Dendritic calcium transients in the leech giant glial cell in situ

Glial cells have been shown to respond to neuronal activity with changes in the membrane potential and the intracellular Ca2+ concentration. In order to get closer to glial structures associated with neuronal synapses, we hav e now looked at Ca2+ signalling in the glial processes ("glial dendrites") in response to neurotransmitters and neuronal activity. Single giant glial cells in situ of isolated ganglia of the leech Hirudo medicinalis were fill ed iontophoretically with the Ca2+-sensitive dyes Oregon green 488 BAPTA-1 or Fluo-3. Relative Ca2+-dependent fluorescence changes in response to bath and focal application of the ionotropic glutamate receptor agonist kainate (50 mu M) and of 5-hydroxytryptamine (5-HT, 100 mu M) were recorded in gli al dendrites, using confocal laser scanning microscopy. The amplitudes of t he [Ca2+](i) transients in the dendritic processes were 2-4 times larger th an those recorded in the cell body. Electrical stimulation of a nerve root (20 Hz for 15 s) elicited [Ca2+](i) transients in glial dendrites (n = 32) that were reduced by the ionotropic glutamate receptor antagonist 6-cyano-7 -nitroquinoxaline-2,3-dione (CNQX; n = 14). The results demonstrate that ne uronal activity can evoke [Ca2+](i) transients not only in glial cell bodie s but also in glial dendrites, where these transients display regional vari ation. This may reflect local release of neurotransmitters Like glutamate a nd 5-hydroxytryptamine and/or regional differences in the density of glial receptors. GLIA 26:109-118, 1999. (C) 1999 Wiley-Liss, Inc.