Lateral feedback from monophasic horizontal cells to cones in carp retina. II. A quantitative model

About half of the monophasic horizontal cells in carp retina receive input from both red- and green-sensitive cones. Since the horizontal cells feed back to cones, the color and feedback pathways result in wavelength- and intensity-dependent changes of the dynamics and of the receptive field amplitude profile of the horizontal cell responses. In this paper we present a quantitative model that describes adequately the color and spatial coding and the dynamics of the responses from monophasic horizontal cells in carp. Lateral feedback plays a distinct role in this model.     

A dynamic model of the receptive field of L-cells in the carp retina

A dynamic model of the receptive field of L2-cells in the carp retina is developed by using our experimental results on the basis of physiological and morphological evidences. Linear spatial summation is assumed in the model for the interactions among L2-cells. Linear forward and feedback loops are also assumed for the interactions between L2-cells and cones. The model has dynamic properties similar to the ones of the receptive field of L2-cells: L2-cells respond faster as the size of a light spot is enlarged and the L2-cells nearer to the center of the light spot respond faster. It is suggested that the faster responding properties of L2-cells are due to the feedback action.     

Dynamic characteristics of the receptive field of L-cells for monochromatic lights

We applied the Wiener theory to analyse receptive field responses of L-cells in the carp and studied some dynamic properties of the receptive field of L-cells for monochromatic light stimuli. The L-cells were stimulated by each monochromatic light modulated in white-noise fashion. They responded almost linearly to all the monochromatic light stimuli. The impulse responses of the L-cells became larger in amplitude and faster in latency, peak response time, and repolarising phase as a spot of monochromatic light was enlarged. The L-cells seem to respond like a lowpass filter and the cutoff frequency of their gain characteristics increases with the enlargement of the monochromatic light spot. The relation between shift of cutoff frequency and spot diameter was monotonic increasing for each monochromatic light.     

Color opponency in cone-driven horizontal cells in carp retina. Aspecific pathways between cones and horizontal cells

The spectral and dynamic properties of cone-driven horizontal cells in carp retina were evaluated with silent substitution stimuli and/or saturating background illumination. The aim of this study was to describe the wiring underlying the spectral sensitivity of these cells. We will present electrophysiological data that indicate that all cone-driven horizontal cell types receive input from all spectral cone types, and we will present evidence that all cone-driven horizontal cell types feedback to all spectral cone types. These two findings are the basis for a model for the spectral and dynamic behavior of all cone-driven horizontal cells in carp retina. The model can account for the spectral as well as the dynamic behavior of the horizontal cells. It will be shown that the strength of the feedforward and feedback pathways between a horizontal cell and a particular spectral cone type are roughly proportional. This model is in sharp contrast to the Stell model, where the spectral behavior of the three horizontal cell types is explained by a cascade of feedforward and feedback pathways between cones and horizontal cells. The Stell model accounts for the spectral but not for the dynamic behavior of the horizontal cells.     

Modeling of the vertebrate visual system. II. Application to the turtle cone retina

The model of the vertebrate cone retina was adapted to the turtle retina with its red cone- and L-channel-dominances. The model consists of an ordering of four spatial organizations of unit hexagons, weighted inputs for all cones in the receptive fields, and linear polarization factors based on data from literature on turtle retina. Data generated by the model for spatial and chromatic patterns of receptive fields, intensity-response curves, dynamic ranges for cones, horizontal and bipolar cells proved remarkably consistent with literature. The model also generates observed phenomena such as near-field enhancement of cones due to stray light effects and electrical coupling of like-cones and far-field decrease in responses due to negative feedback from L-type horizontal cells to cones. Annular stimuli were shown to be more effective than spot stimuli for horizontal cells. The formal approach of the model demonstrates factors which play roles in various observed phenomena and all aspects of model can be displayed and tested both qualitatively and quantitatively.     

The role of retinal bipolar cell in early vision: an implication with analogue networks and regularization theory

A linear analogue network model is proposed to describe the neuronal circuit of the outer retina consisting of cones, horizontal cells, and bipolar cells. The model reflects previous physiological findings on the spatial response properties of these neurons to dim illumination and is expressed by physiological mechanisms, i.e., membrane conductances, gap-junctional conductances, and strengths of chemical synaptic interactions. Using the model, we characterized the spatial filtering properties of the bipolar cell receptive field with the standard regularization theory, in which the early vision problems are attributed to minimization of a cost function. The cost function accompanying the present characterization is derived from the linear analogue network model, and one can gain intuitive insights on how physiological mechanisms contribute to the spatial filtering properties of the bipolar cell receptive field. We also elucidated a quantitative relation between the Laplacian of Gaussian operator and the bipolar cell receptive field. From the computational point of view, the dopaminergic modulation of the gap-junctional conductance between horizontal cells is inferred to be a suitable neural adaptation mechanism for transition between photopic and mesopic vision. Received: 20 December 1996 / Accepted in revised form: 16 May 1997     

Dynamic model of interaction between cones and horizontal photic cells in the carp retina

A mathematical model is examined of interaction between cones and horizontal L-type cells (HC) in the carp retina using data from intracellular recording of HC spectral response. This model, describing the operation of ionic channels at the membrane of cones and HC, is based on a numerical analog solution to Hodgkin-Huxley differential equations [11] and enables predictions of spectral response levels in HC to be made as a function of time.M. L. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 4, pp. 461–466, July–August, 1989.     

Simulated bipolar cells in fovea of human retina

The static model developed in Part I is used to study spectral responses of C-type bipolar cells (BC). Once unique loci are adjusted to their proper wavelengths, and with a specified set of absorption spectra for cones, spectral responses of C-type BCs are dependent on only the balance between BC receptive field center and surround responses. This is true regardless of cone mosaic or BC receptive field organization. The unique yellow loci for the r-g channel is set at 576.7 nm while the unique green locus for the blue-center BC is set at 517.7 nm. A unique orange locus for a combined r-g and bl-y channels is set at 600 nm by multiplying the blue-center BC response spectra by a factor of six before adding to the r-g channel.     

Effects of long-term spectral deprivation on the morphological organization of the outer retina of the blue acara (Aequidens pulcher)

To investigate the developmental plasticity of colour vision, we reared fish with a trichromatic cone system (Aequidens pulcher) under three near-monochromatic lights, differentially stimulating each spectral cone type from the larval stage to the age of at least one year. Control conditions comprised white lights of two intensities. The treatments did not affect the visual pigments, hut led to significant changes in cone outer segment lengths. Furthermore, in the blue-reared group the density of single cones within the retina was reduced by two-thirds after 18 months of exposure, while no changes were observed in the other groups. The connectivity of cone horizontal cells with the single cones was influenced by the intensity and spectral composition of the rearing lights: H1 cells were more sensitive to the spectral component, whereas H2 cells responded to intensity cues. In the blue-light group the dynamics of horizontal cell synaptic spinule formation and degradation were severely compromised. These observations show that long-term spectral deprivation leads to significant morphological changes at the level of photoreceptors and horizontal cells. While the reactions of photoreceptors may be interpreted mostly in terms of compensation, the functional consequences of the changes observed on the horizontal cell level remain to be determined electrophysiologically.     

Spatiotemporal testing and modeling of catfish retinal neurons.

The responses of retinal neurons depend on the interaction of both temporal and spatial aspects of a light stimulus. We developed a linear spatiotemporal model of receptor and horizontal cell layers in the catfish retina based on reciprocal interactions between both layers and coupling within each. Horizontal cell transfer properties were measured experimentally using white-noise intensity modulated light spots of different diameters and were compared with analytical predictions based on the model. Good agreement was obtained with a reasonable choice of model space-constants and feedback parameters. Furthermore, the same set of parameter values determined from spot experiments enabled accurate prediction of experimental horizontal cell responses to traveling gratings. The proposed feedback connections from horizontal cells to receptors quicken the time-course of responses in both layers and sharpen receptive fields.     

Electronic simulation of ganglion cells of generalized vertebrate cone retina

Electronic simulation of generalized vertebrate cone retina consists of 43x41 grid of red-, green-, and blue-sensitive cones. Each retinal element is simulated by a linear summator in series with a leaky integrator and spatial-temporal properties are developed by spatial organization of cone mosaic into unit hexagons and interplay of antagonistic inputs of differing time courses. Model has full compliments of horizontal and bipolar cells including color- and noncolor coding as well as single- and double-opponent receptive fields for bipolar cells. Electronic simulation also has negative feedback from L-horizontal cells to cones. Ganglion cells are formed by convergence of 7 bipolar cells, either all same and thus homogeneous, or else with a central-DPBC (or HPBC) and 6 surround-HPBCs (or DPBCs) and thus non-homogeneous. Responses of color- and non-color-coded ganglion cells as well as single- and double-opponents are investigated with stationary and moving light spots using white and colored lights. While responses to stationary light spots are predictable from digital models, responses to moving spots are complicated by differing time lags of components involved in total response. Therefore, responses to moving stimuli are more readily simulated by analogue models.     

Cobalt ions enhance light responsiveness of carp cone horizontal cells in low calcium

Effects of cobalt ions (Co2+) on horizontal cells in low extracellular calcium were examined in isolated, superfused carp retinas. While 0.1mmol/L Co2+ completely suppressed both rod- and cone-driven horizontal cells in normal Ringer's solution, it enhanced light responses of cone horizontal cells in low (0.1mmol/L) calcium. The enhancement of the cone horizontal cell response by Co2+ was not caused by changes in light responsiveness of cone photoreceptors. Moreover, application of 50μmol/L IBMX, an inhibitor of phosphodiester enzyme, reduced the suppressive effect of 0.1 mmol/L Co2+ in normal Ringer's solution. In consequence, the above-described enhancement of the cone horizontal cell light responsiveness may be due to a depolarization of cones caused by low calcium, which increases the activity of voltage-dependent calcium channels at cone terminals.     

Differential modulation by AMPA of signals from red- and green-sensitive cones in carp retinal luminosity-type horizontal cells

Intracellular recordings were made from luminosity-type horizontal cells (LHCs) in the isolated superfused carp retina and the effect of AMPA (α-amino-3-hydroxy-5-methylisoxa-zole-4-propionic acid), a glutamate receptor agonist, on these cells was studied. AMPA suppressed the responses of LHCs driven by red-sensitive (R-) cones whereas it potentiated the responses driven by green-sensitive (G-) cones. The AMPA effect could be completely blocked by GYKI 53655, a specific AMPA receptor antagonist, indicating the exclusive involvement of AMPA-preferring receptors. The AMPA effect persisted in the presence of picrotoxin (PTX) or di-hydrokainic acid (DHK), suggesting that the feedback from LHCs onto cones and glutamate transporters on cones may not be involved. It is suggested that there may exist different AMPA receptor subtypes with distinct characteristics on LHCs, which mediate signal transfer from R- and G-cones to LHCs, respectively.     

Differential modulation by AMPA of signals from red- and green-sensitive cones in carp retinal luminosity-type horizontal cells

Intracellular recordings were made from luminosity-type horizontal cells (LHCs) in the isolated superfused carp retina and the effect of AMPA (α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid), a glutamate receptor agonist, on these cells was studied. AMPA suppressed the responses of LHCs driven by red-sensitive (R-) cones whereas it potentiated the responses driven by green-sensitive (G-) cones. The AMPA effect could be completely blocked by GYKI 53655, a specific AMPA receptor antagonist, indicating the exclusive involvement of AMPA-preferring receptors. The AMPA effect persisted in the presence of picrotoxin (PTX) or dihydrokainic acid (DHK), suggesting that the feedback from LHCs onto cones and glutamate transporters on cones may not be involved. It is suggested that there may exist different AMPA receptor subtypes with distinct characteristics on LHCs, which mediate signal transfer from R-and G-cones to LHCs, respectively.     

明适应条件下鲤属鱼L-型外水平细胞反应的给光-瞬变成分

在明适应条件下鲤属鱼 L-型外水平细胞的反应显示明显的给光-瞬变成分(on-transient)、它与刺激波长有关——对蓝、绿光的反应比对红光的反应有更明显的瞬变成分,其光谱特性提示它与绿敏锥细胞的输入信号有关。与已报道的其它动物 L 型水平细胞的给光-瞬变成分不同,它的出现在一定范围内与网膜受照射的面积无关。绿色(502nm)和红色(706nm)闪光同时照射所引起反应的给光-瞬变成分比各自单独刺激时要显著得多,提示它也与绿敏锥细胞和红敏锥细胞输入的相互作用有关。     

A "melanopic" spectral efficiency function predicts the sensitivity of melanopsin photoreceptors to polychromatic lights

Photoreception in the mammalian retina is not restricted to rods and cones but extends to a small number of intrinsically photosensitive retinal ganglion cells expressing the photopigment melanopsin. These mRGCs are especially important contributors to circadian entrainment, the pupil light reflex, and other so-called nonimage-forming (NIF) responses. The spectral sensitivity of melanopsin phototransduction has been addressed in several species by comparing responses to a range of monochromatic stimuli. The resultant action spectra match the predicted profile of an opsin:vitamin A-based photopigment (nomogram) with a peak sensitivity (λ(max)) around 480 nm. It would be most useful to be able to use this spectral sensitivity function to predict melanopsin's sensitivity to broad-spectrum, including "white," lights. However, evidence that melanopsin is a bistable pigment with an intrinsic light-dependent bleach recovery mechanism raises the possibility of a more complex relationship between spectral quality and photoreceptor response. Here, we set out to empirically determine whether simply weighting optical power at each wavelength according to the 480-nm nomogram and integrating across the spectrum could predict melanopsin sensitivity to a variety of polychromatic stimuli. We show that pupillomotor and circadian responses of mice relying solely on melanopsin for their photosensitivity (rd/rd cl) can indeed be accurately predicted using this methodology. Our data therefore suggest that the 480-nm nomogram may be employed as the basis for a new photometric measure of light intensity (which we term "melanopic") relevant for melanopsin photoreception. They further show that measuring light in these terms predicts the melanopsin response to light of divergent spectral composition much more reliably than other methods for quantifying irradiance or illuminance currently in widespread use.     

Unit responses of the clare-bishop cortical association area in the cat to photic stimulation

Electrical activity of single unit in the Clare-Bishop visual association area of the cortex was studied in acute experiments on cats immobilized with Flaxedil and after pretrigeminal sections. The method of extracellular recording of action potentials of single units was used. The experimental results showed that 95.5% of cells responding to visual stimulation responded to movement of a spot of light in the receptive field of the neurons, and 55% of the cells responded selectively to the direction of movement. Some neurons responded to movement of a stimulus only when it entered and left the receptive field. About 85.3% of cells responded to a flashing spot of light, and also to a general change in the intensity of illumination of the receptive field. The receptive field of neurons of the Clare-Bishop area in most cases were in the form of stripes with their long axis horizontal. The results point to the important role of this cortical association area in the central analysis of visual information.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSSR, Erevan. Translated from Neirofiziologiya, Vol. 10, No. 1, pp. 22–29, January–February, 1978.     

Activity of long-wavelength cones under scotopic conditions in the cyprinid fish Danio aequipinnatus

In carp (Cyprinus) and goldfish (Carassius), long-wavelength cones are reported to be active under scotopic conditions. Using the electroretinogram (ERG), we tested another cyprinid fish, Danio aequipinnatus, which contains A₁-based visual pigments and for which we had previously measured the spectral sensitivities of individual cones. Dark adaptation curves show a rod/cone break at about 45 min. When thoroughly dark-adapted, the spectral sensitivity function is broader than can be accounted for by self-screening of rhodopsin, but it can be modeled by an additive combination of rods and the 560-nm cones. Dim, red background light causes adaptation of rods and a broadening of the spectral sensitivity function, which can be simulated by increasing the proportion of cones in the model. Brighter red backgrounds adapt the 560-nm cones. Because of the effect of red adapting lights, the ERG evidence for the participation of long-wavelength cones close to visual threshold appears to be different in Danio than in the goldfish Carassius. Accepted: 14 June 1997     

Colour perception of single and mixed monochromatic lights in the blowfly Lucilia cuprina

Colour perception of spectral lights and mixtures of two monochromatic lights of blue and yellow wavelengths was studied in the blowfly Lucilia cuprina by using a generalization test in which the fly had to compare these lights in memory with coloured papers (blue, green, yellow and red) represented in the test array. Flies trained to a monochromatic light in the wavelength range of 429–491 nm responded to blue; those trained to 502–511 nm to green; and those trained to 522–582 nm to yellow. The maximal generalization for blue was found at 429 nm and that for yellow at 543 nm. Flies trained to the mixtures responded neither to blue, green nor yellow, when the blue component was mixed with the yellow component in a ratio of approximately 1 3. It seems that the fly perceives the mixtures as a neutral or an achromatic light. Colour loci of coloured papers, spectral lights and mixtures of two monochromatic lights used formed blue, yellow and neutral clusters in a colour triangle with respect to generalization responses to test colours.     

Analyses of bipolar cell responses elicited by polarization of horizontal cells

Simultaneous intracellular recordings were made from a bipolar cell and a horizontal cell in the carp retina. The properties of the bipolar cell were studied while injecting current into the horizontal cell. Hyperpolarization of horizontal cells, irrespective of their type, elicited a hyperpolarizing response in on-center bipolar cells and a depolarizing response in off-center bipolar cells. Analyses of the ionic mechanisms of bipolar cell responses revealed that depolarization of horizontal cells simulated and hyperpolarization opposed the effect of central illumination. The effect of polarization was exerted in such a manner that each type of horizontal cells modified the transmission from those photoreceptors from which they receive main inputs. In on- center bipolar cells, for example, the L-type horizontal cells receiving inputs mainly from red cones modified the cone-bipolar transmission accompanied by a conductance change of K+ and/or Cl- channels, and the intermediate horizontal cells receiving inputs from rods modified the rod-bipolar transmission accompanied by a conductance change of Na+ channels. In off-center bipolar cells, the effect of polarization of any type of horizontal cells was mediated mainly by conductance changes of Na+ channels. Feedback mechanisms from horizontal cells to photoreceptors could explain these results reasonably well.