EFFECTS OF PROLONGED UNIOCULAR DARK-ADAPTATION ON THE DIRECT-CURRENT ELECTRORETINOGRAM OF PIGMENTED AND ALBINO RABBITS

The direct-current electroretinogram of seven pigmented and seven albi no rabbits was recorded from both eyes for almost 4 h in response to r epeated identical light stimuli. Stimulus duration was 10 s, light int ensity was 6.8 x 10(2) lux, and the interval between the beginning of succeeding light stimuli was 3 min. The dark-adaptation period precedi ng light stimulation was 30 min for one of the eyes ('unoccluded eye') and 150 min for the contralateral eye ('occluded eye'), which was pat ched during the first part (117 min) of the experiment. In pigmented a nimals, the b- and c-wave amplitudes of the unoccluded eye slowly incr eased during the first part of the experiment but not significantly du ring the second. The a-wave amplitude was not significantly changed. A fter removal of the cover, the a- and b-wave amplitudes of the occlude d eye immediately attained but did not exceed the level of those in th e unoccluded eye, irrespective of the light adaptation induced by the stimulus flashes previously presented to the unoccluded eye. (Control experiments on six pigmented rabbits confirmed that stimuli identical to those used in the main part of the study caused a light adaptation, since a decrease in a- and b-wave amplitudes occurred after the first light stimulus following an initial dark-adaptation period of 2 h for both eyes.) In albino rabbits, electroretinogram responses were clear ly discernible in the occluded eye also during the first part of the e xperiment, probably because of transillumination of the head. In other respects, the results were essentially similar to those of pigmented animals. The observation that occluded eyes did not dark adapt better, as judged by the electroretinogram responses, than contralateral eyes given repeated light adaptive stimuli may indicate the presence of a mechanism for transfer of adaptation information between the eyes.