Neurogenesi nuovi neuroni

Is it possible to create new neurons? This is how the brain regenerates

One is led to think that the

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have yours development phasebetween childhood and adolescence, and that its structure subsequently remains unchangedwith an age adult in which particular care must be taken of the few remaining neurons. The reality is partially different: if it is true that in the development phase neurogenesis, i.e. the process of creation of new neurons in the central nervous system, it is particularly intense and lively, even in adulthood new neurons populate our brain with particular intensity in some specific areas. Both endogenous factors, such as dopamine which influences the production of new neurons, and environmental factors, such as stress and physical activity.

How new neurons are created: neurogenesis

For neurogenesis we mean the process of brain development in which new neurons are generated. There are six stages which describe the entire span of the formation of new neurons, and are the genesisthe migrationthe differentiationthe adjustment and, finally, the plasticity.

Genesis occurs through the activity of progenitor cellsor neural stem cells, which over time stabilize in specific brain niches: the subgranular zone in the dentate gyrus of the hippocampus, and the subventricular arealocated along the walls of the lateral ventricles. Here the neuroblaststhat is, the new neurons that are not yet mature, which undertake their migration phase towards a damaged area of ​​the brain that needs to be repopulated or replaced.

In the differentiation phase, cells transform into mature neurons with specific functions. Thanks to the expression of specific neuronal markers, a series of molecular and cellular events occurs that change different characteristics of the shape of the neuron, such asextension of the axons (i.e. the longest arm of the neurons), allowing it to connect effectively with neighboring neurons. This process is called synaptogenesisbecause it leads to the creation of new synapses, connections between neurons.

Axon structure

From the beginning of differentiation the cell already enters a regulation phase, i.e. a dynamic moment and particularly plastic which is influenced by factors such as environment, experience, and the number of times that neuron is stimulated. Once it becomes operational, if everything goes well and the cell survives, the established synaptic connections will consolidate and become an integral part of the neuronal circuits. When this occurs in a mature person’s brain then we talk about “adult neurogenesis“.

What helps give birth to new neurons throughout the stages of life

The birth of new neurons is a phenomenon that occurs continuously throughout our existencebut the intensity and areas affected by this process change over the years. We have the most intense phase before being born, in the womb, when a brain still needs to be created from scratch.

Just already after a few months from birth there is one significant decrease in neurogenetic activity, which continues throughout childhood and adolescence, until settling at much lower levels in adulthood. The populations of progenitor cells decrease and they specialize, localizing themselves in the niches mentioned previously: the subgranular area in the hippocampus and the subventricular one. Research on animal models, especially rodents, has shown that the production of new neurons outside these niches is reduced dramatically (or is almost absent) with age.

In the’hippocampusnew neurons play a crucial role in cognitive functions such as memory and learning, as well as in emotional processes and adaptation to stress. Instead, adult neurogenesis in subventricular zone appears to be the most active and contributes to the constant regeneration of interneurons in the olfactory bulb, which needs a lot of neuronal turnover (especially in rodents). For humans, it is still the subject of debate to what extent this second area contributes to neuronal renewal, although some recent studies suggest that the activity of this area may be more limited than that observed in mouse models.

Elderly neurogenesis

As the years pass, in many species – including humans – the rate of adult neurogenesis tends to decline reduce. However, the persistence of some levels of neurogenesis hippocampal has been documented until old agealthough with wide variations from person to person. Environmental factors (e.g. physical exercise, cognitive stimulation, stress) and molecular factors (e.g. growth factors, hormones) can modulate this residual neurogenesis significantly, for better or worse depending on the factor we take into consideration.

The role of dopamine and neurodegenerative diseases

A fundamental role in the production of new neurons in the adult brain is that of dopamine, which affects neurogenesis in the adult brain, particularly in the subventricular area, so much so that block the signal with certain neurotoxins it can significantly reduce the birth of cells. This feature is of great interest in research on Parkinsona disease linked to the progressive loss of dopaminergic neurons, where it is hoped to exploit the regenerative mechanism to repair the damaged circuits.

In other neurodegenerative disorders such asAlzheimer’s and the disease of Huntingtonsimilar alterations are observed: in Huntington’s, for example, the increase in new cells does not translate into functioning neurons, even if interventions on the brain microenvironment (such as the use of growth factors) could favor their survival and integration. In Alzheimer’s, however, the formation of new neurons in the hippocampus is compromised.

Despite everything we have said, it remains the debate opened on how long neurogenesis persists in adult human beings, given that some research documents its presence even in advanced age, while others question its actual extent.