Class Of Cones Research Articles

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 λmax 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 λmax of rhodopsins and isorhodopsins appears to be linear, such that the difference in λmax 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.

Genetic basis of total colourblindness among the Pingelapese islanders.

Complete achromatopsia is a rare, autosomal recessive disorder characterized by photophobia, low visual acuity, nystagmus and a total inability to distinguish colours. In this disease, cone photoreceptors, the retinal sensory neurons mediating colour vision, seem viable but fail to generate an electrical response to light. Achromatopsia, or rod monochromatism, was first mapped to 2p11-2q12 (MIM 216900; ref. 3), where it is associated with missense mutations in CNGA3 (ref. 4). CNGA3 encodes the alpha-subunit of the cone cyclic nucleotide-gated cation channel, which generates the light-evoked electrical responses of cone photoreceptors. A second locus at 8q21-q22 has been identified among the Pingelapese islanders of Micronesia, who have a high incidence of recessive achromatopsia (MIM 262300). Here we narrow the achromatopsia locus to 1.4 cM and show that Pingelapese achromatopsia segregates with a missense mutation at a highly conserved site in CNGB3, a new gene that encodes the beta-subunit of the cone cyclic nucleotide-gated cation channel. Two independent frameshift deletions establish that achromatopsia is the null phenotype of CNGB3. Combined with earlier findings, our results demonstrate that both alpha- and beta-subunits of the cGMP-gated channel are essential for phototransduction in all three classes of cones.

Role of Microstructure in Dynamic Fatigue of Glass‐Ceramics after Contact with Spheres

Dynamic fatigue data are reported for fine‐ and coarse‐grained micaceous glass‐ceramics after contact damage with spheres. The strengths of indented specimens are measured at stressing rates from ∼10−2 to 104 MPa·s−1 in water. The strength degradation is substantially faster in the coarse‐grained structure, and is accelerated further by multicycle contact loading. Failures originate from contact sites in all cases but undergo a progressive transition from classical cone cracks to quasi‐plastic microcrack zones with increases in the grain size and the number of contact cycles. The results highlight the particularly deleterious effect of quasi‐plastic damage accumulation on lifetime.

Cone pigment gene expression in individual photoreceptors and the chromatic topography of the retina.

Human trichromatic vision is based on three classes of cones: L, M, and S (long-, middle-, and short-wavelength sensitive, respectively). Individuals can have more than one M and/or more than one L pigment gene on the X chromosome along with an S pigment gene on chromosome 7. In some people the X-linked pigment gene array can include polymorphic variants that encode multiple, spectrally distinct cone photopigment subtypes. A single-cell, polymerase chain reaction approach was used to examine visual pigment gene expression in individual human cone cells and identify them as L or M. The ratio of L:M pigment gene expression was assayed in homogenized retinal tissues taken from the same eyes. Results indicate that there is a close correspondence between the cone ratio determined from counting single cells and the L:M pigment mRNA ratio estimated from homogenized pieces of retina. The results also show that the different pigment genes in one array are often expressed at very different levels, giving rise to unequal numbers of L and M cones. Expression of only one photopigment gene was detected in each cone cell. However, individual males can have more than the classically described three spectrally distinct cone types in their retinas.

Photoreceptor classes and transmission at the photoreceptor synapse in the retina of the clawed frog,Xenopus laevis

The photoreceptor population in Xenopus consists of a green-sensitive rod (lambda(max) = 523 nm), a blue-sensitive rod (lambda(max) = 445 nm) and three classes of cone. The largest cone is red-sensitive (lambda(max) = 611 nm). The intermediate cone is presumed to be blue-sensitive based on physiological criteria, whereas the miniature cone may be UV-sensitive. Horizontal cells (HC) are of two sorts: axon-bearing and axonless. The axon-bearing HC is of the luminosity type and probably contacts all types of photoreceptor. The axonless HC is of the chromaticity type and contacts only intermediate (blue) cones and at least one type of rod. During development dendrites of HCs and bipolar neurons penetrate photoreceptor bases. A progressive maturation of HC and bipolar synapses with rods and cones occurs between tadpoles stages 37/8 and 46. Neighboring rods and cones are joined by gap junctions. During this same period, the outer segments are laid down and photopigments synthesized. A linear relation was found between the quantum capturing ability of the rod and its absolute threshold. Mature rods of the Xenopus retina release glutamate in a calcium-dependent manner. Glutamate release was found to be a linear function of calcium influx through L-type calcium channels. Both types of HC possess ionotropic glutamate receptors of the AMPA subtype.

A journey in color space

The idea that the first stage in normal daylight vision is characterized by three processes having different spectral sensitivities was established early in the 19th century by Young1 and linked clearly to experimental data on color matching by Maxwell.2 Hering's3 notion of opponent processes was grounded in facts of color appearance. A number of “opponent process” theories were developed to account for color appearance, in which the signals from the receptors were combined to form two channels conveying chromatic information and a third carrying achromatic information.4 More recently psychophysical, as opposed to phenomenological, evidence has been advanced in support of the existence of opponent mechanisms.5–12 While these articles provided evidence for the interaction of cone signals, they did not determine in detail the weights of the contributions of the different classes of cones to the second stage (and higher-order) mechanisms. The work discussed here was intended to determine the weights of the second-stage mechanisms by psychophysical means.13 Quantitative reanalysis of the results of habituation experiments demonstrated the existence of higher-order mechanisms that respond to the sums of the signals from second-stage mechanisms.14 Diverse evidence from other psychophysical experiments including detection and discrimination of chromatic pulses,14 and coherence of plaid patterns,15 confirmed the existence of higher-order mechanisms. Single unit recording from striate cortex in monkey revealed cells having the spectral sensitivities implied by the psychophysical results.16 Electrical recording of responses in monkey lateral geniculate nucleus (LGN) revealed single units with weights corresponding to the cardinal directions psychophysically determined.17 LGN cells show no sign of fatigue but units in V1 do.18 They also exhibit the wide range of spectral sensitivities required of higher-order mechanisms. Studies of the influence of the chromatic content of stimuli on vernier acuity and motion thresholds and on temporal modulation sensitivity support the conjecture that, while chromatic stimuli are processed solely by the parvocellular system, luminance stimuli are processed by both magno- and parvocellular neurons. The variation of the relative sensitivity of the L and M cones with temporal frequency, together with analysis of the statistics of color appearance of small, brief, near threshold monochromatic stimuli and data from Stiles's increment threshold experiment19 suggest that the numerosity ratio of L:M cones in the normal human fovea is more likely to be 1:1 than 2:1. © 2000 John Wiley & Sons, Inc. Col Res Appl, 26, S2–S11, 2001

Color—luminance relationships and the McCollough effect

The McCollough effect is an orientation-specific color aftereffect induced by adapting to colored gratings. We examined how the McCollough effect depends on the relationships between color and luminance within the inducing and test gratings and compared the aftereffects to the color changes predicted from selective adaptation to different color-luminance combinations. Our results suggest that the important contingency underlying the McCollough effect is between orientation and color-luminance direction and are consistent with sensitivity changes within mechanisms tuned to specific color-luminance directions. Aftereffects are similar in magnitude for adapting color pairs that differ only in S cone excitation or L and M cone excitation, and they have a similar dependence on spatial frequency. In particular, orientation-specific aftereffects are induced for S cone colors even when the grating frequencies are above the S cone resolution limit. Thus, the McCollough effect persists even when different cone classes encode the orientation and color of the gratings.

THE ENERGY AND ANGULAR DISTRIBUTIONS OF LOW-ENERGY He+ SCATTERED FROM Al(111)

Measurements of 500 eV 4 He + scattered from Al(111) surfaces provide detailed information about the scattering process and surface crystallography. We report various observations concerning collision inelasticity, multiple scattering, and shadow-cone focusing effects. A large inelastic energy loss of the scattered He + is observed, which causes multiple-scattering events at oblique incidence angles to have energies below the elastic single-scattering energy. Inelastic He + scattering from clean, ordered Al(111) shows interesting intensity variations as a function of azimuthal orientation and incidence angle. At a critical incidence angle, where the top edge of a shadow cone intersects a nearest-neighbor Al surface atom, the scattered ion intensity exhibits 60° azimuthal periodicity. At a more glancing angle of incidence, a double-peaked structure appears. The scattered He + intensity varies as a function of incidence angle, as expected from classical shadow cone calculations.

Influence of cold rolling and strain rate on plastic response of powder metallurgy and chemical vapor deposition rhenium

The plastic response of two kinds of rhenium processed via powder metallurgy (PM) and chemical vapor deposition (CVD) were investigated under uniaxial compression over a range of strain rates. The PM rhenium, further cold rolled to 50 and 80 pct of the original thickness, was also investigated to assess the influence of cold work on the plastic behavior. A strong basal texture was detected in all the preceding materials as a result of processing and cold work. Both CVD and PM rhenium exhibited an increase in yield strength and flow stress with increasing strain rate. In PM rhenium, cold work resulted in an increase in hardness and yield strength and a decrease in the work hardening rate. The deformed microstructures revealed extensive twinning in CVD rhenium. At large strains, inhomogeneous deformation mode in the form of classical cup and cone fracture was noticed.

Visual pigments, cone oil droplets, ocular media and predicted spectral sensitivity in the domestic turkey ( Meleagris gallopavo)

A microspectrophotometric survey conducted on the retinal photoreceptors of the domestic turkey ( Meleagris gallopavo) revealed the presence of five different types of vitamin A 1-based visual pigment (rhodopsin) in seven different types of photoreceptor. A single class of rod contained a medium wavelength-sensitive visual pigment (wavelength of maximum absorbance, λ max, 504 nm). Four different types of single cone contained visual pigment maximally sensitive to wavelengths in either the long (LWS, λ max 564 nm), medium (MWS, λ max 505 nm), short (SWS, λ max 460 nm) or violet (VS, λ max 420 nm) spectral ranges. The LWS, MWS and SWS single cones contained pigmented oil droplets with cut-off wavelengths ( λ cut) at 514, 490 and 437 nm, respectively. The VS single cone contained a transparent oil droplet which displayed no significant absorbance above 330 nm. A single class of double cone was also identified, both the principal and accessory members of which contained the LWS cone visual pigment. The principal member contained an oil droplet with a λ cut at 436 nm. No oil droplet was observed in the accessory member. The use of a glycerol-based cell mountant, which reduced wavelength dependent measurement artefacts in the microspectrophotometric measurements, is described. Predictions of cone effective spectral sensitivity, incorporating measurements of the spectral transmission of the ocular media, suggest that turkeys have considerable sensitivity to wavelengths in the ultraviolet-A (UV-A, 315–400 nm) spectral range. This has implications for both the visual ecology of wild birds and the welfare of intensively farmed individuals.

Heat Kernels of Lorentz Cones

AbstractWe obtain an explicit formula for heat kernels of Lorentz cones, a family of classical symmetric cones. By this formula, the heat kernel of a Lorentz cone is expressed by a function of time t and two eigenvalues of an element in the cone. We obtain also upper and lower bounds for the heat kernels of Lorentz cones.

Visual pigments and oil droplets in the retina of a passerine bird, the canary Serinus canaria: microspectrophotometry and opsin sequences

The visual receptors of the passeriform bird Serinus canaria, the canary, have been examined microspectrophotometrically and the sequences of the opsins determined. Rods have a maximum absorbance ( λ max) at 506 nm. Four spectral classes of single cone are present: long-wave-sensitive (LWS) containing a photopigment with λ max at 569 nm, middle-wave-sensitive (MWS) with λ max at 505 nm, short-wave-sensitive (SWS) with λ max at 442 nm, and ultraviolet-sensitive (UVS) with λ max at about 366 nm. Double cones possess the 569-nm pigment in both members. Typical combinations of photopigment and oil droplet occur in most cone classes. An ambiguity exists in the oil droplet of the single LWS cones. In some birds, LWS cones are paired with an R-type droplet, whereas in the majority of canaries the LWS pigment is paired with a droplet similar to the P-type of double cones. Mechanisms of spectral tuning within each opsin class are discussed.

The arrangement of the three cone classes in the living human eye.

Human colour vision depends on three classes of receptor, the short- (S), medium- (M), and long- (L) wavelength-sensitive cones. These cone classes are interleaved in a single mosaic so that, at each point in the retina, only a single class of cone samples the retinal image. As a consequence, observers with normal trichromatic colour vision are necessarily colour blind on a local spatial scale. The limits this places on vision depend on the relative numbers and arrangement of cones. Although the topography of human S cones is known, the human L- and M-cone submosaics have resisted analysis. Adaptive optics, a technique used to overcome blur in ground-based telescopes, can also overcome blur in the eye, allowing the sharpest images ever taken of the living retina. Here we combine adaptive optics and retinal densitometry to obtain what are, to our knowledge, the first images of the arrangement of S, M and L cones in the living human eye. The proportion of L to M cones is strikingly different in two male subjects, each of whom has normal colour vision. The mosaics of both subjects have large patches in which either M or L cones are missing. This arrangement reduces the eye's ability to recover colour variations of high spatial frequency in the environment but may improve the recovery of luminance variations of high spatial frequency.

Cone receptor variations and their functional consequences in two species of hamster.

Results from earlier experiments indicate that different species of rodent vary both in the number of cone types found in their retinas and in the spectral sensitivities of the cone pigments. These features have now been examined in two types of hamster commonly used for research purposes: Syrian golden hamsters (Mesocricetus auratus) and Siberian dwarf hamsters (Phodopus sungorus). Electroretinogram (ERG) flicker photometry, behavioral discrimination tasks, and opsin antibody labeling were used to investigate hamster photoreceptors and their visual consequences. Results from the three approaches support the following conclusions: (1) The retinas of both species have an abundant population of rods containing a photopigment with peak sensitivity of about 498-500 nm; (2) Siberian dwarf hamsters have two classes of cone: one with maximum sensitivity in the ultraviolet (c. 360 nm), the other with peak sensitivity closely similar to that of its rod; and (3) Syrian golden hamsters have a class of cone with peak sensitivity at about 506 nm, but they lack a second cone type. Implications of these alternative arrangements are discussed.

Variational Inequality with Fuzzy Convex Cone

In this study, we discuss one type of variational inequality problem with a fuzzy convex cone \tilde{X}, denoted by VI(\tilde{X}, f). Different classes of fuzzy convex cones which are considered in different context of the problems will be discussed. According to the existence theorem, an approach derived from the concepts of multiple objective mathematical programming problems for solving the VI(\tilde{X}, f) is proposed. An algorithm is developed to find its fuzzy optimal solution set with complexity analysis.

Macular pigment densities derived from central and peripheral spectral sensitivity differences

Estimates of the density spectrum of the macular pigment (Wyszecki G, Stiles WS. Color Science: Concepts and Methods, Quantitative Data and Formulas. 1st ed. New York: Wiley, 1967); (Vos JJ. Literature review of human macular absorption in the visible and its consequences for the cone receptor primaries. Institute for Perception. Soesterberg, The Netherlands, 1972) are partially based on the difference between central and peripheral spectral sensitivities, measured under conditions chosen to isolate a single cone class (Stiles WS. Madrid: Union Internationale de Physique Pure et Appliquée. 1953:1:65–103). Such derivations assume that the isolated spectral sensitivity is the same at both retinal locations, save for the intervening macular pigment. If this is true, then the type of cone class mediating detection should not influence the calculated difference spectrum. To test this assumption, we measured central and peripheral spectral sensitivities in a deuteranope, a protanope and a normal trichromat observer: (a) for short-wave sensitive (S-) cone detection; and (b) for long-wave sensitive (L-) cone detection (deuteranope), for middle-wave sensitive (M-) cone detection (protanope) or for both L- and M-cone detection (normal trichromat). The difference spectra determined for L- or M-cone detection deviate significantly from those measured for S-cone detection, at wavelengths below 450 nm. A theoretical analysis suggests that the discrepancies are owing, in part, to regional variation in the optical density of the cone pigments; and that such receptor variation cannot be ignored when deriving the standard density spectrum of the macular pigment.

Effect of Starting Powder on Damage Resistance of Silicon Nitrides

The role of starting powder in the resistance of silicon nitride (Si3 N4) ceramics to strength‐impairing contact damage is studied. Si2N4 materials are prepared from three starting powders, at selectively increasing hot‐pressing temperatures to coarsen the microstructures: (i) from relatively coarse α‐phase powder, essentially equiaxed α‐Si3N4 grains, with limited, slow transformation to β‐Si3N4 grains toward the latter half of the temperature range; (ii) from relatively fine α‐phase powder, a more rapid transfor‐mation to β‐Si3N4, with attendant grain elongation; (iii) from fine β‐phase powder, an essentially equiaxed β‐Si3N4 structure over the entire temperature range. The resulting microstructures thereby provide a spectrum of β/α phase ratios and grain sizes and shapes for investigation. Indentations with hard spheres (Hertzian test) are used to induce damage into the Si3N4 specimens. Examination of the indentation sites indicates a competition between brittle and quasi‐plastic damage modes: in structures with relatively equiaxed grains, the damage takes the form of classical cone cracking; in structures with large elongate grains, the damage is distributed beneath the contact as grain‐localized microfailures within a subsurface “yield” zone. Bend tests on specimens containing single‐cycle contact damage reveal those structures with well‐developed cone cracks to be highly susceptible to strength degradation. The microstructures with the greatest resistance to strength loss are those formed from fine α‐phase starting powder at intermediate firing temperatures (1700°C), with characteristic large, elongate β grains. Implications of the results in the context of other mechanical properties, e.g., toughness, wear, and fatigue resistance, are discussed.

Visual pigments, oil droplets and cone photoreceptor distribution in the european starling (Sturnus vulgaris)

Microspectrophotometric measurements of retinal photoreceptors from the European starling (Sturnus vulgaris) revealed four classes of single cone, containing visual pigments with wavelengths of maximum absorbance (<IMG src="/images/symbols/lambda.gif" WIDTH="8" HEIGHT="12" ALIGN="BOTTOM" NATURALSIZEFLAG= "3">max) at 563, 504, 449 and close to 362 nm. The two longer-wave-sensitive single cones contained brightly coloured oil droplets which cut off light below 572 and 514 nm, respectively. The 449 nm <IMG src="/images/symbols/lambda.gif" WIDTH="8" HEIGHT="12" ALIGN="BOTTOM" NATURALSIZEFLAG="3">max pigment was associated with a 'colourless' oil droplet with peak measured absorptance below 400 nm. The ultraviolet-sensitive visual pigment was paired with a transparent oil droplet which showed no significant absorption above 350 nm. A single class of double cone was identified, both members of which contained the longwave-sensitive (<IMG src="/images/symbols/lambda.gif" WIDTH="8" HEIGHT= "12" ALIGN="BOTTOM" NATURALSIZEFLAG="3">max 563 nm) visual pigment. The principal member of the double cone contained an oil droplet with a topographically variable cut-off wavelength below 471 nm; the oil droplet found in the accessory member was only measured in the ventral retina and displayed three distinct peaks of absorption at approximately 430, 450 and 480 nm. Rod photoreceptors had a <IMG src="/images/symbols/lambda.gif" WIDTH="8" HEIGHT="12" ALIGN="BOTTOM" NATURALSIZEFLAG="3">max at 503 nm. A new polynomial for fitting visual pigment templates to ultraviolet-sensitive visual pigment data is given. Topographic density measurements of the different cone classes were made using Nitroblue-tetrazolium chloride to label selectively bleached photoreceptors. The two classes of shortwave-sensitive single cone were more abundant in the dorsal retina, and longwave-sensitive single cones were notably less abundant in the dorso-temporal region of the retina, which subserves binocular vision.

Evolution of colour vision in vertebrates.

The expression of five major families of visual pigments occurred early in vertebrae evolution, probably about 350-400 million years ago, before the separation of the major vertebrate classes. Phylogenetic analysis of opsin gene sequences suggests that the ancestral pigments were cone pigments, with rod pigments evolving last. Modern teleosts, reptiles and birds have genera that possess rods and four spectral classes of cone each representing one of the five visual pigment families. The complement of four spectrally distinct cone classes endows these species with the potential for tetrachromatic colour vision. In contrast, probably because of their nocturnal ancestry, mammals have rod-dominated retinas with colour vision reduced to a basic dichromatic system subserved by only two spectral classes of cone. It is only within primates, about 35 millions years ago, that mammals 're-evolved' a higher level of colour vision: trichromacy. This was achieved by a gene duplication within the longer-wave cone class to produce two spectrally distinct members of the same visual pigment family which, in conjunction with a short-wavelength pigment, provide the three spectral classes of cone necessary to subserve trichromacy.

Spectral sensitivity of the feedback signal from horizontal cells to cones in goldfish retina.

The spectral sensitivity of cones in isolated goldfish retina was determined with whole-cell recording techniques. Three spectral classes of cones were found with maximal sensitivities around 620 nm, 540 nm, and 460 nm. UV-cones were not found because our stimulator did not allow effective stimulation in the UV range. The spectral sensitivity of the cones closely matched the cone photopigment absorption spectra at the long wavelength side of the spectrum, but deviated significantly at shorter wavelengths. Surround stimulation induced an inward current in cones due to feedback from horizontal cells. The spectral sensitivity of this feedback signal was determined in all three cone classes and found to be broader than the spectral sensitivity of the cones recorded from, and to be spectrally nonopponent. These data are consistent with a connectivity scheme between cones and horizontal cells in which the three horizontal cell systems feed back to all cone systems and in which all horizontal cell systems receive input from more than one cone system.