Response of intraventricular macrophages after a penetrant cerebral lesion.

The response of epiplexus and supraependymal cells to extravasated blood after a penetrant cerebral lesion was investigated. Epiplexus cells respond more actively than supraependymal cells. The epiplexus cells tend to aggregate near areas of extravasation of erythrocytes, this being most marked 6 hours after injury. Epiplexus cells lose their smooth surface appearance, retract their filopodia and adopt a more spherical form, with short microvilli or blebs. Numerous inclusion vesicles develop; some contain disrupted erythrocytes 6-12 hours after injury and these are still present 24-30 hours after injury. By 8-16 days after injury epiplexus cells resume a smooth surface appearance and the number of inclusion vesicles is much reduced. This suggests reversion to a quiescent state, from an earlier active state.