Light-evoked NMDA receptor-mediated currents are reduced by blocking D-serine synthesis in the salamander retina.

Experiments were carried out in the retina of the tiger salamander (Ambystoma tigrinum) to evaluate the importance of D-serine synthesis on light-evoked N-methyl D-aspartate (NMDA) receptor-mediated components of ganglion cells and contributions to the proximal negative field potential. We blocked the synthesis of D-serine through brief exposures of the retina to phenazine ethosulfate and validated the changes in the tissue levels of D-serine using capillary electrophoresis methods to separate and measure the amino acid enantiomers. Ten minute exposures to phenazine ethosulfate decreased D-serine levels in the retina by about 50% and significantly reduced the NMDA receptor contribution to light responses of the inner retina. This is the first report of a linkage between D-serine synthesis and NMDA receptor activity in the vertebrate retina.