A Comparison of Light-Induced Rod Degeneration in Two Teleost Models
Albino rainbow trout, Oncorhynchus mykiss, are resistant to light damage, losing only their rod outer segments (ROS) in full daylight (10,000 to 100,000 lux) at 11°C. 1 To compare light damage in albino trout with light damage in albino rodents, we analyzed central retinal structure in albino trout exposed to full daylight, indoor dim day-light (30 lux-30 days or longer) and strong constant light (3000 lux). In albinos remaining outdoors or placed in constant light, ROS volume was reduced but the number of photoreceptor nuclei did not decline. Albinos placed in dim daylight re-grew ROS to 60% or more of normal volume but when returned to outdoor raceways lost most of their ROS volume within 5 days. Outdoor albinos placed in dim daylight replaced ROS much more slowly. In neither case was there a change in number of photoreceptor nuclei. In affected albinos there is apparently little rod cell death during the initial phases of light insult to ROS or thereafter. This confirms that most rod cells with ROS damage survive and retain capacity to re-grow ROS, and any which undergo apoptosis are replaced by cells derived from rod progenitors.
To ascertain whether the 11°C temperatures at which trout were held was protective, we exposed albino and normal oscars, Astronotus oscellatus, to 3000 lux constant light at 28°C. Albinos lost -50% of their rod nuclei over 14 days and normals appeared unaffected. Thus, retinal photo-degeneration in 3000lux constant light in albino trout at 11°C was limited to ROS loss, whereas ROS destruction lead to loss of rod cell bodies in albino oscars at 28°C. The ability to use ambient temperature to preclude or permit light damage to proceed to cell death in a cone rich, diurnal retina could be exploited to study mechanisms for susceptibility to and resistance to photo-degeneration.
KeywordsRetinal Pigment Epithelium Constant Light Outer Nuclear Layer Light Damage Cone Outer Segment
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