Group I metabotropic glutamate receptors are expressed in the chicken retina and by cultured retinal amacrine cells

Glutamate is well established as an excitatory neurotransmitter in the vert ebrate retina. Its role as a modulator of retinal function, however, is poo rly understood. We used immunocytochemistry and calcium imaging techniques to investigate whether metabotropic glutamate receptors are expressed in th e chicken retina and by identified GABAergic amacrine cells in culture. Ant ibody labeling for both metabotropic glutamate receptors 1 and 5 in the ret ina was consistent with their expression by amacrine cells as well as by ot her retinal cell types. In double-labeling experiments, most metabotropic g lutamate receptor 1-positive cell bodies in the inner nuclear layer also la bel with anti-GABA antibodies. GABAergic amacrine cells in culture were als o labeled by metabotropic glutamate receptor 1 and 5 antibodies. Metabotrop ic glutamate receptor agonists elicited Ca2+ elevations in cultured amacrin e cells, indicating that these receptors were functionally expressed. Cytos olic Ca2+ elevations were enhanced by metabotropic glutamate receptor 1-sel ective antagonists, suggesting that metabotropic glutamate receptor 1 activ ity might normally inhibit the Ca2+ signaling activity of metabotropic glut amate receptor 5. These results demonstrate expression of group I metabotro pic glutamate receptors in the avian retina and suggest that glutamate rele ased from bipolar cells onto amacrine cells might act to modulate the funct ion of these cells.