Activity-induced Ca2+ transients in nerve and glial cells in the leech CNS

We have measured activity-induced Ca2+ transients in Retzius neurones, neuropile glial cells, and extracellular spaces of isolated ganglia of 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 intracellular Ca2+ in both neurones and glial cells, which amounted to 24 +/- nM (n = 15) and 17 +/- 14 nM (n = 7), respectively. The extracellular Ca2+ declined by 160 +/- 73 microM (n = 6) during stimulation. Intra- and extracellular Ca2+ transients were reduced by the glutamate/kainate receptor blocker CNQX (6-cyano-7-dinitroquinozaline-2,3-dione; 50 microM). 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/kainate receptors.