Synaptic Transmission with the Glia

Glia are the most numerous cells in the central nervous system, with well-established roles in providing structural, metabolic, and trophic support to neurons. However, the classic view that glial cells are subservient to neurons has been challenged by recent findings indicating that perisynaptic glial cells (such as astrocytes and oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system) can be recruited for neurotransmission and exert a modulatory action on synaptic function. This new vision of “tripartite synapses,” composed of perisynaptic glia in addition to pre- and postsynaptic terminals (1, 5), certainly makes this one of the most exciting discoveries in current neurobiology. This review will focus mainly on the rapid reciprocal communication between neurons and glia involving glutamate as the signaling molecule. However, this form of communication does not appear to be restricted to glutamatergic districts and may imply the release of transmitters other than glutamate from either the neurons or the glia (11).