Proliferation of epithelial cells in the adult primate choroid plexus.

An adult rhesus monkey was injected intraperitoneally with [H3] thymidine (2.3 microCi/gram body weight) and perfused 90 minutes later with a mixture of aldehydes. One and a half micrometer plastic sections were then cut and dipped into liquid emulsion for radioautography. Labeled cells were observed in the choroid plexus of the anterior lateral ventricle; cell identification was evaluated using electron micrographs taken from serial thin sections of re-embedded. radioautographic 1.5-micron sections. The ultrastructure and location of both mitotic figures and labeled cells confirmed the presence of undifferentiated basal choroid plexus epithelial cells in the adult primate central nervous system.