ABSTRACT
The electroretinogram (ERG) was recorded in the dark from photo-entrained albino rabbits, using a constant-intensity, 500-nm, 50- or 100-msec stimulus at 1-min intervals. Under these conditions, the b-wave of the ERG was previously shown to decrease in amplitude at the time of the morning rod photoreceptor disc shedding event. We have extended our observations to rabbits housed in continuous darkness. The present data show that in constant darkness the change in retinal sensitivity continues to occur, but with a period slightly less than 24 hr. Unilateral dark adaptation, achieved by eyepatching, alters the timing of the event only in the retina of the occluded eye. Thus, the change in retinal sensitivity shares the characteristics of endogenous rhythmicity and intraocular control that have been demonstrated by histologic methods for mammalian rod disc shedding. We also report elongation of rod outer segments in some regions of the albino rabbit retina after continuous darkness.
Subject(s)
Darkness , Retina/physiology , Sensory Deprivation/physiology , Animals , Cell Count , Dark Adaptation/physiology , Electroretinography , Phagosomes , Photic Stimulation , Rabbits , Retina/cytology , Rod Cell Outer Segment/anatomy & histology , Time FactorsABSTRACT
Hemicholinium-3 effects on the albino rabbit neural retina have been described, but effects on the retinal pigment epithelium (RPE) have not been closely examined. We have studied retinal morphology and function in Dutch belted (pigmented) rabbits after single intravitreal injections of Hemicholinium-3 or saline. DC electroretinogram recordings show a decrease in a, b, and c-wave amplitudes, with the c-wave affected first. Experiments with sodium iodate show that the early decrease in the c-wave results from a loss of the RPE component of the c-wave, rather than the retinal Slow PIII component. After two days, ophthalmoscopic abnormalities of the fundus are severe in a large area with pigmentary changes. A sharp boundary appears between normally pigmented and depigmented fundus, indicative of a critical threshold for damage. The RPE contains clumped melanin. Pigmented cells are seen away from the basement membrane, an early histological observation temporally correlated with a loss of barrier function seen in fluorescein angiograms. After 10 days, apparent proliferation of non-pigmented RPE cells coincides with re-establishment of the barrier. Rod photoreceptor outer segments are lost 4-7 days after injection in the depigmented regions of the fundus, but outer segments are spared in normally pigmented fundus areas. This regional pattern is distinct from that seen in albino rabbit retina where outer segment loss is fairly uniform. We conclude that Hemicholinium-3 affects the RPE in pigmented rabbits in addition to known effects on retinal cholinergic neurons and photoreceptor disc synthesis.
Subject(s)
Hemicholinium 3/pharmacology , Pigment Epithelium of Eye/drug effects , Retina/drug effects , Animals , Electroretinography/drug effects , Fluorescein Angiography , Fundus Oculi , Melanocytes/ultrastructure , Photoreceptor Cells/drug effects , Photoreceptor Cells/ultrastructure , Pigment Epithelium of Eye/pathology , Rabbits , Retina/pathology , Vitreous Body/drug effectsABSTRACT
We hypothesize that the b-wave of the electroreginogram (ERG) can provide a precise, noninvasive measure of the morning rod disc shedding event. ERGs were recorded in the dark from photoentrained rabbits using a 500 nm test light. Histological examination of the pigment epithelium confirmed that an increase in large phagosome content occurred shortly after light onset. In albino rabbits the b-wave decreased in amplitude at about 30 min after the time of normal light onset. The corresponding decrease in sensitivity required to produce this change in amplitude was 0.11 log unit. No ERG effect was seen in pigmented rabbits.
