Agonist action of (RS)-α-methyl-4-carboxyphenylglycine (MCPG) in the amygdala

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Abstract
Glutamatergic excitatory postsynaptic potentials (EPSPs) in the basolateral amygdala (BLA) are reduced in amplitude following agonist activation of presynaptic metabotropic glutamate receptors (mGluR). In this study, the effect of a presumed mGluR antagonist, (RS)-α-methyl-4-carboxyphenylglycine (MCPG), was investigated on the EPSP recorded intracellularly in BLA neurons. Superfusion of MCPG (500 μM) significantly reduced the amplitude of evoked EPSPs. In the presence of MCPG, postsynaptic responses to α-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA, 1 μM) were unaltered while responses to N-methyl-d-aspartate (NMDA, 3-5 μM) were potentiated. These data suggest that the MCPG-induced reduction of EPSP amplitude is due to a mGluR agonist action at a presynaptic mGluR ‘autoreceptor’.