[Justin_Is_Here (OP)]

What are experiments conducted and theories made to find the cause of cell ageing? Is it true that brain cells never age? Why?

[evan_au]

What are experiments conducted and theories made to find the cause of cell ageing?

One effect is the shortening of telomeres as cells divide. There are very few cells in the body which do not suffer this effect.

Another aging effect is copying errors while duplicating the human cell's approximately 3 billion DNA bases. Despite several checks made during DNA duplication, no copying method is perfect, and a few new mutations occur every time a cell divides. These mutations can result in cell death, cell degradation or a cell becoming cancerous.

Is it true that brain cells never age?

I think it would be more accurate to say that most areas of the brain don't grow new cells; this is unlike most parts of the body, where there is a regular turnover of new cells.

It is possible for the brain to learn new tricks, by strengthening or weakening the synapse links between existing nerve cells. Some specific areas of the brain like the hippocampus are able to generate new neurones throughout life.

Brain cells can age and die, and progressive loss of neurones occurs from a young age. Processes seen in Alzheimer's,  Huntington's and Mad Cow diseases cause the progressive buildup of abnormal protein plaques in the brain, which causes inflammation and kills brain cells at an accelerated rate, resulting in brain shrinkage, dementia and eventual death.

[evan_au]

Is it true that brain cells never age?

I see that there is a class-action lawsuit in the USA, where the National Football League is facing a potential bill of over $1 Billion for brain damage players sustained from repeated concussions (and other injuries).

Concussion can kill brain cells, causing premature brain aging and dementia.

Presumably this concussion risk also applies to other football codes, including games that involve "head"ing the ball, or being tackled to the ground.

[Justin_Is_Here (OP)]

Evan_au, What is the reason of ageing and death of brain cells, as you've said that brain cells age and die?
Its certainly cannot by shortening of telomeres or mutation as they require cell division and brain cells do not divide.
Please give a site to support your answer.
(I mean other than victims of neuro degenerative diseases)

[evan_au]

What is the reason of aging and death of brain cells?

Ignoring:

• diseases of the brain (eg Alzheimer's, Lewy-body, encephalitis, Huntinton's Jakob-Creutzfield, epilepsy, prions), which produce most of the cases of brain degeneration...
  
• strokes and vascular dementia (accentuated by smoking, heart conditions, lack of exercise and diabetes)
  
• diseases of the body (eg heart failure, atherosclerosis, kidney failure, liver damage, loss of lung function, autoimmune, etc)
  
• accidents/brain injuries (physical trauma or chemical poisoning from food or medication, drinking to excess or long-term stress)
  
• bacteria, viruses, parasites and the resulting immune response & inflammation (eg polio, syphilis, malaria)
  
• brain cancer
  
• malnutrition (and over-nutrition)
  
• Loss of plasticity, which occurs in most areas of the human brain as children (an age-related issue) 

Some other common causes are:

• Parkinson's Disease: This is caused by the death of dopamine-producing neurones in the brain. For most patients, the cause of cell death is unknown, although genetic causes have been identified for a small proportion of cases.
  
• Loss of ability to make new memories: It is seen that retention of memories, speed in recall and ability to create new memories declines with age. This is related to functioning of the hippocampus.
  
• Stem cells: It has been seen that areas of the brain containing the most stem cells are adjacent to the hippocampus, where most memories are stored. To create new memories throughout life, it is likely that new cells are being spawned in the hippocampus, which means that the stem cells must be continually dividing throughout life, and suffer the same copying errors as other cells in the body.
  
• Random mutations: Even in the absence of cell division, brain cells are continually bombarded by radiation from the environment, both natural and man-made, as well as damage from free radicals produced by normal metabolism. This causes breaks in the DNA, which must be repaired - up to 1 million events per cell, per day. This repair process is somewhat risky, especially in the case of double-strand breaks. This damage can affect both nuclear DNA and mitochondrial DNA.
  
• Apoptosis: If DNA repair is unsuccessful, the cell commits suicide.
  
• Partial Repair: DNA repair can cause loss of epigenetic markers, production of malformed proteins and distorted regulatory signals. This results in impaired cell function and cell death.
  
• Intracellular transport: Efficient transport of chemicals down long axons is vital for health of brain connectivity in the white matter.
• Stimulation: Nerve cells become less active when presented with no stimulation. This applies at the level of the neurone and the whole person, leading to the philosophy of "Use it or Lose it". (Advertisement: The Naked Scientists can help here!)