Evidence for both photopic and scotopic characteristics in the c-wave of chicken and frog ERG

The c-wave in achromats

In congenital total color blindness direct current recordings of the electroretinogram displayed a negativity following the b-wave, not present in recordings of normal eyes. This negativity, preceding the onset of the c-wave, is probably caused by the lack of cone contribution to the positive c-wave component.

A cone-triggered c-wave in the chicken ERG time integration characteristics

The c-waves recorded from the cone-dominant retina of the chicken proved to be cone-triggered. The time course and time integration properties of this retinal potential were compared with those of the rod-triggered c-wave recorded in the frog under scotopic conditions. The results clearly demonstrate that there is no evidence for time integration in cone-triggered c-waves but that rod-triggered c-waves follow the Bunsen-Roscoe law over more than 2 log units. We propose that these time-related differences may be used in other species as a differentiation criterion between cone-triggered and rod-triggered c-waves.

Interaction between photoreceptors and pigment epithelium in developing pigeon retina: an electrophysiological and ultrastructural study

In pigeons as in other vertebrates, the electroretinogram (ERG) first can be recorded simultaneously with the appearance of the photosensitive lamellae in the developing outer segments. At around 4-6 days after the bird has hatched a small negative-positive complex (a-b-wave) appears. Simultaneously, a c-wave can be recorded and the termination of the stimulus is followed by a positive d-wave. The ERG amplitude progressively increases during the first month as the lamellar structures complete their maturation. The c-wave amplitude shows a steady increase in the early post-hatching period which parallels the a-b complex maturation. In newly hatched pigeons the retinal pigment epithelial (RPE) cell consists of a small soma and long villi which extend toward the photoreceptors. During maturation a progressive increase in RPE thickness and number of cytoplasmic elements can be observed.

Photopic c-wave in the chicken ERG: sensitivity to sodium azide, epinephrine, sodium iodate, barbiturates, and other general anesthetics

The c-wave recorded in the chicken electroretinogram proved to be a cone-triggered component. The questions arose whether its reactivity to various specific drugs (sodium iodate, sodium azide, epinephrine, or barbiturates) were similar to those described for classic rod-triggered c-waves. We also tested the sensitivity of the chicken c-wave to various general anesthetics. Urethane was found to be the drug that best preserves the c-wave in electrophysiological recordings.

Some problems involved in employing the ERG c-wave in pharmacological experiments: conditioning in pigmented rabbits

The large inter- and intra-individual variations in ERG c-waves have prevented the application of the component in pharmacological experiments on the retinal pigment epithelial function. We examined some of the problems involved in employing the c-wave in pharmacological experiments using rabbit retinas. 1) Under our experimental conditions, the c-wave amplitudes in some rabbits reached equilibrium under intermittent stimuli, while in others they increased with time and did not reach a constant level in 3 h. 2) The c-wave amplitudes of the right and left eyes were similar, indicating that the contralateral eye can be used as a control during local administration of drugs. 3) The c-wave amplitude under 50 lux light had smaller inter-individual variations than that in the dark. This may be a useful indicator of the retinal pigment epithelium function when drugs are administered systemically.