Color receptor identities of goldfish cones.

Goldfish retinas were exposed to spectral lights, then incubated with nitroblue tetrazolium chloride. Diformazan deposits revealed that five morphologically distinct cone types were segregated into three color classes: red long double and long single cones, green short double and long single cones, and blue short single and miniature short single cones.

Red-green cone interactions in the increment-threshold spectral sensitivity of primates.

Threshold spectral sensitivity of primate eyes is the upper envelope of the sensitivity of three response channels. Sensitivity in the green and red channels is modeled as linear difference functions reflecting neural interaction between cones containing photopigments with 535- and 575-nanometer peaks. Sensitivity in the blue channel seems determined by a single class of cones containing a 445-nanometer photopigment.

Chromatic organization of primate cones.

The distribution of baboon retinal cones were mapped histochemically by light-stimulated reduction of nitroblue tetrazolium chloride. Blue cones were distributed regularly in the periphery: red and green cones were distributed randomly everywhere. The ordering of cone densities was green > red > blue.

Adaptive evolution of color vision genes in higher primates.

The intron 4 sequences of the three polymorphic alleles at the X-linked color photo-pigment locus in the squirrel monkey and the marmoset reveal that the alleles in each species are exceptionally divergent. The data further suggest either that each triallelic system has arisen independently in these two New World monkey lineages, or that in each species at least seven deletions and insertions (14 in the two species) in intron 4 have been transferred and homogenized among the alleles by gene conversion or recombination. In either case, the alleles in each species apparently have persisted more than 5 million years and probably have been maintained by overdominant selection.

Immunohistochemical localization of cyclic GMP in goldfish retina.

The immunocytochemical procedure for cyclic GMP (cGMP) localization has been modified by the development of: 1) an anti-cGMP antibody depleted control serum and 2) a tissue preadsorption procedure that greatly reduces nonspecific fluorescence. cGMP remaining associated with tissue sections following prolonged exposure to aqueous buffer was determined, by extraction and measurement by radioimmunoassay, to be approximately 38% of the initial cGMP content. Application of this improved immunohistochemical procedure to goldfish retinas reveals the highest concentrations of cGMP to be associated with the cone inner segments and nuclei of the photoreceptors. This retinal distribution of cGMP is in good agreement with that independently determined by microdissection studies. The validity of this procedure is therefore strengthened and cautions to its application and interpretation are outlined.

Detection of a light-sensitive pool of cGMP in goldfish cone color receptors by immunocytochemistry.

A procedure for the immunocytochemical localization of cGMP in the goldfish retina is described. The procedure is then used to evaluate the presence of cGMP in cone color receptors in retinas from dark-adapted and light stimulate fish. The results show that cone color receptors in dark-adapted retinas contain large amounts of immunocytochemically defined cGMP in the ellipsoid region, which are greatly reduced after light exposure.

Sensitivity of the blue-sensitive cones across the central retina.

We measured increment thresholds up to 5 degrees eccentricity using a 10' dia flash viewed against 10(4) td of 572-nm background. We found two distinct sensitivity profiles, one with flash wavelengths 410-470 nm and another with 520-580 nm. Spectral sensitivity plots indicate blue-sensitive cones and green-sensitive cones for the two profiles, respectively. Sensitivity of blue-sensitive cones is maximum at 1 degree eccentricity. Measurements at greater eccentricities are susceptible to adaptation to test field. The light-collecting area of blue-sensitive cones raised to a power follows the sensitivity profile of blue-sensitive cones.

Researches on a unilaterally blue-blinded rhesus monkey.

Psychophysical measures of hue (wavelength) discrimination and spectral sensitivity were collected over a 3-year-period on a rhesus monkey whose right eye had been exposed to intense blue light 10 years prior and had shown a pronounced loss of blue sensitivity in an increment-threshold, spectral-sensitivity task. Hue discrimination, to a somewhat greater degree than spectral sensitivity, revealed large differences between the normal and blue-exposed eye. The difference limens were in some cases 100 nm for the blue-exposed eye compared to 10-15 nm for the normal eye. The hue-discrimination functions from the blue-exposed eye were similar in form to those from human tritanopes (blue-blind humans), and those from the monkey's normal eye were similar to those from normal humans. Detailed functions, where the variable wavelength was shorter as opposed to longer than the reference wavelength, were shown separately for each of the monkey's eyes; those from the blue-exposed eye were very similar to analogous functions from the one case where they have been shown separately for a human tritanope.

Color vision following intense green light exposure: data and a model.

Hue discrimination, spectral sensitivity, and mathematical models of both are presented for a rhesus monkey which was exposed to intense green light. One of the monkey's eyes was blue-blinded in a previous experimental procedure and the other was color normal. The results of green light exposure showed a loss of sensitivity on both measures, with greater loss in the blue-blinded eye. Although there was considerable loss of hue-discrimination in the blue-green spectral regions, hue-discrimination at the point of best discrimination, 590 nm, remained unaffected. This pattern of results poses difficulties for models of hue discrimination, and has resulted in the proposed model employing three opponent color channels. The number of free-parameters are minimized and the integration between spectral sensitivity and hue discrimination enhanced by deriving parameters used in modeling hue discrimination from spectral sensitivity or vice versa.

Red-green interactions in the spectral sensitivity of primates as derived from ERG and behavioral data.

Different techniques were used to manipulate the inhibitory interaction between the red and green photoreceptors (R and G cones) of rhesus and human primates. The response techniques that were used were the corneal electroretinogram (ERG) and psychophysical increment-threshold spectral sensitivity functions. Red-green opponency, as measured by the depth of the notch at 580 nm, is removed by intravitreal injection of bicuculline but not by strychnine. Therefore, red-green opponency is mediated by GABA and not glycine. The depth of the notch is dependent upon stimulus size. Between 30' and 15' test light diameters, this sign of red-green opponency disappears. Psychophysical increment thresholds are shown to produce the notch while decrements do not and intravitreal APB is shown to reduce the notch, evidence that red-green opponency is carried by the "ON" and not the "OFF" bipolar pathways of the retina. Red and green annuli are shown to selectively reduce red and green inhibition, as though there were selective reduction of the surround response in center-surround organized red-green receptive fields.

Red/green opponency in the rhesus macaque ERG spectral sensitivity is reduced by bicuculline.

Spectral-sensitivity curves were derived from the a-, b-, and d-waves of rhesus monkey ERGs after injection of bicuculline, strychnine, or no drug. Without drug injection, the a- and d-wave curves were well-fit by an additive model of weighted photoreceptor absorption spectra, while the b-wave curve requires inhibitory terms to produce an adequate fit. Bicuculline, but not strychnine, reduced the weight assigned to the inhibitory terms in a dose-dependent fashion, to the point that no inhibition was evident. The results suggest that GABAergic synapses are required for the expression of red/green color opponency in primate bipolar cells.

Cone connections of the horizontal cells of the rhesus monkey's retina.

The presence in the rhesus monkey's retina of a second morphological type of horizontal cell (H2), described by Kolb et al. (1980), is confirmed. Both types of cell are here further described. Their cone connections are quantified and compared with those of mammals and other vertebrates. The dendrites and axons of the H2 type of cell contact only cones as do the dendrites of the H1 cell (originally described by Polyak (1941)) which has an axon contacting only rods. The dendrites of foveal H2 cells contact between 11 and 14 cones; those of H1 contact 7. The number of cones that each type of cell contacts increases with increasing distance from the fovea, so that, by 5-6 mm eccentricity, H2-type cells synapse with between 20 and 30 cones, and the H1 cells with 12-15. The qualitatively estimated coverage factors of each are 3 or 4; every cone synapses with more than one of both types. Neither type of horizontal cell makes chromatically specific connections that are anatomically recognizable, unlike the situation in some teleostean and turtle retinae. Individual horizontal cells, particularly those connected to foveal cones, may have different ratios of chromatic input. At equivalent eccentricities, up to about 6 mm from the fovea, the dendritic fields of H2 horizontal cells are about twice the size of H1 cells and contact about twice the number of cones. These relative differences are closely similar to those of the cat's horizontal cells and it is suggested that they are a basic feature of most placental mammals. The organization of foveal cone fibres within Henle's layer is described. The distribution of primate cone telodendria, gap junctions and synapses in the outer plexiform layer are briefly reviewed and compared with those of other vertebrate retinae.