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Depression of GABAergic input to identified hippocampal neurons by group III metabotropic glutamate receptors in the rat
Author(s) -
Kogo Naoki,
Dalezios Yannis,
Capogna Marco,
Ferraguti Francesco,
Shigemoto Ryuichi,
Somogyi Peter
Publication year - 2004
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/j.0953-816x.2004.03394.x
Subject(s) - metabotropic glutamate receptor , gabaergic , neuroscience , hippocampal formation , glutamate receptor , metabotropic receptor , inhibitory postsynaptic potential , pyramidal cell , excitatory postsynaptic potential , biology , chemistry , receptor , biochemistry
The release of GABA in synapses is modulated by presynaptic metabotropic glutamate receptors (mGluRs). We tested whether GABA release to identified hippocampal neurons is influenced by group III mGluR activation using the agonist L‐(+)‐2‐amino‐4‐phosphonobutyric acid (L‐AP4) on inhibitory postsynaptic currents (IPSCs) evoked in CA1 interneurons and pyramidal cells. In interneurons, characterized with biocytin and immunolabelling for somatostatin, evoked IPSCs were depressed by 50 µ m L‐AP4 (activating mGluR4 and 8) to 68 ± 6% of control, but they were rarely depressed in pyramidal cells (96 ± 4% of control). At 300–500 µ m concentration (activating mGluR4, 7 and 8), L‐AP4 depressed IPSCs in both interneurons (to 70 ± 6%) and pyramidal cells (to 67 ± 4%). The change in trial‐to‐trial variability and in paired‐pulse depression indicated a presynaptic action. In interneurons, the degree of IPSC depression was variable (to 9–87%), and a third of IPSCs were not affected by L‐AP4. The L‐AP4‐evoked IPSC depression was blocked by LY341495. The depression of IPSCs was similar in O‐LM cells and other interneurons. The lack of cell‐type selectivity and the similar efficacy of different concentrations of L‐AP4 suggest that several group III mGluRs are involved in the depression of IPSCs. Electron microscopic immunocytochemistry confirmed that mGluR4, mGluR7a and mGluR8a occur in the presynaptic active zone of GABAergic terminals on interneurons, but not on those innervating pyramidal cells. The high variability of L‐AP4‐evoked IPSC suppression is in line with the selective expression of presynaptic mGluRs by several distinct types of GABAergic neuron innervating each interneuron type.