Adult brains generate thousands of new brain cells, called neurons, each day; however only a small fraction of them survive. The rest die and are consumed by scavenger cells called phagocytes. Until now, scientists have not fully understood how this process works, which phagocytes are unique in the brain and how the removal of dead neurons influences the production of new ones.
In humans, neurogenesis, or the formation of new neurons, largely ceases
in most areas of the brain during adulthood. However, evidence is
strong that substantial numbers of new neurons are naturally generated
in two parts of the brain: the hippocampus, which is involved in
forming, organizing and storing memory; and the olfactory bulb, involved
in the perception of odor.
Researchers at the University of Virginia Health System have made a
pivotal discovery in understanding this complicated process, and their
findings could one day help scientists devise novel therapies to promote
neurogenesis in the adult brain. This could re-establish brain function
in patients suffering from depression, post-traumatic stress disorder
and other mental disorders in which adult neurogenesis is impaired.
The findings appear in a study published online July 31 in the journal Nature Cell Biology.
The study was led by Jonathan Kipnis, associate professor of
neuroscience, and Kodi S. Ravichandran, chair of the Department of
Microbiology and director of the U.Va. Center for Cell Clearance.
Zhenjie Lu, a senior research associate in the Department of
Neuroscience, is the first author on this work and was instrumental in
combining the methodologies in the Kipnis lab (which focuses on basic
mechanisms underlying neurological disorders) and the Ravichandran lab
(which focuses on cell clearance) to address adult neurogenesis through a
combination of studies in normal and genetically altered mice, and
studies using neuronal cultures.
Through their research, the scientists discovered that certain types of
progenitor cells, called the doublecortin (DCX)-positive neuronal
progenitors (or "newborn neurons"), serve a dual role in regulating
production and elimination of new brain cells. Progenitor cells
generally act as a repair system for the body, replenishing special
cells and maintaining blood, skin and intestinal tissues. This new
discovery points to the ability of these cells to clean each other out,
which ultimately benefits the regeneration process.