[Communicating junctions of glial cells in the central nervous system]

In the brain, in vivo as in vitro, glial cells represent the main cell population which communicates through intercellular channels forming gap junctions. These cells, and specially the astrocytes, also express a large variety of ionic channels and membrane receptors. The combination of biochemical, immunological and electrophysiological techniques has allowed to determine that connexin 32 is present in oligodendrocytes while connexin 43 is the major junctional protein in astrocytes. The conductance and permeability of gap junctions in astrocytes are controlled by endogenous compounds released from neurons or endothelial cells. This suggests that gap junctional communication in astrocyte networks exhibits some degree of plasticity and are under the control of other brain cell populations. The expression of connexins and the regulation of junctional permeability in astrocytes may contribute to several glial functions such as intercellular calcium signalling and metabolic trafficking within the brain.