A NOVEL METABOTROPIC GLUTAMATE-RECEPTOR EXPRESSED IN THE RETINA AND OLFACTORY-BULB

A novel metabotropic glutamate receptor, mGluR8, was identified by scr eening a mouse retina cDNA library. This receptor is most related to m GluR4, mGluR7, and mGluR6 (74%, 74%, and 70% identical amino acid resi dues, respectively). Similar to these receptors, stimulation by L-glut amate or L-2-amino-4-phosphonobutyrate (L-APB) of Chinese hamster ovar y (CHO) cells stably transfected with mGluR8 result in the inhibition of forskolin-stimulated adenylyl cyclase. In situ hybridization studie s revealed a strong expression of the mGluR8 gene in the olfactory bul b, accessory olfactory bulb, and mammillary body. A weaker expression was found in the retina, and in scattered cells in the cortex and hind brain. During development, the distribution of mGluR8 expression was m ore widespread. These results extend the diversity of metabotropic glu tamate receptors in the CNS. Because at least two APE receptors are ex pressed in the retina, the use of this drug to block selectively the O N pathway needs to be reconsidered. The pharmacology and expression of mGluR8 in mitral/tufted cells suggest it could be a presynaptic recep tor modulating glutamate release by these cells at their axon terminal s in the entorhinal cortex.