The effects of kainate receptor-preferring glutamate
ligands were tested on the electroretinogram (ERG) of the
Xenopus retina. Kainate, domoic acid, and 5-iodowillardiine
(20–100 μM) acted similarly in every respect.
They increased peak amplitudes of the ERG a-,
b-, and d-waves significantly over controls.
The AMPA-specific antagonist, GYKI 53655, prevented a kainate-induced
increase in ERG a- and d-waves, but was
without effect on an increase in the b-wave. Once
the effect of agonist on the b-wave had peaked,
the ERG began to subside, leading to its nearly complete
disappearance within 20 min. Prior exposure to GYKI followed
by a combination of GYKI + agonist did not significantly
slow the rate of b-wave disappearance. Our results
indicate that (1) AMPA receptors contribute to ERG a-
and d-waves. (2) The kainate-evoked increase in
ERG a-, b-, and d-waves probably
results, in part, from an excitotoxic swelling of inner
retinal processes. (3) The inner retina has a population
of GYKI-resistant, kainate-sensitive receptors which may
contribute to b-wave generation.