Form and function of cat retinal ganglion cells

Fractals in the Neurosciences: A Translational Geographical Approach

The chapter presents three new fractal indices (fractal fragmentation index, fractal tentacularity index, and fractal anisotropy index) and normalized Kolmogorov complexity with proven applicability in geographic research, developed by the authors, and the possibility of their future use in neuroscience. The research demonstrates the relevance of fractal analysis in different fields and the basic concepts and principles of fractal geometry being sufficient for the development of models relevant to the studied reality. Also, the research highlighted the need to continue interdisciplinary research based on known fractal indicators, as well as the development of new analysis methods with the translational potential between fields.

Characterization of retinal ganglion cell, horizontal cell, and amacrine cell types expressing the neurotrophic receptor tyrosine kinase Ret

We report the retinal expression pattern of Ret, a receptor tyrosine kinase for the glial derived neurotrophic factor (GDNF) family ligands (GFLs), during development and in the adult mouse. Ret is initially expressed in retinal ganglion cells (RGCs), followed by horizontal cells (HCs) and amacrine cells (ACs), beginning with the early stages of postmitotic development. Ret expression persists in all three classes of neurons in the adult. Using RNA sequencing, immunostaining and random sparse recombination, we show that Ret is expressed in at least three distinct types of ACs, and ten types of RGCs. Using intersectional genetics, we describe the dendritic arbor morphologies of RGC types expressing Ret in combination with each of the three members of the POU4f/Brn3 family of transcription factors. Ret expression overlaps with Brn3a in 4 RGC types, with Brn3b in 5 RGC types, and with Brn3c in one RGC type, respectively. Ret⁺ RGCs project to the lateral geniculate nucleus (LGN), pretectal area (PTA) and superior colliculus (SC), and avoid the suprachiasmatic nucleus and accessory optic system. Brn3a⁺ Ret⁺ and Brn3c⁺ Ret⁺ RGCs project preferentially to contralateral retinorecipient areas, while Brn3b⁺ Ret⁺ RGCs shows minor ipsilateral projections to the olivary pretectal nucleus and the LGN. Our findings establish intersectional genetic approaches for the anatomic and developmental characterization of individual Ret⁺ RGC types. In addition, they provide necessary information for addressing the potential interplay between GDNF neurotrophic signaling and transcriptional regulation in RGC type specification.

Genetic interactions between Brn3 transcription factors in retinal ganglion cell type specification

Background

Visual information is conveyed from the retina to the brain via 15–20 Retinal Ganglion Cell (RGC) types. The developmental mechanisms by which RGC types acquire their distinct molecular, morphological, physiological and circuit properties are essentially unknown, but may involve combinatorial transcriptional regulation. Brn3 transcription factors are expressed in RGCs from early developmental stages, and are restricted in adults to distinct, partially overlapping populations of RGC types. Previously, we described cell autonomous effects of Brn3b (Pou4f2) and Brn3a (Pou4f1) on RGC axon and dendrites development.

Methods and Findings

We now have investigated genetic interactions between Brn3 transcription factors with respect to RGC development, by crossing conventional knock-out alleles of each Brn3 gene with conditional knock-in reporter alleles of a second Brn3 gene, and analyzing the effects of single or double Brn3 knockouts on RGC survival and morphology. We find that Brn3b loss results in axon defects and dendritic arbor area and lamination defects in Brn3a positive RGCs, and selectively affects survival and morphology of specific Brn3c (Pou4f3) positive RGC types. Brn3a and Brn3b interact synergistically to control RGC numbers. Melanopsin positive ipRGCs are resistant to combined Brn3 loss but are under the transcriptional control of Isl1, expanding the combinatorial code of RGC specification.

Conclusions

Taken together these results complete our knowledge on the mechanisms of transcriptional control of RGC type specification. They demonstrate that Brn3b is required for the correct development of more RGC cell types than suggested by its expression pattern in the adult, but that several cell types, including some Brn3a, Brn3c or Melanopsin positive RGCs are Brn3b independent.

GABAergic mechanisms for shaping transient visual responses in the mouse superior colliculus

An object that suddenly appears in the visual field should be quickly detected and responded to because it could be beneficial or harmful. The superficial layer of the superior colliculus (sSC) is a brain structure capable of such functions, as sSC neurons exhibit sharp transient spike discharges with short latency in response to the appearance of a visual stimulus. However, how transient activity is generated in the sSC is poorly understood. Here, we show that inhibitory inputs actively shape transient activity in the sSC. Juxtacellular recordings from anesthetized mice demonstrate that almost all types of sSC neurons, which were identified by post hoc histochemistry, show transient spike discharges, i.e., ON activity, immediately after visual stimulus onset. ON activity was followed by a pause before the visual stimulus was turned off. To determine whether the pause reflected the absence of excitatory drive or inhibitory conductance, we injected depolarizing currents juxtasomally, which enabled us to observe inhibition as decreased discharges. The pause was observed even under this condition, suggesting that inhibitory input caused the pause. We further found that local application of a mixture of GABAA and GABAB receptor antagonists additively diminished the pause. These results indicate that GABAergic inputs produce transient ON responses by attenuating excitatory activity through the cooperative activation of GABAA and GABAB receptors, allowing sSC neurons to act as a saliency detector.

Morphologies of mouse retinal ganglion cells expressing transcription factors Brn3a, Brn3b, and Brn3c: analysis of wild type and mutant cells using genetically-directed sparse labeling

The mammalian retina contains more than 50 distinct neuronal types, which are broadly classified into several major classes: photoreceptor, bipolar, horizontal, amacrine, and ganglion cells. Although some of the developmental mechanisms involved in the differentiation of retinal ganglion cells (RGCs) are beginning to be understood, there is little information regarding the genetic and molecular determinants of the distinct morphologies of the 15-20 mammalian RGC cell types. Previous work has shown that the transcription factor Brn3b/Pou4f2 plays a major role in the development and survival of many RGCs. The roles of the closely related family members, Brn3a/Pou4f1 and Brn3c/Pou4f3 in RGC development are less clear. Using a genetically-directed method for sparse cell labeling and sparse conditional gene ablation in mice, we describe here the sets of RGC types in which each of the three Brn3/Pou4f transcription factors are expressed and the consequences of ablating these factors on the development of RGC morphologies.

The development of retinal ganglion cells in a tetraploid strain of Xenopus laevis: a morphological study utilizing intracellular dye injection

The morphological development of retinal ganglion cells was examined in a tetraploid strain of Xenopus frogs. The enlarged cells of the tetraploid strain facilitate the application of intracellular techniques. Using an in vitro retinal preparation and Nomarski optics, intracellular recording and dye injection were carried out under visual control on ganglion cells in central retina from 2 days of development (stage 24) to metamorphosis (stage 64). We identified three phases in the morphological differentiation of ganglion cells. During the first phase (stages 24-30), all cells were neuroepitheliallike in form and possessed robust resting potentials in the range of -35 to -60 mV, and dye-coupling was occasionally observed between neighboring cells. During the second phase of ganglion cell development (stages 31-45) the neurons had begun to elaborate axons and dendrites. These cells possessing neurites had resting potentials between -15 and -30 mV, and no dye-coupling was observed between neighbors. During the third and final phase of maturation, from stage 46 onward, three distinct morphological types of ganglion cells could be identified. Type I cells had the smallest somata and the smallest-diameter dendritic arborizations. The profusely branched dendrites of these cells ramify extensively throughout the inner plexiform layer. Type II cells had large somata, intermediate-diameter dendritic fields, and a highly elaborate dendritic branching pattern. These cells were seen to arborize within two sublamina in the inner plexiform layer. Type III cells had large somata, the largest-diameter dendritic fields, and a dendritic arbor with long primary branches but little higher-order branching. These large dendritic fields were confined to a single sublamina of the inner plexiform layer, abutting the inner nuclear layer. While most phase 3 cells showed radial axon trajectories from the soma to the optic disc, a minority of cells (1-5%) with erratic and nonradial axon trajectories were also observed. Our data provide a morphological description of ganglion cell maturation in the central retina of Xenopus. We show that very early in development (as early as stage 46) three distinct morphological types of retinal ganglion cells are present, which correspond to the three classes of ganglion cells previously described in adult Xenopus (Chung et al., '75).

Survival and axonal regeneration of retinal ganglion cells in adult cats

Axotomized retinal ganglion cells (RGCs) in adult cats offer a good experimental model to understand mechanisms of RGC deteriorations in ophthalmic diseases such as glaucoma and optic neuritis. Alpha ganglion cells in the cat retina have higher ability to survive axotomy and regenerate their axons than beta and non-alpha or beta (NAB) ganglion cells. By contrast, beta cells suffer from rapid cell death by apoptosis between 3 and 7 days after axotomy. We introduced several methods to rescue the axotomized cat RGCs from apoptosis and regenerate their axons; transplantation of the peripheral nerve (PN), intraocular injections of neurotrophic factors, or an antiapoptotic drug. Apoptosis of beta cells can be prevented with intravitreal injections of BDNF+CNTF+forskolin or a caspase inhibitor. The injection of BDNF+CNTF+forskolin also increases the numbers of regenerated beta and NAB cells, but only slightly enhances axonal regeneration of alpha cells. Electrical stimulation to the cut end of optic nerve is effective for the survival of axotomized RGCs in cats as well as in rats. To recover function of impaired vision in cats, further studies should be directed to achieve the following goals: (1). substantial number of regenerating RGCs, (2). reconstruction of the retino-geniculo-cortical pathway, and (3). reconstruction of retinotopy in the target visual centers.

The receptive fields of cat retinal ganglion cells in physiological and pathological states: where we are after half a century of research

Studies on the receptive field properties of cat retinal ganglion cells over the past half-century are reviewed within the context of the role played by the receptive field in visual information processing. Emphasis is placed on the work conducted within the past 20 years, but a summary of key contributions from the 1950s to 1970s is provided. We have sought to review aspects of the ganglion cell receptive field that have not been featured prominently in previous review articles. Our review of the receptive field properties of X- and Y-cells focuses on quantitative studies and includes consideration of the function of the receptive field in visual signal processing. We discuss the non-classical as well as the classical receptive field. Attention is also given to the receptive field properties of the less well-studied cat ganglion cells-the W-cells-and the effect of pathology on cat ganglion cell properties. Although work from our laboratories is highlighted, we hope that we have given a reasonably balanced view of the current state of the field.

The intrinsic temporal properties of alpha and beta retinal ganglion cells are equivalent

BACKGROUND

Mammalian retinal ganglion cells have been traditionally classified on the basis of morphological and functional criteria, but as yet little is known about the intrinsic membrane properties of these neurons. This study has investigated these properties by making patch-clamp recordings from morphologically identified ganglion cells in the intact retina.

RESULTS

The whole-cell configuration of the patch-clamp technique was used to assess the temporal tuning characteristics of alpha and beta cells, the two most extensively studied ganglion cell classes. Fourier analysis was used to examine discharge patterns in response to sinusoidal currents of different frequencies (1-50 Hz). With few exceptions, neurons responded in a stereotypic fashion to changes in temporal modulation, with their output initially increasing and then decreasing as a function of stimulus frequency. Moreover, peak responses in both cell classes were obtained at equivalent temporal frequencies. At high stimulus rates, response probability decreased, but the spikes remained phase-locked to the stimulus cycle, thereby enabling populations of cells to convey temporal information. A small number of ganglion cells did not show an appreciable decrease in output as a function of stimulus frequency, but these cells were not confined to either ganglion cell class.

CONCLUSIONS

These findings provide the first evidence that the intrinsic temporal properties of alpha and beta cells are alike. Furthermore, the responses obtained to direct current injections were strikingly similar to those described previously with temporally modulated visual stimuli, suggesting that intrinsic membrane properties may shape the visual responses of alpha and beta cells to a larger degree than has been commonly assumed.

The light response of retinal ganglion cells is truncated by a displaced amacrine circuit

The vertebrate retina contains ganglion cells that appear to be specialized for detecting temporal changes. The characteristic response of these cells is a transient burst of action potentials when a stationary image is presented or removed, and often a strong discharge to moving images. These transient and motion-sensitive responses are thought to result from processing in the inner retina that involves amacrine cells, but the critical interactions have been difficult to reveal. Here, we used a cell-ablation technique to remove a subpopulation of amacrine cells from the mouse retina. Their ablation changed transient ganglion cell responses into prolonged discharges. This suggests that transient responses are generated, at least in part, by a truncation of sustained excitatory input to the ganglion cells and that the ablated amacrine cells are critical for this process.

An efficient method that reveals both the dendrites and the soma mosaics of retinal ganglion cells

A method of using neurobiotin to stain both the dendrites and the soma mosaics of retinal ganglion cells in fresh retinae is described. This method is simple to use and efficient in revealing morphological details for a large number of retinal ganglion cells. It has five advantages over currently available staining methods. (1) It stains all ganglion cells in the whole retina or in a selected retinal area, permitting ganglion cell distributions across the retina to be obtained. (2) It reveals cell dendrites in great detail, especially in regions outside the area centralis. The dendritic field mosaics and, therefore the dendritic field coverage factors, of different ganglion cell types across the whole retina can be obtained easily. (3) It works reliably, efficiently, and does not require the expensive set-up or the pains-taking work needed when staining cells through intracellular injection. (4) It works under both in vivo and in vitro settings, permitting the use of retinae from animals sacrificed for other purposes and the use of postmortem human retinae. (5) The end product of the visualization process is optically dark and electron dense, permitting specimens to be examined under both light and electron microscopes.

Demonstration of direct input from the retina to the lateral habenular nucleus in the albino rat

The projection from the retina to the habenular complex was studied using fluorescent retrograde tracers in the albino rat (Wistar, Japan Clea). Following separate unilateral injections of Fluoro-Gold (FG), Fluoro-Ruby (FR), or 4-acetamido,4- isothiocyanostilbene-2,2'-disulfonic acid (SITS) into the lateral habenular nucleus (LHB), a small population of ganglion cells was labeled sporadically, predominantly those in the nasal retina contralateral to each injection site. Most of them were small cells, ranging from 9 to 16 mu m in diameter, roughly corresponding to the type III ganglion cell in the rat retina. Additionally, all of the structures previously described as regions projecting to the LHB were confirmed. Upon re-examination of previous brain sections of albino rats which had undergone monocular enucleation, degenerating retinal nerve axons and/or their terminals, stained by a modified selective silver impregnation method, were observed in the well-documented end regions of retinal afferents as well as the LHB. The degenerating retino-habenular nerve terminals were distributed sparsely and restricted mainly to the caudal part of the LHB contralateral to the side of ocular enucleation. The present experimental data provide evidence for the existence of a non-image forming retino-habenular pathway in the albino rat. We suggest that, besides serving as a point of convergence for some of the major conduction channels of the limbic and striatal systems, the LHB may play more general integrative roles, including participation in the integration of visual information.

Bifurcated projections of retinal ganglion cells bilaterally innervate the lateral geniculate nuclei in the cat

Cats were injected with the fluorescent retrograde tracers, Fluoro-Gold (FG) and Evans Blue (EB), into the left and right lateral geniculate nuclei (LGN), respectively. About 4.56% of the ganglion cells in the temporal retina were double-labeled by these dyes. 4.7% of these cells were of the large type, 30.3% were of the medium type, and 65% were classified as cells of the small type. These results indicate that members of all three ganglion cell size classes, mainly those of small type, bilaterally innervate the LGN via axonal bifurcation.

Immunocytochemical identification of cone bipolar cells in the rat retina

We studied the morphology of bipolar cells in fixed vertical tissue sections of the rat retina by injecting the cells with Lucifer Yellow and neurobiotin. In addition to the rod bipolar cell, nine different putative cone bipolar cell types were distinguished according to the position of their somata in the inner nuclear layer and the branching pattern and stratification level of their axon terminals in the inner plexiform layer. Some of these bipolar cell populations were labeled immunocytochemically in vertical and horizontal sections using antibodies against the calcium-binding protein recoverin, the glutamate transporter GLT-1, the alpha isoform of the protein kinase C, and the Purkinje cell marker L7. These immunocytochemically labeled cell types were characterized in terms of cell density and distribution. We found that rod bipolar cells and GLT-1-positive cone bipolar cells occur at higher densities in a small region located in the upper central retina. This area probably corresponds to the central area, which is the region of highest ganglion cell density. A second peak of rod bipolar cell density in the lower temporal periphery matches the retinal area of binocular overlap. The population densities of the immunocytochemically characterized bipolar cells indicate that at least 50% of all bipolar cells are cone bipolar cells. The variety and total number of cone bipolar cells is surprising because the retina of the rat contains 99% rods. Our findings suggest that cone bipolar cells may play a more important role in the visual system of the rat than previously thought.

A retrograde double-labelling study of retinal ganglion cells that project ipsilaterally to vLGN and LPN rather than dLGN and SC, in albino rat

We studied ipsilaterally projecting, double-labeled retinal ganglion cells that have bifurcating axons by retrograde fluorescent double-labeling in albino rats. Ten albino (Wistar, Japan Ceca) rats of either sex, weighing 350-400 g were used. With the rats in a state of deep anesthesia, we pressure-injected 0.02 microliter of 15% Evans blue (EB) into the right ventral lateral geniculate nucleus (vLGN), and 4% Fluoro-gold (FG) iontophoretically into the right posterior lateral thalamic nucleus (LP). The animals were perfused with formol-saline 48-72 h later and both the brain and eyes were exercised. The brain was sectioned coronally, and each retina was removed and mounted flat on a glass slide. Double-labeled cells were found in the ventral temporal crescent of the retina. In one animal and total number of ipsilaterally labeled cells was 566, and the percentage of double-labeled vLGN and LP projecting cells, single-labeled vLGN projecting cells, and single-labeled LP projecting cells were 29.8, 58.8 and 11.3, respectively.

Receptive-field properties of Q retinal ganglion cells of the cat

The goal of this work was to provide a detailed quantitative description of the receptive-field properties of one of the types of rarely encountered retinal ganglion cells of cat; the cell named the Q-cell by Enroth-Cugell et al. (1983). Quantitative comparisons are made between the discharge statistics and between the spatial receptive properties of Q-cells and the most common of cat retinal ganglion cells, the X-cells. The center-surround receptive field of the Q-cell is modeled here quantitatively and the typical Q-cell is described. The temporal properties of the Q-cell receptive field were also investigated and the dynamics of the center mechanism of the Q-cell modeled quantitatively. In addition, the response vs. contrast relationship for a Q-cell at optimal spatial and temporal frequencies is shown, and Q-cells are also demonstrated to have nonlinear spatial summation somewhat like that exhibited by Y-cells, although much higher contrasts are required to reveal this nonlinear behavior. Finally, the relationship between Q-cells and Barlow and Levick's (1969) luminance units was investigated and it was found that most Q-cells could not be luminance units.

Immunocytochemical analysis of bipolar cells in the macaque monkey retina

Transfer of visual information from photoreceptors to ganglion cells within the retina is mediated by specialized groups of bipolar cells. At least 10 different morphological types of bipolar cells have been distinguished in Golgi studies of primate retina. In the present study, bipolar cell populations in the macaque monkey retina were identified by their differential immunoreactivity to a spectrum of antibody markers. This enabled their spatial density and photoreceptor connections to be analysed. An antibody against the beta isozyme of protein kinase C (PKCA beta) labelled many cone bipolar cells. Invaginating (presumed ON) cone bipolar cells and rod bipolar cells were preferentially labelled with a monoclonal antibody raised against rabbit olfactory bulb. Flat (presumed OFF) bipolar cells were labelled with an antiserum against the glutamate transporter protein (GLT-1). Different populations of diffuse cone bipolar cells, which contact 5-10 cones, could be distinguished. The GLT-1 antiserum preferentially labelled the flat diffuse bipolar cell type DB2 (Boycott and Wässle, 1991, Eur. J. Neurosci. 3:1069-1088) as well as flat midget bipolar cells. Antibodies to calbindin (CaBP D-28K) labelled the flat diffuse bipolar cell type DB3 and (possibly) the invaginating diffuse bipolar cell type DB5. An antibody against the alpha isozyme of PKC labelled an invaginating diffuse bipolar cell type (DB4) as well as rod bipolar cells. Comparison of the spatial density of cone bipolar cell populations with that of photoreceptors suggests that each bipolar cell class provides a complete coverage of the cone array (each cone is contacted by at least one member of every bipolar cell class). These results support the classification scheme of Boycott and Wässle (1991) by showing that different diffuse bipolar cell classes express different patterns of immunoreactivity, and they reinforce the view that different spatial and temporal components of the signal from the photoreceptor array are processed in parallel within the primate retina.

Single retinal ganglion cells projecting bilaterally to the lateral geniculate nuclei or superior colliculi by way of axon collaterals in the cat

In most mammals with frontalized eyes, retinal ganglion cells in the nasal or temporal retina send their axons to the contralateral or ipsilateral half, respectively, of the brain. Previous studies in the cat, however, have indicated a retinal region of "nasotemporal overlap" from which arise the retinal projections to both the contralateral and ipsilateral halves of the brain. The present study thus examined in the cat whether any retinal ganglion cells give rise to bifurcating axons that innervate both halves of the brain. By employing fluorescent retrograde double labeling, we investigated whether or not single retinal ganglion cells project bilaterally to the lateral geniculate nuclei or superior colliculi by way of axon collaterals. After Fast Blue was injected into the lateral geniculate nucleus on one side and Diamidino Yellow was injected contralaterally into the lateral geniculate nucleus, 100-200 ganglion cells in each retina were double labeled with both tracers. These double-labeled cells were distributed primarily in the temporal retina, including the region around the vertical meridian and, additionally, in the nasal retina. About 60-80% of the double-labeled cells had large cell bodies (more than 25 microns in diameter), and the others had medium-sized ones (15-25 microns in diameter). The pattern of distribution of double-labeled cells, which was observed after the combined injection into both superior colliculi, was similar to that seen after the combined injection into both lateral geniculate nuclei; more than 90% of double-labeled cells, however, were large.(ABSTRACT TRUNCATED AT 250 WORDS)

Bilateral projections of single retinal ganglion cells to the lateral geniculate nuclei and superior colliculi in the albino rat

Employing fluorescent retrograde double/triple labeling, we investigated bilateral projections of single retinal ganglion cells to the lateral geniculate nuclei (LGN) and superior colliculi (SC) in the albino rat. After separate injections of Fast Blue (FB) and Diamidino Yellow (DY), respectively, into the right and left LGN, a large number of retrogradely-labeled cells were distributed all over the retina contralateral to each injection. Ipsilaterally projecting ganglion cells, which were labeled with one tracer injected into the LGN, were found predominantly in the lower-temporal retinal region; approximately 56% (120-140 cells per retina) of them were further labeled with the other tracer injected into the contralateral LGN. The vast majority of these double-labeled cells were of large type (more than 20 microns in diameter). Similar findings were obtained after separate injections of FB and DY, respectively, into the right and left SC, or respectively, into the right SC and left LGN. After separate injections of FB, DY and rhodamine-B-isothiocyanate, respectively, into the bilateral LGN and unilateral SC, or respectively, into the unilateral LGN and bilateral SC, a number of cells triple-labeled with all tracers were localized in the lower-temporal retinal region; most of them were of large type. Thus, the bilateral projections from the lower-temporal retinal region representing binocular vision in the rat are indicated to be achieved not only by separate populations of ganglion cells each exclusively serving one side of the brain, but also by axon collaterals from single ganglion cells; the ganglion cells projecting bilaterally to the LGN or/and SC are primarily of large type corresponding probably to the Y cell in the cat retina.

Beta-like ganglion cells in the South American opossum retina: a Golgi study

Using the Golgi technique we investigated the morphology of the ganglion cells of the South American opossum retina. We focused our attention on a type of ganglion cell which has a relatively small dendritic field diameter and a medium-sized soma, making it a morphological equivalent of beta ganglion cells of cat retina. Both radial sections of the retina, where the stratification level of ganglion cells dendrites can be observed in the inner plexiform layer (IPL), and flat preparations of the retina, where the whole dendritic field of the ganglion cells can be examined and quantified, have been studied. Usually these cells have one to three primary dendrites, giving rise to short spiny branches. The dendrites of these cells are segregated in two groups, one with dendritic trees arborizing in the inner two thirds and another group arborizing in the outer third of the IPL. The two groups of beta-like cells probably represent the physiological ON- and OFF-center types of ganglion cell as found in cat retina. The mean cell body and dendritic field diameters of 47 cells were 18.5 +/- 1.6 microns, (size range 16-21 microns) and 91.5 +/- 16 microns (range 54-133 microns), respectively. Cell body and dendritic fields sizes were homogeneous across the retina of the opossum. In the opossum the relatively large dendritic fields of the beta-like ganglion cells in the area centralis are consistent with the poor visual acuity of this species.

Localization and function of dopamine in the adult vertebrate retina

Dopamine (DA) has satisfied many of the criteria for being a major neurochemical in vertebrate retinae. It is synthesized in amacrine and/or interplexiform cells (depending on species) and released upon membrane depolarization in a calcium-dependent way. Strong evidence suggests that it is normally released within the retina during light adaptation, although flickering and not so much steady light stimuli have been found to be most effective in inducing endogenous dopamine release. DA action is not restricted to those neurones which appear to be in "direct" contact with pre-synaptic dopaminergic terminals. Neurones that are several microns away from such terminals can also be affected, presumably by short diffusion of the chemical. DA thus affects the activity of many cell types in the retina. In photoreceptors, it induces retinomotor movements, but inhibits disc shedding acting via D2 receptors, without significantly altering their electrophysiological responses. DA has two main effects upon horizontal cells: it uncouples their gap junctions and, independently, enhances the efficacy of their photoreceptor inputs, both effects involving D1 receptors. In the amphibian retina, where horizontal cells receive mixed rod and cone inputs, DA alters their balance in favour of the cone input, thus mimicking light adaptation. Light-evoked DA release also appears to be responsible for potentiating the horizontal cell-->cone negative feed-back pathway responsible for generation of multi-phasic, chromatic S-potentials. However, there is little information concerning action of DA upon bipolar and amacrine cells. DA effects upon ganglion cells have been investigated in mammalian (cat and rabbit) retinae. The results suggest that there are both synaptic and non-synaptic D1 and D2 receptors on all physiological types of ganglion cell tested. Although the available data cannot readily be integrated, the balance of evidence suggests that dopaminergic neurones are involved in the light/dark adaptation process in the mammalian retina. Studies of the DA system in vertebrate retinae have contributed greatly to our understanding of its role in vision as well as DA neurobiology generally in the central nervous system. For example, the effect of DA in uncoupling horizontal cells is one of the earliest demonstrations of the uncoupling of electrotonic junctions by a neurally released chemical. The many other, diverse actions of DA in the retina reviewed here are also likely to become model modes of neurochemical action in the nervous system.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphological types of projection neurons in layer 5 of cat visual cortex

Pyramidal cells in layer 5 of the visual cortex have multiple cortical and subcortical projection sites. Previous studies found that many cells possess bifurcating axons and innervate more than one cortical or subcortical target, but cells projecting to both cortical and subcortical targets were not observed. The present study examines the morphology of cells in cat visual cortex projecting to the superior colliculus, the main subcortical target of layer 5, and cells in layer 5 projecting to cortical areas 18 and 19. The neurons that give rise to these different projections were retrogradely labelled and intracellularly stained in living brain slices. Our results show that cells within each projection group have several morphological features in common. All corticotectal cells have a long apical dendrite forming a large terminal tuft in layer 1. Their cell bodies are medium sized to large, and their basal dendrites form a dense and symmetrical dendritic field. Corticocortical cells in layer 5 have a very different morphology: their apical dendrites are short and they never reach higher than layers 2/3. Their cells bodies are small to medium sized and they have fewer basal dendrites than corticotectal cells. Thus there are two morphologically distinct projection systems in layer 5, one projecting to cortical and the other one to subcortical targets, suggesting that these two systems transmit different information from the visual cortex. Among the corticotectal cells with the largest cell bodies we found some cells whose basal and apical dendrites were almost devoid of spines. Spiny and spinefree corticotectal cells also have different intrinsic axon collaterals and therefore play different roles in the cortical circuitry. While many spiny corticotectal cells have axon collaterals that project to layer 6, spinefree corticotectal cells have fewer axon collaterals and these do not arborize in layer 6. We suggest that the two morphological types of corticotectal cells might be related to functional differences known to exist among these cells. We discuss how the presence or absence of spines affects the integration of the synaptic input and how this might be related to the cells' functional properties.

Morphology of identified projection neurons in layer 5 of rat visual cortex

We studied the morphology of neurons in layer 5 of rat visual cortex (area 17) projecting to the contralateral hemisphere and the superior colliculus. Double labelling with fluorescent tracers indicated that these projections arise from different populations of cells. To reveal the morphology of the cells we stained retrogradely labelled neurons intracellularly in living brain slices. Callosal projecting pyramidal cells have 3-6 basal dendrites and an apical dendrite which never reaches higher than layer 3. Corticotectal cells have 6-8 basal dendrites and a prominent apical dendrite which always forms a large tuft in layer 1. Thus, neurons in the same cortical layer that give rise to different projections also differ in their morphology. However, each population of neurons has a rather stereotyped dendritic branching pattern, despite a large variation in soma size.

Immunological, morphological, and electrophysiological variation among retinal ganglion cells purified by panning

Two different monoclonal antibodies to the Thy-1 antigen, T11D7 and 2G12, were used to purify and characterize retinal ganglion cells from postnatal rat retina. Although Thy-1 has been reported to be a specific marker for ganglion cells in retina, retinal cell suspensions contained several other types of Thy-1-positive cells as well. Nevertheless, a simple two-step "panning" procedure allowed isolation of ganglion cells to nearly 100% purity. We found that postnatal ganglion cells differed in antigenic, morphological, and intrinsic electrophysiological characteristics, and that these properties were correlated with one another. Minor variations of this panning protocol should allow rapid, high yield purification to homogeneity of many other neuronal and glial cell types.

Comparative development of cell properties in cortical area 18 of normal and dark-reared kittens

The development of visual cell properties was studied in cortical Area 18 (A18) of normal (NRs) and dark-reared kittens (DRs), from 2 weeks of age to adulthood. In addition to the orientation selective (S) and non-selective (NS) cells, we describe a new type of non-selective cell with a peripheral zone (NSp), which could be either an intermediate form between NS and S cells and included in a sequential model or an immature form of the S cells whose responses are affected by peripheral stimulations. Using accurate coordinates for the area centralis position relative to the optic disc projection as a function of age, we show that: a) the extent of the visual field increases with age in DRs and NRs; b) the retinotopic organization is always present; c) receptive fields, large in the NS cells, reduce to the size of mature S cells as soon as the cells acquire orientation selectivity. This process can occur after only 6 h of visual experience; d) velocity preference shifts toward high velocities, though more so in NRs than in DRs. An interpretation of the development of these properties is proposed, taking into account eye growth, the growth of dendritic fields and the formation of new connections. A comparison with previous results obtained in Area 17 (A17) shows a similar time course of the specification (NRs) and of the despecification (DRs) processes, although the development of A18 is postponed by about 2 weeks. Moreover, the "adult-like" binocular distribution of ocular dominance depends upon visual experience in A18, while it does not in A17.

Immunocytochemical localization of LANT-6-like immunoreactivity within neurons in the inner nuclear and ganglion cell layers in vertebrate retinas

LANT-6 is a hexapeptide (H-Lys-Asn-Pro-Tyr-Ile-Leu-OH) isolated from chicken small intestine, which resembles the COOH-terminal half of neurotensin, except for the amino acid substitutions Lys/Arg and Asn/Arg. The present report concerns the immunocytochemical staining of vertebrate retinas using an antiserum directed against LANT-6. In the retinas from goldfish, bird and turtle, cells in both the inner nuclear and ganglion cell layers were labeled, but in the frog no cells were labeled specifically and in the rat only cells in the ganglion cell layer were labeled. Labeled cell bodies in the inner nuclear layer gave rise to processes which were seen primarily within the following laminas of the inner plexiform layer (IPL): in the goldfish, lamina 3; chicken, laminae 1, 3 and 4; and turtle, laminae 3, 4 and 5. The cell bodies of the labeled neurons in the ganglion cell layer gave rise to dendrites which entered the IPL and axons which descended to the optic fiber layer. The cells with LANT-6-like immunoreactivity were distributed in both the central and peripheral parts of the retina in all the species examined except frog. Measured by radioimmunoassays, the levels of LANT-6-like-immunoreactivity in extracts of turtle, chicken, and goldfish retinas were 5-30 times those for neurotensin-like immunoreactivity, however no LANT-6-like immunoreactivity was detected in frog. Multiple chromatographic analyses indicated that while the LANT-6-like immunoreactivity in chicken retina was indistinguishable from synthetic LANT-6, LANT-6-like immunoreactivity in turtle and goldfish retinas was primarily associated with large molecular forms. Treatment of turtle LANT-6-like immunoreactivity with pepsin, an enzyme known to mimic processing for neurotensin precursors, yielded 3 major peptides, one of which co-chromatographed with synthetic LANT-6. The present immunocytochemical localization of LLI within cells in the inner nuclear and ganglion cell layers, coupled with the biochemical characterization of LANT-6 in the vertebrate retinas and brains, suggests that neuropeptides such as LANT-6 may play a role in visual processing both within the retina and within the visual pathways to the brain.

Alpha ganglion cells in the rabbit retina

In the rabbit retina a distinctive morphological class of large ganglion cells was demonstrated by a combination of intracellular staining with Lucifer Yellow and the quantification of reduced silver-stained preparations. The class is called alpha because of the qualitative and quantitative resemblance to the alpha cells of the cat's retina. Rabbit alpha cells change their size with location on the retina. In the high ganglion cell density region of the visual streak, their somata are about 15 micron in diameter, and their dendritic fields have diameters as small as 180-220 micron. The largest alpha cells in the inferior periphery have soma diameters of 30 micron and dendritic field diameters of 960 micron. There is a considerable scatter of sizes at any retinal location. Alpha cell density changes from about 55/mm2 in the streak to about 3/mm2 in far periphery, and the cells make up 1-1.4% of the ganglion cell population. Dendritic trees stratify in either an inner or an outer sublamina of the inner plexiform layer, suggesting an on/off dichotomy in the response to light. Each of the inner and outer branching subtypes is distributed in a regular mosaic, and the dendritic trees cover the retina completely and economically. The possibility is discussed that the alpha cells are the brisk transient/Y cells of physiology.

Effects of antibodies to large retinal ganglion cells on developing retinogeniculate pathways in the cat

We investigated the effects of polyclonal antibodies, produced against ox large retinal ganglion cells, on the developing retinogeniculate pathways of cats. Four-week-old kittens were given an intraocular injection of either a low or a high concentration of the antibodies and effects were assessed 35-69 weeks later. After a low concentration (110 micrograms/33 microliter volume) injection, the density of retinal alpha-cells (the morphological counterpart of Y-cells) was reduced 44% in area centralis and 37% in peripheral retina. After a high concentration (333 micrograms/33 microliter volume) injection, alpha-cell density was reduced 76% in area centralis and 91% in peripheral retina. The same concentration of antibodies had no consistent effect on the numbers of medium- or small-size retinal ganglion cells. Electrophysiological recordings from single neurons in layers A and A1 of the lateral geniculate nucleus (LGN) revealed a 53% decrease in the percentage of Y-cells after a low-concentration injection and an 82% decrease after a high-concentration injection. There was a concomitant increase in the percentage of LGN cells that were non-responsive to light or that responded too poorly to be classified. No change was observed in the percentages of LGN X-cells or cells with mixed response properties. The reduced encounter rate of LGN Y-cells was not accompanied by significant changes in LGN cell-body size. Together, the results indicate that the immunoablation technique produces a large and apparently selective reduction of the Y-cell retinogeniculate pathway in developing kittens.

Effect of light deprivation upon the morphology of axon terminals in the dorsal lateral geniculate nucleus of mouse: an electron microscopical study using serial sections

Two populations of morphologically different large axon terminals have been observed electron microscopically in the dorsal lateral geniculate nucleus of mice raised in complete darkness from birth up to 19 days of age. One population includes larger terminals indistinguishable from the large terminals present in control animals, i.e. they have round synaptic vesicles, rather pale mitochondria, membrane saculae, coated vesicles, and asymmetric contacts with encrusted dendritic spines of portions of dendrites of geniculo-cortical relay neurons. The other population includes large terminals which also have asymmetric contacts with encrusted dendritic spines or portions of dendrites of geniculo-cortical relay neurons, but they show darker mitochondria, absence of both membrane saculae and coated vesicles, and significantly higher synaptic vesicle density and smaller size than the large control ones. We suggest that the latter population of terminals could be inactive due to the absence of visual input.

Termination patterns of individual X- and Y-cell axons in the visual cortex of the cat: projections to area 18, to the 17/18 border region, and to both areas 17 and 18

Horseradish peroxidase was injected intracellularly into single, physiologically identified X- and Y-cell geniculocortical axons that projected to area 18, to the 17/18 border region, or to both areas 17 and 18 via branching axons. The axon terminal fields in cortex were labeled anterogradely, and the cell bodies of the axons in the A-laminae, lamina C, and the medial interlaminar nucleus (MIN) of the dorsal lateral geniculate nucleus (LGN) were labeled retrogradely. The laminar projections in area 18 of eight Y-cells and one geniculate, non-Y-cell were analyzed. Most of the cells arborized densely within layer IVa and the lower 200 to 400 microns of layer III. Most provided little or no input to layer IVb or layer VI. Thus, the laminar projections of Y-cells to layer IV of area 18 were similar to those of their area 17 counterparts, although the input to layer III was greater and rose much higher in area 18 than in area 17. The terminal arbors in area 18 were two to three times larger in lateral extent than those in area 17. They spread over 2.0 to 2.8 mm2 of layer IV and occupied proportionately much greater regions of area 18 than the Y-cell arbors in area 17. This may partially account for the large receptive fields of cortical cells in area 18, and it indicates that a small region of area 18 may receive converging inputs from a relatively wide retinotopic region of the LGN. The terminal arbors were also highly asymmetric, generally being two to four times longer anteroposteriorly than mediolaterally. These asymmetric arbors may form the structural basis for the anisotropic organization of the retinotopic map in area 18. We recovered three cells (two Y, one X) whose axons arborized in the border zone between areas 17 and 18. One Y-cell axon had a receptive field located in the ipsilateral visual hemifield and it arborized in a small region restricted almost exclusively to the border zone. The other two cells had receptive fields on or adjacent to the vertical meridian, and they terminated on either side of the 17/18 border region as well as within it. Thus, geniculate afferents representing the ipsilateral hemifield or the vertical meridian appear to have different patterns of termination on and adjacent to the 17/18 border zone. Also, some X-cell input may invade area 18 in the region immediately adjacent to the border zone.(ABSTRACT TRUNCATED AT 400 WORDS)

The development of visual acuity in very young kittens. A study with forced-choice preferential looking

The development of visual acuity was studied longitudinally in young kittens, using a modification of the forced-choice preferential looking method (FPL) devised by Teller et al. [Vision Res. 14, 1433-1439 (1974)] for human infants. Acuity, defined as the spatial frequency which yields 70% correct responses by a naive observer, shows a 16-fold increase between 2 and 10 weeks of age. At comparable ages, acuity evaluated by this method falls short of the acuity values obtained with the mumping stand or with electrophysiological methods. FPL acuity estimated with a more lenient criterion (58%) comes close to the resolution of the highest-resolving single cells in the striate cortex. These results suggest that the preferential looking procedure provides a method that can be used in kittens over a wide age range, including ages at which it is impossible to use the jumping stand method.

Retinal ganglion cells that project to the dorsal lateral geniculate nucleus in the macaque monkey

Horseradish peroxidase was deposited in the optic nerve to retrogradely label and reveal the dendritic form of all classes of ganglion cell, or it was injected into the dorsal lateral geniculate nucleus to reveal only those classes projecting to the thalamus. The results were compared with those of the accompanying paper in which the ganglion cells projecting to the midbrain are selectively revealed. Two major classes of ganglion cells are described, the P alpha and P beta cells. For both classes dendritic field size increases with eccentricity from the fovea and there is no overlap in the two classes at any given eccentricity. Cell body size shows a similar mean difference but with a slight overlap. Both cell bodies and dendritic fields are larger along the temporal horizontal meridian than the nasal horizontal meridian, for P alpha and for P beta cells, but these differences are reduced when naso-temporal differences in ganglion cell density are taken into account, that is, size correlates closely with density. Injections restricted to the parvocellular layers of the lateral geniculate nucleus labelled almost exclusively P beta cells, whereas injections confined to the magnocellular layers labelled almost exclusively P alpha cells. As midbrain injections label no P beta cells and few P alpha cells it can be shown that about 80% of ganglion cells are P beta cells projecting to parvocellular lateral geniculate nucleus, and that about 10% are P alpha cells projecting to magnocellular layers. The coverage factor, that is the number of cells covering each point on the retina, varied from 1.9-2.3 for P beta cells, and from 2-7 for P alpha cells. Comparing the results with those of comparable investigations on cats and rabbits shows a much clearer segregation of the terminal targets of different classes of ganglion cell in monkeys, the greatest difference being the absence in the monkey of a projection to the geniculate from gamma- and epsilon-like cells. Further, axons which branch and innervate both thalamus and midbrain are rare in monkeys but common in other mammals. Comparing the results with those from physiological investigations suggests that the P beta cells correspond to colour-opponent cells, whereas P alpha cells correspond to the achromatic broad-band magnocellular cells.

Seeing with the visual cortex

A short analysis of the input-output organization of the primary visual cortical areas in the cat and monkey is followed by a description of the salient microelectrophysiological properties of retino-geniculo-cortical system neurons. It is concluded that a strict hierarchical model of cortical processing of visual information is no longer tenable.

The structural correlate of the receptive field centre of alpha ganglion cells in the cat retina

The correlation between the receptive field centre and the dendritic tree of individual brisk transient, or alpha, ganglion cells in the cat retina was investigated by a combination of physiological and anatomical techniques. The sizes of receptive field centres of brisk transient (Y) cells were measured with a flickering spot of light. Contour maps and response (or sensitivity) profiles were measured at mesopic and scotopic backgrounds. Recording positions on the retina and nearby blood vessels were back-projected onto the receptive field plots on the tangent screen. After recording, whole amount preparations of the retinae were stained by a reduced silver method to stain all alpha cells together with their dendritic trees. By comparing the landmarks on the screen plot with those of the whole mount it was possible to identify the recorded cells in the preparation and to study their morphology. The dendritic tree of an alpha cell determines the position, size and shape of its receptive field centre. The mesopic receptive field centres were found to be a factor of 1.4 +/- 0.13 larger than their respective dendritic fields. It is suggested that the dendritic fields of presynaptic neurones (bipolar and amacrine cell processes) add to the ganglion cell dendritic tree to produce the larger centre summating area.

Two spatio-temporal filters in human vision. 1. Temporal and spatial frequency response characteristics

We have studied visual detection of a circular target moving across a spatially and/or temporally modulated background. Illumination, It, for threshold detection of the target has been measured as a function of background modulation frequency and changes in It associated with background modulation provide a means of determining the frequency response characteristics of visual channels. Temporal frequency responses obtained with temporally modulated, spatially uniform backgrounds have pass-band characteristics and the temporal frequency for peak response increases with increase in mean background illumination. These temporal frequency responses resemble those of the de Lange (1954) filter, but the latter incorporates the incremental thresholds for steady backgrounds. The amplitude of this temporal response saturates at low (approximately 40%) background modulation, decreases to zero as the target velocity falls to zero, and is maximum for a circular target of diameter 2 degrees. The spatial characteristics of this temporal filter were measured with a background field consisting of alternate steady and flickering bars. The resulting spatial frequency curve peaks at 1 cycle deg-1 for all background illuminations and is independent of the background grating orientation. This spatial response differs significantly from the IMG spatial functions observed with a background grating (Barbur and Ruddock, 1980). The spatial and temporal responses reviewed above exhibit similar parametric variations and we therefore associate them with a single spatio-temporal filter, ST2. A second temporal response, with low-pass frequency characteristics, was observed with a background field consisting of two matched gratings, presented in spatial and temporal antiphase. This response has parametric properties similar to those of the IMG spatial response described previously by Barbur and Ruddock (1980), thus we associated the two sets of data with a single spatio-temporal filter, ST1. We show that the ST2 responses can be obtained by combining ST1 responses, and we present a network incorporating the two filters. We review other psychophysical studies which imply the activity of two spatio-temporal filters with properties of the kind revealed in our studies. We argue that filter ST1 has properties equivalent to those of X-type and filter ST2 has properties equivalent to those of Y-type electrophysiological mechanisms.

X and Y cells in the lateral geniculate nucleus of macaque monkeys

1. Cells of the lateral geniculate nucleus (l.g.n.) in macaque monkeys were sorted into two functional groups on the basis of spatial summation of visually evoked neural signals. 2. Cells were called X cells if their responses to contrast reversal of fine sine gratings were at the fundamental temporal modulation frequency with null positions one quarter of a cycle away from positions for peak response. Cells were called Y cells if their responses to such stimuli were at twice the modulation frequency and were approximately independent of spatial phase. 3. Ninety-nine percent of the cells in the four dorsal parvocellular layers of the l.g.n. were X cells; about seventy-five percent of the cells in the two ventral magnocellular layers were also X cells. The remainder were Y cells. 4. We confirmed previous findings that magnocellular cells had a shorter latency of response to electrical stimulation of the optic chiasm. 5. Magnocellular cells had much higher contrast sensitivities than did parvocellular cells. 6. Therefore, two distinct classes of X cells exist in the macaque l.g.n.: parvocellular X cells and magnocellular X cells. The great difference in their properties suggests that they have different functions in vision. The Y cells in the magnocellular layers form a third functional group with spatial properties distinctly different from the X cells. 7. We propose that the magnocellular layers of the macaque monkey's l.g.n. may be homologous to the A and A1 layers of the cat's l.g.n.

Reduction in numbers of large ganglion cells in cat retina following intravitreous injection of antibodies

Antibodies were prepared against large ganglion cells isolated from bovine retina and injected into the vitreous chamber of 1 eye in 6 adult cats. The other eye of each cat received either a control pre-immune gamma-globulin injection or was untreated. After a survival time of 9-86 days, ganglion cell density was assessed from Nissl-stained retinal whole-mounts. In each cat, there were fewer large ganglion cells (alpha-cells) in the immunoglobulin-injected retina than in the control retina. The reduction in large ganglion cells occurred in patches adjacent to areas of approximately normal large ganglion cell density. Counts of the number of large ganglion cells in both eyes of the 6 cats indicated that the immunoglobulin injected eyes had from 8% to 61% (mean 32%) fewer large ganglion cells than the paired control eyes. This was significantly greater than the difference in the number of large ganglion cells between pairs of normal or control-injected eyes. The magnitude of the effect was not related to the survival time following the immunoglobulin injection. Cell size measures of all ganglion cells in selected areas of retina indicated that the small ganglion cells were unaffected by the antibodies. However, there was a suggestion that the largest of the medium size ganglion cells were affected in addition to the large ganglion cells. Counts of total ganglion cells per unit area in affected regions of retina revealed a reduced overall density, suggesting that the ganglion cells were lost rather than decreased in size. These results indicate that antibodies to the large ganglion cells can be used to reduce the number of large ganglion cells (alpha-cells) in the cat retina. Since these cells correspond to the Y-cell functional class of ganglion cells in the cat retina, the antibodies may provide a useful tool for studying Y-cell function in the visual pathways.

Retinal ganglion cells: a functional interpretation of dendritic morphology

The electrical properties of the different anatomical types of retinal ganglion cells in the cat were calculated on the basis of passive cable theory from measurements made on histological material. Standard values for the electrical parameters were assumed (R1= 70 Ω cm, Cm= 2 μF cm-2,Rm= 2500 Ω cm2). We conclude that these neurons need not be equipotential despite their small dimensions, mainly because of their extensive branching. The interactions between excitation and inhibition when the inhibitory battery is near the resting potential can be strongly nonlinear in these cells. To characterize the different types of ganglion cells in terms of this property we introduce the factor by which the soma depolarization induced by a given excitatory input is reduced by inhibition. In this framework we analyse some of the integrative properties of an arbitrary passive dendritic tree and we then derive the functional properties that are characteristic for the various types of ganglion cells. Our main results are: (i) Nonlinear saturation at the synapses may be made effectively smaller by spreading the same (conductance) input among several subunits on the dendritic field. Subunits are defined as regions of the dendritic field that are somewhat isolated from each other and roughly equipotential within. (ii) Shunting inhibition can specifically veto an excitatory input, if it is located on the direct path to the soma. TheFvalues can then be very high even when the excitatory inputs are much larger than the inhibitory, as long as the absolute value of inhibition is not too small. Inhibition more distal than excitation is much less effective. (iii) Specific branching patterns coupled with suitable distribution of synapses are potentially able to support complex information processing operations on the incoming excitatory and inhibitory signals. The quantitative analysis of the morphology of cat retinal ganglion cells leads to the following specific conclusions: (i) None of the cells examined satisfies Rail’s equivalent cylinder condition. The dendritic tree cannot be satisfactorily approximated by a non-tapering cylinder. (ii) Under the assumption of a passive membrane, the dendritic architecture of the different types of retinal ganglion cells reflects characteristically different electrical properties, which are likely to be relevant for their physiological function and their information processing role: (a) α cells have spatially inhomogeneous electrical properties, with many subunits. Within each subunit nonlinear effects may take place; between subunits good linear summation is expected.Fvalues are relatively low. (b) β cells at small eccentricities have rather homogeneous electrical properties. Even distal inputs are weighted rather uniformly. Electrical inhomogeneities of the a type appear for P cells at larger eccentricities.Fvalues are low. (c) γ-like cells have few subunits, each with high input resistance underlying nonlinear saturation effects possibly related to a sluggish character.Fvalues are high: inhibition of the shunting type can interact in a strongly nonlinear way with excitatory conductance inputs. (d) δ-like cells show many subunits with a high input resistance, covering well the dendritic area. Within each subunit inhibition on the direct path to the soma can specifically veto a more distal excitation. It is conjectured that such a synaptic organization superimposed on the δ cell morphology underlies directional selectivity to motion. (iii) Most of our data refer to steady-state properties. They probably apply, however, to all light evoked signals, since transient inputs with time to peak of 30 ms or more can be treated in terms of steady-state properties of the ganglion cells studied. (iv) All our results are affected only slightly by varying the parameter values within reasonable ranges. If, however, the membrane resistance were very high, all ganglion cells would approach equipotentiality. ForRm= 8000 Ω cm2subunits essentially disappear in all types of ganglion cells (for steady state inputs). Our results concerning nonlinear interaction of excitation and inhibition ( values) would, however, remain valid even for much larger values ofRmand for any value ofR1larger than 30-50 Ω cm. The critical requirement is that peak inhibitory conductance changes must be sufficiently large (around 5 x 10-8S) with an equilibrium potential close to the resting potential. Underestimation of the diameters of the dendritic branches may affect these conclusions (Fcould be significantly lower).

Analysis of orientation bias in cat retina

1. Responses of cat retinal ganglion cells to a drifting sinusoidal grating stimulus were measured as a function of the grating orientation and spatial frequency.2. The response at fixed frequency and contrast varied with orientation in the manner of a cosine function. A new measure was introduced to quantify this orientation bias in the response domain on an absolute scale of 0-100%. Under experimental conditions designed to maximize the effect, the mean bias for 250 cells was 16% and the range was 0-46%. In 70% of cells there was significant bias.3. Orientation bias varied with spatial frequency and was maximal near the high-frequency limit. The majority of biassed cells preferred the same orientation at high and low frequencies but in some cells a reversal occurred: the orientation which gave maximum response at high frequencies gave minimum response at low frequencies. The greatest variation of cut-off frequency with orientation was (2/3) octave.4. Orientation bias was due to neural, not optical, factors. Nevertheless, the phenomenon could often be imitated by deliberately introduced optical astigmatism of up to 4 dioptres for brisk-sustained units and over 10 dioptres for brisk-transient units.5. The grating orientation preferred by cells varied systematically with position in the visual field. The central tendency was for the grating which yielded maximum response to lie parallel to the line joining the cell to the area centralis. This generalization failed for units within 2 degrees of the centre of the area centralis.6. Analysis of orientation bias indicates a functional asymmetry of receptive fields such that the centre mechanism, and sometimes also the surround mechanism, is elongated along the line joining cell to area centralis.

Optic nerve components may not be equally susceptible to damage by acrylamide

Cells in the lateral geniculate nucleus of rats treated with the neurotoxin acrylamide were classified as X or Y according to the criterion of linear summation. Compared with control animals, they had a lower ratio of X to Y cells. It is argued that this effect may be related to differences in axon diameter, the thinner fibres in the optic nerve being more susceptible to damage.

Retinal projection to the nucleus of the optic tract in the cat as revealed by retrograde transport of horseradish peroxidase

Retrograde transport of horseradish peroxidase injected iontophoretically into the nucleus of the optic tract of cats revealed that the direction-selective cells in this pretectal nucleus receive direct retinal projections from small retinal ganglion cells, the so-called gamma-cells. These cells from a horizontal band on the contralateral retina. Few labeled cells are found in the ipsilateral temporal retina. The input from the contralateral retina is 10 times more numerous than from the ipsilateral one. In both retinae the highest concentration of labeled cells is near the area centralis.

The retinal projection to the thalamus in the cat: a quantitative investigation and a comparison with the retinotectal pathway

The projection of cat retinal ganglion cells to the thalamus was examined using the method of retrograde axonal transport of horseradish peroxidase (HRP). After the injection site was determined physiologically, HRP was applied by one of three methods: iontophoretic injection of minimal amounts, single pressure injections and multiple pressure injections. Iontophoretic injections into single laminae of the dorsal part of the lateral geniculate nucleus (LGNd) revealed that laminae A and A1 receive almost exclusively axon terminals from alpha and beta cells. Single pressure injections elucidated the retinotopic organization of the LGNd. Multiple injections lead to HRP uptake in the whole LGNd including parts of adjacent thalamic nuclei and revealed that at least 77% of all retinal ganglion cells project to the thalamus. This pathway is made up of all alpha cells, all beta cells and almost half of the gamma cells. The thalamus receives its visual input predominantly from the ipsilateral temporal and the contralateral nasal retina; some alpha cells were also labeled in the contralateral temporal retina. The shape of the decussation line was analyzed and its width was found to be proportional to the average ganglion cell spacing along the dorsoventral axis of the retina. From a comparison of the retinothalamic and retinotectal pathways, an estimate of the number of cells with bifurcating axons could be given. The axons of all alpha cells, 10% of the beta cells, and every second gamma cell bifurcate; this amounts to 30% of the retinal ganglion cells.