"Everyday experience leads us to suppose that thoughts pass through the mind with a rapidity that defies the laws of physics. It comes as a stunning surprise to discover that almost the exact opposite is true: the brain is slow—very slow— by comparison with the fundamental forces of the physical world," Jean-Pierre Changeux in The Physiology of Truth: Neuroscience and Human Knowledge.
Neurons use electricity to send signals through the body and brain. Early on it was thought that neurons connected directly with other neurons to allow the transmission. In the 1920s this assumption was found not to be true. Instead, there is generally a gap between communicating neurons. The gap is called the synaptic cleft and a chemical synapse carries the converted electrical signal across the synaptic cleft where it is reconverted into an electrical signal in the receptor neuron. In terms of raw speed, it's a little like putting regularly spaced sand traps on a NASCAR race course. Chances for problems and quirks in this process are numerous. The last thing it needs is an inability to replace diseased or destroyed neurons.
Until two recent studies at the Schepens Eye Research Institute in Boston, scientists assumed that only two parts of the brain contained neural stem cells and could regenerate brain tissue. Scientists believed that when neurons died in other areas of the brain, they were lost forever along with their functions.
The first of the two Schepens studies, both conducted in the adult brains of mice, demonstrated that neural stem cells exist in every part of the brain but are mostly kept dormant by chemical signals from support cells known as astrocytes.
The second study identified specific molecules in the brain that are responsible for awakening and putting to sleep brain stem cells, which, when activated, can transform into neurons (nerve cells) and repair damaged brain tissue. Specifically, the team discovered that in the areas where stem cells were dormant, astrocytes were producing high levels of two related molecules--ephrin-A2 and ephrin-A3. They also found that removing these molecules (with a genetic tool) activated the sleeping stem cells.
"The findings in both papers should have a far-reaching impact," says principal investigator, Dr. Dong Feng Chen, associate scientist at Schepens Eye Research Institute and assistant professor of ophthalmology at Harvard Medical School. Chen believes that tapping the brain¹s dormant, but intrinsic, ability to regenerate itself is the best hope for people suffering from brain-ravaging diseases such as Parkinson¹s or Alzheimer¹s disease or traumatic brain or spinal cord injuries.
Adapted from the Schepens Eye Research Institute release through EuekaAlert!.
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