ABSTRACT
INTRODUCTION Advances in methodology have been critical to the rapid advances in the understanding of the functioning central nervous system (CNS). A tacit concept unique to the mammalian brain is that its functions are overwhelmingly due to the properties of its electrically excitable cells, the neurons. However, nonexcitable cells within the CNS outnumber the neurons; a class of these is collectively referred to as the neuroglia. The neuroglia are comprised of the astroglia or astrocytes, oligodendroglia or oligodendrocytes, and microglia. The term neuroglia was erron eously coined by the German pathologist Virchow in 1850, postulating that neurons were embedded in a connective tissue matrix to which he gave the name neuroglia, or nerve glue. Although erroneous, this term, has persisted for over a century as the preferred generic term for these cells.1*2 Two forms of astrocytes have been recognized in mammalian CNS, commonly referred to as the fibrous astrocyte and protoplasmic astrocyte.2 The fibrous astrocytes possess many thin processes, which are filled with bundles of filaments, consisting predominantly of the astrocyte-specific glial fibrillary acidic protein (GFAP). The protoplasmic astrocyte also possesses numerous processes, but they are shorter and in situ tend to insinuate in complex patterns between the neurons and their processes right down to the synaptic boutons where they contact the neuronal soma or dendritic processes. The protoplasmic astrocyte has a much lower density of intermediate filaments and often will not stain for GFAP in situ, but will stain for the nonspecific intermediate filament component vimentin,3 glutamine synthetase (GS), or S I00
protein.4 In situ the fibrous astrocytes are localized to the white matter whereas protoplasmic astrocytes are found exclusively in the gray matter.
