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Glutamate is concentrated in and released from parallel fiber terminals in the dorsal cochlear nucleus: A quantitative immunocytochemical analysis in guinea pig
Author(s) -
Osen Kirsten K.,
StormMathisen Jon,
Ottersen Ole Petter,
Dihle Beate
Publication year - 1995
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.903570311
Subject(s) - glutamate receptor , immunolabeling , biology , neurotransmitter , parallel fiber , synaptic vesicle , dorsal cochlear nucleus , biophysics , cochlear nucleus , neuroscience , glutamatergic , neurotransmission , colocalization , immunogold labelling , microbiology and biotechnology , biochemistry , brainstem , anatomy , excitatory postsynaptic potential , ultrastructure , vesicle , central nervous system , inhibitory postsynaptic potential , immunohistochemistry , membrane , receptor , immunology
Abstract The present paper addresses the identity of the neurotransmitter(s) of the parallel fibers in the molecular layer of the dorsal cochlear nucleus, A brainstem center in the pathway for sound perception. The distribution of putative neurotransmitter amino acids was studied by using postembedding single‐ and double‐immunolabeling procedures. Perfusion‐fixed brains and immersion‐fixed slices from in vitro release experiments were evaluated. Quantitative immunogold analyses revealed that the parallel fiber terminals were significantly enriched with glutamate immunoreactivity compared with other terminals, dendrites, and glial processes. Within the parallel fiber terminals, the gold particles signaling the presence of glutamate were concentrated over vesicle clusters relative to the axoplasmic matrix. Furthermore, the parallel fiber terminals, but not the parent granule cell bodies, could be depleted of glutamate immunoreactivity by exposure to depolarizing concentrations of K + in vitro. This depletion was partly dependent on Ca 2+ In double‐labeled preparations, the glutamine:glutamate ratio was by far higher in glial processes than in other types of profile. Aspartate immunoreactivity was mainly concentrated in neuronal cell bodies and dendrites and was very low in fiber terminals, particularly in those of the parallel fibers. These data indicate that parallel fiber terminals contain a glutamate pool that is associated with synaptic vesicles and that can be subject to release. The glial processes that are found in proximity to the terminals may provide them with the glutamine required for glutamate replenishment. No evidence was found for a neurotransmitter role of aspartate in the parallel fibers. © 1995 Wiley‐Liss, Inc.