Expert: John Locke - 9/29/2010

Question
As I understand it the brain, at least in part can grow new neurons.  I was wondering if the brain had a particular neuron growing center that lit-up signaling 'grow' to the part of the brain where the new neurons were needed or perhaps a persons DNA played a part or some other mechanics?

Answer
Thanks for using AllExperts. The brain's inability to regrow neurons is not due to some intrinsic characteristic of the neurons themselves; instead, neurons are limited in their ability to regrow because of inhibitor factors released by other cells in the central nervous system. When the brain is injured, it heals by forming what is known as a glial scar, which cannot conduct nerve impulses and which neurons cannot grow across. The glial scar is mostly a dense collection of astrocytes, which are supporting cells to neurons in the CNS, that crowds out potential neuron regeneration. Astrocytes and other central nervous system cells known as microglia and oligodendrocytes also secrete chemicals that inhibit the natural regenerative ability of neurons. At the same time, they promote the formation of glial scars. Neurons never have an opportunity to regrow because they are inhibited quickly after the initial injury occurs.

Compare this to the peripheral nervous system. When a nerve in the PNS is injured, there is no release of inhibitory factors or suppression of neuron regrowth. In fact, the neurons are quite capable of regrowing parts of themselves when damaged by using the surrounding cells as a framework on which to build. The net effect of this is that neurons in the PNS can recover from injury and reform damaged neural pathways, albeit quite slowly.

In answer to your question, there is no central control over the ability of neurons to regrow in the brain. Certain areas may be more robust in terms of their neuron networks, or they may be less inhibitory to neuron regrowth, but all the control of neuron regrowth occurs locally. Individual neurons have within themselves the ability to divide and/or to regrow damaged parts, but that ability is usually suppressed by other cells in the CNS. To speak to the second part of your question, individual genetic variation probably does play a role in the ability to regenerate neurons, but I cannot speak very much to that subject. There is quite a bit of ongoing research in this field: by inhibiting the inhibitory factors for nerve regeneration, it could potentially be possible for neurons in the brain to regrow after injury.

There is an excerpt here that summarizes the discussion quite well:
http://scienceweek.com/2005/sw051202-6.htm