The direct current electroretinogram and the standing potential of the rabbit under different stimulus and adapting conditions

Abstract: The electroretinograrn (ERG) reflects the summation of electrical responses generated by neurons and non-neuronal cells in the retina and pigment epithelium in response to light. The major ERG components are the fast, negative a-wave, the fast, positive b-wave and the slow, positive c-wave. The ERG is superimposed on the standing potential of the eye (SP).Experiments were performed on albino and pigmented rabbits under general anesthesia. The aim was to study the development of the ERG with time in response to repeated light stimuli of different intensities (Paper I) or different interstimulus intervals (Paper II). The effects of a prolonged uniocular dark adaptation period (Paper III) and the influence of possible diurnal rhythms (Paper IV) were investigated, as was the long-term development and reproducibility of the ERG in experiments performed on consecutive days (Paper V). The influence of intravitreally injected dopamine at different concentrations on the development of the ERG was also studied (Paper VI).When using light stimuli of high intensity and short interstimulus interval (Papers I and II) the c-wave amplitude was immediately reduced after the first stimulus, but recovered to a large extent. The parallel behavior of the c-wave and SP suggested the presence of a pigment epithelial mechanism behind the recovery of the c-wave. The a- and b-wave amplitudes were immediately reduced, but recovered only to a limited extent. The final amplitudes of the b-and c-waves and to a large extent also of the a-wave seemed to be fairly independent of stimulus intensity.When one eye was dark adapted and the other eye simultaneously exposed to repeated widely spaced light stimuli of moderate intensity (Paper III) the b- and c-wave amplitudes of the unoccluded eye slowly increased during the course of several hours, but the a-wave amplitude was more stable. When the cover was removed from the previously occluded eye the a- and b-wave amplitudes immediately attained the level of those recorded from the contralateral eye, which had been light adapted by the stimuli. The phenomenon may suggest a mechanism for transfer of information between the eyes.The development of the ERG amplitudes and the SP was studied during the course of the day by repeating identical series of light stimuli every hour, and by commencing the experiments at different points of time (Paper IV). The amplitude of the b-wave did not reach relative stability until 2.5 to 3.5 hours after the beginning of dark adaptation, and that of the cwave continued to rise throughout the experiments. Since the pattern was similar in experiments starting in the morning and in the afternoon, it seems less probable that diurnal rhythms caused the findings.The long-tenn development of the ERG during several hours of stimulation with light of high intensity was studied in identical experiments performed on consecutive days (Paper V). In addition to the findings described in Papers I and II, a peak in the b-wave amplitude was observed 20-21 min after the start of light stimulation. There were no significant differences between experiments performed on consecutive days.The effects of intravitreally injected dopamine of different concentrations on the development of the ERG was studied in Paper VI. During exposure to repeated light stimuli of moderate intensity the b- and c-wave amplitudes were reduced with a decreased or even abolished amplitude increment with time in the eye injected with dopamine, and the responses were related to the concentration of the drug. The peaks in the b-and c-wave amplitude seen in the control eye when frequent stimuli of high intensity were used were abolished in the eye injected with dopamine at higher concentrations of the drug. Thus, dopamine may affect the adaptive process of the retina.