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

Copyrightę The Japanese Pharmacological Society 1996

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