11-cis-retinal and Albinism--Ocular

To quantify the rate at which light in a ganzfeld produces photoisomerizations in mouse rods in situ, we measured the rate of rhodopsin bleaching in eyes of recently euthanized mice with fully dilated pupils. The amount of rhodopsin declined as a first-order (exponential) function of the duration of the exposure at the luminance of 920 scot cd m(-2): the rate constants of bleaching were 8.3 x 10(-6) and 2.8 x 10(-5) s(-1) (scot cd(-1)m2)(-1) for C57B1/6 and 129P3/J mice, respectively. When the approximately 3-fold difference in effective areas of the pupils of the mice are taken into consideration, the bleaching rates for both strains become essentially the same, 2.6 x 10(-6) fraction rhodopsin (scot Td s)(-1). Assuming 7 x 10(7) rhodopsin molecules per rod, this bleaching rate yields the result that a flash of 1 scot Td s produces 181 photoisomerizations per rod, a value close to that derived from analysis of the collecting area of the rod for axially propagating light. We measured the electroretinograms of mice of the two strains reared under controlled illumination conditions (2 and 100 lux), and compared their properties, using the calibrations to determine the absolute sensitivities of the b-wave and a-waves. The intensity that produces a half-saturating rod b-wave response is 0.3-0.6 photoisomerizations rod(-1), and the amplification constant of the rod a-wave is 5-6 s(-2) photoisomerization(-1), with little dependence on the strain.

Topics: Albinism, Ocular; Animals; Electroretinography; Eye; Lighting; Mice; Mice, Inbred C57BL; Models, Biological; Photic Stimulation; Retina; Retinal Rod Photoreceptor Cells; Rhodopsin; Rod Cell Outer Segment; Species Specificity; Vision, Ocular

Two previous studies have shown that N(G)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of neuronal nitric oxide synthase, protects retinas of albino rats and mice from damaging levels of light. The aims of the present study were two-fold: (1) to confirm the protective effect of L-NAME on wild type albino rats and (2) to determine if L-NAME protects the retinas of transgenic rats with P23H and S334ter rhodopsin mutations. In the first study, albino rats born and raised in 5-10 lux cyclic light were injected intraperitoneally with either L-NAME or its inactive isomer D-NAME 30 min before being placed in bright light (2700 lux) for 24hr. Electroretinograms (ERGs) were recorded before light treatment and 2 days after cessation of exposure, and eyes were enucleated for morphologic evaluation. L-NAME, but not D-NAME provided structural protection of photoreceptor cells from light damage. The functional rescue was not statistically significant between the drug treated groups. In the second study, albino WT, P23H transgenic, and S334ter transgenic rats were born and raised in 400 lux cyclic light. Three week old animals received daily intraperitoneal injections of L-NAME or D-NAME for 4 weeks, and the same drugs were added to their drinking water. At 7 weeks of age, the ERG sensitivity curves and the outer nuclear layer thickness of both transgenic groups were significantly reduced compared to WT controls. However, administration of L-NAME did not protect against retinal degeneration caused by the rhodopsin mutation in either strain of transgenic (P23H and S334ter) rats. Thus, although photoreceptor cell death in light damage and inherited retinal degenerations share a common apoptotic mechanism, there must be significant 'up-stream' differences that allow selective neuroprotection by L-NAME.

Topics: Albinism, Ocular; Animals; Animals, Genetically Modified; Electroretinography; Enzyme Inhibitors; Female; Light; Male; Mutation; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Radiation Injuries, Experimental; Rats; Rats, Sprague-Dawley; Retinitis Pigmentosa; Rhodopsin

Ocular melanin synthesis modulates rod photoreceptor production, because in albino eyes, rod numbers are reduced by approximately 30%. In this study, rod numbers and ocular rhodopsin concentrations were measured in intermediate pigmentation phenotypes to determine whether proportional reductions in melanin are correlated with proportional changes in rod numbers. Further, patterns of cell production and death were examined around the time of birth, when rod production peaks, to determine whether there are abnormalities in these features associated with hypopigmentation.. Four mouse pigmentation phenotypes were used: fully pigmented, albino, Beige, and Himalayan. The latter two are intermediate-pigmentation phenotypes, with Beige having markedly more pigment than Himalayan. Ocular melanin concentrations were measured during development and at maturity. Rods were counted at maturity and measurements of ocular rhodopsin undertaken. Mitotic and pyknotic cells were also counted in neonates.. Rods and ocular rhodopsin were reduced in both Beige and Himalayan mice below levels found in fully pigmented mice, but not to levels found in albino animals. This was more marked in Himalayan than Beige mice, reflecting the lower concentration of melanin found in the former compared with the latter, both in development and at maturity. Although patterns of cell production were elevated in the hypopigmented animals, such patterns varied.. Rod numbers are modulated within a range between that in fully pigmented and albino phenotypes by the concentration of ocular melanin. However, in these animals, there is no obvious correlation between these events and patterns of cell production and death in neonates.

Topics: Albinism, Ocular; Animals; Animals, Newborn; Cell Count; Cell Differentiation; Cell Survival; Eye Proteins; Iris; Melanins; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Mitosis; Pigment Epithelium of Eye; Retinal Rod Photoreceptor Cells; Rhodopsin