Neurogenesis: The Birth of New Neurons in the Adult Brain

For many years, scientists believed that the brain stopped creating new neurons after childhood. However, recent research has revealed a surprising truth: the brain retains the ability to generate new neurons throughout life – a process known as neurogenesis. This blog post explores the mechanisms and locations of neurogenesis in the adult brain, along with its potential implications for brain health.

The Process of Neurogenesis

Neurogenesis relies on the presence of neural stem cells (NSCs). These stem cells reside in two specific areas of the adult brain:

  • Subventricular zone (SVZ): Situated near the ventricles, the SVZ is the primary source of new neurons for the olfactory bulb, responsible for our sense of smell.
  • Subgranular zone (SGZ): Located within the hippocampus, the SGZ generates new neurons important for learning, memory, and mood regulation.

NSCs have the remarkable ability to self-renew (divide) and differentiate into mature neurons. This differentiation process involves a complex series of signaling pathways that determine the specific type of neuron generated.

Adult neurogenesis is a process with distinct stages. The process of adult neurogenesis 󰠏 stem cells (left) giving rise to rapidly di- viding progenitors, which in turn develop into immature and eventually mature neurons (right) 󰠏 is shown in schematic form in both the hippocampal SGZ (top row) and SVZ (bottom row). In both the SVZ and SGZ, stem cells express the markers GLAST, Nestin, and GFAP (see green band across the bottom). Stem cells in both the SGZ and SVZ divide infrequently to self-renew and give rise to transit amplify- ing progenitors. SGZ: Self-renewal in the SGZ is dependent on Notch signaling. Transit amplifying progenitors give rise to lineage-restricted neuroblasts, both of which proliferate to expand their population. Several pathways converge to promote proliferation of these populations in the SGZ. Notch and DISC1 promote basal proliferation, while TrkB promotes proliferation in response to antidepressants (AD). DISC1 may promote proliferation by inhibiting GSK3beta and cell cycle exit. Notch signaling also negatively regulates cell cycle exit. Overexpression of Ascl1 in SGZ progenitors leads to a change in fate from neuronal to oligodendrocyte. This is specific to the SGZ. Once SGZ neuroblasts exit the cell cycle, they differentiate into neurons and extend dendrites. Maturation and survival of newborn neu- rons is positively regulated by many pathways, including Cdk5, NMDAR, TrkB, and Notch, while DISC1 negatively regulates maturation. SVZ: Intrinsic regulation of SVZ neurogenesis is less clear, but it is known that Notch signaling maintains ependymal cells in a differ- entiated state. Without Notch, these cells can contribute to SVZ neurogenesis. Smad4, a downstream target of BMP signaling, is required to inhibit oligodendrocyte differentiation of SVZ progenitors. The colored bands on the very bottom of the schematic illustrate the distinct, but overlapping, stages of neurogenesis in both the SGZ and SVZ that are transfected by lentivirus and retrovirus.

The Extent of Neurogenesis

The rate of neurogenesis varies across different brain regions and throughout life. During embryonic development and early childhood, neurogenesis is extremely active, establishing the intricate network of neurons underlying all brain functions.

In adulthood, neurogenesis continues, but at a slower pace. Studies in animal models suggest that environmental enrichment, physical exercise, and learning can increase adult neurogenesis. Conversely, stress, depression, and aging have been shown to suppress neurogenesis.

The Functional Significance of Neurogenesis

The newly formed neurons in the adult brain integrate into existing circuits, potentially contributing to several critical functions:

  • Olfactory function: Neurogenesis in the SVZ is essential for maintaining a good sense of smell.
  • Learning and memory: New neurons in the hippocampus play a role in forming memories and spatial navigation.
  • Mood regulation: Adult neurogenesis in the hippocampus may influence mood and emotional processing.

More research is needed to fully understand the specific contributions of adult-born neurons to complex brain functions.

Researchers investigating neurogenesis may find resources from suppliers like Maxanim, a provider of research-grade reagents, valuable for their investigations.

The growth and function of axons. The process of neurogenesis provides pools of neurons that migrate into their appropriate positions (left), that extend axons along reproducible paths (middle), and that are eventually wired up into the synaptic circuits which convey information across the nervous system, thus coordinating behavior (orange arrows: action potentials; yellow: presynaptic sides).

Future Directions and Therapeutic Potential

Understanding the mechanisms that regulate neurogenesis holds significant potential for therapeutic development. Scientists are exploring ways to stimulate neurogenesis as a treatment strategy for various neurological disorders, including:

  • Alzheimer's disease
  • Parkinson's disease
  • Depression
  • Stroke

While significant challenges remain, research on neurogenesis offers a promising avenue for developing novel therapies to promote brain health and resilience throughout life.

in News
Neurogenesis: The Birth of New Neurons in the Adult Brain
Gen store June 3, 2024
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