(ORDO NEWS) — Scientists closely studying the cell architecture of neurons in the brain have found a key structural difference between primates and non-primates in the neurons of the cerebral cortex, the cells that make up the brain.
The results provide a better understanding of this highly complex organ and how the shape and function of neurons can vary across species. In addition, thanks to this study, we can learn more about the evolution of humans and animals.
Key to the differences in neurons is the axon fiber – the thin part of the neuron through which electrical impulses are transmitted. Until now, it was believed that these axons almost always grow from the cell body, but a new study shows that they can also originate from dendrites – processes that connect nerve cells to each other.
These axon-bearing dendrites are much more common in non-primates, such as cats and pigs, than in primates, the team found. The study was based on existing archival tissues and samples and included analysis of over 34,000 individual neurons.
“A unique aspect of the project is that the team worked with archival tissues and slide preparations that included material that had been used for years to educate students,” says neuroscientist Petra Wahle from the Ruhr University Bochum in Germany.
The researchers studied samples from mice, rats, pigs, cats, ferrets, macaque monkeys and humans. While axon-bearing dendrites have been found in all species, they were significantly more abundant in non-primates.
The most important part of the study was the use of the latest high-resolution microscopy techniques, which allow close-up examination of the development of cells, which was made possible by the use of five different methods of staining the studied cells.
“This made it possible to detect the beginning of axons, accurately tracked at the micrometer level, which is sometimes not so easy with conventional light microscopy,” says Wahle.
More research will be needed to understand why some animal species have a higher percentage of axon-bearing dendrites than others and what their evolutionary advantage is for the animals that use them.
Neurons usually act as gatekeepers when it comes to deciding which signals will and will not be transmitted, according to other inputs they also receive.
This is known as somatodendritic integration. One of the differences between axon-carrying dendrites is the ability to bypass these gates and independently choose which messages get into the brain’s network.
We don’t yet know how this affects information processing in the brain, but over time we’ll get more clues. The researchers found that animal domestication did not affect the number of these axon-bearing dendrites: they have a similar ratio in pigs and boars.
Also, it appears that animals of different species are born with them rather than developing them as they mature.
With so many neurons to keep an eye on – tens of billions in some cases – the brain isn’t an easy part of the body to study, but that doesn’t stop scientists. We are constantly learning more about how neurons are made and how they work.
“Our results expand current knowledge of the distribution and ratio of axon-bearing dendritic cells in the neocortex of non-animals, which are strikingly different from primates, where these cells are predominantly found in deeper layers and white matter,” the researchers write in the published paper.
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