The number and distribution of proliferating cells in the rat's rostral migratory stream as identified by means of two different proliferation markers.

In the brains of adult rodents, the cells arising in the subventricular zone of the lateral ventricles maintain the ability to divide when migrating to the olfactory bulb along the rostral migratory stream (RMS). Dividing cells in the RMS are most frequently revealed through immunohistochemical detection of an exogenous marker of proliferation, 5-Bromo-2-deoxyuridine (BrdU), which incorporates into DNA during the S-phase of mitosis. The more recently recognized antigen Ki-67 (also known as Kiel-67 and MKI67), an endogenous protein expressed in nuclei at all stages of mitosis, is also used for proliferation detection. BrdU and Ki-67 are often used as alternative methods, but they have not previously been compared in the RMS. We analyzed the numbers and distribution of cells labeled either with BrdU or Ki-67 within the RMS of adult rats. The first group of animals received a single i.p. dose of BrdU. In the second group, dividing cells were visualized by Ki-67 immunohistochemistry. Some sections from brains of BrdU-treated rats were also immunostained for Ki-67. Labeled cells were counted in the three anatomical parts of the RMS (vertical arm, elbow and horizontal arm) using a method for unbiased estimation of cell density. The distribution of proliferating cells was similar for both markers. Most BrdU and Ki-67 positive cells were located in the vertical arm and in the elbow, but a caudo-rostral reduction in cell divisions was more evident with Ki-67 labeling. The number of Ki-67 positive cells significantly exceeded the number of BrdU positive cells in all parts of the RMS. Our results indicate that BrdU and Ki-67 are not interchangeable markers for evaluation of proliferative activity in the RMS.