Predominant expression of group-II metabotropic glutamate receptors in thegoldfish brain

Group-II metabotropic glutamate (mGlu) receptors (mGlu2/3 receptors) were h ighly expressed in various regions (telencephalon, optic tectum, and cerebe llum, but not vagal lobe) of the goldfish brain. In the,goldfish telencepha lon, expression of mGlu2/3 receptors was even higher than in the rat cerebr al cortex. In contrast, mGlu5 receptors showed low levels of expression in all goldfish brain regions, whereas mGlu1a receptors were only expressed in the,goldfish cerebellum. Pharmacological activation of group-II mGlu recep tors with the selective agonists, 2R,4R-4-aminopyrrolidine-2,4-dicarboxylic acid and (2, 3,2'R,3'R)-2-(2,3-dicarbaxycyclopropyl) glycine, reduced the evoked release of glutamate from goldfish brain synaptosomes, whereas agoni sts of group-I and -III mGlu receptors (3,5-dihydroxy-phenylglycine and L-2 -amino-4-phosphonobutanoate) were inactive. The predominance of group-II ov er group-I mGlu receptors in the goldfish brain may provide a natural defen se against excitotoxic neuronal death and contribute to the unusually high resistance of goldfishes against hypoxic brain damage. (C) 1999 Published b y Elsevier Science B.V. All rights reserved.