ERG Measurements of the Spectral Sensitivity of Common Chimpanzee (Pan troglodytes)

The spectral sensitivity of the common chimpanzee (Pan troglodytes) was measured with electroretinogram (ERG) flicker photometry. Chromatic adaptation conditions were used to establish the presence of S-, M- and L-cone pigments. Each of 26 chimpanzees showed substantial and approximately equivalent adaptational changes over the middle and long wavelengths implying an absence of any significant polymorphic variations in the M- and L-cone pigments. As inferred from ERG measurements, the S-cone pigment of the chimpanzee has a spectral peak of about 430 nm. Chimpanzee spectral sensitivity measurements were compared to those obtained from equivalently tested normal human trichromats. The spectral sensitivity of the two species is very similar, chimpanzees being slightly more sensitive to short wavelength lights and slightly less sensitive to long wavelength lights than human subjects. Curve-fitting analyses suggest that spectral filtering may be lower in the chimpanzee lens than it is in the human lens, and that the L/M cone ratio is lower in the chimpanzee. Copyright © 1996 Elsevier Science Ltd.     

Physiology of Normal and Abnormal Colour Vision

The physiology of colour vision is reviewed in the light of recent neurophysiological and anatomical studies in vertebrate retinas. The physiological correlate of trichromasy is the existence of three classes of cone cells, each possessing exclusively one of three photopigments with maximum spectral sensitivity at either 440 nm, 540 nm or 570 nm. The electrical responses of single cells of the various types within the retina and lateral geniculate nucleus exhibit both spatial and chromatic coding which is opponent in character. The horizontal and amacrine cells show sophisticated responses which demonstrate their important roles in the processing of information about colour vision. Human abnormal colour vision is reviewed in the light of recent psychophysical studies. Red-green dichromasy is due to the absence of one of the two photopigments normally active in the red-green range of the spectrum. In the red-green anomalous trichromasies one of the photopigments active in that range is replaced by an abnormal photopigment although the spectral loci of the peak sensitivity of these photopigments and the shape of their absorption curves have not yet been accurately identified. The traditional association of mono-chromasy with a rod-only retina has been challenged by the finding of cone cells in histological preparation of eyes of achromats, and the psychophysical evidence that more than one receptor type participates in visual function. One of these receptor types is the normal rod but the other may be a normal blue-sensitive cone or a cone filled with rhodopsin, the rod photopigment.     

Cone pigment variations in four genera of new world monkeys

Previous research revealed significant individual variations in opsin genes and cone photopigments in several species of platyrrhine (New World) monkeys and showed that these in turn can yield significant variations in color vision. To extend the understanding of the nature of color vision in New World monkeys, electroretinogram flicker photometry was used to obtain spectral sensitivity measurements from representatives of four platyrrhine genera (Cebus, Leontopithecus, Saguinus, Pithecia). Animals from each genus were found to be polymorphic for middle to long-wavelength (M/L) sensitive cones. The presence of a short-wavelength sensitive photopigment was established as well so these animals conform to the earlier pattern in predicting that all male monkeys are dichromats while, depending on their opsin gene array, individual females can be either dichromatic or trichromatic. Across subjects a total of five different M/L cone pigments were inferred with a subset of three of these present in each species.     

Detection of quantum flux modulation by single photopigments in human observers.

The action spectra of single cone photopigments of trichromatic human observers were measured by a modification of the exchange threshold technique. The quantum flux of two superimposed 2° fields, 540 and 640 nm. was adjusted to the inverse ratio of the sensitivity of either chlorolabe or erythrolabe at these wavelengths, so that one of the photopigments made a constant quantum catch. The 540 and 640 nm lights were flickered sinusoidally in counterphase above the flicker fusion frequency of the blue cones so that when the quantum fluxes were equated for chlorolabe. only erythrolabe could detect the alternation, and vice versa. This flickering field was superimposed upon a 12° background which was variable in both quantum flux and wavelength. At any wavelength between 410 and 690 nm the log of the reciprocal of the number of quanta required to extinguish the flicker of the540/640 field described the log sensitivity at that wavelength of the only photopigment capable of detecting the flicker. The log sensitivity curves thus obtained were consistent with other measures of the cone photopigments of dichromatic and trichromatic human observers.     

The gecko visual pigments. I. The thermosensitive property

The photosensitive retinal pigments of geckos extracted into aqueous digitonin solutions are characterized by an especially high sensitivity to temperature. Unlike frog rhodopsin, these pigments are bleached when the temperature is raised from 5°C. Even an increase of 5–10°C, produces some bleaching. The effect of a step increase in temperature is to bleach away the pigment to some equilibrium level depending on the magnitude of the temperature increase. Restoring the temperature back to 5°C results in a rapid regeneration of photopigment, often completely reversible. The loss and regeneration of pigment density follows closely the change in temperature, being, in effect, a thermometric property. This behavior of the gecko pigments follows temperatures up to about 30°C. Above 30°C other effects apparently occur which remain to be studied in detail. The action of these mild temperatures has been hypothesized to be an attack on the opsin, changing its conformation in an easily reversible manner. No isomerization of the 11-cis retinal is conceived to occur. This hypothesis supports the idea of an effect of mild heat quite different from light and also different from the action of higher temperatures. The former is considered to lead to isomerization as a primary process while the latter is usually viewed as resulting in a denaturation of the visual protein. The unique thermal lability of the gecko photopigments suggests that these substances may be of special value in the study of certain chemical and biological problems in visual science.     

The visual pigments,oil droplets and spectral sensitivity of the pigeon

Microspectrophotometer measurements of the oil droplets and visual pigments in the receptors of the pigeon have demonstrated the presence of at least five types of oil droplet and four visual pigments. The oil droplets act as cut-off filters, their wavelengths of 50% transmission varying depending from which area of the retina they come, but lying between 600 and 610, 560 and 570, 470 and 554, 470 and 476 and below 430 nm, and effectively cutting off light below these wavelengths. The rod receptors contain a rhodopsin withλ_max 503 nm. The dominant cone visual pigment hasλ_max 567 nm and is found in both members of the double cone and three types of single cone. Two further types of single cone contain a green-absorbing pigment (λ_max about 515 nm) and another type of single cone a blue-absorbing pigment (λ_max about 460 nm). From the transmission characteristics of the oil droplets and the absorbance spectra of the cone visual pigments, the effective spectral sensitivities of each cone type has been derived and directly related to the spectral sensitivities of isolated units in the retina and optic tectum and to the overall photopic sensitivity of the pigeon as measured behaviourally and electrophysiologically.     

Proceedings: The transmuted visual pigments of geckos

The visual pigments of geckos, like the visual cells, appear to be unique in certain respects and to pose a number of important questions to visual science. The gecko photopigments are characterized by a broad spectral distribution from close to 500 nm, in some species, to the region of 530 nm in other species. These pigments appear to be especially sensitive to NH₂OH and are destroyed by this reagent in the dark and at 5°C, at concentrations which leave the usual rhodopsins unaffected. In some species the photopigment appears to be susceptible, in part at least, to treatment of the retina with potassium alum prior to extraction. In these respects the gecko pigments appear to resemble iodopsin from the chicken retina. A singular property of the gecko photopigments is their extreme lability to mild temperature increases above 5°C. Up to about 30°C the thermal Bleaching of pigment is rapidly and often completely reversed when the temperature is returned to 5°C. This thermal lability is in sharp contrast to the behavior of frog rhodopsin which is unaffected by temperatures up to 35°C, at least in the time required to bleach the gecko pigments to equilibrium levels. The difference in action of heat and light in bleaching visual pigments is especially well illustrated with the gecko pigments, light acting by isomerizing the chromophore, heat by altering the conformation of the protein without such isomerization. a unique product, as yet unidentified, appears to result from the action of mild temperatures on the gecko pigments. The nature of this product and what it may reveal about the chemical structure of visual pigments are problems for the future.     

Spectral sensitivity and visual pigment absorbance

A discrepancy has been noted between the spectral absorbance of visual pigments in solution and the scotopic spectral sensitivity of the retina. Studies on the isolated, intact retinae ofRana pipiens andGekko gekko have shown that the absorbance of visual pigments in the intact retina is greater at longer wavelengths than the absorbance of the pigments in solution. The increased absorbance of frog rhodopsin in the intact retina can be correlated with the scotopic spectral sensitivity of the frog. These findings are extrapolated to explain the difference between the spectral absorbance of human rhodopsin (P493₁) in solution and the scotopic spectral sensitivity of man, which has a spectral maximum of 497 nm.     

Spectral sensitivities of the seahorses Hippocampus subelongatus and Hippocampus barbouri and the pipefish Stigmatopora argus

The Syngnathidae are specialized diurnal feeders that are known to possess a retinal fovea and use independent eye movements to locate, track, and strike individual planktonic prey items. In this study, we have investigated the spectral sensitivities of three syngnathid species: a pipefish and two seahorses. We used spectrophotometry to measure the spectral transmission properties of ocular lenses and microspectrophotometry to measure the spectral absorption characteristics of visual pigments in the retinal photoreceptors. The pipefish, Stigmatopora argus, together with the seahorse Hippocampus subelongatus, is found in "green-water" temperate coastal seagrass habitats, whereas the second seahorse, H. barbouri, originates from a "blue-water" tropical coral reef habitat. All species were found to possess short wavelength absorbing pigment(s) in their lenses, with the 50% cut-off point of S. argus and H. subelongatus at 429 and 425 nm respectively, whereas that of H. barbouri was located at 409 nm. Microspectrophotometry of the photoreceptors revealed that the rods of all three species contained visual pigment with the wavelength of maximum absorption (lambda(max)) at approximately 500 nm. The visual pigment complement of the cones varied between the species: all possessed single cones with a lambda(max) close to 460 nm but H. barbouri also possessed an additional class of single cone with lambda(max) at 430 nm. Three classes of visual pigment were found in the double cones, the lambda(max) being approximately 520, 537, and 560 nm in the two seahorses and 520, 537, and 580 nm in the pipefish. The spectral sensitivities of the syngnathids investigated here do not appear to conform to generally accepted trends for fishes inhabiting different spectral environments. The influence of the specialized feeding regime of the syngnathids is discussed in relation to our findings that ultra-violet sensitivity is apparently not necessary for zooplanktivory in certain habitats.     

L, M and L-M hybrid cone photopigments in man: deriving lambda max from flicker photometric spectral sensitivities

Using heterochromatic flicker photometry, we have measured the corneal spectral sensitivities of the X-chromosome-linked photopigments in 40 dichromats, 37 of whom have a single opsin gene in their tandem array. The photopigments encoded by their genes include: the alanine variant of the normal middle-wavelength sensitive photopigment, M(A180); the alanine and serine variants of the normal long-wavelength sensitive photopigment, L(A180) and L(S180); four different L-M hybrid or anomalous photopigments, L2M3(A180), L3M4(S180), L4M5(A180) and L4M5(S180); and two variants of the L-cone photopigment, encoded by genes with embedded M-cone exon two sequences, L(M2; A180) and L(M2; S180). The peak absorbances (lambda max) of the underlying photopigment spectra associated with each genotype were estimated by correcting the corneal spectral sensitivities back to the retinal level, after removing the effects of the macular and lens pigments and fitting a template of fixed shape to the dilute photopigment spectrum. Details of the genotype-phenotype correlations are summarized elsewhere (Sharpe, L. T., Stockman, A., J?gle, H., Knau, H., Klausen, G., Reitner, A. et al. (1998). J. Neuroscience, 18, 10053-10069). Here, we present the individual corneal spectral sensitivities for the first time as well as details and a comparison of three analyses used to estimate the lambda max values, including one in which the lens and macular pigment densities of each observer were individually measured.     

A grey squirrel spectral sensitivity by heterochromatic flicker and its implications

A behavioural spectral sensitivity curve for the grey squirrel (Sciurus carolinensis leucotis). at a light level about 3.5 log units above its scotopic threshold, is found by heterochromatic flicker photometry.The overall sensitivity maximum is near 525 nm, and there is a dip in the curve near 491 nm. significant at the ± 95% confidence level, as found in other squirrels.The possible contribution of a colour-opponent system is considered. In view of Loew's MSP identification of P500 in the r-type, and P543 in the c-type receptors, the relationship of the squirrel's visual performance to these pigments is discussed.In the absence of any other receptor type, the possibility is considered that the structurally ambiguous r-type might take part in antagonistic interaction at photopic levels, as well as mediating scotopic vision.     

The visual pigments and oil droplets of the chicken retina

Microspectrophotometer measurements of the oil droplets and visual pigments in the receptors of the chicken have led to the conclusion that there are six types of oil droplet and three visual pigments. Four of the oil droplet types apparently act as cut-off filters, their wavelengths of 50% transmission lying at 575, 520, 497, 454 and effectively cutting off light below these wavelengths. The rod receptors contain a rhodopsin of λ_max 506 nm and no oil droplet. Three types of single cone and both members of the double cones contain a pigment of λ_max 569 nm, while the fourth type of single cone contains a pigment of λ_max 497 nm. Calculations of the light transmitted by the oil droplet and absorbed by the cone pigment suggest that two of the single cone types have narrow spectral sensitivity curves of λ_max 606 and 533 nm, while the other three cone types have rather broad curves. all peaking at 569 nm, but with different cut-off points in the blue and near-u.v. regions. Interactions between these could lead to a blue-sensitive mechanism. The maxima of the two narrow-band sensitivities seem to coincide with critical regions in the spectral distribution of light in the bird's natural environment.     

Modelling the Rayleigh match

We use the photopigment template of Baylor et al. (1987) to define the set of Rayleigh matches that would be satisfied by a photopigment having a given wavelength of peak sensitivity (lambda(max)) and a given optical density (OD). For an observer with two photopigments in the region of the Rayleigh primaries, the observer's unique match is defined by the intersection of the sets of matches that satisfy the individual pigments. The use of a template allows us to illustrate the general behavior of Rayleigh matches as the absorption spectra of the underlying spectra are altered. In a plot of the Y setting against the red-green ratio (R), both an increase in lambda(max) and an increase in optical density lead to an anticlockwise rotation of the locus of the matches satisfied by a given pigment. Since both these factors affect the match, it is not possible to reverse the analysis and define uniquely the photopigments corresponding to a specific Rayleigh match. However, a way to constrain the set of candidate photopigments would be to determine the trajectory of the change of match as the effective optical density is altered (by, say, bleaching or field size).     

The relationship between cone pigments and behavioural sensitivity in a New World monkey (Callithrix jacchus jacchus).

Microspectrophotometric measurements of visual pigments and behavioural measurements of spectral sensitivity are reported for individual marmosets from 3 family groups. The sex differences and polymorphism that characterise the long-wave cone pigments in this species are well reflected by variations in the behavioural sensitivities. With one exception, the pattern of inheritance is compatible with a genetic model in which the long-wave pigment is specified by a single polymorphic locus on the X-chromosome. Measurements are also reported for the spectral absorbance of the marmoset lens, and these are used to reconstruct short-wave behavioural sensitivity from the microspectrophotometric measurements of the short-wave cones.     

Photoreceptor signals and vision. Proctor lecture

In recent years, there has been rapid progress in understanding the properties and mechanism of generation of the light-evoked electrical signals of vertebrate rods and cones. The graded hyperpolarization that carries information over the length of the cell is generated by closure of cation-selective aqueous pores in the surface membrane of the outer segment. These pores are controlled cooperatively by cyclic GMP, which acts continuously in darkness to keep the pores open. Photoisomerization of rhodopsin or cone pigment produces the rapid amplified activation of phosphodiesterase, which lowers the concentration of cGMP, thereby lowering the conductance of the surface membrane. Calcium ions, once thought to relay excitation to the light-sensitive channels, do not play this role. Instead, they appear to participate in a feedback control mechanism that regulates the nucleotide cascade. Although some general features of the transduction mechanism are now understood, a number of important questions remain. How is the nucleotide cascade shut off? Where does Ca act? What is the structure of the light-sensitive channel? How are stereotyped single photon responses produced? Primate photoreceptors are no longer off limits to single cell electrophysiology. Analysis of the response properties and dark noise of primate rods gives a physiological basis for several fundamental features of human rod vision: single photon detection, poor temporal resolution, the "dark light," rod saturation, scotopic spectral sensitivity, and, perhaps, after-image signals. Primate cones show less sensitive but faster responses shaped by a resonance which may figure in the flicker sensitivity of human cone vision. The spectral sensitivity of the three types of primate cones has been determined over the entire visible region. These sensitivities satisfactorily predict human color matching. The spectral sensitivity curves indicate that the pigment in a given cone is very pure, and that individual cones of a given type normally contain pigments with very similar or identical spectral properties.     

Application of an invariant spectral form to the visual pigments of crustaceans: implications regarding the binding of the chromophore

Visual pigment absorption spectra were measured in single photoreceptors of a stomatopod, a crayfish, a hermit crab, and five species of brachyuran crab. All fitted a Mansfield (1985) invariant form for visual pigment, the form also fitted by vertebrate retinal-based visual pigments. This is consistent with a theoretical model based on the structure of visual pigment molecules (Greenberg et al., 1975; Honig et al., 1976) which predicts that spectral bandwidth decreases as lambda max increases. The conformation to the invariant form implies that for any given chromophore bandwidth times lambda max is a constant.     

Spectral sensitivity of the photointrinsic iris in the red-eared slider turtle (Trachemys scripta elegans)

Our goal in this study was to examine the red-eared slider turtle for a photomechanical response (PMR) and define its spectral sensitivity. Pupils of enucleated eyes constricted to light by ∼11%, which was one-third the response measured in alert behaving turtles at ∼33%. Rates of constriction in enucleated eyes that were measured by time constants (1.44-3.70 min) were similar to those measured in turtles at 1.97 min. Dilation recovery rates during dark adaptation for enucleated eyes were predicted using line equations and computed times for reaching maximum sizes between 26 and 44 min. Times were comparable to the measures in turtles where maximum pupil size occurred within 40 min and possessed a time constant of 12.78 min. Hill equations were used to derive irradiance threshold values from enucleated hemisected eyes and then plot a spectral sensitivity curve. The analysis of the slopes and maximum responses revealed contribution from at least two different photopigments, one with a peak at 410 nm and another with a peak at 480 nm. Fits by template equations suggest that contractions are triggered by multiple photopigments in the iris including an opsin-based visual pigment and some other novel photopigment, or a cryptochrome with an absorbance spectrum significantly different from that used in our model. In addition to being regulated by retinal feedback via parasympathetic nervous pathways, the results support that the iris musculature is photointrinsically responsive. In the turtle, the control of its direct pupillary light response (dPLR) includes photoreceptive mechanisms occurring both in its iris and in its retina.     

Visual pigment reconstitution in intact goldfish retina using synthetic retinaldehyde isomers

A protocol has been developed for reconstituting visual pigments in intact retinae by delivering synthetic isomers of retinal incorporated in phospholipid vesicles. Calibration curves have been constructed relating the lambda(max) of the native porphyropsins (visual pigments based on 11-cis 3-dehydroretinal) of the rods and four spectral classes of cone in the goldfish, and the equivalent photosensitive pigments regenerated from 11-cis retinal (rhodopsins) and the commercially available isomer, 9-cis retinal (isorhodopsins). The relationship between the lambda(max) of rhodopsins and isorhodopsins appears to be linear, such that the difference in lambda(max) changes sign at about 380 nm. We therefore conclude that the protocol for reconstituting visual pigments with 9-cis retinal is suitable for all classes of vertebrate opsin-based photopigments.     

The thermal contribution to photoactivation in A2 visual pigments studied by temperature effects on spectral properties

Effects of temperature on the spectral properties of visual pigments were measured in the physiological range (5-28 degrees C) in photoreceptor cells of bullfrog (Rana catesbeiana) and crucian carp (Carassius carassius). Absorbance spectra recorded by microspectrophotometry (MSP) in single cells and sensitivity spectra recorded by electroretinography (ERG) across the isolated retina were combined to yield accurate composite spectra from ca. 400 nm to 800 nm. The four photoreceptor types selected for study allowed three comparisons illuminating the properties of pigments using the dehydroretinal (A2) chromophore: (1) the two members of an A1/A2 pigment pair with the same opsin (porphyropsin vs. rhodopsin in bullfrog "red" rods); (2) two A2 pigments with similar spectra (porphyropsin rods of bullfrog and crucian carp); and (3) two A2 pigments with different spectra (rods vs. long-wavelength-sensitive (L-) cones of crucian carp). Qualitatively, the temperature effects on A2 pigments were similar to those described previously for the A1 pigment of toad "red" rods. Warming caused an increase in relative sensitivities at very long wavelengths but additionally a small shift of lambdamax toward shorter wavelengths. The former effect was used for estimating the minimum energy required for photoactivation (Ea) of the pigment. Bullfrog rod opsin with A2 chromophore had Ea = 44.2 +/- 0.9 kcal/mol, significantly lower (one-tailed P < 0.05) than the value Ea = 46.5 +/- 0.8 kcal/mol for the same opsin coupled to A1. The A2 rod pigment of crucian carp had Ea = 42.3 +/- 0.6 kcal/mol, which is significantly higher (one-tailed P < 0.01) than that of the L-cones in the same retina (Ea = 38.3 +/- 0.4 kcal/mol), whereas the difference compared with the bullfrog A2 rod pigment is not statistically significant (two-tailed P = 0.13). No strict connection between lambdamax and Ea appears to exist among A2 pigments any more than among A1 pigments. Still, the A1 --> A2 chromophore substitution in bullfrog opsin causes three changes correlated as originally hypothesized by Barlow (1957): a red-shift of lambdamax, a decrease in Ea, and an increase in thermal noise.     

Spectral sensitivity of melatonin suppression in the zebrafish pineal gland

The pineal gland of the zebrafish (Danio rerio) is a clock-containing photoreceptive organ. Superfused pineal glands kept in darkness display rhythmic melatonin production that lasts for days, with high melatonin levels during the night and low levels during the day. Nocturnal light, however, evokes an acute suppression of melatonin synthesis in the photoreceptor cells. Towards characterizing zebrafish pineal photopigment that is involved in the acute melatonin suppression we have measured the spectral sensitivity of melatonin-suppression response in superfused pineal glands. The effect of 2 h light exposure of seven wavelengths (lambdaavg 408, 460, 512, 560, 608, 660 and 697+/-10-15 nm) at multiple irradiances (10(7)-10(14) photons/cm2/s) was determined, and an action spectrum was plotted. The resultant action spectrum provides evidence for the involvement of multiple photopigments in melatonin suppression. The most efficient melatonin-suppression response was achieved by exposure to light of around 512 nm; however, another peak of lower irradiance sensitivity was observed in the middle to long wavelengths. Opsins-specific RT-PCR analysis confirmed the expression of exo-rhodopsin and visual red-sensitive opsin in the pineal gland, while other zebrafish visual opsins as well as VA and VAL opsins were not detected. Dartnall monograms for exo-rhodopsin and visual red-sensitive opsin account for most but not all of the spectral sensitivity features. Therefore, additional pineal photopigments may contribute to the melatonin-suppression response in the pineal gland.