Microglia A Anatomy

Microglia can be present in three states: resting, activated, and phagocytotic. The morphology of microglia differs from that of other glial cells in that it changes in response to the CNS perturbations. Thus, under normal conditions microglia are in the resting state, but they will become activated or phagocytotic in response to CNS injury and will invade the CNS. These changes in morphology are intimately linked with microglial function, as will be discussed later. The first selective stain for microglia was silver carbonate developed by Rio Hortega and, although unreliable, was the standard method for 50 years. The most reliable current histochemical staining method for identifying resting microglia uses the enzymes thia-mine pyrophosphatase and nucleoside diphosphatase. Activated microglia can be distinguished from resting microglia in that they exhibit increased activity of enzymes that are absent from resting microglial cells. These enzymes include acid phosphatase, 5'-nucleoti-dase, oxidoreductase, nitric oxide synthase, lysosomal proteinases, plasminogen activator, lysozyme, purine nucleoside phosphorlyase, and elastase. However, these enzymes are not specific markers for activated microglia because they are found in other glial cells. Resting microglia can be distinguished both by their unique morphology and by their phenotype. Morphologically they have highly branched processes, a small amount of perinuclear cytoplasm, and a small, dense, and heterochromatic nucleus, and they can be positively distinguished as the only cells that express the CR3 complement receptor. At the ultrastructural level they are recognizable as true parenchymal constituents of the nervous system, i.e., they are located outside of the vascular basement membrane. Microglia are not a homogeneous cell population throughout the brain because their morphology varies with brain area. Specifically, in gray matter areas of the brain, resting microglia tend to be profusely ramified with processes extending in all directions, whereas resting microglia in white matter align to their cytoplasmic extensions in parallel but also at right angles to nerve fiber bundles.

Anxiety and Depression 101

Anxiety and Depression 101

Everything you ever wanted to know about. We have been discussing depression and anxiety and how different information that is out on the market only seems to target one particular cure for these two common conditions that seem to walk hand in hand.

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