The number
of young neurons in intermediate to advanced stages of development was the same across people of all ages.
With an electron microscope, they also looked for the characteristic long, slender, simple shapes
of young neurons.
«We don't think that what they are identifying
as young neurons actually are,» says Arturo Alvarez - Buylla of the University of California, San Francisco, who coauthored the recent paper that found no signs of neurogenesis in adult brains.
Thus, with
fewer young neurons in the irradiated rats, more dopamine is released when cocaine is administered.
In his study, some of the cells his team initially flagged as
young neurons turned out to be mature cells upon further investigation.
A basic tenet of neural development is that
young neurons make far more connections than they will actually use, with very little specificity.
The team found that people have large numbers of neural stem cells and progenitors early in life — an average of 1618
young neurons per square millimeter of brain tissue at birth.
Syntaphilin - deficient mature neurons therefore regained the ability to regrow after injury, just
like young neurons, and removing syntaphilin from adult mice facilitated the regeneration of their sciatic nerves after injury.
Now scientists have successfully restored full youthful plasticity in adult mice by
transplanting young neurons into their brain — curing their severe visual impairments in the process.
For example, brain organoids so far can feature only
relatively young neurons, and some genes that scientists would like to study don't become active until much later stages of brain development.
«Although running induces both substantial changes in number and morphology
of young neurons as well as significant changes in learning behavior, this does not prove a causal relationship,» noted Professor Bischofberger, «Nevertheless, our results, together with previous findings, suggest that the enhanced pattern separation during memory testing is most likely mediated via running - induced increase in adult neurogenesis.»
Because
these young neurons are typically more excitable than their more mature counterparts, exercise should result in more anxiety, not less.
By adulthood the supply of
young neurons had petered out entirely.
In the nervous system, many such interactions guide the extensions of
young neurons to their right destinations.
Young neurons (pink), responsible for encoding new memories, must compete with mature neurons (green) to survive and integrate into the hippocampal circuit.
And they specify that the genes in question relate primarily to the development of synapses, the junctions between brain cells which are their transmission nodes; as well as the targeting of axonal fibers and the ability of
young neurons to migrate.
The young neurons must mature and create millions of connections in the brain before they can become functional and start producing dopamine.
«It doesn't mean
that young neurons are bad,» he says.