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AMPA receptor modulation in previously frozen mouse brain sections: Opposite effects of calcium in the cortex and hippocampus
Author(s) -
Lapierre Luc,
Valastro Barbara,
Miceli Dom,
Massicotte Guy
Publication year - 2000
Publication title -
hippocampus
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.767
H-Index - 155
eISSN - 1098-1063
pISSN - 1050-9631
DOI - 10.1002/1098-1063(2000)10:6<645::aid-hipo1002>3.0.co;2-u
Subject(s) - ampa receptor , chemistry , glutamate receptor , nmda receptor , hippocampus , p type calcium channel , calcium , sgk1 , long term depression , neuroscience , hippocampal formation , t type calcium channel , biophysics , receptor , biochemistry , voltage dependent calcium channel , biology , phosphorylation , organic chemistry
Various forms of synaptic plasticity in the brain have been proposed to result from modifications in the properties of glutamate receptors by calcium‐dependent mechanisms. In the present study, changes in glutamate receptors elicited by calcium treatment of previously frozen mouse brain sections were evaluated by qualitative as well as quantitative analysis of tritiated ligand binding to both α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionate (AMPA) and N‐methyl‐D‐aspartate (NMDA) glutamate receptor subtypes. Quantitative analysis revealed that 3 H‐AMPA binding was reduced in a dose‐dependent manner by calcium in the cerebral cortex and striatum formations. However, an opposite change in AMPA receptor properties was observed in the hippocampus, as calcium generated an increase of AMPA binding in all hippocampal fields. Analysis of the saturation kinetics of 3 H‐AMPA binding showed that the calcium‐induced augmentation of AMPA binding in the stratum radiatum of the CA 1 region was due to an alteration in the maximal number of sites, while the reduction of binding elicited by calcium in the cortex appeared to be due to modified AMPA receptor affinity. Calcium‐induced downregulation of AMPA receptor affinity in the cortex and striatum was affected by baicalein, a selective inhibitor of the lipoxygenase pathways of arachidonic acid metabolism, whereas the same inhibitor did not modify calcium‐mediated upregulation of receptor number in the CA 1 region of the hippocampus. On the other hand, the effect of calcium appeared to be specific for the AMPA receptor, as the same treatment did not affect glutamate binding to the NMDA glutamate receptor subtype. Our results suggest the possibility that, depending on the brain regions, calcium ions may generate opposite modulation of AMPA receptor properties. Because the regulation of AMPA receptors by calcium‐dependent enzymes has been implicated in synaptic plasticity, our results suggest that regional variations in the effect of calcium on AMPA binding account for differential plasticity at glutamatergic synapses. Hippocampus 2000;10:645–653. © 2000 Wiley‐Liss, Inc.