Neuron-glia cross talk revealed in reverberating networks by simultaneous extracellular recording of spikes and astrocytes’ glutamate transporter and K+ currents

Abstract

Astrocytes uptake synaptically released glutamate with electrogenic transporters (GluT) and buffer the spike-dependent extracellular K+ excess with back-ground K+ channels. We studied neuronal spikes and the slower astrocytic signals on reverberating neocortical cultures and organo-typic slices from mouse brains. Spike trains and glial responses were simultaneously captured from individual sites of multielectrode arrays (MEA) by splitting the recorded traces into appropriate filters and reconstructing the original signal by deconvolution. GluT currents were identified by using DL-threo-β-benzyloxyaspartate (TBOA). K+ currents were blocked by 30 μM Ba2+, suggesting a major contribu-tion of inwardly rectifying K+ currents. Both types of current were tightly correlated with the spike rate, and their astrocytic origin was tested in primary cultures by blocking glial proliferation with cytosine β-D-arabinofuranoside (AraC). The spike-related, time-locked inward and outward K+ currents in different regions of the astrocyte syncy-tium were consistent with the assumptions of the spatial K+ buffering model. In organotypic slices from ventral tegmental area and prefron-tal cortex, the GluT current amplitudes exceeded those observed in primary cultures by several orders of magnitude, which allowed to directly measure transporter currents with a single electrode. Simul-taneously measuring cell signals displaying widely different ampli-tudes and kinetics will help clarify the neuron-glia interplay and make it possible to follow the cross talk between different cell types in excitable as well as nonexcitable tissue.