Abstract
Most of the pre- and postsynaptic structures in the central nervous system are in close apposition to astrocytic processes, making it likely that the molecules expressed on the perisynaptic membranes mediate communication between neurons and astrocytes. In the nucleus of the solitary tract (NTS), extracellular ATP activates presynaptic P2X receptor channels (P2X), the Ca2+ entry through which facilitates glutamate release and initiates synaptic transmission in the absence of action potentials (Kato & Shigetomi, 2001; Shigetomi & Kato, 2004). Our hypothesis is that these presynaptic P2X receptors mediate the presynaptic action of the gliotransmitter ATP released from "synaptic processes" of the astrocytes. Immunohistochemical and electron microscopic analyses revealed a large number of GFAP-positive astrocyte processes surrounding NTS neurons and in close appositions of astrocyte processes and the presynaptic structures. Application of ATP in the vicinity of dendritic synapses in time- (–hundreds milliseconds) and space- (3 micrometers) delimited manners using laser-based photolysis of caged ATP in the brainstem slices resulted in an immediate release of glutamate. In a subset of small NTS neurons showing high-frequency spontaneous miniature EPSCs (mEPSCs), perturbation of glial ATP production with fluoroacetate immediately resulted in a sustained decrease in the mEPSC frequency. These data argue for a potential role of presynaptic P2X-Rs as an interface between astrocyte-derived ATP and initiation of the synaptic transmission without presynaptic excitation. Supported by MEXT, Japan 17300123 & 18053022. [J Physiol Sci. 2007;57 Suppl:S10]
