An aftereffects paradigm was used to behaviorally measure contrast sensitivity of cats to gratings of three different test spatial frequencies after adaptation to gratings of various spatial frequencies, contrasts, and durations. Post-adaptation reductions in sensitivity occurred even after short periods of adaptation (<7 s) and could be as large as 1.0 log unit under some conditions. The magnitude of the adaptation effect varied monotonically with (1) adaptation grating contrast, (2) duration, and (3) the contrast sensitivity for the test grating. Average half-width (at half-height) of the spatial-frequency tuning curves constructed from the data was 1.4 octaves, and was not dependent upon the level of adaptation or the spatial frequency of the test grating. Post-adaptation psychometric functions of the cats showed reduced slopes and maxima suggesting that, unlike humans, in cats apparent contrast grows more slowly with increases in physical contrast after contrast adaptation. All of the characteristics observed are in excellent agreement with electrophysiologically measured properties of neurons in striate cortex of cats. In addition, there was a remarkable similarity of the cat tuning functions, both in shape and bandpass, to those measured in man with a similar paradigm suggesting that (1) the two visual systems are sufficiently similar to make the cat a useful spatial vision model and (2) there is a common functional plan to all mammalian visual systems despite significant anatomical differences between species.

Acute hypoxemia (low PaO2) leads to changes in oxygen consumption and electrical responses of the outer retina of cats, but inner retinal ERG components and ganglion cell responses have been shown to be quite resistant to hypoxemia. The purpose of this study was to determine whether the resistance of the inner retina depends on (1) the stimulus conditions, specifically the degree of light adaptation; and (2) the ability of the photoreceptors to increase glycolysis during hypoxemia. To address these issues, recordings of single ganglion cell action potentials and of the b-wave and scotopic threshold response (STR) of the electroretinogram (ERG) were made from the eyes of anesthetized cats during hypoxemia alone and hypoxemia plus hypoglycemia. Ganglion cells appeared to be equally resistant to hypoxemia at high and low backgrounds (3.3 to 9.7 log equivalent quanta(555 nm)-deg-2-s-1), and the STR, recorded with dim stimuli during dark adaptation, when photoreceptor oxygen consumption is most susceptible to hypoxemia, was unchanged until PaO2 was below 30 mm Hg. The amplitude of the b-wave was similarly resistant to hypoxemia when the animal was normoglycemic. During hypoglycemia, however, both the b-wave and the STR became more sensitive to hypoxemia, beginning to change at PaO2s as high as 50 mm Hg when blood glucose was 40–50 mg/dl. It is argued that hypoglycemia limits or prevents the increased glycolytic ATP production that would ordinarily occur when the photoreceptor oxygen supply decreases, and that increased photoreceptor glycolysis is essential in the protection of the retina against mild hypoxemia.

In vertebrates, it has been shown that binocular visual experience is necessary to develop normal spatial vision. We have investigated whether this is also true for an invertebrate, the praying mantis. The praying mantis is a predatory insect in which prey localization involves the use of binocular disparities. We raised mantids which had one eye occluded throughout development and tested monocular visual fixation and binocular distance estimation in the adult animals. The results revealed that both fixation and prey catching behavior were normally functional in the monocularly reared animals. Thus we conclude that, in mantids, binocular vision is based on a fixed mode of development.

Green, blue and short-wavelength-red rod hue biases are strongest and most reliable with large, dimly-mesopic, extra-foveal stimuli but tend to diminish when stimuli are confined to a small area of the central fovea. This study explores how the stimulation of foveal and extra-foveal areas interact in determining rod hue biases, and whether large stimuli are as effective for revealing rod hue biases when foveally centered as when eccentrically centered. We assessed rod influence by measuring wavelengths of unique green and unique yellow (with 1-s duration, 1 log scot td stimuli and a staircase procedure) under bleached and dark-adapted conditions. We measured unique hues with foveally centered 2°- and 7.4°-diameter disks, a 7.4° (outer) × 2° (inner) diameter annulus, and a 7°-eccentric, 7.4°-diameter disk. The rod green bias (shift of unique yellow locus) was typically <10 nm and remained fairly constant across spatial configurations, indicating no special foveal influence. The rod blue bias (shift of unique green) varied more among observers and spatial configurations, reaching up to 47 nm. However, stimuli covering the fovea typically produced no rod blue bias. Thus, the present results add differences in spatial dependence (i.e., foveal/extra-foveal interaction) between green and blue rod biases to previously demonstrated differences (e.g., differences in amount of light level dependence, in time course and in the spectral range influenced by each bias).

The existence of multiple areas of extrastriate visual cortex raises the question of how the response properties of each area are derived from its visual input. This question was investigated for one such area in the cat, referred to here as the Clare-Bishop area (Hubel & Wiesel, 1969); it is the region of lateral suprasylvian cortex that receives input from area 17. A novel approach was used, in which kainic acid was injected locally into the Clare-Bishop area, making it possible to record directly from afferent inputs.

The response properties of the great majority of a sample of 424 presumed afferents resembled cells in areas 17 and 18. Thus, a systematic comparison was made with cells from area 17's upper layers, the source of its projection to the Clare-Bishop area (Gilbert & Kelly, 1975), to see whether these afferents had distinctive properties that might distinguish them from cells projecting to areas 18 or 19. Some differences did emerge: (1) The smallest receptive fields typical of area 17 were relatively scarce among afferents. (2) Direction-selective afferents were more abundant than were such cells in area 17. (3) End-stopped afferents were extremely rare, although end-stopped cells were common in area 17's upper layers.

Despite these differences, afferents were far more similar in their properties to cells in areas 17 and 18 than to cells in the Clare-Bishop area. Compared to the latter, afferents showed major discrepancies in receptive-field size, in direction selectivity, in end-stopping, and in ocular dominance distribution. These differences seem most likely to stem from circuitry intrinsic to the Clare-Bishop area.

Previous studies have shown that with the use of tinted lenses (or colored filters), individuals with red–green color vision deficiency (CVD) report an improvement in their performance on certain color vision tests. In this context, this study examines the effects of a digitally generated red-colored filter and identifies the mechanism mainly responsible for the changes in red–green CVD observers’ performance on a D-15 arrangement test performed using the filter. We simulate the red filter digitally with the spectral transmittance similar to that of the X-Chrom, which is a red-tinted lens. Fourteen red–green CVD subjects are subjected to the D-15 test on a computer monitor under four filter conditions, consisting of one condition without the filter and three conditions with the filter, corresponding to the opacity of the red filter. The results show that while the simulated red filter improves the performance of deutans to arrange the caps in the D-15 test, this is not the case for protans. In addition, considerations based on the human cone-contrast model enable us to identify that the improvement in deutan observers largely results from the increase in the luminance contrast between stimuli and a background. To summarize, the red filter simulated in this study induces different changes in the red–green CVD observer luminance contrast between the protan and deutan types, with the result that the performance of deuteranopes improves while that of protanopes deteriorates.

Horizontal cells of the vertebrate retina have large receptive fields as a result of extensive gap junction coupling. Increased ambient illumination reduces horizontal cell receptive field size. Using the isolated goldfish retina, we have assessed the contribution of nitric oxide to the light-dependent reduction of horizontal cell receptive field size. Horizontal cell receptive field size was assessed by comparing the responses to centered spot and annulus stimuli and from the responses to translated slit stimuli. A period of steady illumination decreased the receptive field size of horizontal cells, as did treatment with the nitric oxide donor (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (100 μM). Blocking the endogenous production of nitric oxide with the nitric oxide synthase inhibitor, NG-nitro-l-arginine methyl ester (1 mM), decreased the light-induced reduction of horizontal cell receptive field size. These findings suggest that nitric oxide is involved in light-induced reduction of horizontal cell receptive field size.

A nonlinear interaction between signals from at least two spatially displaced receptors is a fundamental requirement for a direction-selective motion detector. This paper characterizes the nonlinear mechanism present in the motion detector pathway that provides the input to wide-field directional neurons in the nucleus of the optic tract of the wallaby, Macropus eugenii. An apparent motion stimulus is used to reveal the interactions that occur between adjacent regions of the receptive fields of the neurons. The interaction between neighboring areas of the field is a nonlinear facilitation that is accurately predicted by the outputs of an array of correlation-based motion detectors (Reichardt detectors). Based on the similarity between the output properties of the detector array and the real neurons, it is proposed that the interaction between neighboring regions of the receptive field is a second-order nonlinearity such as a multiplication. The results presented here for wallaby neurons are compared to data collected from directional systems in other species.

Here we examine further the basis for directional selectivity (DS) in simple cells of the cat's striate cortex. We use a distinctly different input stimulus and different analysis of the output signal for the same type of space-time inseparable receptive field (RF) that was measured with flashing bars in the companion paper (Emerson, 1997). As in the companion paper, we have mimicked a popular “linear” model with a single “branch” that consists of a linear spatiotemporal filter followed by a soft threshold, which should mimic any simple cells that have a single subunit. Counterphase sinusoidal measurements of such a configuration always generate elliptically shaped polar plots of amplitude versus temporal phase, often pinched along the minor axis because of a high threshold. However, for many spatiotemporal frequencies, such polar phase plots, as measured in simple cells by others, show a consistent rotational phase skew. Here we apply counterphase analysis to the same 2-branch model as developed in the companion paper. We show that the model accounts for the skew as the summation of signals from linear filters separated spatially and temporally by approximately 90 deg (i.e. in spatiotemporal phase quadrature), each separated from the output stage by a soft-threshold nonlinearity. We also prove conclusively that such skew cannot be generated by a single-subunit configuration. This demonstration supports the proposed two-subunit structure for DS simple cells, such as in the example from the companion paper, which has strong linear contributions from its inseparable RF. The presence of at least two nonlinear subunits appears to be an obligatory concomitant of DS in all visual cortical cells. The primary function of these subunits may be to enhance the strength of responses to images moving in the preferred direction, as in complex cells. However, subunits may also aid in identifying the moving object through overcoming, at least partially, the phase-concealing properties of the neuron's threshold by generating a steady signal that effectively decreases the threshold for the preferred direction.

Larvae of the tobacco hornworm moth Manduca sexta were reared on either a carotenoid-supplemented or a carotenoid-deficient diet. The former yields fortified adults with normal visual function, whereas visual sensitivity and rhodopsin content are reduced by 2−4 log units in the compound eyes of the deprived moths reared on the latter. We characterized the retinoids of fortified retinas and investigated the recovery of visual function in deprived moths that were provided with retinaldehyde as a source of photopigment chromophore. Retinoids were identified and measured by high-performance liquid chromatography (HPLC). Fortified retinas contained mainly 3-hydroxyretinaldehyde (R3); 11-cis R3 predominated in dark-adaptation, all-trans in light-adaptation, indicating that R3 is the photopigment chromophore. No retinoids could be measured in deprived eyes. Retinaldehyde (R1) was delivered to the retinas of deprived moths by “painting” solutions of 11-cis or all-trans R1 in dimethylsulfoxide (DMSO) on the corneal surfaces of the compound eyes or on the head capsule between the eyes. 11-cis R1 induced rapid recovery: during 3 days, sensitivity rose to within a log unit of that measured from fortified animals. By 7 days, sensitivity was close to normal. Although rhodopsin and P-face particle densities of photoreceptor membranes increased, neither rose to the levels found in fortified animals. All-trans R1 induced only a slight increase in sensitivity that could have resulted from some nonspecific isomerization of the all-trans to the 11-cis isomer; we found no evidence for a retinal isomerase that functions in darkness. Small amounts of R3 were measured in recovering retinas, indicating some conversion of R1 to R3. However, the chromophore of most of the rhodopsin that was synthesized must have been R1. It is possible that rhodopsin did not reach normal levels in the retina even after a week of recovery because the normal chromophore R3 was not provided. Although the rhodopsin that initially formed in recovering moths may have resulted from the association of the chromophore with pre-existing opsin, the extent of eventual recovery indicates that opsin synthesis was stimulated by 11-cis R1.

The retina displays numerous processes that follow a circadian rhythm. These processes are coordinated through the direct action of light on photoreceptive molecules and, in the absence of light, through autocrine/paracrine actions of extracellular neuromodulators. We previously described the expression of the genes encoding the secreted heparin-binding growth factors, midkine-a (mdka) and midkine-b (mdkb), in the retina of the zebrafish. Here, we provide evidence that the expression of mdka and mdkb follows a daily rhythm, which is independent of the presence or absence of light, and we propose that the expression of mdka is regulated by the circadian clock. Both qualitative and quantitative measures show that for mdka, the levels of mRNA and protein decrease during the night and increase during the subjective day. Qualitative measures show that the expression of mdkb increases during the second half of the subjective night and decreases during the second half of the subjective day. Within horizontal cells, the two midkine paralogs show asynchronous circadian regulation. Though intensely studied in the contexts of physiology and disease, this is the first study to provide evidence for the circadian regulation of midkines in the vertebrate nervous system.

Using the whole-cell patch clamp technique, we have examined the voltage-gated currents present in adult chicken cone cells. When calcium and calcium-gated currents are blocked, hyperpolarizing voltage steps elicit slowly increasing inward currents as has been shown for photoreceptors in other species. Unlike the case for other species, chicken cones appear to lack the inward-rectifying cationic current Ih that contributes to the shaping of the photovoltage. Instead of Ih, these cones possess an anionic inward-rectifying current that in kinetics, activation range and probably function is remarkably similar to Ih. This anion channel is unusual in that both nitrate and acetate are more permeant than chloride ions.

The sudden displacement of the retinal image during a saccade raises the visual threshold of human observers to foveal stimuli. The fall in visual sensitivity observed during this phenomenon, known as saccadic suppression, seems to occur very early in the visual processing chain. The lateral geniculate nucleus (LGN) is a likely locus for the multiple retinal and extraretinal interactions occurring during saccadic eye movements, therefore we used the responses of relay cells of adult cats to simulate a pychophysical experiment. We first measured the responses of X and Y relay cells (27 X and 13 Y) to central spots of optimal size and different contrasts. The spots were presented either alone or time locked with the rapid movement of a large, high-contrast peripheral pattern, referred to as shift. We measured the percentage of trials on which the relay cell fired more spikes when the spot (contrast: 0.03–1.0) was present than when it was absent. In experiments with human observers the task was to indicate, by a keypress, which of two otherwise identical temporal intervals contained the spot. The shift reduces the sensitivity (raises the contrast threshold) of neurones in the cat relay cells to brief, stationary targets presented to the receptive-field center. The suppression of visual sensitivity is significantly greater in Y cells than in X cells (average sensitivity ratios 5.6 ± 5.4 in Y cells, 1.59 ± 0.9 in X cells: P < 0.001, U test). The shift also reduces the sensitivity of human observers to the same target. This suggests that the LGN is a potential locus for the modulation of visual responses that leads to saccadic suppression.

Müller cells are highly permeable to potassium ions and play a major role in maintaining potassium homeostasis in the vertebrate retina during light-evoked neuronal activity. Potassium fluxes across the Müller cell's membrane are believed to underlie the light-evoked responses of these cells. We studied the potassium currents of turtle Müller cells in the retinal slice and in dissociated cell preparations and their role in the genesis of the light-evoked responses of these cells. In either preparation, the I–V curve, measured under voltage-clamp conditions, consisted of inward and outward currents. A mixture of cesium ions, TEA, and 4-AP blocked the inward current but had no effect on the outward current. Extracellular cesium ions alone blocked the inward current but exerted no effect on the photoresponses. Extracellular barium ions blocked both inward and outward currents, induced substantial depolarization, and augmented the light-evoked responses, especially the OFF component. Exposing isolated Müller cells to a high potassium concentration did not cause any current or voltage responses when barium ions were present. In contrast, application of glutamate in the presence of barium ions induced a small inward current that was associated with a substantially augmented depolarizing wave relative to that observed under control conditions. This observation suggests a role for an electrogenic glutamate transporter in generating the OFF component of the turtle Müller cell photoresponse.

Calcium plays an integral role in intracellular signaling and process control in neurons. In the outer retina, it is a key component to the phototransduction cycle and neurotransmitter release in photoreceptor and bipolar cell terminals. It also contributes to the responses of horizontal and bipolar cells. In the dark, horizontal cells are depolarized and calcium enters via calcium permeant AMPA receptors and voltage-activated calcium channels. As a result, horizontal cells must be capable of handling high calcium loads without sustaining damage. The aim of this study was to examine the components determining the intracellular calcium levels in H2 horizontal cells in the retina of white bass. Calcium responses were evoked in isolated cells by depolarizing voltage steps and monitored by conventional imaging techniques. The responses consisted of two components: calcium entry through voltage-gated calcium channels and subsequent release from intracellular stores by calcium-induced calcium release (CICR). Under control conditions, changes in calcium levels reached 541 nM on average from a basal level of 60 nM. When release from CICR stores was blocked with ryanodine or dantrolene, calcium levels barely reached 180 nM. The threshold level needed to trigger CICR was dependent on the duration of the applied depolarization and increased in response to shorter pulses.

The motion after-effect (MAE) lasts longer when the test period does not immediately follow adaptation, a phenomenon called storage. Does storage of the MAE occur if the test target is present but rendered phenomenally invisible owing to the presence of a rival target presented to the other eye during the storage period? Our experiment addressed this question. Following adaptation to a drifting grating, an intervening period preceded testing with a stationary grating. During this period, the adapted eye either viewed the test target immediately or was occluded, and the unadapted eye either viewed a high-contrast rival target or was occluded. Thus four conditions were employed. The duration of the residual MAE was found to be longer for the rivalry condition (grating and rival target viewed) than for the normal MAE condition (grating viewed), and comparable to that in the stored MAE condition (both eyes occluded). Thus, the MAE is stored when the test target is rendered invisible due to binocular rivalry, indicating that a suppressed target is ineffective at promoting decay of the MAE. So while suppression does not prevent information about the adapting grating from reaching the site of generation of the MAE (Lehmkuhle & Fox, 1975), it can prevent information about the test target from reaching the site of the stored MAE. Current models attribute the MAE to reduced responsiveness of direction-selective cortical neurons (Sutherland, 1961; Barlow & Hill, 1963). Thus, storage should reflect a differential return of these adapted cells to preadapted response levels, dependent on postadaptation stimulation. From our results we deduce that storage does not occur at all sites at which motion adaptation occurs. Rather, decay of the MAE is dependent on postadaptation stimulation at higher levels of adaptation, and independent at earlier levels.

The phototransduction cascade in invertebrate photoreceptors has not been fully elucidated. It has been proposed that in Limulus ventral photoreceptor cGMP is the intracellular second messenger that directly controls the gating of the light-dependent channels (Johnson et al., 1986; Bacigalupo et al., 1991). Recently, a putative cGMP-gated channel cDNA, Lcng1, has been cloned from Limulus and shown to be expressed in the brain and the ventral eye (Chen et al., 1999). In this study, we sought to more specifically localize the LCNG1 transcript and protein. In situ hybridization was used to determine whether the gene is expressed in glia or photoreceptor cells in the ventral eye. The results clearly demonstrated that Lcng1 mRNA is transcribed in the ventral photoreceptors. On Western blots probed with a polyclonal antibody raised against the C-terminus of LCNG1, a 100-kDa band and an 80-kDa band was labeled in the membrane protein preparations from brain and ventral eye, respectively. The labeling of these bands was blocked by preabsorption of the antibody with the antigen, indicating the labeling specificity. Immunocytochemistry and confocal microscopy were applied to investigate the subcellular localization of this antigen. Immunolabeling was highly localized in the transducing lobes of ventral eye photoreceptors and lateral eye photoreceptors. In both cases, the labeling was associated with membrane regions specialized for phototransduction, but the exact pattern appeared to be somewhat different in the two eyes. Preabsorption of the antiserum with antigen abolished the labeling, confirming specificity. The results lend support to the hypothesis that a cGMP-gated channel is directly involved in the phototransduction process.

Zebrafish are an existing model for genetic and developmental studies due to their rapid external development and transparent embryos, which allow easy manipulation and observation of early developmental stages. The application of the zebrafish model to vision research has allowed for examination of retinal development and the characteristics of different retinal cell types, including bipolar cells. In particular, bipolar cell development, including differentiation, maturation, and gene expression, has been documented, as has physiological properties, such as voltage- and ligand-gated currents, and neurotransmitter receptor and ion channel expression. Mutant strains and transgenic lines have been used to document how bipolar cell connections and/or development may be altered, and toxicological studies examining how environmental factors may impact bipolar cell activity have been performed. The purpose of this paper was to review the existing literature on zebrafish bipolar cells, to provide a comprehensive overview of current information pertaining to this retinal cell type.

Vertebrate photoreceptors respond to light with changes in membrane conductance that reflect the activity of cyclic-nucleotide gated channels (CNG channels). The functional features of these channels differ in rods and cones; to understand the basis of these differences we cloned CNG channels from the retina of striped bass, a fish from which photoreceptors can be isolated and studied electrophysiologically. Through a combination of experimental approaches, we recovered and sequenced three full-length cDNA clones. We made unambiguous assignments of the cellular origin of the clones through single photoreceptor RT-PCR. Synthetic peptides derived from the sequence were used to generate monospecific antibodies which labeled intact, unfixed photoreceptors and confirmed the cellular assignment of the various clones. In rods, we identified the channel α subunit gene product as 2040 bp in length, transcribed into two mRNA 1.8 kb and 2.9 kb in length and translated into a single 96-kDa protein. In cones we identified both α (CNGA3) and β (CNGB3) channel subunits. For α, the gene product is 1956 bp long, the mRNA 3.4 kb, and the protein 74 kDa. For β, the gene product is 2265 bp long and the mRNA 3.3 kb. Based on deduced amino acid sequence, we developed a phylogenetic map of the evolution of vertebrate rod and cone CNG channels. Sequence comparison revealed channels in striped bass, unlike those in mammals, are likely not N-linked-glycosylated as they are transported within the photoreceptor. Also bass cone channels lack certain residues that, in mammals, can be phosphorylated and, thus, affect the cGMP sensitivity of gating. On the other hand, functionally critical residues, such as positively charged amino acids within the fourth transmembrane helix (S4) and the Ca2+-binding glutamate in the pore loop are absolutely the same in mammalian and nonmammalian species.

A comparative study was made on one Mysticete (the fin whale, Balaenoptera physalus) and one Odontocete species (the striped dolphin, Stenella coeruleoalba) by measuring several morphological characteristics seen in cross sections of the optic nerve. We found that the two cetacean nerves share a number of specializations that distinguish them from the optic nerve of terrestrial mammals. Fiber density is approximately two-fold lower than in land mammals. A corresponding increase in the cross-sectional area occupied by astrocytes is observed. A population of “giant” (up to 15 μm in diameter) optic axons is present in both the B. physalus and the S. coeruleoalba nerve. It is argued that these features probably reflect common adaptations to the constraints imposed by the aquatic environment. “Giant” optic axons might ensure short-latency detection of preys and other targets during navigation while the increased astroglial content might be related to the maintenance of neuronal function during periods of anaerobic metabolism under water.