HISTOCHEMICAL EVIDENCE FOR MICROGLIA-LIKE MACROPHAGES IN THE RAT TRIGEMINAL GANGLION

Of the 4 major cell types in CNS parenchyma, microglia appear to serve the unique functional role of tissue macrophages. The distribution of equivalent cells in the PNS is unclear. Recently, the B-4 isolectin o f Griffonia simplicifolia was shown to bind selectively to microglia a s well as to other macrophages under specific conditions. In the prese nt study, this lectin was used to assess the existence of macrophages in the rat trigeminal ganglion. Vibratome sections of fixed ganglia we re incubated with horseradish peroxidase (HRP)-conjugated isolectin, a n HRP reaction subsequently performed, and sections processed for hist ology and viewed by light microscopy. Staining activity was found to b e localised to a population of cells throughout the ganglion. These ce lls possessed small oval somata and several thin crenated processes, a n appearance typical of ramified microglia. Stained cells also exhibit ed a regular, evenly spaced tissue distribution similar to CNS microgl ia. Finally, similar cells were also labelled by thiamine pyrophosphat ase histochemistry, a cellular marker for CNS microglia/macrophages. I t was concluded that there are microglia-like macrophages in the trige minal ganglion and that these cells may function in immune reactions.