GLUTAMINERGIC RESPONSES OF NEUROPIL GLIAL-CELLS AND RETZIUS NEURONS IN THE LEECH CENTRAL-NERVOUS-SYSTEM

The effects of glutaminergic agonists on neuropile glial cells and on Retzius neurones in the central nervous system (CNS) of the leech, Hirudo medicinalis were investigated using double-barrelled ion-sensitive microelectrodes. In both types of cells, bath-application of l-glutamate (Glu), kainate (Ka) and quisqualate (Qui) elicited substantial membrane depolarizations which were accompanied by increases of the intracellular Na+ activity aNa i and by concomitant decreases of the intracellular K+ activity aK i. In the glial cells, these alterations of aNa i and aK i were preceded by a transient decrease of aK i upon administration of Ka and Qui. In both glial cells and neurones, N-methyl-d-aspartate (NMDA) did not affect Em, aK i and aNa i. As found for Ka, the neuronal as well as the glial responses to glutaminergic agonists persisted during inhibition of synaptic transmission in high Mg2+, low Ca2+ solutions. The results indicate that leech neuropile glial cells have a Ka/Qui-preferring non-NMDA glutamate receptor similar to that in the Retzius neurones. © 1990.