Glutaminergic responses of neuropile glial cells and Retzius neurones 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 aiNa and by concomitant decrease of the intracellular K+ activity aiK. In the glial cells, these alterations of aiNa and aiK were preceded by a transient decrease of aiNa and an increase of aiK upon administration of Ka and Qui. In both glial cells and neurones, N-methyl-D-aspartate (NMDA) did not affect Em, aiK and aiNa. 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.