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GABAergic Terminals (gabaergic + terminal)
Selected AbstractsGABAergic modulation of primary gustatory afferent synaptic efficacyDEVELOPMENTAL NEUROBIOLOGY, Issue 2 2002Andrew A. Sharp Abstract Modulation of synaptic transmission at the primary sensory afferent synapse is well documented for the somatosensory and olfactory systems. The present study was undertaken to test whether GABA impacts on transmission of gustatory information at the primary afferent synapse. In goldfish, the vagal gustatory input terminates in a laminated structure, the vagal lobes, whose sensory layers are homologous to the mammalian nucleus of the solitary tract. We relied on immunoreactivity for the GABA-transporter, GAT-1, to determine the distribution of GABAergic synapses in the vagal lobe. Immunocytochemistry showed dense, punctate GAT-1 immunoreactivity coincident with the layers of termination of primary afferent fibers. The laminar nature and polarized dendritic structure of the vagal lobe make it amenable to an in vitro slice preparation to study early synaptic events in the transmission of gustatory input. Electrical stimulation of the gustatory nerves in vitro produces synaptic field potentials (fEPSPs) predominantly mediated by ionotropic glutamate receptors. Bath application of either the GABAA receptor agonist muscimol or the GABAB receptor agonist baclofen caused a nearly complete suppression of the primary fEPSP. Coapplication of the appropriate GABAA or GABAB receptor antagonist bicuculline or CGP-55845 significantly reversed the effects of the agonists. These data indicate that GABAergic terminals situated in proximity to primary gustatory afferent terminals can modulate primary afferent input via both GABAA and GABAB receptors. The mechanism of action of GABAB receptors suggests a presynaptic locus of action for that receptor. © 2002 Wiley Periodicals, Inc. J Neurobiol 52: 133,143, 2002 [source] Presynaptic diadenosine polyphosphate receptors: Interaction with other neurotransmitter systemsDRUG DEVELOPMENT RESEARCH, Issue 1-2 2001M. Teresa Miras-Portugal Abstract Diadenosine polyphosphates (ApnA n = 2,6) are natural compounds that can play a neurotransmitter role in the synaptic terminals of the central nervous system. Microfluorimetric studies of [Ca2+]i in single synaptic terminals have shown the presence of specific ionotropic receptors for nucleotides and dinucleotides. These dinucleotide receptors may or may not coexist at the same terminal. Aminergic terminals from rat basal ganglia have been immunologically characterised by the presence of the vesicular monoamine transporter 2 after the functional studies. Fifty-eight percent of these terminals respond to nucleotides, and of these, 17% respond only to Ap5A. Cholinergic terminals from rat midbrain were immunologically characterised by the vesicular acetylcholine transporter. Sixty-three percent of these terminals responded to nucleotides, and of these, 22% responded only to Ap5A. The presynaptic ionotropic dinucleotide receptors can coexist not only with the ATP receptors, but also with various subtypes of nicotinic receptors. GABAergic terminals from rat midbrain were immunologically characterised by the vesicular inhibitory amino acid transporter. Fifty-nine percent of these terminals responded to nucleotides, and of these, 17% responded only to Ap5A. The presynaptic dinucleotide receptors, when stimulated, are able to induce the GABA release from synaptosomal preparations. These data clearly show the broad interaction of nucleotides and dinucleotides with other neurotransmitter systems. Drug Dev. Res. 52:239,248, 2001. © 2001 Wiley-Liss, Inc. [source] High level of mGluR7 in the presynaptic active zones of select populations of GABAergic terminals innervating interneurons in the rat hippocampusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2003Peter Somogyi Abstract The release of neurotransmitters is modulated by presynaptic metabotropic glutamate receptors (mGluRs), which show a highly selective expression and subcellular location in glutamatergic terminals in the hippocampus. Using immunocytochemistry, we investigated whether one of the receptors, mGluR7, whose level of expression is governed by the postsynaptic target, was present in GABAergic terminals and whether such terminals targeted particular cells. A total of 165 interneuron dendritic profiles receiving 466 synapses (82% mGluR7a-positive) were analysed. The presynaptic active zones of most GAD-(77%) or GABA-positive (94%) synaptic boutons on interneurons innervated by mGluR7a-enriched glutamatergic terminals (mGluR7a-decorated) were immunopositive for mGluR7a. GABAergic terminals on pyramidal cells and most other interneurons in str. oriens were mGluR7a-immunonegative. The mGluR7a-decorated cells were mostly somatostatin- and mGluR1,-immunopositive neurons in str. oriens and the alveus. Their GABAergic input mainly originated from VIP-positive terminals, 90% of which expressed high levels of mGluR7a in the presynaptic active zone. Parvalbumin-positive synaptic terminals were rare on mGluR7a-decorated cells, but on these neurons 73% of them were mGluR7a-immunopositive. Some type II synapses innervating interneurons were immunopositive for mGluR7b, as were some type I synapses. Because not all target cells of VIP-positive neurons are known it has not been possible to determine whether mGluR7 is expressed in a target-cell-specific manner in the terminals of single GABAergic cells. The activation of mGluR7 may decrease GABA release to mGluR7-decorated cells at times of high pyramidal cell activity, which elevates extracellular glutamate levels. Alternatively, the presynaptic receptor may be activated by as yet unidentified endogenous ligands released by the GABAergic terminals or the postsynaptic dendrites. [source] Selective GABAergic innervation of thalamic nuclei from zona incertaEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2002P. Barthó Abstract Thalamocortical circuits that govern cortical rhythms and ultimately effect sensory transmission consist of three major interconnected elements: excitatory thalamocortical and corticothalamic neurons and GABAergic cells in the reticular thalamic nucleus. Based on the present results, a fourth component has to be added to this scheme. GABAergic fibres from an extrareticular diencephalic source were found to selectively innervate relay cells located mainly in higher-order thalamic nuclei. The origin of this pathway was localized to zona incerta (ZI), known to receive collaterals from corticothalamic fibres. First-order nuclei were innervated only in zones showing a high density of calbindin-positive neurons. The large GABA-immunoreactive incertal terminals established multiple contacts preferentially on the proximal dendrites of relay cells via symmetrical synapses with multiple release sites. The distribution, ultrastructural characteristics and postsynaptic target selection of extrareticular terminals were similar to type II muscarinic acetylcholine receptor-positive boutons, which constituted up to 49% of all GABAergic terminals in the posterior nucleus. This suggests that a significant proportion of the GABAergic input into certain thalamic territories involved in higher-order functions may have extrareticular origin. Unlike the reticular nucleus, ZI receives peripheral and layer V cortical input but no thalamic feedback; it projects to brainstem centres and has extensive intranuclear recurrent collaterals. This indicates that ZI exerts a conceptually new type of inhibitory control over the thalamus. The proximally situated, multiple active zones of ZI terminals indicate a powerful influence on the firing properties of thalamic neurons, which is conveyed to multiple cortical areas via relay cells which have widespread projections to neocortex. [source] GAT-1 regulates both tonic and phasic GABAA receptor-mediated inhibition in the cerebral cortexJOURNAL OF NEUROCHEMISTRY, Issue 5 2008Luca Bragina Abstract ,-Aminobutyric acid 1 (GAT-1) is the most copiously expressed GABA transporter; we studied its role in phasic and tonic inhibition in the neocortex using GAT-1 knockout (KO) mice. Immunoblotting and immunocytochemical studies showed that GAT-2 and GAT-3 levels in KOs were unchanged and that GAT-3 was not redistributed in KOs. Moreover, the expression of GAD65/67 was increased, whereas that of GABA or VGAT was unchanged. Microdialysis studies showed that in KOs spontaneous extracellular release of GABA and glutamate was comparable in WT and KO mice, whereas KCl-evoked output of GABA, but not of glutamate, was significantly increased in KOs. Recordings from layer II/III pyramids revealed a significant increase in GABAAR-mediated tonic conductance in KO mice. The frequency, amplitude and kinetics of spontaneous inhibitory post-synaptic currents (IPSCs) were unchanged, whereas the decay time of evoked IPSCs was significantly prolonged in KO mice. In KO mice, high frequency stimulation of GABAergic terminals induced large GABAAR-mediated inward currents associated with a reduction in amplitude and decay time of IPSCs evoked immediately after the train. The recovery process was slower in KO than in WT mice. These studies show that in the cerebral cortex of GAT-1 KO mice GAT-3 is not redistributed and GADs are adaptively changed and indicate that GAT-1 has a prominent role in both tonic and phasic GABAAR-mediated inhibition, in particular during sustained neuronal activity. [source] | ||||||||||