bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evidence for calcium/calmodulin dependence of spinule retraction in retinal horizontal cells
Authors: Schmitz Yvonne , Kohler Konrad , Zrenner Eberhart 
Published: June 2009

AbstractHorizontal cells of the carp retina alter their synaptic connections with cones during dark and light adaptation. At light onset, dendrites of horizontal cells, which are positioned laterally at the ribbon synapse, form “spinules,” little processes with membrane densities. Spinules are retracted again during dark adaptation. Spinule retraction is also elicited upon glutamate application to the retina. In the present study, we address the question whether calcium/calmodulin-dependent pathways are involved in dark- and glutamate-evoked spinule retraction. Light-adapted retinas were isolated and subsequently dark adapted during incubation in media of different calcium concentrations. Spinule retraction was clearly blocked in low-calcium solutions (5 μM and 50 nM CaCl2). Incubation in medium containing cobalt chloride (2 mM) had the same effect. Both treatments blocked the glutamate-induced spinule retraction as well. These results indicate that spinule retraction is induced by a calcium influx into horizontal cells. To investigate whether calmodulin, the primary calcium receptor in eukaryotic cells, is present at the site of spinule formation, light- and dark-adapted retinas, embedded in LR White resin, were labelled with an antibody against calmodulin and gold-conjugated secondary antibodies. Horizontal cell dendrites at the ribbon synapse revealed strong calmodulin immunoreactivity, which was more than twice as high in light- as in dark-adapted retinas. The incubation of isolated retinas with the calmodulin antagonists W5 and W13 inhibited spinule retraction. In summary, these results suggest that spinule retraction may be regulated by calcium influx into horizontal cells and subsequent calcium/calmodulin-dependent pathways.
Dark-adapted thresholds at 10– and 30–deg eccentricities in 10–week-old infants
Authors: Hansen Ronald M. , Fulton Anne B. 
Published: June 2009

AbstractWe tested the hypothesis that the dark-adapted sensitivity of the near central retina is lower than that of peripheral retina in 10–week-old infants. A spatial two alternative forced-choice psychophysical method was used to estimate the threshold for 2–deg spots presented 10 deg and 30 deg from the center of a screen. Each 10–week-old infant (n = 11) and adult (n = 5) subject was tested at both eccentricities. Every infant's threshold at 10 deg is higher than that at 30 deg. The median difference between the infants' thresholds at 10 deg and 30 deg is about 0.5 log unit. Whereas the scotopic thresholds of adults at 10 deg and 30 deg are virtually identical, the thresholds of infants' near central retina are higher than those in more peripheral retina. Delayed maturation of the near central rod outer segments with consequent lower quantum catch may be the primary determinant of this infantile sensitivity pattern.
Interlaminar connections of the superior colliculus in the tree shrew. II: Projections from the superficial gray to the optic layer
Authors: Lee Psyche , Hall William C. 
Published: June 2009

AbstractThis study of the tree shrew, Tupaia belangeri, provides evidence for an intracollicular pathway that arises in the superficial gray layer and terminates in the optic layer. As a first step, Nissl, myelin, and cytochrome oxidase stains were used to identify the layers of the superior colliculus in the tree shrew. Second, anterograde and retrograde axonal transport methods were used to determine relationships between laminar borders and patterns of connections. Intraocular injections of wheat germ agglutinin conjugated to horseradish peroxidase showed that the border between the superficial gray and optic layers in the tree shrew is marked by a sharp decrease in the density of retinotectal projections. The optic layer also could be distinguished from the subjacent intermediate gray layer by differences in connections. Of the two layers, only the intermediate gray layer received projections following injections of wheat germ agglutinin conjugated to horseradish peroxidase within substantia nigra pars reticulata. Similarly, following injections of horseradish peroxidase or biocytin in the paramedian pons, the intermediate gray but not the optic layer contained labeled cells of origin for the main premotor pathway from the tectum, the predorsal bundle. Next, cells in the superficial gray layer were intracellularly injected with biocytin in living brain slices. Axons were traced from narrow and wide field vertical cells in the deep part of the superficial gray layer to the gray matter surrounding the fiber fascicles of the optic layer. Small extracellular injections of biocytin in brain slices showed that the optic layer gray matter contains a population of stellate cells that are in position to receive the input from the superficial layer. Finally, small extracellular injections of biocytin in the intermediate gray layer filled cells that sent prominent apical dendrites into the optic layer, where they may be directly contacted by the superficial gray layer cells. Taken together, the results support the hypothesis that the optic layer is functionally distinct from its adjacent layers, and may provide a link in the transfer of information from the superficial, retinal recipient, to the intermediate, premotor, layer of the superior colliculus.
Soma and axon diameter distributions and central projections of ferret retinal ganglion cells
Authors: Fitzgibbon T. , Wingate R. J. , Thompson I. D. 
Published: June 2009

AbstractUsing a combination of retrograde horseradish peroxidase (HRP) labelling, silver staining, and electron microscopy, we have assessed the relationship between retinal ganglion cell soma size and axon diameter in the adult ferret(Mustela putorius furo).Retinal ganglion cells were labelled following injections of HRP into the lateral geniculate nucleus (LGN), superior colliculus (SC), or LGN+SC. The soma size distributions following LGN, SC, or LGN+SC injections were all unimodal showing considerable overlap between different cell classes. This was confirmed for alpha cells, identified on the basis of dendritic filling or from neurofibrillar-stained retinae. Analysis of the soma size and axon diameters of a population of heavily labelled retinal ganglion cells showed a significant correlation between the two. However, the overall distribution of intraretinal axon diameter was bimodal with an extended tail. Analysis of the ganglion cell distributions in the adult ferret indicates that beta cells comprise about 50.5–55%, gamma 42.5–47%, and alpha 2.5% of the ganglion cell population. This implies that the proportion of gamma, beta, alpha cells in both cat and ferret retina is highly conserved despite differences in visual specialization in the two species.
Contrast normalization and a linear model for the directional selectivity of simple cells in cat striate cortex
Authors: Tolhurst D.J. , Heeger D.J. 
Published: June 2009

AbstractPrevious tests of the linearity of spatiotemporal summation in cat simple cells have compared the responses to moving sinusoidal gratings and to gratings whose contrast was modulated sinusoidally in time. In particular, since a moving grating can be expressed as a sum of modulated gratings, the response to a moving grating should be predictable (assuming linearity) from the responses to modulated gratings. However, these simple linear predictions have shown varying degrees of failure (e.g. Reid et al., 1987, 1991), depending on the directional selectivity of the neurons (Tolhurst & Dean, 1991). We demonstrate here that the failures of these linear predictions are, in fact, explained by the contrast-normalization model of Heeger (1993). We concentrate on the ratio of the measured to predicted moving grating responses. In the context of the contrast-normalization model, calculating this ratio turns out to be particularly appropriate, since the ratio is independent of the precise details of the linear front-end mechanisms ultimately responsible for directional selectivity. Hence, the contrast-normalization model can be compared quantitatively with this ratio measure, by varying only one free parameter. When account is taken both of the expansive output nonlinearity and of contrast normalization, the directional selectivity of simple cells seems to be dependent only on linear spatiotemporal filtering.
Is the input to a GABAergic or cholinergic synapse the sole asymmetry in rabbit's retinal directional selectivity?
Authors: Grzywacz Norberto M. , Tootle John S. , Amthor Franklin R. 
Published: June 2009

AbstractWe examined contrast, direction of motion, and concentration dependencies of the effects of GABAergic and cholinergic antagonists, and anticholinesterases on responses to movement of On—Off directionally selective (DS) ganglion cells of the rabbit's retina. The drugs tested were curare and hexamethonium bromide (cholinergic antagonists), physostigmine (anticholinesterase), and picrotoxin (GABAergic antagonist). They all reduced the cells' directional selectivity, while maintaining their preferred-null axis. However, cholinergic antagonists did not block directional selectivity completely even at saturating concentrations. The failure to eliminate directional selectivity was probably not due to an incomplete blockade of cholinergic receptors. In a extension of a Masland and Ames (1976) experiment, saturating concentrations of antagonists blocked the effects of exogenous acetylcholine or nicotine applied during synaptic blockade. Consequently, a noncholinergic pathway may be sufficient to account for at least some directional selectivity. This putative pathway interacts with the cholinergic pathway before spike generation, since physostigmine eliminated directional selectivity at contrasts lower than those saturating responses. This elimination apparently resulted from cholinergic-induced saturation, since reduction of contrast restored directional selectivity. Under picrotoxin, directional selectivity was lost in 33% of the cells regardless of contrast. However, 47% maintained their preferred direction despite saturating concentrations of picrotoxin, and 20% reversed the preferred and null directions. Therefore, models based solely on a GABAergic implementation of Barlow and Levick's asymmetric-inhibition model or solely on a cholinergic implementation of asymmetric-excitation models are not complete models of directional selectivity in the rabbit. We propose an alternate model for this retinal property.
The topographical relationship between two neuronal mosaics in the short wavelength-sensitive system of the primate retina
Authors: Kouyama Nobuo , Marshak David W. 
Published: June 2009

AbstractThe short wavelength-sensitive (blue) cone bipolar cells was found to have a nonrandom distribution by analyzing the nearest neighbors and by calculating the density recovery profile (DRP). Blue cones had been shown previously to have a nonrandom distribution (Curcio et al., 1991). The relationship between the two arrays was then analyzed by calculating the cross-correlational density recovery profile (cDRP), which indicates the local density of blue cones around each blue cone bipolar cell. Although both cell types appeared to be distributed uniformly at the macroscopic level, the cDRP was 1.7 times higher within 15 μm of each bipolar cell perikaryon than in the surrounding area. The area of higher density was approximately the same as that in which the blue cone bipolar cells made synaptic contacts with blue cones. The finding that the blue cones and the blue cone bipolar cells were closer together than expected suggests that the positions of the perikarya of these neurons were influenced by their synaptic connections or other developmental interactions.
The receptive field of the primate P retinal ganglion cell, I: Linear dynamics
Authors: Benardete Ethan A. , Kaplan Ehud 
Published: June 2009

AbstractThe ganglion cells of the primate retina include two major anatomical and functional classes: P cells which project to the four parvocellular layers of the lateral geniculate nucleus (LGN), and M cells which project to the two magnocellular layers. The characteristics of the P-cell receptive field are central to understanding early form and color vision processing (Kaplan et al., 1990; Schiller & Logothetis, 1990). In this and in the following paper, P-cell dynamics are systematically analyzed in terms of linear and nonlinear response properties. Stimuli that favor either the center or the surround of the receptive field were produced on a CRT and modulated with a broadband signal composed of multiple m-sequences (Benardete et al., 1992b; Benardete & Victor, 1994). The first-order responses were calculated and analyzed in this paper (part I). The findings are: (1) The first-order responses of the center and surround depend linearly on contrast. (2) The dynamics of the center and surround are well described by a bandpass filter model. The most significant difference between center and surround dynamics is a delay of approximately 8 ms in the surround response. (3) In the LGN, these responses are attenuated and delayed by an additional 1–5 ms. (4) The spatial transfer function of the P cell in response to drifting sine gratings at three temporal frequencies was measured. This independent method confirmed the delay between the (first-order) responses of the center and surround. This delay accounts for the dependence of the spatial transfer function on the frequency of stimulation.
The receptive field of the primate P retinal ganglion cell, II: Nonlinear dynamics
Authors: Benardete Ethan A. , Kaplan Ehud 
Published: June 2009

AbstractThe receptive-field properties of retinal ganglion cells (RGCs) provide information about early visual processing. In the primate retina, P cells form the largest class of RGCs (Rodieck, 1988). A detailed exploration of the dynamics of the two subdivisions of the P-cell receptive field—the center and the surround—was undertaken. In the preceding paper (Benardete & Kaplan, 1996), the first-order responses of the center and the surround of P cells were described, which were obtained with a new technique, the multiple m-sequence stimulus (Benardete & Victor, 1994). In this paper, the investigation of P-cell responses measured as S-potentials in the lateral geniculate nucleus (LGN) is continued, and significant nonlinear, second-order responses from the center and the surround are described. These responses are quantified by fitting a mathematical model, the linear-nonlinear-linear (LNL) model (Korenberg, 1973; Korenberg & Hunter, 1986; Victor, 1988) to the data. In a second series of experiments, demonstration that steady illumination of the surround modifies the gain of the center to contrast signals (see also Kaplan & Shapley, 1989) is made. In P ON cells, increasing the steady illumination of the surrounddecreasesthe gain and speeds up the center's first-order response. In P OFF cells, increasing the steady illumination of the surroundincreasesthe gain of the center while speeding up the response. The results of both sets of experiments are related to the known anatomy and physiology of the P cell.
Retinotopic organization of the superior colliculus in relation to the retinal distribution of afferent ganglion cells
Authors: Berson D.M. , Stein J.J. 
Published: June 2009

AbstractSensory representations in the brain exhibit topographic variations in magnification. These variations have been thought to reflect regional differences in the density of innervation at the sensory receptor surface. In the primate visual cortex, for example, local magnification factors have been reported to be proportional to the corresponding densities of retinal ganglion cells. We sought to learn whether this principle also operates in a second major retinofugal pathway—the projection to the superior colliculus. In cats, we first used retrograde transport to determine the retinal distributions of the ganglion cells that project to the colliculus. Then, we compared the numbers of colliculopetal ganglion cells in selected retinal sectors to the areas of the corresponding collicular representations. Collicular areal magnification was not simply proportional to the density of afferent ganglion cells, being instead at least 5-fold greater than expected in the representation of the central visual field. These data imply that incoming retinal afferents are more widely spaced in the central regions of the tectal map than in the map's periphery. Such variations in afferent density appear to play as large a role as the distribution of ganglion cells in determining the metric of the collicular map.
On the distribution of gamma cells in the cat retina
Authors: Stein J.J. , Berson D.M. 
Published: June 2009

AbstractGanglion cells of the cat retina that are neither alpha nor beta cells are often lumped for convenience into a single anatomical group—the gamma cells (Boycott & Wässle, 1974; Stone, 1983; Wässle & Boycott, 1991). Defined in this way, gamma cells are the morphological counterpart to the physiological W-cell class, which includes all ganglion cells that are neither Y (alpha) nor X (beta) cells. We have estimated the retinal distribution of gamma cells by using retrograde transport to label ganglion cells innervating the superior colliculus and by assuming that these included virtually all gamma cells and no beta cells. We excluded labeled alpha cells on the basis of soma size. Our data suggest that gamma cells represent just under half of the ganglion cells in most of the nasal retina, but only about a third of those in thearea centralisand temporal retina. Gamma cells do not appear to be more highly concentrated in the nasal visual streak than are other ganglion cells. In the temporal retina, gamma cells with crossed projections to the brain are apparently at least twice as common as those with uncrossed projections.
Functional properties of a metabotropic glutamate receptor at dendritic synapses of ON bipolar cells in the amphibian retina
Authors: Tian Ning , Slaughter Malcolm M. 
Published: June 2009

AbstractPerforated patch-voltage and current-clamp recordings were obtained from ON bipolar cells in the amphibian retinal slice preparation. The currents produced by the photoreceptor transmitter were compared to the currents produced by selective metabotropic glutamate agonists: L-2-amino-4-phosphonobutyrate (L-AP4, APB) and 1S,3R 1-amino-1,3 cyclopentanedicarboxylic acid (1S,3R ACPD). Both agonists produced currents that were very similar to that produced by the photoreceptor transmitter in terms of conductance and reversal potential. The similarities suggest that the metabotropic glutamate receptors are functionally localized to the synaptic region of ON bipolar dendrites. The synaptic conductance rarely exceeded the non-synaptic conductance. The mean input resistance of ON bipolar neurons was 770 MΩ in the light and 1.2 GΩ in the dark. The average light-regulated synaptic conductance was 57% of the non-synaptic conductance. The L-AP4 regulated conductance averaged 77% of the non-synaptic conductance, while the 1S,3R ACPD regulated conductance averaged 95% of the non-synaptic conductance. This balance between synaptic and non-synaptic conductance indicates that the synapse will not shunt the cell and the conductance ratio serves to maximize incremental gain at the photoreceptor to ON bipolar synapse. This conductance mechanism makes the ON bipolar cell well equipped to relay rod signals.
Shifting relationships between photoreceptors and pigment epithelial cells in monkey retina: Implications for the development of retinal topography
Authors: Robinson S.R. , Hendrickson A. 
Published: June 2009

AbstractThis study examines the spatiotemporal relationships between retinal pigment epithelium (RPE) and photoreceptors (PR) during development ofMacaca nemestrinaretina. Our aim was to learn more about the developmental dynamics of these two important cell populations, particularly whether developmental changes in RPE cell densities mimic those of PR at selected retinal points. Twelve eyes ranging in age from 100 fetal days (Fd) to adulthood were flatmounted; the retinal perimeters were traced; and then sample punches were taken of the RPE and neural retina at the fovea, optic disc, mid- and far-nasal periphery, and far temporal, inferior and superior periphery. The two tissues were gently separated and the RPE cells and photoreceptors from the same region of the punch were counted using Nomarski contrast interference optics. We found that the total number of cones remains stable around 4 million between Fd100 and adulthood, but RPE number increases from 1.6 million at Fd100 to 2.56 million in adulthood. At the fovea, the core:RPE ratio increases from 5.4:1 at Fd100 to 28:1 by adulthood. In the temporal periphery by contrast, the cone:RPE ratio declines from 2.2:1 at Fd100–110 to less than 1:1 in the adult. In the vicinity of the optic disc, the ratio of (cones + rods): RPE remains around 35:1 throughout development, but in the retinal periphery it decreases to the adult value of 22:1. These changing ratios indicate that photoreceptors and RPE cells are redistributed independently during development, and that these two cellular sheets slide over one another to achieve their final distribution. This situation suggests that the forces or factors causing foveation are intrinsic to the neural retina.
Organization of retinal ganglion cell axons in the optic fiber layer and nerve of fetal ferrets
Authors: Fitzgibbon T. , Reese B. E. 
Published: June 2009

AbstractPrevious authors have hypothesized that retinotopic projections may be influenced by ‘preordering’ of the axons as they grow towards their targets. In some nonmammalian species, axons are reorganized at or near the optic nerve head to establish a retinotopic order. Data are ambiguous concerning the retinotopy of the mammalian retinal nerve fiber layer and whether fibers become reorganized at the optic nerve head. We have examined this question in fetal and newborn ferrets (Mustela putorius furo) by comparing the arrangement of axons in the retinal nerve fiber layer with that in the optic nerve. Dil or DiA crystals were implanted into fixed tissue in the innermost layers of the retinal periphery, or at a location midway between the periphery and the optic nerve head. Fluorescence labelling was examined in 100–200 μm Vibratome sections, or the eyecup and nerve were photooxidized and 1–2 μm longitudinal or transverse sections were examined. Regardless of fetal age, eccentricity or quadrant of the implant site, a segregation of labelled peripheral axons from unlabelled central ones was not detected within the nerve fiber layer. Axons coursed into the nerve head along the margin of their retinal quadrant of origin, often entering the optic nerve as a radial wedge, thus preserving a rough map of retinal circumference. However, peripheral axons were in no way restricted to the peripheral (nor central) portions of the nerve head or nerve, indicating that the optic axons do not establish a map of retinal eccentricity. Our results demonstrate that (1) the nerve fiber layer is retinotopic only with respect to circumferential position and (2) optic axons are not actively reorganized to establish a retinotopic ordering at the nerve head. The present results suggest that any degree of order present within the optic nerve is a passive consequence of combining the fascicles of the retinal nerve fiber layer; optic axons are not instructed to establish, nor constrained to maintain, a retinotopic order within the optic nerve.