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At least 19 recordsLinked to original sources
PubMed1987

Tryptamine and some related molecules block the accumulation of a light-sensitive pool of cyclic AMP in the dark-adapted, dark-incubated mouse retina.

Dark-adapted retinas of mice (C57BL/6J) incubated in the dark in media containing 1 mM 3-isobutylmethylxanthine (IBMX) or 5 mM Co2+ accumulate cyclic AMP (cAMP). A portion of this pool is light sensitive, as light can prevent or reverse its accumulation. Similarly, tryptamine, serotonin, 5-methoxytryptamine, bufotenine, and 5-methoxydimethyltryptamine can block the accumulation of the light-sensitive pool of cAMP, whereas tryptophan, melatonin, N-acetylserotonin, 5-methoxytryptophol, and tetrahydro-beta-carbolines are inactive. The phenomenon is not seen with mutant mouse retinas (rd/rd), which lack most photoreceptors, but persists in abnormal retinas containing photoreceptors but with extensive neuronal depletion in the inner retina. Tryptamine also inhibits cAMP accumulation in either dark or light-adapted retinas exposed to forskolin alone but not in media containing high levels of forskolin plus 1 mM IBMX. There is some suggestion that serotonin 5-HT-2 antagonists can partially reverse the action of the tryptamines, but hitherto undescribed receptors may be involved. Current data suggest that photoreceptors are the target for the action of the tryptamines.

1-Methyl-3-isobutylxanthine↗
PubMed1977

Dark adaptation in diabetics.

Dark adaptation in diabetics was recorded with Goldmann-Weeker's adaptometer and analysed according to the stages of retinopathy by Scott. Dark adaptation curves in diabetics were divided into three groups; normal dark adaptation; subnormal one which showed normal first curve of dark adaptation and impaired second curve; abnormal dark adaptation which showed impaired dark adaptation in the whole course. The cases with normal dark adaptation were found to be few in the stages Ia, II and IIIa of retinopathy. Subnormal dark adaptation was rarely found in the stages Ia, II, IIIa and IIb of retinopathy. Abnormal dark adaptation was recorded in most patients with diabetic retinopathy and found in all th stages of retinopathy. A 5% level of significance was statistically recognized in the thresh old at 35 min after light adaptation between the stages IIIa and IIIb of retinopathy. From this viewpoint, significance in severity of diabetic retinopathy was discussed.

Dark Adaptation↗
PubMed1975

Intracellular recordings of rod responses during dark-adaptation.

1. Dark-adaptation of rod photoreceptors has been studied in the isolated axolotl (Ambystoma mexicanum) retina by intracellular recordings. Rod responsiveness was greatly reduced immediately after a 30 sec partial bleach, but partially recovered with time in the dark. 2. In parallel spectrophotometric measurements using isolated retinas, regeneration of the rod pigment could not be detected after a 30 sec bleach. 3. During rod dark-adaptation, the response of a rod to a given stimulus increased in amplitude, duration, and rate of rise but did not recover completely to the dark-adapted values. Response latency was lengthened immediately after a bleach but ultimately returned to the dark-adapted level. 4. The time courses of dark-adaptation determined on the basis of the intensity of a stimulus needed to evoke a response having a criterion amplitude, a criterion duration, or a criterion rate of rise were similar. On the other hand changes in latency of the response and magnitude of the saturated amplitude followed different time courses. Change in log threshold was found to be related to change in saturated amplitude by an exponential function during dark-adaptation. 5. After bleaching 10% or less of the rod pigment, the kinetics of both recovery of log threshold and decrease in absorbance at 400 nm (metarhodopsin II+free retinal) could be described by two concurrent first-order processes having similar time constants. However, after bleaching more than 10% of the rod pigment, changes in sensitivity and absorbance did not follow parallel time courses. 6. Metarhodopsin III cannot be solely responsible for setting the axolotl rod sensitivity since rod thresholds decrease monotonically during dark-adaptation whereas meta III concentration reaches a peak 3 min after the bleach and decreases thereafter.

Ambystoma↗
PubMed1977

On the photocycle and light adaptation of dark-adapted bacteriorhodopsin.

Pulsed Nd laser (25 ns, 530 nm) photolysis experiments were carried out at room temperature in aqueous suspensions of dark- and light-adapted fragments of the purple membrane of Halobacterium halobium. It is shown that the (50%) 13-cis isomeric component (BR13-cis) of dark-adapted bacteriorhodopsin (BRDA) undergoes a photocycle involving a characteristic transient absorbing in the neighborhood of 610 nm. At relatively high excitation intensities BR13-cis is converted to the same 410 nm (M) transient that characterized the photocycle of the all-trans isomer (BRtrans) of light-adapted bacteriorhodopsin (BRLA). This process, which competes with the generation of the "610" species, is attributed to the photo-induced conversion, during the pulse, of BR13-cis (or of its primary photoproduct "X") to a species in the BRtrans photocyte. The relationship between these observations and the mechanism of BRDA hv leads to BRLA adaptation at low excitation intensities (for which a quantum yield limit, 0 less than or equal to (3.5 +/- 0.7) X 10(-2) , is established) is discussed.

Bacteriorhodopsins↗
PubMed1989

Photocycles of bacteriorhodopsin in light- and dark-adapted purple membrane studied by time-resolved absorption spectroscopy.

Nanosecond time-resolved absorption spectra have been measured throughout the photocycle of bacteriorhodopsin in both light-adapted and dark-adapted purple membrane (PM). The data from dark-adapted samples are interpretable as the superposition of two photocycles arising independently from the all-trans and 13-cis retinal isomers that coexist in the dark-adapted state. The presence of a photocycle in dark-adapted PM which is indistinguishable from that observed for light-adapted PM under the same experimental conditions is demonstrated by the observation of the same five relaxation rates associated with essentially identical changes in the photoproduct spectra. This cycle is attributed to the all-trans component. The cycle of the 13-cis component is revealed by scaling the data measured for the light-adapted sample and subtracting it from the data on the dark-adapted mixture. At times less than 1 ms, the resulting difference spectra are nearly time-independent. The peak of the difference spectrum is near 600 nm, although there appears to be a slight (approximately 2 nm) blue-shift in the first few microseconds. Subsequently the amplitude of this spectrum decays and the peak of the difference spectrum shifts in two relaxations. Most of the amplitude of the photoproduct difference spectrum (approximately 80%) decays in a single relaxation having a time constant of approximately 35 ms. The difference spectrum remaining after this relaxation peaks at approximately 590 nm and is indistinguishable from the classical light-dark difference spectrum, which we find, in experiments performed on a much longer time scale, to peak at 588 nm. The decay of this remaining photo-product is not resolvable in the nanosecond kinetic experiments, but dark adaptation of a completely light-adapted sample is found to occur exponentially with a relaxation time of approximately 2,000 s under the conditions of our experiments.

Bacteriorhodopsins↗
PubMed1992

Fundus pigmentation and the dark-adapted electroretinogram.

Dark-adapted electroretinograms were obtained over a 3.6-log range of stimulus intensities from 17 black and 15 white normal subjects. Subjects were grouped on the basis of light or dark fundus pigmentation, determined from digitized fundus photographs. B-wave amplitudes for each group were fitted by the Naka-Rushton equation, and the measures Vmax, log K, and n were determined. The luminance-response functions revealed that subjects with light fundi had larger b-wave amplitudes at all luminance levels. There was a significant difference between groups for Vmax and n but not for log K. A comparison of b-wave implicit times showed no significant difference between subjects with dark and light fundi. Ancillary tests and multiple regression analysis suggested that the relationship between Vmax and fundus pigmentation could not be attributed to age, gender, refractive error, axial length or intraocular pressure. The results have implications for the collection of normative electroretinographic data and for the interpretation of electroretinogram results.

Adolescent↗
PubMed1975

Effect of blood vitamin A levels on the dark adaptation of mineworkers.

The average dark adaptation time for newly recruited Black mineworkers is longer than that reported for Whites. While this longer dark adaptation time may result from a number of pathological conditions, its most likely cause is a deficiency of vitamin A in the diet. A study was conducted in which the vitamin A level of the blood and the dark adaptation times were correlated in a group of Black mineworkers upon arrival and again after 4 - 6 months continuous work underground in a gold mine. The study indicated that a very marked decrease occurred in the miners' serum vitamin A level between the time of arrival at the mine and the second examination. This difference was found to be highly significant. This decrease was accompanied by an increase in mean dark adaptation time, which was significant at the 5% level. These observations accord with the findings of a previous study and are indicative of an inadequate dietary intake of vitamin A during the period when the miners were on the mine diet.

Adult↗
PubMed1977

Influence of anesthetics, ethyl alcohol, and Freon on dark adaptation of monkey cone ERG.

Cone dark adaptation curves were measured in a rhesus monkey using the electroretinogram (ERG) response to a 40 Hz flickering stimulus. The influence of anesthetics on the time course of dark adaptation was studied. All volatile anesthetics tested (methoxyflurane, halothane, enflurane, ether, chloroform) retarded dark adaptation but to different degrees; urethane, ethyl alcohol, and Freon 11 also retarded dark adaptation. No effect was found for barbiturates and ketamine. It seems unlikely that metabolites play a role in the observed phenomena. A literature survey reveals that several studies on dark adaptation or visual pigment regeneration might have suffered from influences of the anesthetic used. The cause of the phenomenon might lie either in anesthetics-induced membrane changes or in hindrance of the isomeration of 11-trans retinal to 11-cis retinal.

Anesthetics↗
PubMed1990

Uv-visible spectroscopy of bacteriorhodopsin mutants: substitution of Arg-82, Asp-85, Tyr-185, and Asp-212 results in abnormal light-dark adaptation.

The light-dark adaptation reactions of a set of bacteriorhodopsin (bR) mutants that affect function and color of the chromophore were examined by using visible absorption spectroscopy. The absorbance spectra of the mutants Arg-82 in equilibrium Ala (Gln), Asp-85 in equilibrium Ala (Asn, Glu), Tyr-185 in equilibrium Phe, and Asp-212 in equilibrium Ala (Asn, Glu) were measured at different pH values during and after illumination. None of these mutants exhibited a normal dark-light adaptation, which in wild-type bR causes a red shift of the visible absorption maximum from 558 nm (dark-adapted bR) to 568 nm (light-adapted bR). Instead a reversible light reaction occurs in the Asp-85 and Asp-212 mutants from a blue form with lambda max near 600 nm to a pink form with lambda max near 480 nm. This light-induced shift explains the appearance of a reversed light adaptation previously observed for the Asp-212 mutants. In the case of the Tyr-185 and Arg-82 mutants, light causes a purple-to-blue transformation similar to the effect of lowering the pH. However, the blue forms observed in these mutants are not identical to those formed by acid titration or deionization of wild-type bR. It is suggested that in all of these mutants, the chromophore has lost the ability to undergo the normal 13-cis, 15-syn to all-trans, 15-anti light-driven isomerization, which occurs in native bR. Instead these mutants may have as stable forms all-trans,syn and 13-cis,anti chromophores, which are not allowed in native bR, except transiently.

Arginine↗
PubMed1975

Rushton's paradox: rod dark adaptation after flash photolysis.

1. Rod dark adaptations after a photoregenerating flash and quantum-equivalent 30 sec bleach are found to be in exact agreement, while the measured rhodopsin regenerations are grossly different. This finding confirms and clarifies "Rushton's paradox', the failure of the Dowling-Rushton equation (linking log sensitivity linearly with unregenerated rhodopsin) to account for human rod dark adaptation after flash photolysis. 2. The hypothesis that the agreement between rod dark adaptation curves after a photoregenerating flash and after a quantum-equivalent 30 sec bleach is coincidental is rejected on the basic of two classes of experiments. 3. Rod "bleaching' adaptation is demonstrated to be entirely determined by the number of rhodopsin molecules which absorb at least one quantum in a temporal period T, whose range includes the time interval 600 musec less than or equal T less than or equal 30 sec. This generalization obtains over the entire scotopic energy range (congruent to 3 log units) where rod dark adaptations has been studied. 4. Thus, the state of "bleaching' adaptation is determined by some by-product of the normal chain of events in scotopic excitation. About this by-product three important deductions are made: (i) its production is a monotonic function of the initial effective quantum absorptions; (ii) its production occurs before the metarhodopsin I leads to to metarhodopsin II dark reaction; (iii) it cannot be any photoproduct of the rhodopsin cycle.

Dark Adaptation↗
PubMed1977

A rapid test for dark adaptation.

With the known relationship between defects in dark adaptation and vitamin A deficiency, liver disease, and retinal degenerative changes, the development of a practical and simple test of dark adaptation has taken on some importance. Standard dark adaptation testing instruments are somewhat impractical, expensive, and not generally available. Therefore a simple, in expensive test for evaluation of dark adaptation is desirable. Using established standards of macular dark adaptation, a test was designed that appears to be relatively simple, reasonably accurate, and rapid. The test and equipment are described.

Automobile Driver Examination↗
PubMed1979

Lateral interactions in human cone dark adaptation.

1. The course of cone dark adaptation after exposure to a strong bleaching light depends on the size of the bleached region. Threshold for brief, tiny test flash centred in the bleached region is elevated more, and recovery is retarded by a small bleach. This effect has its parallel in the sensitization effect observed with steady backgrounds. 2. Previous results, that a similar sensitization effect is not observed in rod dark adaptation, are confirmed. 3. This sensitization effect in cone dark adaptation does not transfer binocularly, and is unaffected by pressure blinding during the bleaching exposure. 4. Threshold following a small bleach may be lowered by adding a steady annular background to the region surrounding the bleached patch. Conversely, bleaching the area surrounding a small, steady background can lower threshold for a test flash centred on the background. 5. These interactions between backgrounds and bleaches may be explained if bleaches produce long-lasting signals from neurones in the bleached area, which then lead into a spatially opponent stage of processing. 6. It is likely that the persisting signals come from the cone receptors, since the Bunsen-Roscoe Law (intensity-time reciprocity) holds for small bleaches as well as large, for durations up to about 3 sec.

Dark Adaptation↗
PubMed1976

Experimentally induced variations in the dark adaptation functions of a severe strabismic amblyope.

Dark adaptation curves were determined for an amblyopic and a normal control subject following a variety of preadaptation conditions. Sizable between-eye differences were found in the dark adaptation functions of only the amblyope; the magnitude of such differences varied with this subject's distance from the light preadapting screen and with the effective size of his pupils during the light preadaptation period. Marked differences were also found between the dark adaptation functions of both eyes of the amblyopic subject and those of the normal subject. The preadaptation-dependent changes in the dark adaptation function of the amblyopic subject are hypothesized to result from anomalies of amblyopic eye light adaptation which are referable to disturbances of retinal receptor alignment.

Age Factors↗
PubMed1989

Colour vision and dark adaptation in diabetic patients after photocoagulation.

Colour vision and dark adaptation were studied in 60 diabetic patients treated with photocoagulation. An acquired colour vision defect was found in 50% and a defective dark adaptation in 77% of the patients. Both colour vision and dark adaptation were defective in 47% of the patients. Colour vision defect only was found in 3% and dark adaptation defect only in 30% of the patients. Neither of these defects was found in 20% of the patients. The Farnsworth-Munsell 100-hue test showed a blue-yellow axis in 24 of the 30 colour defective patients. In the patients with an impaired dark adaptation, the range of the cone and rod threshold elevations from the normal upper limit was from 0.2 to 1.4 log units. The Farnsworth-Munsell 100-hue test scores showed a significant positive correlation to the values of both cone and rod thresholds.

Adult↗
PubMed1989

Subliminal light control of dark adaptation kinetics in Phycomyces phototropism.

The dark adaptation kinetics of Phycomyces phototropism depend critically on the experimental protocol. When sporangiophores that had been light-adapted to a fluence rate of 1 W m-2 at 447 nm were exposed to dim unilateral light, the adaptation kinetics showed exponential decay (6 min time constant). However, when light-adapted sporangiophores were kept for variable intervals in darkness (i.e. in presence of traditional red safelight) and then exposed to dim unilateral test light, the decay kinetics of adaptation were biexponential with a rapid decay during the first minute (1 min time constant), followed by a slow recovery (11 min time constant). Thus, the dim subliminal light given after the sporangiophores had been adapted to 1 W m-2, was actually perceived, and exerted control over the dark-adaptation process. The observed acceleration of dark-adaptation kinetics constitutes a novel light effect of the sporangiophore. At wavelength 383 nm this effect was not observed. Because a beta-carotene lacking mutant, L91 (genotype carB), was unmodified in dark-adaptation kinetics measured in the presence or absence of subliminal light, it appears that beta-carotene is not involved in the photocontrol of adaptation.

Dark Adaptation↗
PubMed1986

Effect of tyrosine administration on dopa accumulation in light- and dark-adapted retinas from normal and diabetic rats.

The interaction of tyrosine concentration and lighting on in vivo dihydroxyphenylalanine (dopa) accumulation rate was studied in retinas of normal and diabetic rats. In both groups of rats, dopa accumulation and in vitro hydroxylase activity were higher in retinas exposed to light than in those adapted to darkness. In light-adapted diabetic rats, though, retinal tyrosine level, dopa accumulation, and in vitro tyrosine hydroxylase activity were all below normal. In both normal and diabetic rats exposed to light, tyrosine injection raised retinal tyrosine concentrations and stimulated dopa accumulation. Injection of tyrosine into dark-adapted rats raised retinal tyrosine level but did not enhance dopa accumulation. Together, these results suggest that in vivo retinal amacrine cells will vary their dopa accumulation rate as a function of substrate supply, but only in the light, when tyrosine hydroxylase is activated. They further indicate that dopa accumulation rate remains sensitive to tyrosine supply in the light-activated diabetic retina.

Adaptation, Ocular↗
PubMed1978

Zinc deficiency: a cause of abnormal dark adaptation in cirrhotics.

Six stable alcoholic cirrhotics with serum zinc less than 70 microgram/100 ml had abnormal dark adaptation responses (mean dark adapted final threshold 3.2 +/- 0.6 versus 2.1 +/- 0.2 log lux in 21 age matched controls, P less than 0.01). Serum vitamin A ranged from 15 to 37 microgram/100 ml. Zinc sulfate (220 mg/day) was fed to three patients for 1 to 2 weeks and dark adapted final thresholds fell 0.9, 0.4, and 1.2 log lux without concurrent rises in serum vitamin A. Two patients were treated initially with oral vitamin A (10,000 IU/day) for 2 to 4 weeks, but their final thresholds fell to normal (2.1, 2.2 log lux) only after the addition of zinc for 1 to 2 weeks. The sixth patient, treated with vitamin A and zinc together, attained a normal final threshold in 2 weeks. The improvement in dark adaptation by zinc may be due to enhanced activity of previously depressed retinol dehydrogenase.

Aged↗