ACTIVITY-INDUCED CA2-CELLS IN THE LEECH CNS( TRANSIENTS IN NERVE AND GLIAL)

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.