Electrical coupling among Bergmann glial cells and its modulation by glutamate receptor activation

We studied the characteristics of electrical coupling between Bergmann glial cells in mouse cerebellar slices using Lucifer Yellow injection, patch-clamping cell pairs, and ultrastructural inspection. While early postnatal cells (days 5-7) were not coupled, coupling was abundant at postnatal days 20-24. Coupled cells were arranged perpendicular to the parallel fibers in a parasagittal section, forming a string, rather than a cluster of cells. Electron microscopy revealed that gap junctions were abundant in the distal parts of the processes. Gap junctions between cell bodies and processes were very rare, and no gap junctions were found between cell bodies of adjacent Bergmann glial cells. The junctional conductance was voltage and time independent and could be markedly reduced by halothane. Alkalization of cells (by applying NH4+) increased the junctional conductance to 150%, while acidification of the cell interior (by removing NH4+) led to a decrease to 70%. Activation of AMPA receptors induced a blockade of the junctional conductance to 30% of the control. This link is most likely mediated by the influx of Ca2+ via the receptor since this effect was not observed in Ca(2+)-free medium, suggesting that Ca2+ entry via the kainate receptor pore led to the closure of gap junctions. These studies indicate that electrical coupling between Bergmann glial cells is not only developmentally regulated but also controlled by physiological stimuli.