Regional heterogeneity among astrocytes in the central nervous system

Previously assumed as passive structural and metabolic support elements for the neurons, astrocytes are now considered to have key roles in normal physiology, in brain development and in the pathology of the nervous system. Using culture techniques it has been demonstrated that astroglia express receptors functionally coupled to second messenger systems, previously thought to be exclusively localized to neurons. Furthermore, the cells possess uptake carriers for amino acid neurotransmitters and enzyme systems for inactivation of several neurotransmitters. They can also regulate the extracellular ionic milieu including a clearing of K(+) from the extracellular space. With these specific functional characteristics and their strategic anatomy the cells might influence the passage of information between neurons. Data are accumulating that astrocytes are a heterogeneous class of cells both in terms of morphology, surface properties and in their distribution within the central nervous system. Taking such a heterogeneity into account, especially with respect to the expression of membrane receptors astroglia may be able to respond selectively to changes in their humoral environment which may provide new therapeutic approaches. In this acticle some data are presented, predominantly from experiments on primary cultures, on astroglial heterogeneity. Functional implications of such a heterogeneity are discussed.