07 Dec 2001

The discovery of newly born neurons in the adult primate neocortex caused a great stir two years ago, opening, as it seemed, one of the most promising avenues of research into replacing neurons destroyed by neurodegenerative disease. Writing in today's Science, Pasko Rakic of Yale University, Connecticut, and David Kornack of the University of Rochester, New York, dampen this excitement with a report that they cannot find newly born neurons in the neocortex of adult macaques.

Like the original study by Elizabeth Gould and colleagues at Princeton University, New Jersey (Gould et al. 1999), Kornack's and Rakic's did find cells labeled with the BrdU marker for cell division. Some of these cells also appeared to be labeled with a neuronal marker (NeuN), but in each case, when they looked closely, Rakic and Kornack found that they were examining two separate cells--a neuron with NeuN labeling and a closely apposed glial cell with BrdU labeling. De novo generation of glia in the adult mammalian brain is established. Anticipating the objection that their methods were not adequate to find the colabeling, the authors point out that they did find double-labeled, newly generated neurons in the hippocampus and olfactory bulb of the same animals, areas adult neurogenesis clearly occurs.

"Given the number of BrdU-labeled cells that we surveyed in the principal sulcus alone, the probability of missing 38 to 52 percent (or even the revised, lower estimate of 25 percent) [from the Gould group's original and subsequent studies] of the total BrdU-labeled cell population as double-labeled neurons is infinitesimally small," conclude the authors.—Hakon Heimer