WE have measured activity-induced Ca2+ transients in Retzius neurones,
neuropile glial cells, and extracellular spaces of isolated ganglia o
f the leech Hirudo medicinalis using the fluorescent dye fura-2 and Ca
2+-sensitive microelectrodes. Neuronal activity, induced by electrical
side nerve stimulation (20 Hz/1 min), elicited transient rises of int
racellular Ca2+ in both neurones and glial cells, which amounted to 24
+/- 14 nM (n = 15) and 17 +/- 14 nM (n = 7), respectively. The extrac
ellular Ca2+ declined by 160 +/- 73 mu M (n = 6) during stimulation. I
ntra- and extracellular Ca2+ transients were reduced by the glutamate/
kainate receptor blocker CNQX (6-cyano-7-dinitroquinozaline-2,3-dione;
50 mu M). Our results show that neuronal activity evokes Ca2+ signals
not only in neurones, but also in glial cells and suggest that these
Ca2+ transients are partly mediated via activation of glutamate/kainat
e receptors.