Discoveries: Brain Cell Regeneration 

For many years it has been a bedrock principal of neuroscience that all 100 billion of our brain cells exist at birth, that the adult human brain cannot grow new cells and that memory works by a rewiring of old brain brain cells rather than by growing new brain cells to record new data. As of 10/15/99 this is now in question. On that date Princeton neuroscientists Elizabeth Gould and Charles Gross published a study in Science dealing announcing their discovery of the daily growth of new brain cells in the adult macaque monkey brain. Using a chemical tracer, these researchers found a rim-like layer of stem cells over the ventricles deep within the macaques' brain which produced a steady stream of new neurons. The new brain cells migrated up into the cortex at the surface of the brain and established synapses with older cells in the frontal lobes (where personality, planning, decision making and working memory are located) and in the parietal lobes (where visual recognition memory exists). They speculate that this ceaseless train of new brain cells enables the brain to imprint and store new memories in a continuous sequence much like supplying a video camera with fresh video cassettes. If true, then a supply of healthy neurons may exist for treatment of degenerative brain diseases like Alzheimer's and Parkinson's, if they could be channeled to the damages portions of the brain. Since the discovery has not yet been confirmed in human beings, no definite answers are possible now, but an exciting new area of research has been opened up.

Textbook Rewrite: Brain Cells Can Regrow
Friday, 15 October 1999

A Princeton study has added to mounting evidence for the brain's ability to regenerate by showing, in adult monkeys, that new nerve cells are continually added to the cerebral cortex, the largest and most advanced part of the brain.

Elizabeth Gould and Charles Gross report in the current issue of Science that the formation of new neurons or nerve cells, neurogenesis, takes place in several regions of the cerebral cortex that are crucial for cognitive and perceptual functions. Their results strongly imply that the same process occurs in humans. 

"People thought: If the cerebral cortex is important in memory, how could it change?" says Gross. "In fact the opposite view is at least as plausible: if memories are formed from experiences, these experience must produce changes in the brain."

Scientists have observed neurogenesis in birds and rats for many years, but assumed that as evolution advanced and mental capacities increased, the brain supported less and less neurogenesis. Over the last decade evidence has accumulated for neurogenesis in several evolutionarily older parts of the brain such as the olfactory system and the hippocampus, which is believed to play role in memory formation. 

"After the discoveries in the hippocampus", says Gould, "most scientists remained convinced that adult neurogenesis was an anomaly and could not be found in the newer, higher parts of the brain. They believed, for example, that the brain relies on a stable structure for storing memories". 

The Princeton scientists found that the new neurons were formed in the lining of the cerebral ventricles, large fluid-filled structures deep in the center of the brain, and then migrated considerable distances to various parts of the cerebral cortex. This type of migration had never been seen before. 

The study has major implications for theories about how the brain develops. In particular, it casts doubt on the notion that the all-important time for brain development is from zero to three years of age, and raises the likelihood that experiences through adolescence and adulthood can affect the physical structure of the brain. 

For their experiments, Gould and Gross took advantage of the unique properties of a chemical known as BrdU. When cells are exposed to BrdU during cell division, the chemical becomes incorporated into the DNA of newly formed cells. The researchers injected BrdU into rhesus monkeys. Then, at intervals ranging from two hours to seven weeks, looked for evidence of the chemical in neurons in the cerebral cortex. In all cases, there were neurons with BrdU in their DNA, which showed that those cells had to have been formed after the BrdU injection. 

Within the cerebral cortex, the researchers found neurogenesis in three areas: 1) the prefrontal region, which controls executive decision making and short-term memory; 2) the inferior temporal region, which plays a crucial role in the visual recognition of objects and faces, and 3) the posterior parietal region, which is important for the representation of objects in space. 

Interestingly, there was no sign of neurogenesis in a fourth area, the striate cortex, which handles the initial, and more rudimentary, steps of visual processing. 
M. Sleath - The Lab

"While the adult brain previously was thought of as a non-regenerative system for pathway formation, recent studies show how dissociated primordial neurons or stem cells implanted into the adult central nervous system can grow to reconnect neuronal pathways and integrate in a molecular and physiological fashion. Thus, anatomical, neurochemical, molecular, behavioral and functional MRI parameters indicate that regenerative and reconstructive events can also take place in the degenerated adult brain." Neuroregeneration Laboratories, McLean Hospital, Program in Neuroscience, Harvard Medical School



Brain Cells Do Re-grow, Study Confirms

March 6, 2000 (Boston) -- Here's hope for those who fear they lost too many brain cells to youthful dissipation: Researchers at Cornell University have demonstrated that cells from an area of the brain essential for learning and memory can regenerate in a laboratory dish. In the future, the discovery might lead to strategies for replacing brain cells lost to diseases such as Alzheimer's.

Until recently, conventional medical wisdom held that we are born with all the brain cells, or neurons, that we'll ever have and when they're gone, they're gone for good. Over the last few years, though, researchers have shown that in at least one area of the brain, a region known as the hippocampus, there is continual turnover of cells throughout most of our lives. 

In the latest study, Steven A. Goldman, MD, from Cornell University Medical College in New York City, and colleagues took samples of tissues from the hippocampus that had been removed from patients undergoing surgery to repair brain disorders. They were able to tease out cells from a certain area where populations of "seed," or precursor, cells are found. The researchers were able to separate these precursor cells from mature cells, which can no longer divide. They were able to aid the cells in continuing to divide and grow. 

Jack P. Antel, MD, and colleagues from McGill University in Montreal write in an editorial accompanying the study that this approach could ultimately lead to new strategies for repairing and restoring cells lost to diseases or trauma in the hippocampus, and perhaps other regions of the brain.

But in an interview with WebMD, Goldman cautions that "it's a bit early in the game to think in practical terms of using these cells for transplantation purposes."

Among the problems that need to be tackled, Goldman says, are how best to deliver these cells to the brain and ensure that they will survive in sufficient numbers after transplant, and how to direct them to the parts of the brain where they will do the most good.

Many researchers think that memory impairment associated with aging is caused by damage to the hippocampus brought on by lifelong exposure to stress hormones. Several studies have shown that elderly people and rats with significant and prolonged elevation of these stress hormones have smaller hippocampal regions and show declines in memory due to damage to the hippocampus.

"It's a very interesting system," says Ronald McKay, PhD, chief of the laboratory of molecular biology at the National Institute of Neurological Disorders and Stroke. McKay, who has previously demonstrated that reducing stress hormone levels in aged rats can restore the production rate of brain cells in the hippocampus, reviewed the current study for WebMD. 

"The hippocampus has these cells ... which are replaced throughout life from dividing cells, so that whole process of division, ... maturation and death seems to be going on all the time in this structure." 

Although it's tempting to think that seed cells could be grown in the lab to restore cells damaged by neurodegenerative disorders such as Alzheimer's disease, much needs to be learned before such therapies are practical, Goldman and McKay say. 

Instead, these precursor cells are likely to have their first uses in drug-testing labs, where researchers could explore whether specific drugs or combinations could be used to stimulate the growth of new brain cells within the hippocampus, Goldman says.

Vital Information:

Conventional medical wisdom has held that people are born with all of the brain cells they will ever have, and once they are gone, they are permanently gone. 

Now, however, scientists have found that cells in the region of the brain responsible for memory and learning are capable of being regenerated.