Glossary

Alexander's disease Alexander's disease is a leukodystrophy in which there is accumulation within the astrocyte cytoplasmic processes of beaded inclusions, i.e., Rosenthal fibers which contain alpha-B crystallin. The relationship between these abnormal astrocytes and demyelination characteristic of this pathology is not yet clear.

blood-brain barrier The blood-brain barrier is a physical and physiological barrier impeding the passive diffusion of solutes from the blood into the extra-cellular space of the central nervous system. It is also a brain-blood barrier. The highly impermeable tight junctions between endothelial cells forming the capillaries in the central nervous system are responsible for the blood-brain barrier functions. Astrocyte perivascular processes or end-feet form a virtually continuous sheath around the vascular walls. Astrocytes are involved in the induction of the blood-brain barrier property of central nervous system endothelial cells.

gap-junctions Gap-junctions are a group of diverse channels that vary in their permeability, voltage-sensitivity and potential for modulation by intra-cellular factors. They provide a pathway for the selective exchange of small molecules. Astrocytes are connected to each other by gap-junctions which are localized between cell bodies, between processes and cell bodies and between astrocyte end-feet that surround blood vessels. Thus activities of neighboring cells can be synchronized.

glial cells Glial cells are present in the central nervous system and distinct from neurons. They include astrocytes, oligodendrocytes and microglia. Interactions between neurons and glial cells are important during neuronal development and for the normal functioning of the nervous system. Dysfunction of glial cells is involved in many degenerative diseases of the nervous system.

glioma Glioma are the most frequent malignant tumors of the brain. Most of them are of astrocytic origin.

gliosis Astrocytes have a capacity to react mainly in relation to an injury in the central nervous system and constitute reactive gliosis. This reaction is characterized by hypertrophy of astrocytes. There is also an increase in astrocyte intermediary filament numbers and in their constituent the glial fibrillary acidic protein GFAP. There may also be a proliferation of astrocytes, occurring in general close to an acute lesion, but it is not constant. Astrogliosis is observed as a secondary process during aging as well as in many pathological conditions such as Alzheimer disease, brain trauma, ischemia, and multiple sclerosis in demyelinated areas. The physiological role of astrogliosis remains controversial with respect to the beneficial or detrimental influence of reactive astrocytes on central nervous system recovery.

radial glia Radial glia are a particular category of the astrocyte family. Radial glia fan out from the ventricular and subventricular zones where the cell bodies reside, and they extend to the pial surface. During development, radial glia are necessary to neuronal migration to the cortex. After migration has begun to subside, these cells assume a variety of transitional forms and transform into star-shaped astrocytes.

The astrocyte is a major glial cell type of the central nervous system. Astrocytes are star-shaped cells which extend

Encyclopedia of the Human Brain Volume 1

Copyright 2002, Elsevier Science (USA).

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processes terminating in end-feet at the pial surface or on blood vessels. Other cells with a different morphology have key-constitutents of astrocytes, such as glycogen particles and a protein of astrocyte intermediary filaments, the glial fibrillary acid protein (GFAP); thus they are part of the astrocyte family. Among them are embryonic glial fibers (radial glia) necessary for neuronal migration. Development of neuronal pathways and synaptic functions require interactions with astrocytes. Astrocytes help to maintain synaptic functions by buffering ion concentration, clearing released neurotransmitters, and providing metabolic substrates. Their dysfunction is implicated in neurodegenerative diseases. The major brain tumors (glioma) appear to be of astrocytic origin.

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