Undifferentiated cells present in the pars intercerebralis of larval and adult locusts are glial precursors. Autoradiographic and ultrastructural study in vivo and in vitro.

The intercerebral part of the protocerebrum from embryos, larvae and imagos of Locusta migratoria was investigated in vivo and after culture of the brain in vitro using light and electron microscopy. The results showed the presence in embryo and persistence in larva and adult of 2 clusters of mitotically active embryonic cells in the inner part of each half of the pars intercerebralis. The fate of these undifferentiated cells was investigated during postembryonic life by in vitro and in vivo labeling with tritiated thymidine combined with counts of nervous cells of the pars intercerebralis. Autoradiographic results confirmed the mitotic activity of the undifferentiated cells and established the pattern of this activity which declines from the third larval instar to adult stage. Mitoses were never seen in neurons and glial cells. Neurons were unlabeled and their number was constant. Glial cells were labeled and their number increases throughout postembryonic life with a pattern of proliferation similar to the pattern of mitotic activity of the undifferentiated cells. These observations indicate that the undifferentiated cells of the pars intercerebralis of the locust represent a source of glial cells and could be called glioblasts.