Cones Survive Rods in the Light-Damaged Eye of the Albino Rat

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Abstract-Hereditary retinal degeneration in the Royal College of Surgeons (RCS) strain of rat has been shown to produce extensive loss of photoreceptors and a corresponding decline of the electroretinogram, ganglion cell sensitivity, and the sensitivity of the pupillary light reflex. The behaviorally measured thresholds of RCS rats, on the other hand, are reported to be comparable to those for age-matched controls. We report here, that our own behavioral measurements show a clear difference between RCS rats and age-matched controls between four to twelve months of age. The difference in thresholds between RCS and control rats is about three long units at four months of age, and this difference progressively increases until at twelve months, we measure threshold dilierences of over seven log units. Retinal degenerationVisual sensitivity RCS rat INTRODUCI'ION

supporting

confidence: 74%

Section: Discussionmentioning

confidence: 99%

Changes in visual sensitivity with age in rats with heredity retinal degeneration

Trejo

Cicerone

1987

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“…This value is close to the relative sensitivity difference for 500 and 600nm lights measured early in dark adaptation in both the RCS and albino rats we examined. Birch and Jacobs (1975) who used a behavioral method, and Cicerone (1976), who used the electroretinogram, have also reported a visual mechanism in the rat with peak sensitivity at 520nm. This suggests that the same receptor pigment(s) which underlies ganglion cell response in advanced retinal degeneration also determines the photopic spectral sensitivity of the pupillary system of the rat.…”

Section: Durk Udaptcctionmentioning

confidence: 99%

Retinal sensitivity measured by the pupillary light reflex in RCS and albino rats

Trejo

Cicerone

1982

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Abstract-The effects of retinal degeneration on the sensitivity of the retina were studied in the RoyalCollege of Surgeons (RCS) rat by measuring the light reflex of the pupil in response to ganzfeld (full field) flashes. Light reflex thresholds were measured for animals from 32 to 683 days of age, and an age-related decrease in sensitivity of 5.2 log units (maximum) was measured. In contrast, thresholds for non-dystrophic albino controls increased only slightly during a comparable period. RCS rat thresholds increased more for short wavelength light than for long wavelength light.

“…The rat retina contains a small number of cones which cause a shift (to a smaller wavenumber) of m, of action spectra obtained in the dark after bleaching, when cone sensitivity has fully recovered while rod sensitivity remains depressed (Dodt and Echte, 1960;Green, 1971;Cicerone, 1976). Indeed, the shift in the peak of the adult action spectrum from 497.2 f 0.9 nm (dark adapted) to 508.9 f 1.5 nm (after bleaching) is almost certainly so explained.…”

Section: Resultsmentioning

confidence: 99%

“…Indeed, the shift in the peak of the adult action spectrum from 497.2 f 0.9 nm (dark adapted) to 508.9 f 1.5 nm (after bleaching) is almost certainly so explained. It is not possible to calculate an hypothetical action spectrum due to rods alone after this has been allowed for, because we know neither the relative numbers of three kinds of cones Cicerone (1976) found in this retina, nor how their sensitivities pool with rods after bleaching. So the matter remains open.…”

Section: Resultsmentioning

confidence: 99%

“Self-screening” of rhodopsin in rod outer segments

Alpern

Fulton²,

Baker

1987

Ati-Microspcctrophotometry(MSP) shows rhodopsin highly concentrated (about 3.Ommolfl) in rod outer segments (ROS). Calculation of the in uiuo absorption spectrum of human rhodopsin from such data reveals a striking failure to agree with the action spectrum of human rod vision. Agreement is good between the spectral distribution of absorption coefficients and the action spectrum. but the "concentration-broadening" (or "self-screening") introduced by the high end on absorbance at this concentration results in a misfit among the largest in the 93 years comparisons of this kind have been made! To deal with this anomaly, it has been suggested that "conantration-broadening" is inappropriate for rhodopsin in rod vision. This proposal was tested by comparing rod action spectra of 15day-old and adult rats. since the lengths of ROS increase by a factor of about two in maturation. Three lines of cvidena arc inconsistent with it. Although the conundrum remains unexplained. it cannot be dismissed by supposing "self-screening" inappropriate for night vision. Self-screeningRhodopsin Rod vision Elcctroretinogram Absorption spectrum INTRODUCMONThe agreement between the absorption (or absorptance) spectrum of the human rod visual pigment (rhodopsin) and the action spectrum of human night vision became the fundamental datum in visual physiology upon its discovery by Koenig (1894). Though never perfect, this elegant convergence of results from molecular physical chemistry and experimental psychology compels the inference that the initial step linking the physical world to its visual perception by the human brain is photochemical. Continued attempts to improve Koenig's approximate agreement followed as understanding deepened. Unfortunately, the agreement in the most recent comparison, estimating the rhodopsin absorption spectrum in situ from spectral analysis of human rod outer segments (ROS) with a microspectrophotometer (MSP) (Bowmaker and Dartnall, 1980), is almost as poor as that in the initial comparison. TheoryTo be seen, photons must be absorbed. If Z is the incident irradiance [photons of mono-*To whom correspondence should be addressed. chromatic light (of wavenumber, or frequency, m) set-' deg-) and I' the irradiance absorbed, thenwhere c1 is the absorption coefficient of rhodopsin, m, is its wavenumber of peak absorption, c is its concentration and 1 the length of the light path. A plot of Z'(m)Z(q,)/Z'(~)Z(nr) vs m is an absorption spectrum. A plot of Z(m,)/Z(m) vs m for some fixed effect is an action spectrum. Koenig implicitly assumed that at rod threshold, the amount of light absorbed is constant independent of wavelength. This assumption is now a corollary of a general principle of vertebrate photoreception: the principle of univariance (Naka and Rushton, 1966). It is evident from equation (l), assuming univariance, that if the wavenumber dependency of the effect is derived from absorption by rhodopsin alone, the two spectra will be the same.The shape and the width of the absorption spectrum of a pigment varies with ...