15 July 2000
THE BRAIN'S OWN MIRCACLE CURE: NERVE GROWTH FACTORS
In the last column, we took a look at what’s going on in the futuristic world of stem cell research — attempts to develop ways to boost the brain and body’s production of "generalist" cells with limitless potential to generate new cells, including brain cells. This month, we look at research into a key player in the brain’s self-support system: nerve growth factors.
For many years, brain researchers have understood that the creation and survival of brain cells may hinge on nerve growth factors. Growth factors, including neurotrophic brain proteins, are biochemical compounds that switch on the genes of stem cells so they develop into the right specific type of cell, help guide those newly-generated cells to the right part of the brain, and help maintain, protect, and repair brain cells once they’re in place. Ramon Y Cajal, the pioneering brain researcher with pessimistic views about the possibility of neurogenesis in the adult central nervous system, conjectured that the problem with adults might be an absence of the growth factors so abundant in the developing brain of a fetus.
It turns out that adult brains do, indeed, produce growth factors and that these chemicals continue to play a role in brain cell maintenance and repair throughout life. Recent research has focused on identifying the different kinds of growth factor involved in maintaining different kinds of brain cell, and in learning how to manipulate or augment the brain's own growth factors to keep brain cells alive and healthy.
One important finding is that the brain produces extra quantities — five to 50 times normal levels — of growth factors after a brain injury. Also, it has been discovered that glial cells — those traditionally underrated brain cells that help neurons to function properly — produce growth factors essential to the survival of neurons, and migrate to the site of a brain injury immediately after it occurs.
This suggests the possibility that we might help stroke or head-accident victims recover more quickly by stimulating the brain's production of growth factors, or by somehow adding to what the brain is already doing to help itself. One line of current research is in fact exploring the feasibility of injecting growth factors into the site of a brain injury to help the brain recover more quickly. In animal experiments, even neurons apparently destroyed by having their axons cut (rendering them incapable of sending messages to other brain cells) are restored to full function if nerve growth factors are injected up to three weeks after the damage.
Other experiments have shown that aged rats can regain youthful learning curves when growth factors are injected into the same frontal regions of the brain that degenerate in Alzheimer's. Recently, researchers have also successfully grafted in cells that secrete growth factors on an ongoing basis, to prevent cognitive impairment before it even starts. These techniques of boosting the brain's own maintenance and repair mechanisms hold great promise for combating or even preventing age-related dementias such as Alzheimer's.
In the meantime, the news that you can really use is this: the "use it or lose it" principle applies to growth factors as well as to the regeneration of neurons. In fact, raised levels of growth factors may be the reason that an enriched environment enhances survival of newly generated brain cells, aids in recovery from stroke, and helps forestall dementias such as Alzheimer's.
As we've seen in earlier editions of this column, an enriched environment — a lifestyle providing extra physical, social, and mental stimulation — translates into improved performance on intelligence-type tests and into a bigger brain. In her pioneering studies, Berkeley neuroanatomist Marian Diamond attributed the larger brains of enriched-environment rats to larger neurons with richer-branching axons and dendrites and thicker myelin insulation. Later work found evidence for a larger number of neurons in an "enriched" brain as well, and evidence for a doubled rate of new brain-cell production under enriched conditions.
Over the last ten years, a substantial body of research has shown that the environment also has a strong effect on those all-important brain nutrients known as nerve growth factors. A 1990 study revealed high levels of nerve growth factors in enriched-environment rats compared to standard-environment ones.
These findings are important for those worried about declines in learning ability and memory, since the hippocampus is a brain structure central to those skills; it is also one of the brain structures most strongly affected by Alzheimer's.
A subsequent study showed that rats with free access to a running wheel had increased levels of a neurotrophic-type growth factor than rats that had no chance to exercise. In this experiment, too, the extra growth factor molecules showed up in the hippocampus. Very recent studies have proven that exercise increases growth factor levels in older men and women. So we now have proof that the findings about the relationship between an enriched environment and nerve growth factor levels in the brain apply to humans too.
|
