Courtesy of Su-Chun Zhang and Ian Duncan, School of Veterinary Medicine, University of Wisconsin-Madison. See "Generation of Oligodendroglial..." in the bibliography.

Bolt-on brain repairs?
If your sink is dripping, universal replacement parts will sometimes fix it. If your roof is leaking, one shingle is pretty much like the next, as far as its ability to keep the rain out.

But if your memory is "leaking" because your brain cells are dying, don't bother trying to get repair parts. Even the regeneration of neurons we've been breathlessly describing only occurs in two small areas of the brain, which hardly account for all memory problems.

In November, 1998, however, Harvard Medical School researcher Evan Snyder announced the discovery of neural stem cells -- primitive cells that could eventually become universal replacement parts for neurons killed by Alzheimer's disease, oxygen shortages, or even spinal-cord injury.

Snyder's work is part of an on-going revolution in stem-cell research (see "Engraftable Human Neural Stem Cells... " in the bibliography.) Over the past few decades, we've watched blood stem cells turn into many sorts of blood and immune cells, and even rebuild immune systems destroyed by anti-cancer drugs.

More recently,
scientists have isolated and grown more primitive versions of the flexible stem cells in lab dishes. Theoretically, once we learn to direct their growth, these cells could become any cell in the human body.

As we've mentioned, scientists have long believed that neurons don't regenerate, and even the limited contrary evidence may simply represent exceptions that prove the rule. In contrast, the isolation of stem cells could offer a more promising sign that brain repair is just around a couple of scientific corners.

But first, in The Why Files tradition, let's do that "how-it-was-done?" tango.

Snyder isolated human neural stem cells from an aborted fetus and grew them in the lab, then watched them form neurons or glial (support) cells. When the stem cells were transplanted into the brains of immature mice, they formed new neurons and glial cells that looked appropriate to wherever they wound up. (More on Snyder's study.)

Interestingly, although new neurons only form in two small regions of the brain, neural stem cells are found in many areas. The explanation, says Fred Gage of the Salk Institute, is that most of the stem cells become glial (supporting) cells, not neurons, or they just die -- "a reserve pool of cells that are not becoming anything."

Still, the fact that in certain places under certain circumstances, some stem cells do become neurons should be interesting to anyone concerned about neurodegenerative diseases like Alzheimer's or Parkinson's. Figuring out which chemical signals from the brain cause stem cells to convert into neurons could lead to a treatment to restore brain function.

Even if it proved impossible to use chemical signals to induce the brain to grow new neurons, it might be possible to remove stem cells, grow them into whatever cell type was needed, and transplant them back into the brain. Such a "seeding" with stem cells, for example, might reverse the effects of spinal-cord damage or oxygen deprivation.

A brief statement from our lawyer
Before you are deluded into believing that neural stem cells will solve every neurological difficulty, read the fine print:

Nobody knows if the new neurons in brains are actually working. Currently, researchers are trying to seed replacement cells into animals with specific brain damage, and testing whether the transplants are effective.

Nobody knows if transplanted stem cells will spark an immune reaction in a new host, although this does not seem to happen in rodent research.

Many further studies must be undertaken to prove that any of these procedures is safe and effective in people.

Got any neurons left for some reading on our topic?

©1999, University of Wisconsin, Board of Regents.