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He managed to identify microglia between 1919 and 1921 by staining the cells with silver carbonate. [3] His method of staining also led to the discovery of oligodendroglia in 1921, [4] which both he and Penfield are now credited with. [2] However it was Rio Hortega who named the cells. [1]
Microglia are a type of glial cell located throughout the brain and spinal cord of the central nervous system (CNS). [1] Microglia account for about 10–15% of cells found within the brain. [2] As the resident macrophage cells, they act as the first and main form of active immune defense in the CNS. [3]
Further, microglia might be activated but hypertrophy, and fail to transform into fully phagocytic cells. Those microglia that do transform, clear out the debris effectively. Differentiating phagocytic microglia can be accomplished by testing for expression of major histocompatibility complex (MHC) class I and II during Wallerian degeneration. [19]
The exception is microglia, which are derived from hematopoietic stem cells. In the adult, microglia are largely a self-renewing population and are distinct from macrophages and monocytes, which infiltrate an injured and diseased CNS. In the central nervous system, glia develop from the ventricular zone of the neural tube.
Immunofluorescence staining of homeostatic microglia in a healthy adult mouse retina. Microglia are the tissue-resident phagocytes of the central nervous system . CSF1R signaling promotes migration of primitive microglia precursor cells from the embryonic yolk sac to the developing brain prior to formation of the blood-brain-barrier .
Microglia have been implicated in neuropathic pain. They become activated in response to nerve injury, as demonstrated by several animal models. [30] Activated microglia release substances that excite pain-sensitive neurons, including prostaglandins and reactive oxygen species, through the purinergic signaling mechanisms.
Micrograph showing gliosis in the cerebellum. Reactive astrocytes on the left display severe proliferation and domain overlap. Reactive astrogliosis is the most common form of gliosis and involves the proliferation of astrocytes, a type of glial cell responsible for maintaining extracellular ion and neurotransmitter concentrations, modulating synapse function, and forming the blood–brain ...
Classical plaques also include abnormal, swollen neuronal processes deriving from many different types of neurons, along with activated astrocytes and microglia. [ 3 ] [ 4 ] Abnormal neurites and activated glial cells are not typical of most diffuse plaques, and it has been suggested that diffuse deposits are an early stage in the development ...