Adult Neurogenesis

Adult Neurogenesis

Understanding the phenomenon of adult neurogenesis— the process by which new neurons are generated in the adult brain—merits a closer examination of various brain areas, associated promoting and inhibiting factors, and the implications of environmental influences such as exercise and stress.

Brain Areas Involved in Neurogenesis

  • Hippocampus

  • Olfactory bulb

  • Other areas (e.g., caudate nucleus)

  • New neurons predominantly produced in the hippocampus, suggesting a significant role in memory and learning processes.

Identification of Adult Neurogenesis

  • BrdU (Bromo-deoxy-uridine)
      - Acts as a marker for proliferating cells, particularly newly-born neurons.
      - Important in the labeling of dividing cells to assess neurogenesis.

  • Confocal Imaging: Visual evidence from confocal images showcases BrdU-positive cells.
      - Control Group (A) and Runner Group (B) show marked differences in the presence of BrdU-labeled neurons (in red), illustrating the correlation between running and increased neurogenesis (Referencing: van Praag et al., 1999).

Evidence for Adult Neurogenesis in Humans

  • Micrographs: Captured by Linda Kitabayashi from the Salk Institute.
      - Images of hippocampal tissues from adults who died of cancer show proof of neuron formation with BrdU-marked cells in red.
      - Green shading in the left image and dark shading in the right image demonstrate BrdU's integration into the DNA of newly dividing cells, signaling that marked cells became neurons only after BrdU injection, thereby confirming ongoing neurogenesis up until late in life.

Factors Promoting Neurogenesis

  • An Enriched Environment: Mice living in enriched environments show higher counts of hippocampal neurons (referencing: Kempermann et al., 1997).

  • BrdU-Positive Cell Count:
      - Total Cell Count per Dentate Gyrus:
        - Day 1 after last BrdU injection
          - Significant increase in labeled cells among runners compared to controls (p < 0.02).
        - Four weeks after last BrdU injection
          - Enrichment and physical activity (running) significantly enhance the survival of newborn cells (p < 0.02).
          - Graphical representations indicate that exercise correlates with substantial increases in BrdU-positive cell numbers, laying the foundation for neurogenesis.

  • Learning Tasks: Learning tasks that depend on the hippocampus promote neurogenesis (referencing: Gould et al., 1999).

Factors Inhibiting Neurogenesis

  • Stress: Elevated levels of glucocorticoid hormones (stress hormones) are known to inhibit neurogenesis.

Neurotrophins and Exercise

  • Neurotrophins: Substances like BDNF (brain-derived neurotrophic factor) may mediate the beneficial effects of exercise on the brain.

  • BDNF Functions:
      - Supports existing neurons.
      - Increases production of new neurons.
      - Enhances differentiation of new neurons.

  • Mechanism of Action: Exercise can induce BDNF production in the brain, which leads to both neurogenesis and neuroprotection, showcasing the relationship between physical activity and cognitive health.