Glutamatergic mechanisms in the outer retina of larval zebrafish: analysis of electroretinogram b- and d-waves using a novel preparation.

A new preparation is described for recording the electroretinogram (ERG) from larval zebrafish (5-8 days postfertilization) which has allowed the investigation of the pharmacology of cone photoreceptor inputs onto bipolar cells. By using a pharmacological cocktail to isolate the photoreceptors and bipolar cells from inhibitory influences, it was found that an excitatory amino acid transporter (EAAT) presumably linked to a Cl() channel mediates most of the synaptic transmission from the cone photoreceptors to the ON bipolar cells, although metabotropic glutamate receptors (presumably mGluR6) also make a small contribution. On the other hand, alpha-amino-3-hydroxy- 5-methyl-4-isoxazolepropionate (AMPA)/kainate receptors mediate synaptic transmission from cone photoreceptors to OFF bipolar cells. The glutamatergic input mechanisms underlying bipolar cell responses in the larval zebrafish are adultlike and similar to those in other teleost species.