Origin of the R-Potential in the Mammalian Retina

Abstract

The R-potentials, recorded from the mammalian retina, have characteristics very similar to the L-response recorded from the fish. Dr. Grüsser concludes from his localization experiments that the recording site of the electrode is close to the synaptic endings of the cones. As far as we know, no electron microscope studies exist of the cat retina, but the work of Dr. Gloria Villegas on the monkey retina shows that the Müller fibers have their largest expansion at the level of the synaptic endings of the rods and cones. The cone synapses in the fish retina are the largest of their kind (10 µ), and are much larger than those of the cat. We do not believe that it has been possible to obtain any intra-synaptic potentials, as post-synaptic potentials are difficult to be obtained in extra-cellular recordings. Therefore, in analogy with the findings obtained in the fish retina, we are inclined to believe that the R-potential of the cat is either recorded from the Müller fiber at the level of the synaptic endings or, possibly from some ”horizontal cell of glial nature„, located at the level of the bipolars, very close to the outer plexiform layer. We do believe that this kind of potential reflects the post-synaptic activity, as it has been observed in the intra-cellular recordings from the glial extra-neuronal space in the fish retina.

From Instituto Venezolano de Investigaciones Cientificas, Caracas, Venezuela.