Pinocytosis as a select marker of ramified microglia in vivo and in vitro.

Based on previous observations in tissue culture, we hivestigated pinocytotic activity as a poiential cell marker for brain microglia. This functional activity was assessed in three different preparations derived from rat: primary cultures of mixed cerebral cortical cells, tissue slabs of whole cerebrum, and cultures ofisolated or enriched microglial cells. Each preparation was incubated with the fluorescent dye lucifer yellow as a soluble tracer and then processed for light miaoscopy. Under the conditions utilized, ramified microglia specilically exhibited differentially high pinocytotic labeling in all cases; the dye was mainly localized within the cell somata,