This issue is particularly important in short experiments (i.e., days).
If the animal is injected with Brd U over n days, and sacrificed 1 week after the last injection, the cohort of labeled cells is considered to be between 7 and 7−n days old.
It will be important to note here that these cell populations can be traced using relatively specific markers (Figure 1).
In recent years, the labeling of newly born cells in the adult brain has been almost overwhelmingly ruled by the use of 5-bromo-3′-deoxy-uridine (Brd U).
“The underlying principle is straightforward: a permanent marker is brought into a cell of interest at the time point of division and the later fate of this cell is studied.
After the animal is sacrificed, staining is detected by immunohistochemistry using antibodies specifically directed against the analog.
Brd U has been the marker of choice in recent years for several reasons, in part because this method requires no radioactivity unlike the use of tritiated thymidine, which for decades was used to label dividing cell populations during brain development.
The age of labeled cells is equivalent to the survival time (i.e., cells are 1 month old if the animal injected with Brd U was sacrificed 1 month after Brd U injection).
A key limitation of this method is its ability to recognize only a single pool of Brd U incorporated into the body, regardless of when and how it was administered.Therefore, the physiological and quantitative analysis of neuronal subpopulations at different ages is critical to studies of neurogenesis.Such approaches allow cells of different ages to be identified by labeling them according to their probable date of birth.This review summarizes the current research carried out using these techniques and outlines some of the key applications.The accurate labeling of newborn cells in the adult brain poses a fundamental challenge in the study of adult neurogenesis.Furthermore, Brd U staining is readily detected by immunohistochemistry.