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Category: Microbial Genetics and Molecular Biology
Microglia, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555819194/9781555819187_Chap12-1.gif /docserver/preview/fulltext/10.1128/9781555819194/9781555819187_Chap12-2.gifAbstract:
Microglia are the resident macrophages of the brain parenchyma ( 1 ). Although it has long been known that microglia are of myeloid lineage, based on immunocytochemical detection of macrophage-restricted antigens ( 2 ), it has only relatively recently been shown, by fate mapping studies, that these cells are of yolk sac origin and enter the developing neuroepithelium of the central nervous system (CNS) in the embryo ( 3 ). They are present throughout the length of the neuraxis, characterized by their fine processes emanating from a small cell body, and each cell appears to occupy its own territory. The morphology of microglia and their territorial behavior is well illustrated in retina whole mounts ( Fig. 1 ). The density and morphology of the microglia vary between distinct functional divisions of the CNS, with the lowest density found in the cerebellum and perhaps the highest density in the substantia nigra ( 4 ). These regional differences have been well studied in rodents, the most common experimental animal models, and although similar regional differences are seen in the human brain, there are some notable differences. In the rodent brain, the microglia are denser in gray matter than in white matter, while in the human brain, the microglia are denser in the large-fiber tracts that dominate the larger brain ( 5 ).
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Microglia in the outer plexiform layer of the retina of the mouse, illustrating the delicate branching of the processes and the territory occupied by each cell. GFP-labeled cell from a MacGreen mouse with immunocytochemistry. Courtesy of Sallome Murinello.
Microglia in the outer plexiform layer of the retina of the mouse, illustrating the delicate branching of the processes and the territory occupied by each cell. GFP-labeled cell from a MacGreen mouse with immunocytochemistry. Courtesy of Sallome Murinello.
Electron micrograph of a microglia in the adult mouse cortex immunolabeled with F4/80. The thin rim of cytoplasm and the sparse rough endoplasmic reticulum point to the downregulated phenotype of these cells. Ligands expressed in the CNS (left-hand column) engage receptors expressed on the microglia (right-hand column) that inhibit their activation. Other soluble mediators, including the neurotransmitters acetylcholine (ACh) and noradrenaline (NA), are shown at the top of the figure.
Electron micrograph of a microglia in the adult mouse cortex immunolabeled with F4/80. The thin rim of cytoplasm and the sparse rough endoplasmic reticulum point to the downregulated phenotype of these cells. Ligands expressed in the CNS (left-hand column) engage receptors expressed on the microglia (right-hand column) that inhibit their activation. Other soluble mediators, including the neurotransmitters acetylcholine (ACh) and noradrenaline (NA), are shown at the top of the figure.
GFP-labeled microglia in the hippocampus of the normal adult mouse (A), and morphologically activated microglia in the hippocampus of a mouse with prion disease (B). Note the greater density of cells, larger cell bodies, and multiple processes of those in panel B compared to panel A. Courtesy of Diego Gomez-Nicola.
GFP-labeled microglia in the hippocampus of the normal adult mouse (A), and morphologically activated microglia in the hippocampus of a mouse with prion disease (B). Note the greater density of cells, larger cell bodies, and multiple processes of those in panel B compared to panel A. Courtesy of Diego Gomez-Nicola.