Photoreceptor physiology in the rat is governed by the light environment.
Albino rats were born and raised in one of three cyclic (12L: 12D) lighting conditions: (1) 5 lux for 9 weeks, (2) 800 lux for 9 weeks, or (3) 800 lux for 9 weeks, followed by 5 lux for 3 weeks (800:5). After the treatment, the following were determined: (i) retinal function as measured by the electroretinogram (ERG); (ii) retinal morphology, including rod outer segment (ROS) length and outer nuclear layer area; (iii) rhodopsin levels in whole retina and ROS preparations; (iv) fatty acid profile of ROS membranes and (v) retinal antioxidant levels. After 9 weeks, rats raised in 800 lux sustained an irreversible loss of photoreceptors which could not be reversed by then placing them in 5 lux. However, these rats displayed significant alterations in all other parameters measured after the 3 weeks in dim cyclic light. ERGs showed a 60% increase of b-wave maximum amplitude in 800:5 rats at 12 weeks over the value at the time of their change to a dim environment, while a-wave amplitude in 800:5 rats increased more than 2.5 times. This increase can be explained by a combination of increased ROS length and increased ROS membrane concentration of rhodopsin during the three weeks in 5 lux. Polyunsaturated fatty acids predominated in the ROS of 5 lux rats and 800:5 rats, but not in 800 lux animals. Measurements of retinal glutathione enzyme activity and vitamin E and C levels were relatively low in 800:5 rats. Some rats from the 800:5 group were exposed to 2000 lux for 24 hr. Retinas of these rats sustained 50% loss of photoreceptors from this exposure. Comparisons are made to previous studies concerning the effect of cyclic light environments on the retinas of albino rats.
Cullen Eye Institute, Baylor College of Medicine, Houston, Texas 77030.
J S
JS
Penn
L A
LA
Thum
M I
MI
Naash
D000222:Adaptation, Physiological; D000818:Animals; D004596:Electroretinography; D008029:Lighting; D010786:Photoreceptor Cells / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012374:Rod Cell Outer Segment / Q000502:physiology