A Major Breakthrough in Neurogenesis Research

I have written a lot about adult neurogenesis, because it is so incredibly important.

When most of us were in school were taught that the brain is a static structure. That you are born with a certain number of neurons, that constitutes your neural “stash.” And after the age of five you would lose a hundred thousand neurons a day, and if you drank too many martinis it would be two hundred thousand a day. “Facts” and figures repeated from one textbook to another for fifty years. And quite wrong.

Ten years ago it was discovered that there are neural stem cells in the hippocampi of adult rodents. A study published in 1998 provided some evidence that neurogenesis takes place in the adult human hippocampus, but the idea that neurogenesis takes place in adult humans has remained contentious.

Now, an advance online publication on the website of the journal Science provides evidence that neurogenesis may also occur in the olfactory bulb of the human brain.

The whole article, including the pictures is available here. The picture at the top of this article shows new cells appearing in the olfactor bulb.

The investigators examined the rostral migratory stream (RMS) which is the main pathway by which newly born cells from the subventricular zone (SVZ) reach the olfactory bulb in rodents. The researchers discovered that there is a human RMS containing neuroblasts, a.k.a. neural stem cells.

(This is a rat olfactory bulb)

Maurice Curtis and his colleagues examined the brains of cancer patients who had recently died, after having been previously injected with bromodeoxyuridine (BrdU), a chemical that is incorporated into newly synthesized DNA. Cell biologists and oncologists have used the method for years to visualize and monitor the growth of tumors. The researchers found BrdU-positive cells in the olfactory bulbs of the patients’ brains, indicating that they contained newly-generated neurons.

The team then used antibody staining to show that the neuroblasts begin to differentiate into olfactory neurons while migrating through the rostral migratory stream. Upon arriving at the bulb, the cells continued to differentiate, forming mature olfactory neurons.

The patients whose brains were examined were between 38-70 years of age, so the findings show that neurogenesis may occur throughout the duration of the human lifespan. The function of these newly generated cells is unclear, but they may be involved in recognizing and remembering new smells in the later years of life.

The researchers also have preliminary unpublished data that the stem cells not only migrate to the olfactory bulb, but also leave the RMS and migrate into the basal ganglia and cerebral cortex. This is significant, because parts of the basal ganglia degenerate in movement disorders such as Parkinson’s Disease, and specific regions of the cortex degenerate in Alzheimer’s. The possibility that stem cells enter these regions from the RMS could therefore provide a means for developing new treatments for neurodegenerative diseases.

So although at the moment new neurons are only known to be created in a small number of ancient structures in the brain, but that may well change, since the cells are marching over there from regions around the ventricles. After all, why would Nature, the Universe or God have left neural stem cells sitting there unless it was for a good reason? And if adult neurogenesis can be demonstrated in other parts of the brain, then what? An end to the stem cell debates? If the stem cells are already present in the brain, the effort can be directed toward activating and directing them. Could we continue generating new neurons to stave off the dementing illnesses, or is that just science fiction?

The answer is that science fiction is fast becoming science fact. This research will need to be replicated, but I know of several other labs that have already accumulated some similar data to this new paper in Science.