Jpn. J. Pharmacol. 72, 335-346 (1996)
Electrophysiological and Pharmacological Characteristics of Ionotropic
Glutamate Receptors in Medial Vestibular Nucleus Neurons: A Whole Cell Patch
Clamp Study in Acutely Dissociated Neurons
Norio Sakai (1), Hisamitsu Ujihara (2), Kumatoshi Ishihara (3), Masashi
Sasa (3) and Chikako Tanaka (4)
(1) Laboratory of Molecular Pharmacology, Biosignal Research Center,
Kobe University, Kobe 658, Japan
(2) Department of Psychiatry, Kohchi Medical School, Kohchi 783, Japan
(3) Department of Pharmacology, Hiroshima University School of Medicine,
Hiroshima 734, Japan
(4) Hyogo Institute for Aging Brain and Cognitive Disorders, Himeji 670,
Japan
Abstract: A patch clamp study was performed to determine which
subtype of ionotropic glutamate receptors is involved in the glutamate-induced
excitation of the medial vestibular nucleus (MVN) neurons. Whole cell recording
was performed on MVN neurons that were acutely dissociated by enzymatic
and mechanical treatments. Application of glutamate at a concentration of
100 microM produced a current with a reversal potential of approximately
0 mV. The glutamate-induced current was completely blocked by 6-cyano-7-nitroquinoxaline-2,3-dione
(CNQX, 10 microM), a non-N-methyl-D-aspartate (NMDA)-receptor antagonist.
Application of alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid
(AMPA) and kainic acid (KA), non-NMDA-receptor agonists, at concentrations
of 30 and 100 microM produced a concentration-dependent depolarization concomitantly
with an increase in firing rates during current clamp recording. During
voltage clamp recording, glutamate, AMPA and KA elicited a concentration-dependent
current with an equilibrium potential of approximately 0 mV. To clarify
whether NMDA receptors are present in MVN neurons, the effects of glycine
on the glutamate- and NMDA-induced current were examined. Two types of NMDA
receptor-mediated current (types 1 and 2) were obtained in terms of the
difference in sensitivity to both magnesium ion and MK-801, which act on
the NMDA-receptor channel. In the type 1 neurons, the NMDA-induced current
was not apparently blocked by magnesium ion or MK-801, although a larger
current was obtained in the absence of magnesium ion. In the type 2 neurons,
marked blockade of the NMDA-induced current was seen in the presence of
magnesium ion and MK-801, as previously reported in other neurons of the
central nervous system. These findings indicate the presence of both non-NMDA
and NMDA receptors, which are involved in primary afferent transmission,
in the MVN neuron, and two distinct types of NMDA receptors.
Keywords: Medial vestibular nucleus, Patch clamp, Acutely dissociated
neuron, Non-NMDA receptor, NMDA receptor
Copyright© The Japanese Pharmacological Society 1996
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