PMID- 2850617
OWN - NLM
STAT- MEDLINE
DCOM- 19890221
LR  - 20141120
IS  - 0887-4476 (Print)
IS  - 0887-4476 (Linking)
VI  - 1
IP  - 1
DP  - 1987
TI  - Pharmacological aspects of excitatory synaptic transmission to second-order 
      vestibular neurons in the frog.
PG  - 102-23
AB  - Synaptic excitation of second-order vestibular neurons is mediated by two 
      principal afferents: vestibular afferents projecting into the brain via the 
      VIIIth cranial nerve and commissural afferents from the contralateral vestibular 
      nuclear complex. The shape of the excitatory postsynaptic potentials (EPSPs) 
      generated by selectively activating these two inputs differs qualitatively, such 
      that ipsilateral VIIIth nerve afferents generate a faster-rising EPSP than do the 
      commissural afferents. We have investigated the synaptic pharmacology of these 
      two inputs in the isolated, intact medulla of the frog in order to determine the 
      nature of the transmitter substances released by the afferents and the nature of 
      the subsynaptic receptors with which these transmitters interact. Electrical 
      stimulation of the ipsilateral VIIIth cranial nerve evokes in the region of the 
      vestibular nuclear complex a field potential that exhibits a presynaptic 
      (afferent volley) and a postsynaptic (slow negativity) component. Bath 
      application of glutamate receptor antagonists, such as kynurenic acid (KENYA), 
      blocks the postsynaptic component of this field potential in a dose-dependent 
      manner, without affecting the presynaptic volley, suggesting that the VIIIth 
      nerve afferent releases glutamate and/or similar substances as its 
      neurotransmitter. A comparison of the actions of various glutamate receptor 
      antagonists to block this postsynaptic negativity gives a rank order of 
      effectiveness such that KENYA greater than gamma-D-glutamylglycine (gamma DGG) = 
      gamma-D-glutamylaminomethylsulfonic acid (GAMS) greater than 
      gamma-D-glutamyltaurine (gamma DGT) much greater than 
      gamma-D-glutamylaminomethylphosphonic acid (GAMP) greater than 
      D-2-amino-5-phosphonovaleric acid (D-APV) greater than D,L-APV greater than 
      D-2-amino-7-phosphonoheptanoic acid (APH). This rank order of effectiveness 
      suggests that the VIIIth nerve transmitter activates second-order neurons through 
      kainate (KA)/quisqualate (QUIS) synaptic receptors. Intracellular studies support 
      these conclusions. Chemically mediated EPSPs evoked from ipsilateral VIIIth nerve 
      stimulation are completely blocked by high concentrations of KENYA (greater than 
      or equal to 1 mM). Occasionally an extremely short-latency, probably electrically 
      mediated, component to these EPSPs persists in the presence of KENYA. The 
      slower-rising EPSPs evoked from contralateral VIIIth nerve or contralateral 
      vestibular nuclear complex stimulation are also completely blocked by KENYA, 
      suggesting that the transmitter released by the commissural afferents is also 
      glutamate and/or related compounds.(ABSTRACT TRUNCATED AT 400 WORDS)
FAU - Cochran, S L
AU  - Cochran SL
AD  - Brain Research Institute, University of Zurich, Switzerland.
FAU - Kasik, P
AU  - Kasik P
FAU - Precht, W
AU  - Precht W
LA  - eng
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
PT  - Research Support, U.S. Gov't, Non-P.H.S.
PL  - United States
TA  - Synapse
JT  - Synapse (New York, N.Y.)
JID - 8806914
RN  - 0 (Glutamates)
RN  - 0 (Receptors, Glutamate)
RN  - 0 (Receptors, Neurotransmitter)
RN  - H030S2S85J (Kynurenic Acid)
SB  - IM
MH  - Animals
MH  - Ear, Inner/physiology
MH  - Electric Stimulation
MH  - Evoked Potentials/drug effects
MH  - Functional Laterality
MH  - Glutamates/*pharmacology
MH  - In Vitro Techniques
MH  - Kynurenic Acid/pharmacology
MH  - Neurons/drug effects/*physiology
MH  - Rana temporaria
MH  - Receptors, Glutamate
MH  - Receptors, Neurotransmitter/drug effects/physiology
MH  - Synapses/drug effects/*physiology
MH  - Synaptic Transmission/*drug effects
MH  - Vestibule, Labyrinth/*innervation
MH  - Vestibulocochlear Nerve/*physiology
EDAT- 1987/01/01 00:00
MHDA- 1987/01/01 00:01
CRDT- 1987/01/01 00:00
PHST- 1987/01/01 00:00 [pubmed]
PHST- 1987/01/01 00:01 [medline]
PHST- 1987/01/01 00:00 [entrez]
AID - 10.1002/syn.890010114 [doi]
PST - ppublish
SO  - Synapse. 1987;1(1):102-23. doi: 10.1002/syn.890010114.