Following axotomy of the facial nerve, the uptake of [
3H]
-alanine into different types of glial cells in the facial nucleus was studied by autoradiography. A marked proliferation of microglial cells, predominantly in a satellite position to neurons, was accompanied by a localization of [
3H] (
-alanine over astrocytes and oligodendrocytes but not over microglial cells. Microglial cells therefore appear to be a functionally distinct cell type and should not be classified with the macroglia.