PROBLEMS ENCOUNTERED WHEN IMMUNOCYTOCHEMISTRY IS USED FOR QUANTITATIVE GLIAL-CELL IDENTIFICATION IN AUTORADIOGRAPHIC STUDIES OF CELL-PROLIFERATION IN THE BRAIN OF THE UNLESIONED ADULT-MOUSE

We have used sections of adult mouse brain to determine whether antibo dies specific for oligodendroglia (anti-carbonic anhydrase II, CA II; anti-galactocerebroside, GC; anti-myelin basic protein, MBP) and astro glia (anti-glial fibrillary acidic protein, GFAP; anti-S 100 protein) are suitable for quantitative studies of the proliferation and subsequ ent differentiation of these cells. Unlesioned adult mice received a s ingle injection of H-3-thymidine (TdR) and were killed between 1 h and 70 days later. Quantitative evaluations of autoradiographs of 2-mu m- thick serial sections stained immunocytochemically with the antibodies mentioned above or with Richardson's method for histological control led to the following conclusions. Anti-GC and anti-MBP stained only th e oligodendrocytic processes and, thus, cannot be used in well-myelina ted brain areas. Anti-CA II stained only a portion of the differentiat ed oligodendrocytes, but no proliferating cells. Anti-S 100 protein re cognized all the astrocytes, but also many (interfascicular) oligodend rocytes. Anti-GFAP stained only a few astrocytes in the unlesioned mou se; all astrocytes may become GFAP-immunopositive only after wounding the brain. Thus, in contrast to in vitro studies, immunocytochemical s tudies with these antibodies on sections of adult animals cannot be re commended for the quantitative analysis of cell proliferation. In addi tion, our results show that differentiated glial cells proliferate in adult mice. Astro- and oligodendrocytes divide with the same cell cycl e parameters and mode of proliferation up to about 1 month after H-3-T dR injection. In contrast to oligodendrocytes, some astrocytes might r e-enter the cycle after a few weeks of quiescence.