Abstract
Neural-glial communication has been assumed to be mediated by spillover of transmitter from the synaptic cleft. In the cerebellum, Bergmann glia cell (BG) processes encase synapses between presynaptic climbing fiber (CF) and parallel fiber elements and postsynaptic Purkinje cell (PC) spines and glutamate released from these fibers can activate Ca2+-permeable AMPA receptors on BGs. Quantal responses recorded from BGs were not coincident with quantal responses recorded in adjacent PCs sharing the same CF input. By combining electrophysiological recordings and quantitative immunogold electron microscopic analysis, high-concentration (1.5 mM) rapid-transients (0.5 ms) of glutamate were estimated to underlie BG quantal events. We propose that exocytosis can occur from ectopic release sites located directly across from BG membranes. Ectopic release may be necessary to activate low affinity AMPA receptors on BGs, which may provide a geographical cue to guide BG membrane to surround active synapses and ensure efficient glutamate uptake. We have recently started to employ two-photon microscopy to study the result of such neural-glial communication. Morphological refinement of BG processes occurs within a few days in early development and rapid motility and spontaneous remodeling of extracellular space by BG protrusions were observed in minutes. Synaptic activation leads to Ca2+ influx at the tip of the protrusions via Ca2+-permeable AMPA receptors. We are currently probing the mechanisms that manipulate the motility and refinement of BG processes and their effect on synaptic transmission. [J Physiol Sci. 2006;56 Suppl:S45]
