title: Pre-synaptic kainate receptor-mediated facilitation of glutamate release involves PKA and Ca(2+) -calmodulin at thalamocortical synapses.
abstract: We have investigated the mechanisms underlying the facilitatory modulation mediated by kainate receptor (KAR) activation in the cortex, using isolated nerve terminals (synaptosomes) and slice preparations. In cortical nerve terminals, kainate (KA, 100 μM) produced an increase in 4-aminopyridine (4-AP)-evoked glutamate release. In thalamocortical slices, KA (1 μM) produced an increase in the amplitude of evoked excitatory post-synaptic currents (eEPSCs) at synapses established between thalamic axon terminals from the ventrobasal nucleus onto stellate neurons of L4 of the somatosensory cortex. In both, synaptosomes and slices, the effect of KA was antagonized by 6-cyano-7-nitroquinoxaline-2,3-dione, and persisted after pre-treatment with a cocktail of antagonists of other receptors whose activation could potentially have produced facilitation of release indirectly. Mechanistically, the observed effects of KA appear to be congruent in synaptosomal and slice preparations. Thus, the facilitation by KA of synaptosomal glutamate release and thalamocortical synaptic transmission were suppressed by the inhibition of protein kinase A and occluded by the stimulation of adenylyl cyclase. Dissecting this G-protein-independent regulation further in thalamocortical slices, the KAR-mediated facilitation of synaptic transmission was found to be sensitive to the block of Ca(2+) permeant KARs by philanthotoxin. Intriguingly, the synaptic facilitation was abrogated by depletion of intracellular Ca(2+) stores by thapsigargin, or inhibition of Ca(2+) -induced Ca(2+) -release by ryanodine. Thus, the KA-mediated modulation was contingent on both Ca(2+) entry through Ca(2+) -permeable KARs and liberation of intracellular Ca(2+) stores. Finally, sensitivity to W-7 indicated that the increased cytosolic [Ca(2+) ] underpinning KAR-mediated regulation of synaptic transmission at thalamocortical synapses, requires downstream activation of calmodulin. We conclude that neocortical pre-synaptic KARs mediate the facilitation of glutamate release and synaptic transmission by a Ca(2+) -calmodulin dependent activation of an adenylyl cyclase/cAMP/protein kinase A signalling cascade, independent of G-protein involvement.
authors.affiliation: Laboratorio de Neurociencia Celular y Plasticidad, Departamento de Fisiología, Anatomía y Biología Celular, Universidad Pablo de Olavide, Sevilla, Spain.
authors.forename: Yuniesky
authors.initials: Y
authors.lastname: Andrade-Talavera
authors.forename: Paloma
authors.initials: P
authors.lastname: Duque-Feria
authors.forename: Talvinder S
authors.initials: TS
authors.lastname: Sihra
authors.forename: Antonio
authors.initials: A
authors.lastname: Rodríguez-Moreno
mesh_terms: D000465:Algorithms; D000818:Animals; D054737:Calcium-Calmodulin-Dependent Protein Kinase Kinase / Q000502:physiology*; D002540:Cerebral Cortex / Q000187:drug effects / Q000502:physiology*; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D003627:Data Interpretation, Statistical; D055724:Electrophysiological Phenomena; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D005971:Glutamates / Q000378:metabolism*; D066298:In Vitro Techniques; D007608:Kainic Acid / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000378:metabolism; D018408:Patch-Clamp Techniques; D018092:Kainic Acid Receptors / Q000187:drug effects / Q000502:physiology*; D017661:Receptors, Presynaptic / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013569:Synapses / Q000502:physiology*; D013574:Synaptosomes / Q000378:metabolism; D013788:Thalamus / Q000187:drug effects / Q000502:physiology*
chemical_list: D054737:Calcium-Calmodulin-Dependent Protein Kinase Kinase; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D018690:Excitatory Amino Acid Agonists; D005971:Glutamates; D007608:Kainic Acid; D018092:Kainic Acid Receptors; D017661:Receptors, Presynaptic
keywords: calcium calmodulin; kainate receptors; pre-synaptic; slices; synaptosomes; thalamocortical