Generation of new neurons in the adult brain may be essential for learning, memory, and mood. Emerging evidence also indicates that adult neurogenesis is impaired by exposure to radiation. These new perspectives underscore a previously unappreciated risk to the cognitive function and psychological stability after radiation exposure. This risk applies to patients undergoing radiation therapy and to astronauts traveling beyond low-Earth orbit. A new reporter mouse line has been generated, by McKnight Brain Institute (MBI) collaborators in the Enikolopov group at the Cold Spring Harbor Laboratory, to identify at-risk populations of stem and progenitor cells in the adult brain (see green cells in the accompanying figure). It was found, in a collaboration involving the MBI, Cold Spring Harbor, Brookhaven National Laboratory, Neuroscience Associates, and Kennedy Space Center investigators, that early neural progenitors are selectively affected by conditions simulating the space radiation environment; this is reflected both in a decrease in the number of these progenitors in the neurogenic regions and in an increase in the number of dying cells in these regions.
Unexpectedly, it was found that quiescent stem-like cells, rather than their rapidly dividing progeny, constitute the most vulnerable cell population, suggesting a profound impact on the subsequent levels of neurogenesis in the irradiated brain. These findings raise important issues about the possible risks facing astronauts on long duration space missions, and patients exposed to radiation during medical procedures. (From Mignone et al., J. Comp. Neurol., 2004; Encinas et al., Exp. Neurology, 2008).