Signalling Between Neuronal and Glial Cells

Abstract

The maintenance of normal nervous system function appears to involve continuous communication between neurons and their associated cells, the neuroglia. Many possible mechanisms exist for the transfer of information between the two cell types which are separated only by narrow, 200A wide, extracellular clefts. There is increasing evidence that several of these are used. These include: 1) Activity in one cell varies the ionic composition of the extracellular cleft and this change is detected by the other cell. The release of K+ from neurons to depolarize glia is one such example. 2) Neurotransmitter agents, including amino acids and their derivatives, biogenic amines and peptides, used in neuronal signalling also act at membrane or intracellular loci of the nearby glial cells and alter their metabolism. 3) Macromolecules, especially proteins, are exchanged between the cells by phagocytosis or a combination of exocytosis and endocytosis. The accumulation in the extracellular clefts of some substances released from neurons serves as a signal to the glial cells to clear that substance from the extracellular space and maintain the constancy of the extracellular fluid. Although there is evidence for other functional interactions between the cells, for the most part the specific signalling processes are poorly defined and their physiological significance obscure.