Influence of amacrine cells on receptive field organization of ganglion cells of the generalized vertebrate cone retina: Electronic simulation

Two classes of amacrine cells are simulated, small-field and large-field. Small-field amacrine cells are formed by input from a single bipolar cell, while large-field amacrine cell is formed by inputs from same 7 bipolar cells that form the ganglion cell. Only tonic amacrine cells are studied with both chromatic and luminosity types as well as double-and single-opponent receptive fields. Amacrine cells are used in both feedforward to ganglion cells and feedback to bipolar and horizontal cells. Feedback to bipolar cells or feedfoward to ganglion cells affected steady state levels in a predictable fashion. Negative feedback to bipolar cells and positive feedfoward to ganglion cells does not introduce transients to ganglion cells while negative feedback to horizontal cells and negative feedfoward does. Feedback to horizontal cells produces complex effects on bipolar, amacrine and ganglion cells dependent on such factors as center-surround field balance and negative feedback from luminosity type of horizontal cell to cones.     

Electronic simulation of cones,horizontal cells and bipolar cells of generalized vertebrate cone retina

Electronic analogue of my theoretical model of generalized vertebrate cone retina [Siminoff: J. Theor. Biol. 86, 763 (1980)] is presented. Cone mosaic is simulated by 25x21 grid of phototransistors that have colored filters mounted in front of then to produce red-, green-, and blue-sensitive cones arranged in a trichromatic retina. Each retinal element is simulated by Summator-Integrator and unit gain voltage invertes are used to give correct polarities to output voltages. Dynamic properties of retinal elements are developed solely by temporal interplay of antagonistic input voltages with differing time courses, and spatial organization of receptive fields is developed by unit hexagons that precisely define cone input voltages to subsequent elements. Electronic model contains both color- and non-colorcoded channels. Negative feedback from L-horizontal cells to cones, electrical coupling of like-cones, and electrical coupling of like-horizontal cells are simulated by feedfoward circuits. Stray light is present due to light scattering properties of colored filters used to simulate color selectivety of cones. Stationary and moving spots of white and colored lights of varied sizes and intensities are used to study characteristics of electronic analogue. Results demonstrate practicality of electronic simulation to function analogous to real cone retinas to process visual stimuli and give information to higher centers as to size, shape, color and motion of objects in visual world.     

An analogue simulation of the luminosity-channel in the vertebrate cone retina

A frequency analysis was performed on an analogue model of the vertebrate cone retina. Bode plots of magnitude and phase angle shifts were obtained from the various stages of the Model. While the cones were non-linear, the rest of the Model was linear and results could be explained by cascading of lowpass filters with linear summation of antagonistic inputs of differing time constants. The cut-off frequency of the Model was determined by the first stage, which was the cone pedicle, while the slope of the db magnitude versus frequency curve increased for each “synaptic delay” in the pathway. An initial increase in the magnitude of the output voltage at any given stage occurred up to the cut-off frequency and was due to the antagonistic input voltages of differing time courses. Physiological data were discussed in terms of the Model.     

Dynamics of L-type bipolar and phasic amacrine cells in the vertebrate cone retina

The model of the cone-L-HC circuit of the catfish retina (Siminoff 1985a) is extended to Luminosity bipolar cells (BC) and non-linear phasic amacrine cells (AC), but now applicable to the generalized vertebrate cone retina that involves only one cone type. Two types of BC's are simulated by linear transformation of 2 antagonistic inputs of differing time courses; the faster center field hyperpolarization from the cone and the slower surround field depolarization from the L-HC. The phasic AC was made non-linear by various methods: full- or half-wave rectification using either both or only one of the BC's as the inputs with rectification first and then summation or summation first and then rectification. A method is described using Laplace transforms in conjunction with the convolution theorem to obtain the impulse responses of BC's and AC's, in spite of the non-linearities of the AC even when used as feedback to the BC's. Since the input to the BC consists of 2 antagonistic inputs, feedback from the AC reeinforces one input and attenuates the other.     

Modelling and simulation of vertebrate retina

In the present work we investigate the neuronal activities in a vertebrate retina by modelling and simulations using the results of (Oguztöreli, 1979). The basic retinal network considered here consists of interconnected five neurons: a receptor cell (rod or cone), a horizontal cell, a bipolar cell, an amacrine cell, and a retinal ganglion cell. The mathematical model for the basic network is a system of nonlinear ordinary integral differential difference equations. A number of simulations describing the dynamics of the neural activities in the basic network under different conditions are presented, actual and steady-state solutions are discussed. An algorithm is proposed for the determination of the system parameters experimentally.This work was supported by the Natural Sciences and Engineering Research Council Canada under Grant NSERCA-4345 through the University of Alberta     

An analogue model of the luminosity-channel in the vertebrate cone retina

A model of the vertebrate cone retina was tested with physiological stimuli. Results confirm previous findings that, except for photoreceptors, the spatial and temporal properties of simulated retinal elements conform to a linear system. The model is consistent with known physiological correlates. Tonic units detect intensity when the light spot is within the center field, while phasic units detect movement across borders of contrast. There is a dynamic balance between the tonic and phasic channels: the tonic channel is favored by a center field input voltage, while the phasic channel is favored by a surround field input voltage to bipolar cells. The ON discharge of the phasic ganglion cell is developed by the excitatory center field input to the depolarizing-center bipolar cell, which has the shortest delay, while the OFF discharge is the result of the excitatory surround field input voltage to the hyperpolarizing-center bipolar cell, which has the longest delay.     

The cone synapses of cone bipolar cells of primate retina

One each of bipolar cell types DB2 and DB4, together with a flat and an invaginating midget bipolar cell, were taken from a Golgi-stained rhesus macaque retina; then serially sectioned for EM examination of their synapses with cone pedicles. The cone input to the dendrites of the DB2 cell was exclusively at basal junctions; it had a characteristic distribution. Fifty per cent of the basal synapses were with cone pedicle membrane immediately adjacent to the dendrite of a bipolar cell invaginating to end opposite the ribbon of a cone triad (this, therefore, is called triad-associated). The remainder were one or more synapses distant from the triad-associated position (and, therefore, non-triad associated). The DB4 cell had both basal (predominantly in the triad-associated position) and ribbon-related synaptic input. But the basal to invaginating ratio differed from that of our previously published cell; 56% basal, 43% invaginating, as compared with 31% basal and 69% invaginating. Like foveal IMB cells the synapses of the mid-peripheral invaginating midget bipolar cell were exclusively invaginating; but were about 25% more numerous. The flat midget bipolar cell made exclusively basal synapses. These were 2.5 times more numerous than those of foveal flat midget bipolar cells, and 3.5 times the number of invaginating midget bipolar synapses at equivalent eccentricity. The synapses between cones and diffuse and midget bipolar cells are characteristic for each particular bipolar cell type, but the details depend on a cell’s distance from the fovea (eccentricity). A rather constant number of cone pedicle synaptic ribbons 38.6±2.5 (n±:60) was found across mid-peripheral macaque and vervet monkey retinae. The smaller mean number for vervet monkey, 27.4±3.5 (n ±:23), suggests there can also be generic differences in synaptic detail at cone bipolar cell synapses.     

Modelling and simulation of vertebrate retina: Extended network

In a recent work (Oguztöreli, 1980) a mathematical model for studying the neutral activities in a vertebrate retina has been investigated, where the basic retinal network involves interconnected five neurons of different kind. This model is general enough to cover a great variety of neurons in the same retina as well as in the retinas of different species. In the present work we deal with an extension of the basic network considered in (Oguztöreli, 1980). This extended model contains interconnected twelve neurons: three receptor cells, two horizontal cells, two bipolar cells, two amacrine cells and three ganglion cells. The performance of the model under different conditions, and, the experimental determination of the system parameters are discussed. The background of the modelling and simulations can be found in (Oguztöreli, 1979, 1980).This work was supported by grants from the Natural Sciences and Engineering Research Council Canada under Grant NSERC-A-4345 and Grant NSERC G0377 to MNO through the University of Alberta     

Target cells of vitamin D in the vertebrate retina

Using PAP technique, cellular localization of vitamin D-dependent calcium-binding protein (D-CaBP) was investigated in vertebrate retina with monospecific antisera against chick duodenal D-CaBP. In the chick retina, the receptor cells were positive. In the inner nuclear layer, horizontal cells and some bipolar cells were also positive. Some amacrine cells as well as different levels of the inner plexiform layer were also positive for D-CaBP. A few interspersed ganglion cells were positive but their axons forming the optic tract were negative. Müller's cells were negative. In 1-day-old chicks and 4-week-old rachitic chicks there was paucity and absence, respectively, of D-CaBP staining in horizontal cells. In the mouse, rat, and rabbit the receptors had only trace amounts of reaction product in their outer segment and pedicle. Horizontal cells were densely positive throughout their cellular body and processes. Some amacrine cells in the inner nuclear layer were positive. In the mouse and rat three horizontal levels of the outer plexiform layer were very prominent because of their dense staining for D-CaBP. Many ganglion cells were also positive along with their axons forming the optic nerve. In the rabbit, no positive layers were seen in the inner plexiform layer, and ganglion cells with their fibers were negative. In the frog retina there were smaller amounts of D-CaBP in the receptor cells and horizontal cells than that of the chick retina. Also, the fibers of the ganglionic cells were positive for D-CaBP. In all species studied, some amacrine cells were stained for D-CaBP. Because of its possible roles in membrane calcium transport and intracellular Ca++ regulation, it has perhaps similar functions in these positive cells. The synthesis of D-CaBP is dependent upon vitamin D. These positive cells are thus target cells of vitamin D.     

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.     

Response analysis of vertebrate retina

In a recent work (Ouztöreli, 1980) a mathematical model for studying the neural activities in a vertebrate retina has been investigated, where the basic network contains five interconnected neurons: a receptor cell, a bipolar cell, a horizontal cell, an amacrine cell, and a retinal ganglion cell. More recently, in (Ouztöreli and O'Mara, 1980) the basic network has been extended to a larger network containing twelve neurons. In both of these works, the performances of the basic and extended models were discussed under different structural and processing conditions with constant inputs by using the results of one of our earlier work (Ouztöreli, 1979). In the present paper we investigate by simulations the responses of the basic retinal network to piecewise constant and periodic inputs. The step and frequency responses of the extended retinal network will be discussed in a forthcoming paper.This work was partially supported by the Natural Sciences and Engineering Research Council of Canada under Grant A-4345 through the University of alberta     

Receptive field mechanisms of ganglion cells in the cat retina

On the basis of anatomical and physiological results of the vertebrate retina, a method is proposed for analysing the respective fields of ganglion cells in the cat retina. In the model, we assume the following: (a) Ganglion cells receive their input from bipolar and/or amacrine cells. (b) The nonlinearity of ganglion cell responses is due to the activities of transient type amacrine cells. The method has been proved to be effective. According to the results of this investigation, the receptive field properties of X type and Y type ganglion cells are heterogeneous. Thus, it may be considered that their receptive fields consist of center and surround mechanisms. The receptive field properties of X-cells are almost linear and the X-cells seem to receive most of their input from bipolar cells. On the other hand, the ones of Y-cells are highly nonlinear. Consequently, it is conceivable that the Y-cells receive their input mainly from transient type amacrine cells.     

Model feedback mechanism between horizontal cells and photoreceptors of the vertebrate retina

A model with nonlinearity of the photoreceptor presynaptic membrane as its important distinguishing feature was created on the basis of the hypothesis that feedback between the horizontal cells and photoreceptors is effected by a current generated by the subsynaptic membrane of the horizontal cells and leaking partly into the photoreceptors. Measurements with the model also reproduced experimental observations such as depolarization of the cone during hyperpolarization of the horizontal cell in response to the showing of a ring of light or passage of an electric current, and also certain special features of the current-voltage curves of the cones.Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 1, pp. 86–94, January–February, 1977.     

The nonlinear pathway of Y ganglion cells in the cat retina

Retinal ganglion cells of the Y type in the cat retina produce two different types of response: linear and nonlinear. The nonlinear responses are generated by a separate and independent nonlinear pathway. The functional connectivity in this pathway is analyzed here by comparing the observed second-order frequency responses of Y cells with predictions of a "sandwich model" in which a static nonlinear stage is sandwiched between two linear filters. The model agrees well with the qualitative and quantitative features of the second-order responses. The prefilter in the model may well be the bipolar cells and the nonlinearity and postfilter in the model are probably associated with amacrine cells.     

Subsurface cisterns in the vertebrate retina

Structures identified as subsurface cisterns (SSC's) were found in retinal neurons and their processes in the Western grey squirrel, the California and 13-line ground squirrels, the South African clawed toad, and the domestic cat. The SSC's are located in amacrine, bipolar, and ganglion cells; they are connected with the rough endoplasmic reticulum and are associated with specific membrane specializations. SSC's were not seen in the Müller cells, an observation which agrees with earlier reports that these organelles do not exist in glial cells.     

GABAC receptors in the vertebrate retina

In the central nervous system (CNS), the inhibitory transmitter GABA interacts with three subtypes of GABA receptors, type A, type B, and type C. Historically, GABA receptors have been classified as either the inotropic GABA_A receptors or the metabotropic GABA_B receptors. Over the past 10 yr, studies have shown that a third class, called the GABA_C receptor, also exists. GABA_C receptors are found primarily in the vertebrate retina and to some extent in other parts of the CNS. Although GABA_A and GABA_C receptors both gate chloride channels, they are pharmacologically, molecularly, and functionally distinct. The ρ subunit of the GABA_C receptor, which has about 35% amino acid homology to GABA_A receptor subunits, was cloned from the retina and, when expressed inXenopus oocytes, has properties similar to retinal GABA_C receptors. There are probably distinct roles for GABA_C receptors in the retina, because they are found on only a subset of neurons, whereas GABA_A receptors are ubiquitous. This article reviews recent electrophysiological and molecular studies that have characterized the unique properties of GABA_C receptors and describes the roles that these receptors may play in visual information processing in the retina.