Primates differ from other mammals in their neuronal architecture

(ORDO NEWS) — Axons, that is, outgrowths that transmit a nerve impulse to other cells, usually develop from the body of neurons.

But sometimes they are formed from smaller outgrowths – dendrites, through which the neuron itself receives a signal from the outside. A new study has shown that the brain of primates (including humans) is distinguished by a special distribution of these specific neurons.

Neurons, or nerve cells, are the basis of the brain and spinal cord, including humans and other mammals. Each neuron consists of three parts, which differ markedly in structure and function.

These are branching outgrowths that perceive signals from other neurons – numerous dendrites; the soma or body of the neuron, that is, its main part, where the processes of cell vital activity take place and a nerve impulse occurs; and finally, the axon is a long and, as a rule, the only outgrowth that transmits a signal further along the chain.

It is the axons that form the nerve fibers that connect the brain and various organs – for this, such “wires” even have special insulation from glia cells.

As a rule, during the development of a nerve cell, an axon is formed from its body. However, sometimes axons arise as part of dendrites – these are the so-called axon-carrying dendrite (AcD), which are present in some neurons, which are also called AcD.

It is the diversity of cells in the animal brain that is the subject of a new article written by a team of European scientists in the journal eLife.

“A unique feature of the project was the use of tissue samples from storage and ready-made preparations that had been used in classes with students for so long,” said Petra Wahle from the Ruhr University in Bochum (Germany).

Scientists studied the neurons of various vertebrates: from the order of rodents (mouse and rat), whales (pig), carnivores (cat and domestic ferret), as well as primates, including humans and macaques.

Biologists used five different methods of specific staining of neurons, which made it possible to study fine details and confidently distinguish between cells of different groups. In total, they examined more than 34 thousand neurons under a powerful microscope and made rather unexpected conclusions.

The so-called excitatory pyramidal neurons, especially from layers II and III of the cerebral cortex (the same part of the brain that is responsible for cognitive functions and learning), in primates are much less likely to be a special type of AcD.

Surprisingly, among inhibitory interneurons in humans (as well as in cats, by the way), AcD neurons, on the contrary, are more numerous than in other studied animals.

Scientists do not yet undertake to state what caused these features in the architecture of neurons (that is, in their structure) and what evolutionary role such changes could play in primates.

At the same time, it is known that neurons with a dendritic origin of axons are “privileged,” since they generate a response to a stimulus faster and more efficiently than “simple” nerve cells.

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