The role of excitatory amino acid transmitters in the mudpuppy retina: an analysis with kainic acid and N-methyl aspartate.

A variety of glutamate and aspartate analogues were used to characterize the excitatory amino acid receptors in the mudpuppy retina. This approach revealed two general classes of receptors which were represented by the agonists kainic acid and N-methyl aspartic acid. Kainic acid was found to be a potent photoreceptor transmitter agonist on all three types of second-order neurons, and it was a powerful excitant of amacrine and ganglion cells. N-Methyl aspartate had little effect in the outer retina, but it had potent stimulatory effects on inner retinal neurons. N-Methyl aspartate antagonists selectively blocked light responses in some sustained OFF ganglion cells. These results suggest that both photoreceptors and bipolar neurons may use glutamate Or an analogue, whereas aspartate may be utilized by a class of sustained ON amacrine cells.