Group II metabotropic glutamate receptors within the amygdala regulate fear as assessed with potentiated startle in rats.

The contribution to fear and fear learning of amygdala Group II metabotropic glutamate receptors was examined in rats. Pretest intra-amygdala infusions of the Group II receptor agonist LY354740 (0.3 or 1.0 microg/side) significantly disrupted fear-potentiated startle. The same rats were unimpaired when later tested without drug. The Group II receptor agonist (2R,4R)-4-aminopyrrolidine-2,4-dicarboxylate (3.0 microg/side) mimicked the effect of LY354740, and coadministration of the Group II receptor antagonist LY341495 (0.3 microg/side) prevented it. Pretraining LY354740 (0.3 microg/side) infusions also blocked learning. The effects on learning and performance were significantly less pronounced in rats with misplaced cannulas. Thus, Group II metabotropic receptors within or very near the amygdala regulate fear and fear learning and are a potential target for anxiolytic compounds.