(c) NMA (N-methyl-DL-aspartate) or GLY (glycine), which have been reported to suppress the responses of third-order neurons, do not diminish the b- or d-waves, nor the potassium fluxes at ON or OFF. The b-wave and ON potassium fluxes, however, remain undiminished. (b) Conversely, PDA (cis 2,3-piperidine-dicarboxylic acid) or KYN (kynurenic acid), which have been reported to suppress the light responses of OFF bipolar, horizontal, and third-order retinal neurons, causes a loss of the ERG d-wave as well as OFF potassium fluxes. It was found that: (a) application of APB (2-amino-4-phosphonobutyrate), which has previously been shown to selectively abolish the light responsiveness of ON bipolar cells, causes a concomitant loss of the ERG b-wave and ON potassium flux. The application of highly selective pharmacologic agents permitted us to functionally isolate various classes of retinal neurons. Light-evoked intraretinal field potentials (electroretinogram, ERG) have been measured simultaneously with extracellular potassium fluxes in the amphibian retina. A reflection of ON bipolar cell activity.
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