News and reports about stem cell research are frequent in the media, often with optimistic overtones. The public gets the impression that brain repair by stem cells will soon be possible. But many reports are biased and tend to ignore important negative results. This is true, for example, of the regeneration of nerve cells (neurogenesis) in the brain of human adults, and of the role of stem cells in depression, learning and stroke. (Read about studies in Lena´s column.)

Regeneration of nerve cells is not confirmed
It is often stated as an established truth that new nerve cells can replace lost cells even in the adult human brain. But this statement remains unproven today. In 1998 Peter Eriksson and his colleagues at the University of Gothenburg claimed that new neurons can be formed in the hippocampus of the temporal lobe in adult humans. However, in 2001 the Hungarian scientist Laszlo Seress, using markers for cell division, saw a dramatic decline in cell proliferation in human hippocampus after the first year of life. He could not confirm that any of the cells were neurons.

In the Swedish newspaper Dagens Nyheter in October 2006, the science editor wrote that Jonas Frisén at the Karolinska Institute had succeeded in corroborating Eriksson´s finding of neurogenesis in the hippocampus, using a new method to determine the age of nerve cells. But Frisén´s investigation has not yet been published or even submitted for publication. His study was still going on when the article appeared in Dagens Nyheter. Since then nothing important has happened, according to Frisén (personal communication to Lena Carlsson in the middle of December 2006).

In their studies Peter Eriksson and Jonas Frisén are using different techniques to demonstrate neurogenesis. Eriksson utilizes components resembling DNA, and Frisén a technique based on radioactive carbon. Both techniques are measuring material being incorporated into the DNA of dividing cells. It is important to know that such incorporation can occur even in the absence of new nerve cell formation. The results are conclusive only if they are negative, that is, if there is no incorporation, and no new neurons have been formed (see Lena´s column).

The picture is far too positive
As the many serious problems in stem cell research are seldom fully exposed, the picture available to the public is far too glossy. This is not least true of the prospects of cell transplantation in Parkinson´s disease. When Swedish scientists, for example, report on the state of the art in this field they tend to ignore that the two largest and best controlled and analyzed transplantation studies in Parkinson's disease show quite discouraging results, as already commented upon in my previous column.

Admittedly some prominent stem cell researchers mention the great obstacles that must be overcome if stem cell therapy in patients is to become a reality. However, they do not seem to be very anxious to communicate their concern to laymen, such as patients, the general public, granting institutions, or politicians.

A century ago the Nobel Laureate Ramon y Cajal stated that lost nerve cells cannot be replaced. He has not yet been proven wrong. Needless to say, however, his statement was limited to nerve cells. For many other cell types the prospects could be very different.

January, 2007
Arvid Carlsson

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