GFAP-POSITIVE HIPPOCAMPAL ASTROCYTES IN-SITU RESPOND TO GLUTAMATERGICNEUROLIGANDS WITH INCREASES IN [CA2+]

It is becoming increasingly clear that astrocytes play very dynamic an d interactive roles that are important for the normal functioning of t he central nervous system. In culture, astrocytes express many recepto rs coupled to increases in intracellular calcium ([Ca2+](i)). In vivo, it is likely that these receptors are important for the modulation of astrocytic functions such as the uptake of neurotransmitters and ions . Currently, however, very little is known about the expression or sti mulation of such astrocytic receptors in vivo. To address this issue, confocal microscopy and calcium-sensitive fluorescent dyes were used t o examine the dynamic changes in astrocytic [Ca2+](i) within acutely i solated hippocampal slices. Astrocytes were subsequently identified by immunocytochemistry for glial fibrillary acidic protein. In this pape r, we present data indicating that hippocampal astrocytes in situ resp ond to glutamate, kainate, lpha-amino-3-hydroxy-5-methylisoxazole-4-pr opionic acid (AMPA), 1-aminocyclopentane-trans-1,3-dicarboxylic acid ( t-ACPD), N-methyl-D-aspartate (NMDA), and depolarization with increase s in [Ca2+](i). The increases in [Ca2+](i) occurred in both the astroc ytic cell bodies and the processes. Temporally the changes in [Ca2+](i ) were very dynamic, and various patterns ranging from sustained eleva tions to oscillations of [Ca2+](i) were observed. Individual astrocyte s responded to neuroligands selective for both ionotropic and metabotr opic glutamate receptors with increases in [Ca2+](i). These findings i ndicate that astrocytes in vivo contain glutamatergic receptors couple d to increases in [Ca2+](i) and are able to respond to neuronally rele ased neurotransmitters. (C) 1995 Wiley-Liss, Inc.