The Discovery of Adult Mammalian Neurogenesis

Abstract

ABSTrACT Visualizing proliferating cells with 3 H-thymidine autoradiography, we discovered in the early 1960s that the microneurons (granule cells) of the hippocampal dentate gyrus and the olfactory bulb continue to be produced through adulthood. We later demonstrated that the precursors of hippocampal granule cells proliferate in the dentate subgranular zone, and that this secondary germinal matrix is far more prominent in a carnivore (young cats) than in rodents (rats and guinea pigs). By destroying these proliferating precursor cells with low-level X-rays, we prepared rats that lacked 85 percent of the normal complement of granule cells, the same proportion that we found to be generated postnatally with quantitative histology and autoradiography. Behavioral tests established that these " degranulated " rats displayed abnormalities comparable to those following extensive hippocampal lesions. We also showed that the granule cells of the olfactory bulb are generated in the persisting subependymal layer of the anterior forebrain and migrate to the olfactory bulb by way of a hitherto unidentified structure, the rostral migratory stream. We discuss why the neuroscience community may have refused to accept these multipronged demonstrations and our laboratory lost its public financing by the mid-1980s.