A blue sensitive mechanism in the pigeon retina: lambda max 400 nm

Autoshaping as a psychophysical paradigm: Absolute visual sensitivity in the pigeon

A classical conditioning procedure (autoshaping) was used to determine absolute visual threshold in the pigeon. This method provides the basis for a standardized visual psychophysical paradigm.

Spatial and temporal patterns of growth and differentiation of cone oil droplets in the chick retina

Avian cone photoreceptors have an oil droplet in the outer portion of their inner segment that acts as a long-pass cut-off filter between incident light and visual pigment. Chick cone droplets are mainly red, orange, yellow, green, and colorless, and the colors are due to three carotenoid pigments with characteristic absorption spectra. Little is known of the differentiation of this organelle, the natural marker of cones, and the little that is known is largely controversial. We used flat whole-mounts of fresh retinas to study the time and place of the appearance of droplets, their growth rates, the sequence of droplet color differentiation, and the spatial distribution of these colors. We show that droplet differentiation starts on embryonic Day 10 (E10) in a relatively small area above the optic nerve head. The differentiation spreads to the rest of the retina in a manner similar to that of photoreceptor neurogenesis, with three decreasing gradients of droplet size and color between E13-E20: from central to peripheral, dorsal to ventral, and temporal to nasal. The rate of growth of the droplets was not constant, but showed a maximum between E17 and postnatal Day 1 (P1) in most of the retinal zones. Color differentiation started at E16-E17, 5-6 days after their appearance, when the droplets were already of considerable size. Initially, all droplets were colorless, and then turned pale green or yellow to acquire progressively the mature colors. Differentiation ended in the whole retina by P15, with ventral droplets of larger diameter than dorsal ones, the peripheral ones generally larger than the central ones, and with the color distribution varying with the retinal area. Our results show that growth and color differentiation of the droplets is regulated temporally and spatially, and the cones complete differentiation at P15 rather than at prenatal stages, as is thought generally.

Genetic analyses of visual pigments of the pigeon (Columba livia)

We isolated five classes of retinal opsin genes rh1(Cl), rh2(Cl), sws1(Cl), sws2(Cl), and lws(Cl) from the pigeon; these encode RH1(Cl), RH2(Cl), SWS1(Cl), SWS2(Cl), and LWS(Cl) opsins, respectively. Upon binding to 11-cis-retinal, these opsins regenerate the corresponding photosensitive molecules, visual pigments. The absorbance spectra of visual pigments have a broad bell shape with the peak, being called lambdamax. Previously, the SWS1(Cl) opsin cDNA was isolated from the pigeon retinal RNA, expressed in cultured COS1 cells, reconstituted with 11-cis-retinal, and the lambdamax of the resulting SWS1(Cl) pigment was shown to be 393 nm. In this article, using the same methods, the lambdamax values of RH1(Cl), RH2(Cl), SWS2(Cl), and LWS(Cl) pigments were determined to be 502, 503, 448, and 559 nm, respectively. The pigeon is also known for its UV vision, detecting light at 320-380 nm. Being the only pigments that absorb light below 400 nm, the SWS1(Cl) pigments must mediate its UV vision. We also determined that a nonretinal P(Cl) pigment in the pineal gland of the pigeon has a lambdamax value at 481 nm.

Visual pigments and oil droplets from six classes of photoreceptor in the retinas of birds

Microspectrophotometric examination of the retinal photoreceptors of the budgerigar (shell parakeet), Melopsittacus undulatus (Psittaciformes) and the zebra finch, Taeniopygia guttata (Passeriformes), demonstrate the presence of four, spectrally distinct classes of single cone that contain visual pigments absorbing maximally at about 565, 507, 430-445 and 360-380 nm. The three longer-wave cone classes contain coloured oil droplets acting as long pass filters with cut-offs at about 570, 500-520 and 445 nm, respectively, whereas the ultraviolet-sensitive cones contain a transparent droplet. The two species possess double cones in which both members contain the long-wave-sensitive visual pigment, but only the principal member contains an oil droplet, with cut-off at about 420 nm. A survey of the cones of the pigeon, Columba livia (Columbiformes), confirms the presence of the three longer-wave classes of single cone, but also reveals the presence of a fourth class containing a visual pigment with maximum absorbance at about 409 nm, combined with a transparent droplet. No evidence was found for a fifth, ultraviolet-sensitive receptor. In the chicken, Gallus gallus (Galliformes), the cone class with a transparent droplet contains "chicken violet" with maximum absorbance at about 418 nm. The rods of all four species contain visual pigments that are spectrally similar, with maximum absorbance between about 506 and 509 nm. Noticeably, in any given species, the maximum absorbance of the rods is spectrally very similar to the maximum absorbance of the middle-wavelength-sensitive cone pigments.

Ultraviolet vision in a passeriform bird: from receptor spectral sensitivity to overall spectral sensitivity in Leiothrix lutea

A survey of recent results out of spectrophotometric, microspectrophotometric, and behavioral tests concerning the UV vision of the passeriform bird Leiothrix lutea is presented. In the spectrophotometric study it was shown that the ocular media of Leiothrix' eyes are highly transparent to the near UV with lambda T50 at 320 nm. The comparison of the microspectrophotometric and the behavioral data showed a good fit between the peaks of the four single cones' effective sensitivity spectra and the four peaks in the behavioral spectral sensitivity function. The relation further suggests that the behavioral function might be described as the "over-envelope" of the single cone sensitivities. Leiothrix lutea possesses a genuine UV cone type and reveals it's highest sensitivity in the behavioral test to UV light.

The relation between celestial colour gradients and the position of the sun, with regard to the sun compass

Colour gradients along the sky caused by atmospheric scattering were measured on sunny days. It is concluded that whereas the shape of the spectral intensity distribution in the short wavelength range is stable, the distribution at longer wavelengths depends on the direction of measurement. We expressed these relative intensity differences as a spectral contrast. This contrast plotted as a function of angular difference with respect to the position of the sun establishes a smooth gradient. We suggest that the pigeon's UV sensitivity is part of a colour processing system, which is well adapted to employ these gradients in order to derive the sun's position.

The photopic sensitivity of the yellow field of the pigeon's retina to ultraviolet light

The photopic spectral sensitivity of the yellow field of the pigeon's retina to UV light was determined electrophysiologically. The sensitivity curve could be approximated with a model in which the activity of only two cone types were incorporated. In this model, the first type of cone had a maximum sensitivity at 366 nm and was combined with an oil droplet that is completely transparent in the UV wavelength range. The second type had a sensitivity maximum at 415 nm and was associated with an oil droplet cutting off light below 390 nm.

Color mixing in the pigeon. A psychophysical determination in the longwave spectral range

Pigeons were trained to discriminate between spectral lights and additive mixtures in the 580-640 nm range. Two behavioral procedures were used: (I) a simultaneous instrumental discrimination and (II) successive "autoshaping" discrimination. Pigeons were able to make color mixture matches within this spectral range with satisfactory precision. Matchings determined by the animal correspond well to those predicted on the basis of the spectral sensitivities of two (or even three) pigment-droplet combinations present in the pigeon retina.

Four spectral classes of cone in the retinas of birds

The spectral sensitivity of 15 species of birds has been measured by recording transretinal voltages from opened eyecups. With suitable combinations of colored adapting lights, we find that a variety of passerines have four peaks of photopic sensitivity, with maxima at 370, 450, 480, and 570 nm. Additional sensitivity maxima at 510 nm are found in some species. The spectral sensitivity functions are not altered by bathing the retinas in 50 mM sodium aspartate, suggesting that they reflect the properties of cones and do not result from inhibitory interactions between retinal interneurons. Comparison of the results with a general mathematical model that describes spectral sensitivity functions recorded extracellularly from populations of receptors in different states of adaptation (Goldsmith 1986) shows that the retinal spectral sensitivity functions are consistent with the presence of (at least) four types of cone, but indicate as well that many of the cones that are maximally sensitive in the blue and violet likely contain oil droplets that attenuate the deep violet and near uv.

Heterogeneity of chicken photoreceptors as defined by hybridoma supernatants. An immunocytochemical study

Immune cells producing antibodies to chicken photoreceptor membranes were fused with myeloma cells and supernatants of the resulting hybridoma cells were used to test various types of photoreceptor cells in the chicken retina by means of immunocytochemistry. A polyclonal antibody raised against the protein component of bovine rhodopsin was also used. Outer segments of various photoreceptor cells were labelled by the following antibodies: rods were positive with the anti-rhodopsin antibody, both members of the double cones were stained by supernatant A1, while one type of single cones (designated as type A) was specifically labelled by supernatants A5, B3 and D6. The other type of single cones (type B) reacted with anti-rhodopsin and supernatant A1. The results indicate that there are distinct differences in the molecular structure of various photoreceptor outer segments.

Ultraviolet photosensitivity in goldfish: an independent u.v. retinal mechanism

Heart rate conditioned goldfish were sensitive to u.v. stimuli at wavelengths down to 340 nm. A u.v. peak had maximum sensitivity at about 380 nm and was depressed selectively by a u.v. adapting background. An opaque cone restricted light to the eye, reducing the probability of a dermal or pineal gland source of the response. Three experiments demonstrated a retinal origin for the u.v. peak. The conditioned response to u.v. stimuli was abolished following injection of Lidocaine into the eye. U.V. sensitivity remained when the cornea, iris and lens were extirpated. Finally, the u.v. peak showed an orderly change in sensitivity with alteration in adapting u.v. illumination.

The ultraviolet receptor of bird retinas

The eyes of 15 species of birds from 10 families have some cones maximally sensitive at 370 nanometers in the near-ultraviolet. Spectral sensitivity was measured by recording extracellularly in opened eyecups , and a maximum in the ultraviolet was revealed by selectively adapting the retina with yellow background lights. The 370-nanometer spectral sensitivity function is attributed to receptors because its spectral position does not vary with the strength of adaptation and because it is present when the receptor potentials are isolated from the contributions of higher order retinal neurons by exposing the retina to sodium aspartate. These measurements demonstrate the basis for the ultraviolet sensitivity of birds that has been seen in behavioral experiments, and they provide further evidence that many vertebrates share with insects vision in the near-ultraviolet.

Photopic spectral sensitivities of the red and the yellow field of the pigeon retina

The spectral sensitivities of the red field and the yellow field in the retina of the homing pigeon (Columba Livia) were determined on the basis of ERG responses. Between 450 and 550 nm the relative spectral sensitivity of the yellow field turned out to be higher than that of the red field. The results are in agreement with spectral sensitivity data, obtained by behavioural threshold procedures.

Hummingbirds see near ultraviolet light

Three species of hummingbird (Archilochus alexandri, Lampornis clemenciae, and Eugenes fulgens) were trained to make visual discriminations between lights of different spectral content. On the basis of initial choices of feeders following a period of conditioning, birds of all three species were able to distinguish near ultraviolet (370 nanometers, 20-nanometer half bandwidth) from darkness (unilluminated viewing screen) or from the small amount of far red light that leaked through the ultraviolet-transmitting glass filter. A human observer was unable to make either discrimination. The birds were also able to distinguish white lights lacking wavelengths shorter than 400 nanometers from the full spectrum of the quartz-halogen bulbs. One can infer that the cone oil droplets, which have been lost from the retinas of most mammals, provide a potentially more flexible system for restricting the short wavelength end of the visible spectrum than does the filtering action of lens and macula that serves this function in the human eye.

Photoreceptors and oil droplet colors in the red area of the pigeon retina

Six types of photoreceptors in the red area (dorso-temporal quadrant) of the pigeon retina are identified using Golgi impregnation, light microscopy and electron microscopy. Golgi impregnation is used to categorize the receptors into morphological types. Examination of oil droplets in the inner segments of cones in fresh, unfixed tissue shows five different types which can be characterized by color, size and stratification. Therefore, in sections through the length of the receptors examined by electron microscopy, the oil droplets contained in the inner segments of the cones can be identified as to their color by their characteristics (i.e., size and stratification), and the groups of receptors thus classified, further characterized as to the morphology of their terminals. Rods have no oil droplets in their inner segments, and their synaptic terminals are located in the outermost stratum of the outer plexiform layer OPL). Principal members of double cones have yellow oil droplets in their inner segments, while accessory members contain small colorless oil droplets. The synaptic terminals of double cones are located in the same (outermost) stratum of the OPL as rod synaptic terminals. Two types of single, straight cones house either red or orange oil droplets and terminate in the intermediate stratum of the OPL. Oblique single cones with yellow-green oil droplets in their inner segments contribute synaptic terminals to the innermost stratum of the OPL.