Analysis of neurogenesis and programmed cell death reveals a self-renewingcapacity in the adult rat brain

The adult central nervous system was thought to be very limited in its rege nerative potential; however, the discovery that stem cell populations produ ce neurons in the adult brain highlights the dynamics of a previously assum ed 'static' organ, The continuous generation of new neurons in the adult br ain, nevertheless, leads to the question of whether neurogenesis is counter balanced by an accompanying cell death in the same regions. The objective o f this study was to stereologically analyze neurogenesis and programmed cel l death in adult brain regions with known neurogenic activity. Using bromod eoxyuridine (BrdU) to identify newborn cells we find that within a few days of BrdU-labeling the adult dentate gyrus and olfactory bulb generate high numbers of newborn neurons. More importantly, dUTP-nick end labeling (TUNEL ) reveals that areas of adult neurogenesis also contain high numbers of apo ptotic cells. We conclude that programmed cell death may have an important regulatory function by eliminating supernumerous cells from neurogenic regi ons and may thus contribute to a self-renewal mechanism in the adult mammal ian brain. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.