Adult neurogenesis

Original Editor - Samson Chengetanai

Lead Editors  

Historical perspective

"Adult neurogenesis" refers to the ability of the central nervous system (brain and spinal cord) to generate new neurons in adulthood called adult generated neurons[1]. This is as differentiated from "neurogenesis" typically used to describe the processes of neuronal generation that occur during the prenatal (embryonic and fetal) period extending in to the early years of postnatal life.


Back in the 1800s and the first half of the 20th century, scientists and scholars believed that development of new neurons only occurred early in life and would cease at some point during development, so that no new neurons could be formed in the brain or spinal cord after this 'critical age'[2]. Some scientists back then disputed this as fact but had no means of disproving the widely accepted notion, the non-availability of advanced equipment back then and less advanced scientific investigation and laboratoty techniques meant this notion would go unchallenged for a very long time.

Current opinions/Key evidence

In the 1960s, some very brave scientists began to use the more advanced techniques of that time to demonstrate that some mitotic figures could be identified in the brains of adult birds. This generated a lot of interest and a shift of focus was made to the mammalian species which were considered to be more advanced species and closer to the human being. adult neurogenesis was discovered in progressively higher orders of the mammalian species from the rodents (laboratory rats and mice) to the primates such as chimpanzees and monkeys. In 1998 a scientist by the name of Peter Ericksson and his team were the first to conclusively demonstrate that adult generated neurons could be identified in the human brain as well[3]. Two areas have been consistently identified across all species studied to date, which are the subgranular zone of the hippocampus (hippocampus is responsible for spatial memory) and the subventricular zone of the lateral ventricles (the area from which neurons migrate to form the cerebral hemispheres and cerebral cortex in the embryonic and fetal periods)[4].

Adult neurogenesis and neurological disease

Immense interest has been generated around this area, now that adult neurogenesis is known to be a fact, focus has shifted towards determining the factors that affect adult neurogenesis (increase or decrease it rate of occurrence) and the functions of these adult generated neurons. Interstingly it has been shown that such factors as physical exercise, living in an environmentally enriched area and mentally challenging tasks among other things improve the rate of production of new neurons in the adult hippocampus as well as increase the longevity of these newly generated neurons[5][6]. In the same vein, scientists have managed to demonstrate that laboratory animals in which the rates of neurogenesis had been increased by such means as physical exercise performed better at tasks such as learning a new skill or spatial navigation in a novel (new) environment[7]. Incidentally, elevated levels of adult hippocampal neurogenesis have been observed in adults with neurological insults and diseases such as stroke (CVA), Alzheimer's disease, Parkinson's disease and dementia amomgst others[8]. These diseases are characterised by death and destruction of neurons and the elevated levels of neurogenesis are hypothesised to be the body's own way of trying to replace the neurons that would have been lost. 

Physiotherapist's role

Considering that physical exercise and environmental enrichment will improve the levels of adult neurogenesis, physiotherapists can augment the body's own regenerative capacities by working with patients with neurological diseases to promote activities that enhance hippocampal neurogenesis.


1. Promote a healthy lifestyle - eat healthy, avoid the use of drugs. The use of drugs such as methamphetamine decreases the rate of neurogenesis and decreases cognitive functions [9]

2. Develop an exercise regime as part of the treatment programme for neuro patients

Resources




References

  1. Cameron HA, Mckay RD. Adult neurogenesis produces a large pool of new granule cells in the dentate gyrus. Journal of Comparative Neurology. 2001 Jul 9;435(4):406-17
  2. Gross CG. Neurogenesis in the adult brain: death of a dogma. Nature Reviews Neuroscience. 2000 Oct 1;1(1):67-73.
  3. Eriksson PS, Perfilieva E, Björk-Eriksson T, Alborn AM, Nordborg C, Peterson DA, Gage FH. Neurogenesis in the adult human hippocampus. Nature medicine. 1998 Nov 1;4(11):1313-7.
  4. Ming GL, Song H. Adult neurogenesis in the mammalian brain: significant answers and significant questions. Neuron. 2011 May 26;70(4):687-702.
  5. Van Praag H, Kempermann G, Gage FH. Running increases cell proliferation and neurogenesis in the adult mouse dentate gyrus. Nature neuroscience. 1999 Mar 1;2(3):266-70.
  6. Fabel K, Fabel K, Tam B, Kaufer D, Baiker A, Simmons N, Kuo CJ, Palmer TD. VEGF is necessary for exercise‐induced adult hippocampal neurogenesis. European Journal of Neuroscience. 2003 Nov 1;18(10):2803-12.
  7. Ehninger D, Kempermann G. Paradoxical effects of learning the Morris water maze on adult hippocampal neurogenesis in mice may be explained by a combination of stress and physical activity. Genes, Brain and Behavior. 2006 Feb 1;5(1):29-39.
  8. Jin K, Peel AL, Mao XO, Xie L, Cottrell BA, Henshall DC, Greenberg DA. Increased hippocampal neurogenesis in Alzheimer's disease. Proceedings of the National Academy of Sciences. 2004 Jan 6;101(1):343-7.
  9. Van Praag H. Neurogenesis and exercise: past and future directions. Neuromolecular medicine. 2008 Jun 1;10(2):128-40.