there are large differences between the brain of a fish and that of a human, certain characteristics, for example the architecture of neurons, the structure of synapses and the neurotransmitter system, were kept during evolution. ”
These elements are not the only common denominators between the brain of various species, adds the other co -responsible for the study, Professor Patrick Desrosiers, specialist in theoretical physics and neural networks. “The way the neurons are connected to each other also responds to certain rules that transcend the species barrier. There are two forms of connectivity between neurons, he recalls. The first, an anatomical nature, depends on the physical connections between neurons. The second, known as functional, is measured by the coordinated activity of neurons or regions of the brain. Neurons or regions of the brain can be relatively physically distant, but functionally very close. ”
In humans, functional connectivity is measured by using magnetic resonance imaging or electroencephalography. “It is established from the observation of the brain areas which are activated simultaneously either spontaneously or when performing a task. However, the information that can be obtained through these approaches have a low spatial and temporal resolution. They do not allow us to understand what happens on a cellular scale during the formation of neural networks, “said Professor of Koninck.
To fill this gap, doctoral student Antoine Légaré called on optogenetic and neurophotonic tools to measure the activity of more than 54,000 distinct neurons in 65 regions of the brain of zero fishing aged 5 to 7 days. It is about half of all the neurons that make up the brain of this fish at this stage. These data allowed him to map the functional connectivity between neurons and between regions of the brain. He then crossed this data with an atlas in which the anatomical connections of some 4,300 neurons in the brain-zelé brain are collected.
“What Antoine’s remarkable work has highlighted is that the basic principles of the organization of neural networks seem similar to the Zebroker and in humans,” sums up Patrick Desrosiers. I am not saying that the brain of this fish is equal to that of humans, but so far, we have not discovered any characteristic of neural networks on the whole brain level that is exclusive to humans. “
“Even if the brain of the Zea Fish is small, that it has relatively few neurons and that the regions of his brain are organized differently, the way in which information circulates between the regions of his brain presents great similarities with what is observed in humans. This makes it a very interesting model for the study of functional connectivity of the human brain, “said Koninck Professor.
This study is fundamental in nature, but it could have very concrete benefits, continues the researcher. “Certain neurological or psychiatric disorders may result from a disruption in the pruning of neural connections. For example, too large or insufficient pruning that occurs during adolescence could be involved in diseases such as schizophrenia or bipolar disorder. In addition, the Zeabian fish offers a very practical and inexpensive model to study the effect of drugs or certain environmental factors on the development of neural networks. We also want to use it to study how microbiota can influence this development. ”
Signatories of the study published in Science Advances are Antoine Légaré, Mado Lemieux, Vincent Boily, Sandrine Poulin, Arthur Légaré, Patrick Desrosiers and Paul de Koninck.
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