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Protoplasmic astrocytes
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Uniformly distributed within the grey matter [3]
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Bushy appearance, with numerous short, branched, thick processes [50]. The cell body is ovoid or fusiform (see Figure 5)
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• Form the blood–brain barrier
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Their processes exhibit endfeet enveloping the synapses and the blood vessels [51]. The processes express
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• Regulate the blood flow
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• Neuronal metabolism
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• Receptors for neurotransmitters, cytokines, growth factors
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• Implicated in the synapse function
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• Transporters
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• Fluid, ion, pH and transmitter homeostasis [45]
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• Ion channels [7]. In rodents, there is minimal overlapping between the processes of the neighbouring astrocytes [43, 44, 52–54]. In humans, the superposition of the domains occupied by the astrocytes processes is augmented [3]
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Fibrous astrocytes
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Within the white matter, oriented longitudinally, along the nervous fibers bundles [1]
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Star-shaped cells. Posses long, thin and straight processes [45] (see Figure 6)
| |
Their endfeet processes envelop the nodes of Ranvier and the blood vessels [45]
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Interlaminar astrocytes
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In the molecular 1st layer of the cerebral cortex, next to the pial surface
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Spherical cell bodies and processes
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Unknown Support the calcium wave propagation in humans [3]
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Are found only in humans and primates. Their processes are included in the pial glial membrane, creating a thick network of GFAP fibers [46–49]
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Varicose projection astrocytes
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In the 5th and the 6th layers of the cerebral cortex
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Exhibit 1 to 5 long processes (up to 1 mm in length), characterized by evenly (10 μm) spaced varicosities [3, 46]
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Unknown
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Were identified only in humans and chimpanzees. They are GFAP+ cells [3, 46]
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Bergmann glia (epithelial glial cells)
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In the Purkinje-cell and the granular layers of the cerebellar cortex
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Posses long processes extending towards the molecular layer of the cerebellar cortex, in a fan-like arrangement, exhibiting pial vascular endfeet [23]
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Implicated in synapse function: capable to interfere with synaptic transmission by communicating with neurons via the extracellular space, by modulating ion concentrations or transmitter levels in the synaptic cleft [23]
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Display receptors with distinct biophysical and pharmacological features allowing them to sense the activity of synapses [23]
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Fananas cells
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In the molecular layer of the cerebellar cortex
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Posses several short side processes with a characteristic feather-like arrangement [23]
| | |
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Müller cells
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In the 6th layer of the visual retina
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Supportive cells: they form the inner and the outer limiting membranes
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The limiting membranes consist of junctional complexes between the cellular processes of the Müller cells
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The outer membrane separates the external segment of the photoreceptor cells from the cell bodies and the outer membrane separates the retina from the vitrous body [23]
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They have an intense metabolic activity and contain microfilaments and glycogen within their cytoplasm [23]
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Pituicytes
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In the neurohypophysis
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Irregular in shape with many cytoplasmic processes extending in the proximity of the capillaries and surrounding the Herring bodies [24]
| |
Their cytoplasm contains lipid droplets and pigment granules.
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They are immunoreactive for GFAP, vimentin and S100 protein [24]
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Inerstitial epiphysial cells
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In the epiphysis
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Exhibit cytoplasmic processes
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Contain numerous filaments within their processes [23]
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