A Metabotropic Glutamate Receptor Mediates Synaptic Transmission from Blue-Sensitive Cones to ON-Bipolar Cells in Carp Retina
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Glutamate receptors mediate synaptic transmission from photoreceptors to bipolar cells in the vertebrate retina. L-2-amino-4-phosphonobutyrate (L-APB), a group III metabotropic glutamate receptor (mGluR) agonist, was used to identify mGluR6, which mediates rod synaptic input to ON-bipolar cells. A presynaptic mGluR has been similarly identified on red-sensitive cone synaptic terminals . Whether a post-synaptic mGluR is involved in signaling from red-, green-, or blue-sensitive cones to ON-bipolar cells has not, however, been determined in the teleost retina. To characterize the postsynaptic glutamate receptor, electroretinogram (ERG) b-waves (a measure of ON-bipolar cell activity) and intracellular responses from cones to trichromatic stimuli (blue, 455 nm; green, 549 nm; and red, 694 nm) were recorded from light-adapted isolated carp retina.