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 ear ly 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, rathe r than a cluster of cells. Electron microscopy revealed that gap junct ions were abundant in the distal parts of the processes. Gap junctions between cell bodies and processes were very rare, and no gap junction s 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%. Activa tion of AMPA receptors induced a blockade of the junctional conductanc e to 30% of the control. This link is most likely mediated by the infl ux of Ca2+ via the receptor since this effect was not observed in Ca2-free medium, suggesting that Ca2+ entry via the kainate receptor pore led to the closure of gap junctions. These studies indicate that elec trical coupling between Bergmann glial cells is not only developmental ly regulated but also controlled by physiological stimuli. (C) 1996 Wi ley-Liss, Inc.