Distribution and Functional Properties of Glutamate Receptors in the Leech
Central Nervous System.
Dierkes, Paul Wilhelm, Peter Hochstrate, and Wolf-R[umlaut]udiger Schlue.
Institut f[umlaut]ur Neurobiologie, Heinrich-Heine-Universit[umlaut]at
D[umlaut]usseldorf, 40225 D[umlaut]usseldorf, Germany.
APStracts 2:0013N, 1996.
SUMMARY AND CONCLUSIONS
1. The effect of kainate and other glutamatergic agonists on the membrane
potential (E m ), the intracellular Na + activity (aNa i ) and the
intracellular free Ca 2+ concentration ([Ca 2+ ] i ) of identified leech
neurons and neuropile glial cells was measured with conventional and ion-
sensitive microelectrodes, as well as by the use of the iontophoretically
injected fluorescent indicators SBFI and Fura-2. 2. In Retzius neurons, AE, L,
8 and 101 motoneurons, and in the unclassified 50 neurons (Leydig cells) and
AP neurons, as well as in neuropile glial cells, bath application of 100 [mu]M
kainate evoked a marked membrane depolarization and an increase in aNa i and
[Ca 2+ ] i . The kainate-induced aNa i increase persisted in solutions with
high Mg 2+ concentration in which synaptic transmission is blocked. 3. A
membrane depolarization as well as an increase in aNa i and [Ca 2+ ] i was
also evoked by L-glutamate, quisqualate and L- [alpha] -amino-3-hydroxy-5-
methyl-4-isoxazolepropionate (AMPA). The agonist-induced [Ca 2+ ] i increase
was inhibited by 6,7-dinitroquinoxaline-2,3-dione (DNQX). 4. In Ca 2+ -free
solution, the kainate-induced [Ca 2+ ] i increase was abolished in the neurons
and in neuropile glial cells, whereas membrane depolarization and aNa i
increase were unchanged. In Na + -free solution, kainate had no effect on E m
, aNa i or [Ca 2+ ] i in the neurons. 5. In the mechanosensory T, P and N
neurons, kainate induced considerably smaller membrane depolarizations than in
the other neurons or in neuropile glial cells, and it had no significant
effect on aNa i or [Ca 2+ ] i . 6. It is concluded that in leech segmental
ganglia the majority of the neurons and the neuropile glial cells, but
probably not the mechanosensory neurons, possess glutamate receptors of the
AMPA-kainate type. In the neurons, the [Ca 2+ ] i increase caused by
glutamatergic agonists is due to Ca 2+ influx through voltage-dependent Ca 2+
channels which are activated by the agonist-induced membrane depolarization.
Received 14 February 1995; accepted in final form 5 December 1995.
APS Manuscript Number J103-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96