AUTHOR=Bragina Luca , Bonifacino Tiziana , Bassi Silvia , Milanese Marco , Bonanno Giambattista , Conti Fiorenzo 

TITLE=Differential expression of metabotropic glutamate and GABA receptors at neocortical glutamatergic and GABAergic axon terminals

JOURNAL=Frontiers in Cellular Neuroscience

VOLUME=9

YEAR=2015

URL=https://www.frontiersin.org/journals/cellular-neuroscience/articles/10.3389/fncel.2015.00345

DOI=10.3389/fncel.2015.00345

ISSN=1662-5102

ABSTRACT=<p>Metabotropic glutamate (Glu) receptors (mGluRs) and GABA<sub>B</sub> receptors are highly expressed at presynaptic sites. To verify the possibility that the two classes of metabotropic receptors contribute to axon terminals heterogeneity, we studied the localization of mGluR1α, mGluR5, mGluR2/3, mGluR7, and GABA<sub>B1</sub> in VGLUT1-, VGLUT2-, and VGAT- positive terminals in the cerebral cortex of adult rats. VGLUT1-positive puncta expressed mGluR1α (∼5%), mGluR5 (∼6%), mGluR2/3 (∼22%), mGluR7 (∼17%), and GABA<sub>B1</sub> (∼40%); VGLUT2-positive terminals expressed mGluR1α (∼10%), mGluR5 (∼11%), mGluR2/3 (∼20%), mGluR7 (∼28%), and GABA<sub>B1</sub> (∼25%); whereas VGAT-positive puncta expressed mGluR1α (∼27%), mGluR5 (∼24%), mGluR2/3 (∼38%), mGluR7 (∼31%), and GABA<sub>B1</sub> (∼19%). Control experiments ruled out the possibility that postsynaptic mGluRs and GABA<sub>B1</sub> might have significantly biased our results. We also performed functional assays in synaptosomal preparations, and showed that all agonists modify Glu and GABA levels, which return to baseline upon exposure to antagonists. Overall, these findings indicate that mGluR1α, mGluR5, mGluR2/3, mGluR7, and GABA<sub>B1</sub> expression differ significantly between glutamatergic and GABAergic axon terminals, and that the robust expression of heteroreceptors may contribute to the homeostatic regulation of the balance between excitation and inhibition.</p>