Publisher Summary There is evidence that two pathways of intercellular transfer of molecules between neurons and glial cells are quantitatively predominant in the mammalian brain. The first is the route, still unproven in the brain itself, but compatible with many experimental results, that transfers carbon fuel, starting as glucose in the capillaries, through astrocytes to neurons. This chapter discusses the main arguments in favor of its existence, most of which concern the role of lactate in aerobic metabolism and its possible transfer from astrocytes to neurons. The second pathway is the transfer of glutamate from neurons to astrocytes, and the transfer of glutamine in the opposite direction. For the glutamate-glutamine shuttle, the chapter concentrates on an apparent corollary of it, transfer of ammonium from neurons to astrocytes, which clearly falls within the concept of volume transmission.