“Eternal tadpoles” reveal the evolutionary processes of the central nervous system. And in the future, they may help people who have suffered extensive brain damage.
Axolotls — amphibians native to Mexico — have been known to Western science for 150 years. And since then they have never ceased to amaze. They are “perpetual tadpoles” that never grow into their adult, terrestrial form, plus they have remarkable regenerative abilities. You can remove their gills, tail or limbs, and they will recreate those body parts — and fully functional ones at that. They can also regenerate a crushed spine along with the spinal cord, and even eyes. It had also been known for some time that axolotls could rebuild brain tissue, but evidence was lacking that the new neurons could not only reconstitute themselves, but also perform the same functions as their predecessors. The findings, published in Science, shed new light on earlier speculations.
Their authors analyzed a specific part of the axolotl brain — the so-called crescendo. When the vertebrate brain differentiates at the stage of embryonic development, it first divides into three vesicles: the forebrain, midbrain and hindbrain. The former, in turn, at later stages of development is divided into the midbrain and the crescerebrum precisely. This part is responsible in humans for most conscious activities, and also (and these functions are also exhibited by the crescerebrum of other animals, including axolotls) for behavioral reactions or cognitive abilities.
The researchers analyzed whether the cells comprising these specialized areas of the brain would undergo functional regeneration in axolotls. To determine this, they used single neuron gene sequencing technology (known as scRNA-seq) that allows them to determine the exact function of a given cell. It turned out that all brain components that had previously been removed managed to regenerate. What’s more, the researchers showed that these newly formed areas “plugged in” with neural connections to the old parts of the brain, which, according to the study’s authors, suggests that functional regeneration has also occurred here.