RECEPTOR-MEDIATED CALCIUM SIGNALING IN GLIAL-CELLS FROM MOUSE CORPUS-CALLOSUM SLICES

We addressed the question of whether glial cells in intact white matte r tracts express neurotransmitter receptors and we used Ca++ signallin g as a probe to detect the receptor activation, Corpus callosum slices from postnatal mice were bulk-loaded with the Ca++- sensitive fluores cent dye fluo-3, and confocal microscopy was used to measure Ca++ tran sients in response to neuroligands. Glial cell bodies were intensely d ye-loaded and could be discriminated from the diffuse fluorescence of axons. Subpopulations of glial cells from slices obtained at postnatal days 3 to 7 responded with Ca++ signals to ATP, glutamate, histamine, GABA, norepinephrine, serotonin, angiotensin II, bradykinin, and subs tance P. These subpopulations showed a distinct overlap; cells which w ere responsive to substance P always showed Ca++ signalling in respons e to histamine, ATP, GABA, and high K+ (membrane depolarization). GABA -responsive cells almost always showed a [Ca++](i) increase after memb rane depolarization, In brain slices from postnatal day 11 to 18 anima ls, the Ca++ responses were evident for glutamate, ATP, and norepineph rine, while GABA, substance P, serotonin, histamine, or angiotensin II rarely elicited a response, This study demonstrates that white matter glial cells in slices exhibit a large repertoire of neurotransmitter responses linked to Ca++ signalling and that these receptor systems ar e differentially distributed on subpopulations of glial cells. (C) 199 6 Wiley-Liss, Inc.