[Isolation of rod- and cone-mediated c-waves in the chicken ERG using monochromatic stimuli]

Cone-mediated c-wave has recently been recorded from the cone dominant retina, while ERG c-wave had been considered to be mainly a rod-mediated response. However, only a few experiments have been conducted to isolate both rod- and cone-mediated c-waves from same experimental materials. In the present experiment, chicken eyes were used as the cone-dominant retina to isolate rod- and cone-mediated c-waves using monochromatic stimuli. Of monochromatic light at 20nm intervals between 460 and 620nm was adjusted to yield equal energy. In order to obtain criterion voltages of 50 and 100 microV of the c-wave amplitude in dark adaptation and 50 microV in light adaptation, stimulus intensities of the monochromatic lights were attenuated by neutral density filters from a maximal intensity of 7.7 microW/cm2 at the corneal surface. The duration of the stimulus light was 0.15, 5 or 10 seconds, and the stimulus interval was 90 seconds. In dark adaptation, the spectral characteristic of the c-wave at 50 microV criterion voltage was similar to the absorption curve of rhodopsin in rod cells and at 100 microV criterion voltage to a photopic CIE curve. In light adaptation, the spectral characteristic of the c-wave at 50 microV criterion voltage closely resemble that of the photopic CIE curve; these findings indicated that a Purkinje shift was observed in the attitude of the c-wave in the light and dark adaptation. The peak latency of the c-wave in dark adaptation was prolonged together with an increase of the c-wave amplitude, but tended to become shorter by stimuli longer than 580nm. On the other hand, in the light adaptation, the peak latency of the c-wave was evidently shorter than that in the dark adaptation and was constant throughout all the monochromatic stimuli. Based upon the above results, it was concluded that both rod- and cone-mediated c-waves could be isolated from the chicken retina by using the monochromatic stimuli.