Blue-sensitive Cones Research Articles

The ontogeny of ultraviolet photosensitivity in rainbow trout (Salmo gairdneri)

The present study examines the changes in ultraviolet (UV) photosensitivity that occur during the growth of rainbow trout (Salmo gairdneri). A comparison of the ocular media transmission of small (n = 3) and large (n = 3) trout eyes did not reveal large changes in the transmission of UV radiation through the eye. We used the heart-rate conditioning technique to measure spectral sensitivity in immobilized trout. Four trout, each weighing less than 30 g, exhibited a UV-sensitivity peak at 360 nm while four additional trout weighing more than 60 g each exhibited no evidence of UV sensitivity. Spectral-sensitivity measurements of two trout weighing 44 g and 60 g revealed UV sensitivity, but when measured one month later (after a 25% increase in body weight) both fish exhibited no UV-sensitivity peak. At this time their sensitivity appeared to conform to the known blue-sensitive cone mechanism.

H1 horizontal cells of carp retina have different postsynaptic mechanisms to mediate short- versus long-wavelength visual signals.

Vertebrate photoreceptors release neurotransmitter substance(s) tonically in the dark and this release is curtailed by light. Recently, we have become increasingly aware of the possibility that short- and long-wavelength visual signals are mediated differently during the synaptic transmission to second-order retinal neurons. The experiment described here advances this notion further by demonstrating a postsynaptic difference. Treatment of the carp retina by dopamine reduced the gap-junctional coupling of horizontal cells, and we made use of this known effect to measure the input resistance (Rin) of H1-type horizontal cells. Flashes of light increased Rin. This increase, however, was found to be smaller with short wavelengths, even though the comparison was made when voltage responses were equal in amplitude. Often, Rin was even found to decrease at the blue end of spectrum. No single postsynaptic mechanism can account for any equal-voltage Rin difference such as this. The synaptic spectral segregation thus revealed is probably subserved by a dual scheme wherein the transmitter from blue-sensitive cone photoreceptors acts to decrease the membrane conductance of H1 cells whereas the synapses made by red- and green-sensitive cones are of a classical excitatory type.

A horizontal cell selectively contacts blue-sensitive cones in cyprinid fish retina : intracellular staining with horseradish peroxidase

A horizontal cell selectively contacting blue-sensitive cones has been intracellularly stained with horseradish peroxidase in the retina of a cyprinid fish, the roach. The light microscopical morphology of the cell belonged to the H3 category of horizontal cells found in cyprinid fish retinae. In response to spectral stimuli, the cell generated chromaticity-type S-potentials that were hyperpolarizing to blue and depolarizing to yellow-orange. A red-sensitive hyperpolarizing component was absent possibly because of suppression of the negative feedback pathway between luminosity-type (H1) horizontal cells and green-sensitive cones.

FOVEAL AND NON‐FOVEAL MEASURES OF SHORT WAVELENGTH SENSITIVE PATHWAYS IN GLAUCOMA AND OCULAR HYPERTENSION*

Blue-sensitive cone thresholds (the ability to detect blue test lights presented on a bright yellow background) were measured to examine foveal and central vision field sensitivity in groups of 33 glaucoma, 31 ocular hypertension (OHT) and 24 age matched normal subjects. Results showed these thresholds were substantially reduced (in all areas tested) for the glaucoma group (approximately 0.8 log units) and less reduced for the OHT group (approximately 0.2 log units), when compared to the normal group threshold. Measures of red-sensitive and green-sensitive cone thresholds showed no difference for all three groups. Furthermore, 16% of the OHT group showed visual field abnormalities for the blue-sensitive cone threshold measure. We conclude that efforts to detect early function loss in glaucoma and OHT could be improved using these measures in clinical practice.

Equiluminance: spatial and temporal factors and the contribution of blue-sensitive cones.

Equiluminance ratios for red/green, red/blue and green/blue sine-wave gratings were determined by using a minimum-motion heterochromatic matching technique that permitted reliable settings at temporal frequencies as low as 0.5 Hz. The red/green equiluminance ratio was influenced by temporal but not spatial frequency, the green/blue ratio was influenced by spatial but not temporal frequency, and the red/blue ratio was influenced by both. After bleaching of the blue-sensitive cones, there was no change in equiluminance ratios, indicating no contribution of the blue-sensitive cones to the luminance channel even at low temporal and spatial frequencies. The inhomogeneity of yellow pigmentation within the macular region was identified as the source of the spatial-frequency effect on the blue/green ratio.

Identification of new biphasic C-type horizontal cells in cyprinid fish.

New biphasic C-type horizontal cells were identified physiologically and morphologically in the retina of live immobilized crucian carp. These cells, like commonly studied R/G type cells, hyperpolarized to short wavelength lights and depolarized to long wavelength lights, but inverted response polarity at about 560 nm. Spectral sensitivities of hyperpolarizing and depolarizing components showed that they were produced by inputs from blue-sensitive cones and green-sensitive cones respectively. These cells are thus referred to as G/B type horizontal cells. Inputs from blue- and green-sensitive cones were not linearly summated, but interacted strongly at G/B type cells. G/B type cells stained intracellularly with HRP had smaller cell body and dendritic field, distinctly differing from R/G type cells.

Foveal and non-foveal measures of short wavelength sensitive pathways in glaucoma and ocular hypertension

Abstract— Blue-sensitive cone thresholds (the ability to detect blue test lights presented on a bright yellow background) were measured to examine foveal and central vision field sensitivity in groups of 33 glaucoma, 31 ocular hypertension (OHT) and 24 age matched normal subjects. Results showed these thresholds were substantially reduced (in all areas tested) for the glaucoma group (˜ 0.8 log units) and less reduced for the OHT group (˜0.2 log units), when compared to the normal group threshold. Measures of red-sensitive and green-sensitive cone thresholds showed no difference for all three groups. Furthermore, 16% of the OHT group showed visual field abnormalities for the blue-sensitive cone threshold measure. We conclude that efforts to detect early function loss in glaucoma and OHT could be improved using these measures in clinical practice.

Cone photoreceptor mechanisms and the detection of polarized light in fish

Although numerous studies have demonstrated the detection of polarized light in vertebrates, little is known of the photoreceptor mechanisms involved. Recent evidence, however, indicates that cyprinid fishes possess both ultraviolet (UV) and polarization sensitivity suggesting that some vertebrates, like many invertebrates, may employ UV-sensitive cone receptors in polarization sensitivity. In this report, we describe experiments that determine which spectral types of receptors participate in the detection of polarized light. We used a heart-rate conditioning technique to measure increment thresholds of immobilized goldfish for plane-polarized, narrow-band (10 nm half max.) spectral stimuli (380 nm, 460 nm, 540 nm, 660 nm). A typical experiment involved ‘isolating’ the activity of a cone photoreceptor mechanism by chromatic adaptation and measuring increment thresholds for spectral stimuli at e-vector orientations of the polarizer between 0° to 180° in 30° steps. The UV-, green- and red-sensitive cone receptor mechanisms showed clear evidence of polarization sensitivity while the blue-sensitive cone receptor mechanism was polarizationally insensitive. The average amplitude (base to peak height on Fig. 4) of the polarization sensitivity curves (UV-, green- and red-curves) was 0.67 log unit (standard deviation of 0.12 log unit), with the UV-sensitive cone receptor mechanism most sensitive to the vertical e-vector axis and the green- and red-sensitive cone receptor mechanisms most sensitive to the horizontal e-vector axis. The observation that different cone photoreceptor mechanisms have orthogonal polarization sensitivity in fish suggests that the perception of polarized light may enhance the capacity for visual discrimination in lower vertebrates.

Effects of ethyl alcohol on the electrooculogram and color vision.

Color vision tests and electrooculography (EOG) were performed in 6 male and 2 female healthy young trichromatic volunteers between 60 and 130 min after finishing consumption of ethyl alcohol leading to blood levels of approximately 0.07% to 0.16%. The average number of errors in the desaturated Panel D-15 arrangement test rose from 0.86 to 2.0; the average error score in the Farnsworth-Munsell 100-Hue test rose from 26 to 79. The axis of errors in both tests was clearly tritanopic and tetartanopic, pointing to a specific effect of ethyl alcohol on the function of blue-sensitive cones and/or their interaction with longer wavelength-sensitive cones. Ethyl alcohol decreased the size of the light-peak, apparently in a dose-dependent fashion, in each of the 16 eyes by values between 3% and 79%. The effect of alcohol on the EOG light peak was stronger between 30 and 95 min (23% decrease in average) than between 95 and 130 min (14% decrease) after the finish of alcohol administration.

Electron microscopic study of synaptic contacts between photoreceptors and HRP-filled horizontal cells in the turtle retina.

The synaptic contacts between photoreceptors and horizontal cells in the retina of the turtle (Geoclemys) were studied. Horizontal cells were classified into three types according to their intracellularly recorded spectral responses: luminosity, biphasic chromaticity, and triphasic chromaticity horizontal cells (LHC, BHC, and THC). These cells were then iontophoretically filled with horseradish peroxidase (HRP). The various types of photoreceptors located within the dendritic field of the HRP-filled horizontal cells were identified either as rods or as one of the three chromatic types of cones; the latter were identified by the presence and colors of their oil droplets in the inner segments. The synaptic contacts between photoreceptors and labeled horizontal cells were then investigated by light and electron microscopy of serial sections on three LHCs, two BHCs, and one THC. LHCs made synaptic contacts with about 100 photoreceptors, including rods and three chromatic types of cones; two-thirds of these photoreceptors contacted the cell body and the remaining its axon terminal. BHCs contacted about 30 cones; red-, green-, and blue-sensitive cones in the ratio of 3:4:1. THC contacted 20 cones; red- and blue-sensitive cones in the ratio of 2:1. The dendritic processes of HRP-filled horizontal cells were found as the lateral element of the ribbon synaptic complexes. The present finding suggests that the responses of BHC and THC to red flashes are fed directly from red-sensitive cones in addition to the feedback pathway of cone-horizontal cell connections in the previous studies.

Dynamics of chromaticity horizontal cells in the freshwater turtle retina.

A model of the cone-horizontal cell circuit is presented based on morphological evidence recently found in the Reeves' turtle: a luminosity horizontal cell (LHC) that receives inputs from red-, green-, and blue-sensitive cones in the ratio of 15:3:1, a triphasic horizontal cell (THC) that receives inputs from one class of red-sensitive and from blue-sensitive cones in the ratio of 2:1; and a biphasic chromaticity horizontal cell (BHC) that receives inputs from green-sensitive cones as well as from a special class of red-sensitive (i.e. the broad spectrum) and from blue-sensitive cones in the ratio of 3:2:1. A study of the simulated impulse responses strongly suggests that the basic response patterns of the BHC and THC can be readily explained by a simple wiring diagram consisting of direct hyperpolarizing inputs from the appropriate cones and a depolarizing input from the LHC which acts as a voltage inverter. A negative feedback circuit from the LHC to the cone pedicles is included and its negative feedback gain increases as the mean illuminance level (Io) increases. The negative feedback circuit, which promotes adaptation in the cones to changing Io's, is not necessary for opponent polarization in the BHC or THC, but does explain variabilities of impulse responses.

The contribution of blue-sensitive cones to spatial responses of post-receptoral visual channels in man.

Psychophysical methods developed for the investigation of spatial and temporal pathways in human vision have been applied in combination with the two-colour increment threshold technique of W. S. Stiles to study the way in which signals from blue-sensitive cones are transmitted along the visual pathways. A flicker sensitive spatio-temporal filter, designated 'ST2', has been examined by background modulation methods, and spatial filters sensitive to bars of a specific width by grating adaptation methods employing dichoptic presentation of stimuli. It is shown that the blue-sensitive (pi 3) spectral mechanism contributes to both classes of filter response, in a manner similar to that observed for the red-sensitive spectral mechanism. The binocularly driven, bar-sensitive filters have broad-band spectral response characteristics, thus the data demonstrate that signals arising in blue-sensitive cones converge onto a luminance channel. The results of this investigation, together with those previously published for a second (ST1) spatio-temporal filter, describe a variety of post-receptoral responses involving the pi 3 spectral mechanism.

Photoreceptors of a cyprinid fish, the roach: morphological and spectral characteristics

Structure-function studies were undertaken on cones in the retina of the cyprinid fish, the roach,Rutilus rutilus, in order to provide a basis for analysis of colour information by post-receptoral neurones. Measurements were made with two main aims: (i) To determine by microspectrophotometry the absorbance spectra of the photopigments present within the retina, and correlate these with the morphological types of photoreceptor; (ii) To characterize the morphologies of the photoreceptors at both light and electron microscopical levels and determine their relative abundance in the retina. In addition to red-, green-, and blue-sensitive cones, an ultra-violet-sensitive photoreceptor has been found in a sub-population of miniature short single cones. Possible relevance of this finding to vertebrate vision is discussed.

The spectral sensitivity of blue-sensitive pigeon cones: Evidence for complete screening of the visual pigment by the oil-droplets

The relative spectral sensitivity of blue-sensitive pigeon cones was determined using flickerphotometry based on mass ERG-responses from intact subjects during high-level light adaptation. The resulting spectral sensitivity curve can be mimicked by a P460 nomogram screened by an oil-droplet that absorbs 50% at 466 nm. Comparison of the curve with the nomogram indicates that on the average less than 10% of the light that excites the blue-sensitive cones is guided past or diffracted around their oil-droplets.

Synaptic contacts between red-sensitive cones and triphasic chromaticity horizontal cells in the turtle retina

Using combined physiological and anatomical methods, we have shown that triphasic chromaticity horizontal cells (THC) in the turtle retina make ribbon synaptic contacts with about 20 cones, two-thirds were red-sensitive, while the rest were blue-sensitive. The response of THC to red flashes appeared to be generated via synapses from red-sensitive cones; this interpretation differs from those of the previous studies where only blue-sensitive cones were thought to make synaptic contacts with the THC.

The cellular origin of an unusual type of S-potential: an intracellular horseradish peroxidase study in a cyprinid fish retina

L2-type S-potentials are mainly blue/green-sensitive hyperpolarizing responses with a red-sensitive depolarizing component which is either weak or absent. They were first described in the retina of the roach, a cyprinid fish, by Djamgoz (1978, 1984) and Djamgoz & Ruddock (1978, 1979a). The cellular origin of these responses has been determined and characterized by intracellular recording, horseradish peroxidase staining, and light and electron microscopy. They were found to arise in horizontal cells with H2-like morphologies on average (Stell & Lightfoot, 1975). The dendrites of these cells contacted green- and blue-sensitive cone pedicles within which both lateral and central contacts were made at ribbon synapses. The laterally-positioned dendrites had incompletely formed spinules associated with them. A number of similarities between these units and the biphasic, chromaticity (Cb)-type S-potentials have been outlined and it is suggested that L2 units are essentially Cb-units with a weak depolarizing component. In turn, it is suggested that the depolarizing component is reduced as a consequence of the relatively dark-adapted states of the retinae. It is concluded that the negative feed-back pathway that subserves the generation of depolarizing (Cb-type) S-potentials is weak or absent in dark-adapted retinae and that spinules may be the site of this feed-back interaction.

Electrophysiological measurements of the spectral sensitivity of three types of cones in the carp retina.

The spectral sensitivities of red-, green-, and blue-sensitive cones were measured by intracellular recording in the carp retina. The responses from all cones were univariant, i.e., the waveform of a response to any wavelength and at any intensity could be superimposed on the response to other wavelengths if the intensity was properly selected. Red-sensitive cones showed a maximum sensitivity at about 620 nm, green-sensitive cones at about 520 nm, and blue-sensitive cones at about 460 nm. The peak wavelengths and general forms of the spectral sensitivity curves agreed with those of the spectral absorption curves measured by microspectrophotometry (MSP), but the sensitivity of red-sensitive cones at both ends of the spectrum was significantly lower than the spectral absorption determined by MSP.

Spatial and temporal contrast sensitivities of neurones in lateral geniculate nucleus of macaque.

The discharges of single neurones in the parvocellular and magnocellular laminae of the macaque's lateral geniculate nucleus (l.g.n.) were recorded with glass-insulated tungsten micro-electrodes. Linearity of spatial summation was examined using the test devised by Hochstein & Shapley (1976). 2 of 272 parvocellular units and 6 of 105 magnocellular units showed clearly non-linear spatial summation. A quantitative index of non-linearity did not suggest the existence of a distinct 'non-linear' class of magnocellular unit. Spatial contrast sensitivity to moving gratings was measured by a tracking procedure in which contrast was adjusted to elicit a reliable modulation of discharge. With the exception of cells that were driven by blue-sensitive cones, measurements of contrast sensitivity did not reveal distinct subgroups of parvocellular units. All had low sensitivity, and those with receptive fields in the fovea could resolve spatial frequencies of up to 40 cycles deg-1. Magnocellular units had substantially higher sensitivity, but poorer spatial resolution. The higher sensitivities of magnocellular units led to their giving saturated responses to stimuli of high contrast. Responses of parvocellular units were rarely saturated by any stimulus. At any one eccentricity the receptive fields of parvocellular units had smaller centres than did those of magnocellular units. Receptive fields of magnocellular units driven by the ipsilateral eye had larger receptive fields than did those driven by the contralateral eye. Parvocellular units were most sensitive to stimuli modulated at temporal frequencies close to 10 Hz; magnocellular units to stimuli modulated at frequencies nearer 20 Hz. The loss of sensitivity as temporal frequency fell below optimum was more marked in magnocellular than parvocellular units. Changes in temporal frequency altered the shapes of the spatial contrast sensitivity curves of both parvocellular and magnocellular units. These changes could be explained by supposing that centre and surround have different temporal properties, and that the surround is relatively less sensitive to higher temporal frequencies.

Gamma-Aminobutyric acid acts at axon terminals of turtle photoreceptors: difference in sensitivity among cell types.

It has been proposed that horizontal cells of the vertebrate retina have a negative feedback synapse with cone photoreceptors. gamma-Aminobutyric acid (GABA) has been suggested to be a neurotransmitter of monophasic horizontal cells (a subtype of horizontal cells), which have direct connections with red-sensitive and green-sensitive cones. We have examined the feedback hypothesis by measuring the GABA sensitivity of photoreceptors. To eliminate interaction with other cells, we dissociated photoreceptors from the turtle retina enzymatically. The subtype of photoreceptors was identified unequivocally on the bases of the shape of the cell and the color of the oil droplets, which are known to correlate with the spectral sensitivity. Cells were voltage-clamped using "Giga-ohm sealed" suction pipettes in the whole-cell recording configuration, and membrane currents were measured in response to GABA applied ionophoretically at various positions on the cell. It was found that red-sensitive and green-sensitive cones were highly sensitive to GABA and that the sensitivity was localized at the axon terminals. GABA-sensitivity in blue-sensitive cones and in rods was very low. GABA-induced current reversed its polarity near the equilibrium potential of chloride, suggesting that GABA increased chloride conductance. Thus, our findings are consistent with the negative feedback hypothesis.

Chromatic mechanisms in lateral geniculate nucleus of macaque.

This paper introduces a new technique for the analysis of the chromatic properties of neurones, and applies it to cells in the lateral geniculate nucleus (l.g.n.) of macaque. The method exploits the fact that for any cell that combines linearly the signals from cones there is a restricted set of lights to which it is equally sensitive, and whose members can be exchanged for one another without evoking a response. Stimuli are represented in a three-dimensional space defined by an axis along which only luminance varies, without change in chromaticity, a 'constant B' axis along which chromaticity varies without changing the excitation of blue-sensitive (B) cones, a 'constant R & G' axis along which chromaticity varies without change in the excitation of red-sensitive (R) or green-sensitive (G) cones. The orthogonal axes intersect at a white point. The isoluminant plane defined by the intersection of the 'constant B' and 'constant R & G' axes contains lights that vary only in chromaticity. In polar coordinates the constant B axis is assigned the azimuth 0-180 deg, and the constant R & G axis the azimuth 90-270 deg. Luminance is expressed as elevation above or below the isoluminant plane (-90 to +90 deg). For any cell that combines cone signals linearly, there is one plane in this space, passing through the white point, that contains all lights that can be exchanged silently. The position of this 'null plane' provides the 'signature' of the cell, and is specified by its azimuth (the direction in which it intersects the isoluminant plane of the stimulus space) and its elevation (its angle of inclination to the isoluminant plane). A colour television receiver was used to produce sinusoidal gratings whose chromaticity and luminance could be modulated along any vector passing through the white point in the space described. The spatial and temporal frequencies of modulation could be varied over a large range. When stimulated by patterns of low spatial and low temporal frequency, two groups of cells in the parvocellular laminae of the l.g.n. were distinguished by the locations of their null planes. The null planes of the larger group were narrowly distributed about an azimuth of 92.6 deg and more broadly about an elevation of 51.5 deg, which suggests that they receive opposed, but not equally balanced, inputs from only R and G cones. These we call R-G cells.(ABSTRACT TRUNCATED AT 400 WORDS)