Scanning electron microscope observation of intraventricular macrophages (Kolmer cells) in the rat brain.

The choroid plexus and the third ventricle wall of the rat brain were observed by scanning electron microscopy. Macrophages of various shapes known as Kolmer cells were attached to the ependymal surface of the choroid plexus densely covered with microvilli. Some cells possessed numerous fine processes radiating from the centrally located cell body and ending, often with an attenuated web-like tip, among the ependymal microvilli. Others were cells with a few pseudopod-like processes of considerable thickness and length. The latter type was thought to be in locomotion. The same cells were occasionally also found in the third ventricle wall far from the choroid plexus. The Kolmer cells are thought to be scavengers belonging to the whole ventricular system, though they are gatherd mainly on the choroid plexus.