Gap junctions in the brain: where, what type, how many and why?

Gap junctions represent well-documented means of intercellular communication in various tissues, including the brain, where they function as portals allowing the exchange of electrolytes, second messengers and metabolites between cells. In view of the enormous recent surge of information dealing with the cellular and molecular biology of gap junctions in non-nervous tissue, as well as current interest in the cell biology of glia, this review is intended to provide an overview of the molecular and functional implications of gap-junction-mediated intercellular communication in the nervous system.