bluuebunny/crossref_metadata_2025 huggingface dataset:
The horizontal cells of artiodactyl retinae: A comparison with Cajal's descriptions
Authors: Sandman Daniele , Boycott Brian B. , Peichl Leo
Published: June 2009

The morphology of horizontal cells in ox, sheep, and pig retinae as observed after Lucifer Yellow injections are described and compared with the descriptions of Golgi-stained cells by Ramón y Cajal (1893). Horizontal cells in the retinae of less domesticated species, wild pig, fallow and sika deer, mouflon, and aurochs were also examined. All these retinae have two types of horizontal cell; their morphologies are in common, although with some familial differences. Their basic appearance is as Cajal described; except in one important respect, a single axon-like process could not be identified on the external horizontal cells. It is concluded that external horizontal cells of artiodactyls correspond to the axonless (A-type) cells of other mammals. Cajal's internal horizontal cells have a single axon which contacts rods. This type corresponds to the B-type cells of other mammalian retinae. Artiodactyl A- and B-type horizontal cells differ from those of many other mammals in that the B-type dendritic tree is robust and the A-type dendritic tree is delicate. Historically, this morphological difference between orders of mammals has led to some confusion. The comparisons presented here suggest that the morphological types of primate horizontal cells can be integrated into a general mammalian classification.
Anin vitrostudy of retinotectal transmission in the chick: Role of glutamate and GABA in evoked field potentials
Authors: Dye J. C. , Karten H. J.
Published: June 2009

We have developed two brain slice preparations for studying tectofugal visual pathways in the chick: conventional, 400-μm slices (“thin slices”), and “thick slices” which encompass the rostral pole of the optic tectum and the contralateral optic nerve. Stimulation was delivered with a bipolar electrode positioned instratum opticumin thin slices and in the contralateral optic nerve in thick slices. While the latter preparation provided a means of exclusively and unambiguously activating retinal afferents, several lines of evidence also indicated that the evoked field potentials in thin slices were chiefly consequent to retinal afferent excitation: (1) the similarity of evoked field potentials in thin slices to those in thick slice preparations; (2) their precise localization in retinorecipient layers as shown by prelabeling from retina with FITC-coupled cholera toxin; (3) transmission delays appropriate for retinal afferents as established with the thick slice preparation; (4) patterns of labeled afferents resulting from applications of Dil crystals to slices fixed after recording; and (5) the similarity in transmitter pharmacology between thin and thick slice preparations. Pharmacological manipulations carried out with bath-applied antagonists indicated that glutamate is the principal retinotectal transmitter. The broadly active glutamate receptor blocker, kynurenic acid, reversibly eliminated the postsynaptic component of the field potential as confirmed with 0 Ca2+saline. A complete block was also effected by the non-NMDA antagonists CNQX and DNQX. The specific NMDA antagonist, APS, caused a smaller and variable reduction in response amplitude. The GABA antagonist, bicuculline, caused a prolongation of the monosynaptic field epsp in retinorecipient layers and an enhancement of the long-latency, negative wave in cellular layers below, supporting a late, excitation-limiting role for this inhibitory transmitter.
Synaptic Organization of an organotypic slice culture of the mammalian retina
Authors: Sassoè-Pognetto Marco , Feigenspan Andreas , Bormann Joachim , Wässle Heinz
Published: June 2009

Vertical Slices of postnatal day 6 (P6) rat retina were cut and cultured using the roller-tube technique. The organotypic differentiation during a culture period of up to 30 days has been described in a previous study (Feigenspan et al., 1993a). Here we concentrated on the synaptic organization in the retinal slice culture. Electron microscopy revealed the presence of ribbon synapses in the outer plexiform layer and conventional and ribbon syanpses in the inner plexiform layer. Immunofluroscence with antibodies that recognize specific subunits of GABAAor glycine receptors revealed a punctuate distribution of the receptors. They were aggregated in “hot spots” that correspond to a concentration of receptors at postsynaptic sites. Different isoforms of GABAAand glycine receptors occured in the slice cultures. The experiments show that there is a differentiation of synapses and a diversity of transmitter receptors in the slice cultures that is comparable to thein vivoretina.
Possible contributions of magnocellular- and parvocellular-pathway cells to transient VEPs
Authors: Valberg Arne , Rudvin Inger
Published: June 2009

We have measured transient visual evoked potentials (VEPs) to low-contrast luminance stimuli favoring responses of magnocellular pathway cells and to low-contrast red-green stimuli favoring parvocellular cells. Stimuli were square-wave alternating, 3-deg homogeneous disks. Low-contrast stimuli modulated in luminance elicited relatively simple responses. For some observers, a negativity was present that saturated at low contrast. This may be the signature of inputs from magnocellular channels to the visual cortex. The slope of the contrast—response curve for low-contrast stimuli was about the same for all subjects. For medium contrasts, these contrast—response curves displayed an abrupt increase of slope. The shallower slope may reflect the responsivity of magnocellular-pathway inputs to the cortex, whereas the steeper slope may be caused by additional parvocellular activation.

Contrast-response curves for the most sensitive waveforms of the isoluminant green—red modulation also showed two branches, although not as clearly as for luminance. This may indicate parvocellular-mediated activity for small chromatic differences, and a combination of parvocellular and magnocellular inputs for larger contrasts. Curves of time-to-peak response as a function of contrast often changed their monotonous behavior near the kink of the corresponding contrast—response curve, thus supporting the notion of a contribution from several mechanisms to the main waveforms.
Photoresponses of human rodsin vivoderived from paired-flash electroretinograms
Authors: Pepperberg David R. , Birch David G. , Hood Donald C.
Published: June 2009

In the human eye, domination of the electroretinogram (ERG) by theb−wave and other postreceptor components ordinarily obscures all but the first few milliseconds of the rod photoreceptor response to a stimulating flash. However, recovery of the rod response after a bright test flash can be analyzed using a paired-flash paradigm in which the test flash, presented at time zero, is followed at timetby a bright probe flash that rapidly saturates the rods (Birch et al., 1995). In ERG experiments on normal subjects, the hypothesis that a similar method can be used to obtain the full time course of the rod response to test flashes of subsaturating intensity was tested. Rod-only responses to probe flashes presented at varying timestafter the test flash were used to derive a family of amplitudesA(t) that represented the putative rod response to the test flash. These rod-only responses to the probe flash were obtained by computational subtraction of the cone-mediated component of each probe flash response. With relatively weak test flashes (11–15 scot-td-s), the time course of the rod response to the test flash derived in this manner was consistent with a four-stage impulse response function of time-to-peak ≃170 ms.A(170), the amplitude of the derived response at 170 ms, increased with test flash intensity (Itest) to a maximum valueAmoand exhibited a dependence onItestgiven approximately by the relation,A(170)/Amo= 1 - exp(-kItest), wherek= 0.092 (scot-td-s)−1. In steady background light, the falling (i.e. recovery) phase of the derived response began earlier, and the sensitivity parameterkwas reduced several-fold from its dark-adapted value. As the sensitivity, kinetics, and light-adaptation properties of the derived response correspond closely with those of photocurrent flash responses previously obtained from isolated rodsin vitro, it was concluded that the response derived here from the human ERG approximates the course of the massedin vivorod response to a test flash.
The morphology and distribution of horizontal cells in the retina of a New World monkey, the marmoset Callithrix jacchus: A comparison with macaque monkey
Authors: Chan Tricia L. , Goodchild Ann K. , Martin Paul R.
Published: June 2009

The morphology and distribution of horizontal cells was studied in the retina of a New World monkey, the marmoset, Callithrix jacchus, and compared with that of the Old World macaque monkey. Horizontal cells in macaque and marmoset were either labelled with the carbocyanine dye, Dil, and then photoconverted, or were labelled by intracellular injection with Neurobiotin. The marmoset has two types of horizontal cell, H1 and H2, which have dendritic and axonal morphology similar to their counterparts in Old World monkeys and human. The dendritic-field size of both cell types increases with distance from the fovea. Both types make contact with the vast majority of the cones within their dendritic field. The dendrites of H1 cells in marmoset contact almost twice as many cones as H1 cells in macaque at an equivalent eccentricity. With increasing distance from the fovea, H1 cells make contact with more cones but have, on average, fewer terminal knobs inserted in each cone. The increase in dendritic-field area of H1 cells is balanced by a decrease in spatial density (from 4500 cells/mm2 at 25 deg eccentricity to 1000 cells/mm2 in far peripheral retina), so coverage of the retina remains fairly constant, between 5 and 8. Overall, the results show that the qualitative morphological properties, as well as quantitative population properties of horizontal cells, are common to both New World and Old World primates.
GABA-induced inactivation of functionally characterized sites in cat striate cortex: Effects on orientation tuning and direction selectivity
Authors: Crook John M. , Kisvárday Zoltan F. , Eysel Ulf T.
Published: June 2009

Microiontophoresis of γ-aminobutyric acid (GABA) was used to reversibly inactivate small sites of defined orientation/direction specificity in layers II-IV of cat area 17 while single cells were recorded in the same area at a horizontal distance of ~350–700 jam. We compared the effect of inactivating iso-orientation sites (where orientation preference was within 22.5 deg) and cross-orientation sites (where it differed by 45–90 deg) on orientation tuning and directionality. The influence of iso-orientation inactivation was tested in 33 cells, seven of which were subjected to alternate inactivation of two iso-orientation sites with opposite direction preference. Of the resulting 40 inactivations, only two (5%) caused significant changes in orientation tuning, whereas 26 (65%) elicited effects on directionality: namely, an increase or a decrease in response to a cell's preferred direction when its direction preference was the same as that at an inactivation site, and an increase in response to a cell's nonpreferred direction when its direction preference was opposite that at an inactivation site. It is argued that the decreases in response to the preferred direction reflected a reduction in the strength of intracortical iso-orientation excitatory connections, while the increases in response were due to the loss of iso-orientation inhibition. Of 35 cells subjected to cross-orientation inactivation, only six (17%) showed an effect on directionality, whereas 21 (60%) showed significant broadening of orientation tuning, with an increase in mean tuning width at half-height of 126%. The effects on orientation tuning were due to increases in response to nonoptimal orientations. Changes in directionality also resulted from increased responses (to preferred or nonpreferred directions) and were always accompanied by broadening of tuning. Thus, the effects of cross-orientation inactivation were presumably due to the loss of a cross-orientation inhibitory input that contributes mainly to orientation tuning by suppressing responses to nonoptimal orientations. Differential effects of iso-orientation and cross-orientation inactivation could be elicited in the same cell or in different cells from the same inactivation site. The results suggest the involvement of three different intracortical processes in the generation of orientation tuning and direction selectivity in area 17: (1) suppression of responses to nonoptimal orientations and directions as a result of cross-orientation inhibition and iso-orientation inhibition between cells with opposite direction preferences; (2) amplification of responses to optimal stimuli via iso-orientation excitatory connections; and (3) regulation of cortical amplification via iso-orientation inhibition.
Severity of ganglion cell death during early postnatal development is modulated by both neuronal activity and binocular competition
Authors: Scheetz A.J. , Williams Robert W. , Dubin Mark W.
Published: June 2009

The influence of postnatal neuronal activity on the magnitude of retinal ganglion cell death has been studied in cats. A constant blockade of activity in one eye starting just after birth does not change the severity of naturally occurring ganglion cell death, and as in normal animals, the ganglion cell population declines from 250,000 to 160,000 over a 4- to 6-week period. However, the population of retinal ganglion cells in the active untreated eye of monocularly deprived cats is increased 12% above normal (180,000 vs. 160,000 in each of four cases). This increase of 20,000 cells is permanent, and presumably reflects the competitive advantage in their target nuclei that the still active axons have over their silenced companions from the treated eye. Surprisingly, in one animal treated successfully for long duration with TTX in both eyes, the population of ganglion cells was elevated in both eyes (200,000 and 208,000 ganglion cells). This increase matches that achieved by early unilateral enucleation (Williams et al., 1983). Our results demonstrate that the complete blockade of activity reduces the severity of naturally occurring cell death in a population of CNS sensory neurons. The effects of unilateral blockade emphasize that the activity-dependent modulation of neuron death only occurs under conditions that do not place the inactive population of neurons at a competitive disadvantage.
Dark-suppression and light-sensitization of horizontal cell responses in the hybrid bass retina
Authors: Baldridge William H. , Weiler Reto , Dowling John E.
Published: June 2009

The responsiveness of luminosity-type horizontal cells, recorded intracellularly from isolated hybrid bass retinas, decreased after superfusion for 2 h in constant darkness. Responsiveness was subsequently increased (light-sensitized) up to 10-fold after exposure to several short (~0.5 min) periods of continuous illumination. The increase in horizontal cell responsiveness following light-sensitization was due to an increase of peak response amplitude rather than a reduction of peak response time. The increased responsiveness after light-sensitization was intensity-dependent with brighter sensitizing stimuli causing a greater increase than dimmer stimuli. The extent of LHC dark-suppression was affected by the time of day, being greater when induced during the night than during the day. However, there was no significant difference in horizontal cell responsiveness after light-sensitization in retinas studied during the night compared to those studied during the day The responsiveness of light-sensitized horizontal cells from isolated hybrid bass retinas was found to be suppressed by relatively brief periods of darkness. The responsiveness of horizontal cells, that were first light-sensitized, decreased by more than 50% following only 5 min of darkness. Suppression of light-sensitized horizontal cell responsiveness after such a short time in the dark has not been described in other teleost retinas. The suppression of light-sensitized horizontal cell responsiveness in hybrid bass retinas may be rapid in comparison to other teleosts.
Catecholamine-, Indoleamine-, and GABA-containing cells in the chameleon retina
Authors: Bennis Mohamed , Versaux-Botteri Claudine
Published: June 2009

Neurons containing catecholamine, indoleamine, and gamma-aminobutyric acid (GABA) were identified by immunohistochemistry in the chameleon retina. Tyrosine hydroxylase (TH) and serotonin (5HT) were observed mostly in two subtypes of orthotopic amacrine cells differing in their soma size and process distribution within the IPL. Some labelled cells were displaced either to the IPL (5HT) or to the GCL (TH and 5HT). A multiplicity of retinal cell types contained GABA including cones, horizontal, amacrine, and ganglion cells. Our results confirmed those obtained in the retinas of other lizards except for the presence of interstitial and displaced amacrine cells containing TH or 5HT of which this is the first report.
Correspondence between visually evoked voltage-sensitive dye signals and synaptic activity recorded in cortical pyramidal cells with intracellular microelectrodes
Authors: Senseman David M.
Published: June 2009

Fast, multiple-site optical recording of voltage-sensitive dye (VSD) signals and intracellular microelectrode recordings were combined to characterize visually evoked neuronal responses in the visual cortex of the pond turtle,Pseudemys scripta. By using anin vitro, eye-brain preparation stained with the merocyanine oxazolone voltage-sensitive dye, NK-2495 or a close analog, NK-2761, large VSD signals relatively free of vibrational noise could be recorded in single trials following a stroboscopic light flash to the contralateral eye. VSD signals recorded from the same cortical location in repeated trials exhibited considerable variability in the onset, duration, and amplitude of secondary depolarizations. Because of this variability, secondary depolarizations were largely absent in signal-averaged responses. Superposition of VSD signals with intracellular recordings obtained from cortical pyramidal cells revealed a close correspondence between their signal waveforms. The two signals were virtually identical in their onset, initial rate of rise, and time-to-peak. At later periods (>500 ms), the correspondence was less close, especially for large cortical depolarizations. Some of this disparity could be attributed to contamination of the VSD signal by a large intrinsic optical response. A second contribution was a failure of the VSD signal to register asynchronous regenerative effects occurring in single pyramidal cells. It is suggested that the close correspondence between the microelectrode and optical recordings in the early phase of the response may reflect the organization of pyramidal cells into clusters that receive virtually identical synaptic inputs.
Influence of rod adaptation upon cone responses to light offset in humans: II. Results in an observer with exaggerated suppressive rod–cone interaction
Authors: Lange Gudrun , Frumkes Thomas E.
Published: June 2009

In normal observers, sensitivity of cones to rapid sinusoidal flicker decreases by about 0.7 log units as rods progressively dark adapt. However, Arden and Hogg (1985) described a night-vision disorder characterized by normal rod sensitivity but exaggerated suppressive rod-cone interaction (SRCI). We refer to this condition as the exaggerated SRCI syndrome (ESS). The present paper examines the influence of rod-adaptation upon cone-mediated responses to light onset and offset in an observer with ESS. Under all conditions of adaptation examined, sensitivity of cones to rapid-on waveforms is indistinguishable to that of a normal observer tested under identical circumstances; rod sensitivity is also normal. However, the sensitivity of cones to transient decreases in illumination is clearly subnormal under light-adapted conditions. This deficit in cone responsiveness to light offset becomes increasingly subnormal as rods dark adapt and, when completely dark adapted, the ESS observer is nearly blind to 1 Hz rapid-off sawtooth waveforms. These results strongly bolster previous results that suggest that suppressive rod-cone interaction is restricted to the response to transient decreases in illumination.
GABA inhibits ACh release from the rabbit retina: A direct effect or feedback to bipolar cells?
Authors: Linn David M. , Massey Stephen C.
Published: June 2009

The cholinergic amacrine cells of the rabbit retina may be labeled with [3H]-Ch and the activity of the cholinergic population monitored by following the release of [3H]-ACh. We have tested the effect of muscimol, a potent GABAAagonist, on (1) the light-evoked release of ACh, presumably mediatedviabipolar cells, which are known to have a direct input to the cholinergic amacrine cells and (2) ACh release produced by exogenous glutamate analogs that probably have a direct effect on cholinergic amacrine cells. Muscimol blocked the light-evoked release of ACh with an IC50of 1.0μM. In contrast, ACh release produced by nonsaturating doses of kainate or NMDA was not reduced even by 100μM muscimol. Thus, we have been unable to demonstrate a direct effect of GABA on the cholinergic amacrine cells.

GABA antagonists, such as picrotoxin, caused a large increase in the base release and potentiated the light-evoked release of ACh. Both these effects were abolished by DNQX, a kainate antagonist that blocks the input to cholinergic amacine cells from bipolar cells. DNQX blocked the effects of picrotoxin even when controls showed that the mechanism of ACh release was still functional. Together, these results imply that the dominant site for the GABA-mediated inhibition of ACh release is on the bipolar cell input to the cholinergic amacrine cells. This is consistent with previous anatomical and physiological evidence that bipolar cells receive negative feedback from GABA amacrine cells.
A computational model of the amplitude and implicit time of the b-wave of the human ERG
Authors: Hood Donald C. , Birch David G.
Published: June 2009

To improve the usefulness of the ERG in identifying the sites and mechanisms of adaptation, development, and disease processes, a theoretical framework based upon Granit's analysis of the ERG was evaluated. The framework assumes that the ERG is the sum of two potentials, one, P3, generated by the receptors and the other, P2, generated by the cells of the INL. Hood and Birch (1990a, b) demonstrated that the leading edge of the a-wave can be quantitatively described by a model used to describe the response from single rod receptors. This model provides P3(t), a theoretical receptor response as a function of time, for any given flash intensity. The ERGs from normal observers and patients with retinal diseases were analyzed in this framework, first by deriving P2 by computer subtracting the predicted P3(t) responses. This analysis was successful and a computational model of the ERG was then derived. The model of P2(t) was constructed with linear filters and a static nonlinearity and using P3(t) as the input. The ERG for any given flash intensity is then P3(t) + P2(t) The model describes (1) the change both in implicit times and in trough-to-peakb–wave amplitudes with flash intensity for the normal, dark-adapted observers; and (2) the changes inb–wave implicit times and amplitudes for three patients with retinal diseases.

Among the implications drawn from these analyses were as follows: (1) The fits of the Naka-Rushton equation to trough-to-peakb–wave amplitudes must be interpreted with great care. (2) When the INL is affected by retinal disease, theb–wave may be a very poor reflection of INL activity. (3) The implicit time of theb–wave can provide a measure of receptor sensitivity.
Two signals in the human rod visual system: A model based on electrophysiological data
Authors: Stockman Andrew , Sharpe Lindsay T. , Rüther Klaus , Nordby Knut
Published: June 2009

In the human rod visual system, self-cancellation of flicker signals is observed at high rod intensity levels near 15 Hz, both perceptually and in the electroretinogram (ERG). This and other evidence suggests that two rod signals are transmitted through the human retina with different speeds of transmission. Here we report a series of flicker ERG recordings from a normal observer and an observer who lacks cone vision. From these results, we propose a quantitative model of the two rod signals, which assumes (1) that the amplitude of the slow signal grows linearly with log intensity but then saturates at ~1 scot, td; (2) that the amplitude of the fast signal grows linearly with intensity; (3) that there is a difference in time delay of ~33 ms between two rod signals of the same polarity (or of ~67 ms if the signals are of inverted polarity); and (4) that the time delay of both signals declines linearly with log intensity (by ~10 ms per log scot. td). These simple assumptions provide a remarkably good account of the experimental data. Our results and model are relevant to current anatomical theories of the mammalian rod visual system. We speculate that the slower signal in the human ERG may reflect the transmission of the rod response via the rod bipolars and the An amacrine cells, while the faster signal may reflect its transmission via the rod-cone gap junctions and the cone bipolars. There are, however, several objections to this simple correspondence.
Neonatal monocular enucleation and the geniculo-cortical system in the golden hamster: Shrinkage in dorsal lateral geniculate nucleus and area 17 and the effects on relay cell size and number
Authors: Trevelyan A.J. , Thompson I.D.
Published: June 2009

We have examined the effects of neonatal monocular enucleation on the volume of the dorsal lateral geniculate nucleus (dLGN), the area of area 17, and the size and numbers of geniculate relay neurons identified by retrograde transport of HRP from cortex. Compared to values for normal animals, the only significant change contralateral to the remaining eye was an increase in relay cell radius. The effects ipsilateral to the remaining eye were more widespread: we found significant reductions in the volume of the dLGN (27% reduction), the area of striate cortex (22%), and the number (16%) and average soma radius (6%) of geniculate relay neurons. The relay neurons were also more densely packed, suggesting that other geniculate cell types were affected similarly, although this was not explicitly examined. These changes were not uniform throughout the nucleus, and as such, reflected the changes in retinal input. The greatest reduction in cell size occurred in the region of the ipsilateral dLGN receiving the most sparse retinal input subsequent to enucleation. Nor was the shrinkage of the dLGN uniform, being most apparent in the coronal plane especially along the axis orthogonal to the pia; there appeared to be little change in the anteroposterior extent. Shrinkage in area 17 ipsilateral to the remaining eye was the same (about 22%) whether it was defined by myelin staining or transneuronal transport of WGA-HRP. These results show that the transneuronal changes seen in the organization of visual cortex after early monocular enucleation in rodents are associated with only a moderate loss of geniculate relay cells.
Binocular rivalry suppression disrupts recovery from motion adaptation
Authors: Wiesenfelder Heidi , Blake Randolph
Published: June 2009

The motion after-effect (MAE) lasts longer when the test period does not immediately follow adaptation, a phenomenon called storage. Does storage of the MAE occur if the test target is present but rendered phenomenally invisible owing to the presence of a rival target presented to the other eye during the storage period? Our experiment addressed this question. Following adaptation to a drifting grating, an intervening period preceded testing with a stationary grating. During this period, the adapted eye either viewed the test target immediately or was occluded, and the unadapted eye either viewed a high-contrast rival target or was occluded. Thus four conditions were employed. The duration of the residual MAE was found to be longer for the rivalry condition (grating and rival target viewed) than for the normal MAE condition (grating viewed), and comparable to that in the stored MAE condition (both eyes occluded). Thus, the MAE is stored when the test target is rendered invisible due to binocular rivalry, indicating that a suppressed target is ineffective at promoting decay of the MAE. So while suppression does not prevent information about the adapting grating from reaching the site of generation of the MAE (Lehmkuhle & Fox, 1975), it can prevent information about the test target from reaching the site of the stored MAE. Current models attribute the MAE to reduced responsiveness of direction-selective cortical neurons (Sutherland, 1961; Barlow & Hill, 1963). Thus, storage should reflect a differential return of these adapted cells to preadapted response levels, dependent on postadaptation stimulation. From our results we deduce that storage does not occur at all sites at which motion adaptation occurs. Rather, decay of the MAE is dependent on postadaptation stimulation at higher levels of adaptation, and independent at earlier levels.
Packing geometry of human cone photoreceptors: Variation with eccentricity and evidence for local anisotropy
Authors: Curcio Christine A. , Sloan Kenneth R.
Published: June 2009

Disorder in the packing geometry of the human cone mosaic is believed to help alleviate spatial aliasing effects. To characterize cone packing geometry, we gathered positions of cone inner segments at seven locations along four primary and two oblique meridians in an adult human retina. We generated statistical descriptors based on the distribution of distances and angles to Voronoi neighbors. Parameters of a compressed-jittered model were fit to the actual mosaic. Local anisotropics were investigated using correlograms. We find that (1) median distance between Voronoi neighbors increases with eccentricity, but the minimum distance is constant (6–8 μm) across peripheral retina; (2) the cone mosaic is least compressed and jittered at the edge of the foveal rod-free zone; (3) disorder in the foveal center resembles that described by Pu m et al. (1990); (4) cone spacing is 10–15% less in one direction than in the orthogonal direction; and (5) cone spacing is greater in the radial direction (along meridians) than in the tangential direction (along lines of isoeccentricity). The nearly constant minimum distance implies that high spatial frequencies may be sampled even in peripheral retina. Local anisotropy of the cone mosaic is discussed in relation to the growth of the primate retina during development and to the orientation biases of retinal ganglion cells.
Normalization of cell responses in cat striate cortex
Authors: Heeger David J.
Published: June 2009

Simple cells in the striate cortex have been depicted as half-wave-rectified linear operators. Complex cells have been depicted as energy mechanisms, constructed from the squared sum of the outputs of quadrature pairs of linear operators. However, the linear/energy model falls short of a complete explanation of striate cell responses. In this paper, a modified version of the linear/energy model is presented in which striate cells mutually inhibit one another, effectively normalizing their responses with respect to stimulus contrast. This paper reviews experimental measurements of striate cell responses, and shows that the new model explains a significantly larger body of physiological data.
Functional binocular vision is not dependent on visual experience in the praying mantis
Authors: Mathis Ute , Eschbach Sabine , Rossel Samuel
Published: June 2009

In vertebrates, it has been shown that binocular visual experience is necessary to develop normal spatial vision. We have investigated whether this is also true for an invertebrate, the praying mantis. The praying mantis is a predatory insect in which prey localization involves the use of binocular disparities. We raised mantids which had one eye occluded throughout development and tested monocular visual fixation and binocular distance estimation in the adult animals. The results revealed that both fixation and prey catching behavior were normally functional in the monocularly reared animals. Thus we conclude that, in mantids, binocular vision is based on a fixed mode of development.
Synaptic inputs to physiologically defined turtle retinal ganglion cells
Authors: Muller Jay F. , Ammermüller Josef , Normann Richard A. , Kolb Helga
Published: June 2009

Two physiologically distinct, HRP-marked turtle retinal ganglion cells were examined for their morphology, GABAergic, glycinergic, and bipolar cell synaptic inputs, using electron-microscopic autoradiography and postembedding immunocytochemistry. One cell was a color-opponent, transient ON/OFF ganglion cell. Its center response to red was a sustained hyperpolarization, and its center response to green was a depolarization with increased spiking at onset. The HRP-injected cell most resembled G6, from previous Golgi-impregnation studies (Kolb, 1982; Kolb et al., 1988). It was a narrow-field bistratified cell, whose two broad dendritic strata peaked at approximately levels L20–25 (sublamina a) and L60 (sublamina b) of the inner plexiform layer. Bipolar cell synapses onto G6 were found evenly distributed between its distal and proximal dendritic strata, spanning L20–75. These inputs probably originated from several different bipolar cells, reflecting the complexity of the center response. GABAergic inputs were found onto both the distal and proximal strata, from near L20–L85. Only a few glycinergic inputs, confined to dendrites at L50–70, were observed.

A second ganglion cell type that we physiologically characterized and HRP-injected had sustained ON-center, sustained OFF-surround responses. Two examples were studied; both were bistratified in sublamina b, near L60–70 and L85–100, with branches up to near L40. They resembled G10, from previous Golgi-impregnation studies (Kolb, 1982; Kolb et al., 1988). One cell was partially reconstructed to look at the distributions of GABAergic and glycinergic amacrine cell, and bipolar cell inputs. Although synapses from bipolar cells were equally divided between the two major dendritic strata of G10, the inputs to the distal stratum were close to the soma, and the inputs to the more proximal stratum were on the peripheral dendrites. This arrangement may reflect input from two distinct types of ON-bipolar cell. GABAergic and glycinergic inputs to G10 costratified to both strata and to the distal branches; but where glycinergic inputs were found distributed throughout the arbor, GABAergic inputs appeared to be confined to peripheral dendrites. We hypothesize on the neural elements involved and the circuitry that may underlie the physiologically recorded receptive fields of these two very different ganglion cell types in the turtle retina.
The effects of a luminanace-modulated background on the grating-evoked cortical potential in the cat
Authors: Baro John A. , Lehmkuhle Stephen
Published: June 2009

Averaged grating-evoked cortical potentials were recorded from area 17 of awake cats. Peak latency of early components of the visual-evoked potential (VEP) response to stimulus onset increased as a function of spatial frequency, while amplitude tended to be largest at intermediate spatial frequencies. Latency increased and amplitude generally decreased to lower spatial-frequency stimuli (<0.25 cycle/deg) in the presence of a uniform flickering field (UFF). The UFF had a relatively small or opposite effect on peak latency and amplitude for higher spatial-frequency stimuli (>0.50 cycle/deg). The VEP response to stimulus offset was present only at low spatial frequencies and was virtually eliminated by the presence of the UFF. The effects were similar whether the target and UFF background were simultaneously presented or briefly separated; however, the UFF had no effect when the two were spatially separated. The effects of the UFF background on VEP onset response increased with increasing temporal frequency from 2–8 Hz; offset responses were affected similarly at all temporal frequencies. These effects are similar to those observed in humans and suggest that two spatio-temporally tuned mechanisms contribute to the early VEP response. In the cat, the mechanisms seem to correspond to X and Y cells in the dorsal lateral geniculate nucleus.
Centrifugal pathways to the retina: Influence of the optic tectum
Authors: Uchiyama Hiroyuki
Published: June 2009

Two types of centrifugal pathways to the retina have been found in the vertebrates, according to the location of the cell bodies and presence or absence of connections with the optic tectum. One type is represented by the isthmo-optic nucleus (ION) of birds and, therefore, termed “ION-type” retinopetal system. The other type is termed “non-ION-type” retinopetal system. The ION-type retinopetal systems have been found in the cyclostomes, teleosts, reptiles, and birds. This review describes the anatomy and physiology of the ION-type retinopetal systems, mainly of birds and teleosts. On the basis of anatomical and physiological evidence cited in this review, the ION-type retinopetal systems can be regarded as the tectofugal pathways to the retina. The function of the ION-type retinopetal systems is discussed in detail, with special emphasis on their relation to the role of the tectum in mediating visuomotor behavior.
Visual response properties of cortical inputs to an extrastriate cortical area in the cat
Authors: Sherk Helen
Published: June 2009

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

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

Despite these differences, afferents were far more similar in their properties to cells in areas 17 and 18 than to cells in the Clare-Bishop area. Compared to the latter, afferents showed major discrepancies in receptive-field size, in direction selectivity, in end-stopping, and in ocular dominance distribution. These differences seem most likely to stem from circuitry intrinsic to the Clare-Bishop area.
GABA-activated single channel currents in outside-out membrane patches from rat retinal ganglion cells
Authors: Lipton Stuart A.
Published: June 2009

γ-aminobutyric acid (GABA) evokes large whole-cell currents in solitary mammalian retinal ganglion cells studied by the patch-clamp method. This evidence suggests that GABA acts directly on the retinal ganglion cells as an inhibitory transmitter as it does elsewhere in the mammalian central nervous system. Here, single-channel recordings of the currents underlying the GABA-induced responses were studied in outside-out patches of cell membrane. In some other preparations, single GABAA channels recorded in the excised patch configuration have been shown to have altered properties in comparison to responses elicited during whole-cell recording. For example, in cortical neurons single GABA-activated channels in excised patches display accelerated desensitization kinetics as well as rapid rundown of the response. Therefore, in retinal ganglion cells, responses generated by GABA in cell-free patches were compared to whole-cell responses. After determining that the responses to GABA in acutely isolated outside-out patches were indeed similar to those of the whole-cell currents in retinal ganglion cells, the unitary conductances were studied. It was determined that these single-channel events resemble those reported in other nervous tissues with 4 elementary conductances of ~10 pS, 19–22 pS, 30–33 pS, and 45–50 pS at 33–35°C.
Stimulus configuration and location in the visual field affect appetitive responses by the praying mantis,Sphodromantis lineola(Burr.)
Authors: Prete Frederick R.
Published: June 2009

Adult female praying mantises,Sphodromantis lineola(Burr.), were presented with computer-generated black rectangular stimuli that moved horizontally or vertically at 82 deg/s against a homogeneous white background. Both stimulus configuration (orientation in relation to direction) and the retinal location of the stimulus image affected the rate at which mantises responded appetitively (approached or struck at the stimulus). Mantises responded most to square stimuli (12.5 deg × 12.5 deg) when they moved horizontally or vertically through, or horizontally at 24.5 deg below the center of their visual field. Mantises also responded most to vertically (vs. horizontally) oriented rectangular stimuli (12.5 deg × 47 deg) that moved through their visual-field center, irrespective of whether the stimuli moved downward or horizontally. Upward moving stimuli elicited intermediate amounts of behavior with no configuration preference. Mantises did not demonstrate a configuration preference when rectangular stimuli moved ≥24.5 deg outside of the visual-field center. Furthermore, mantises responded very little and demonstrated no configuration preferences to stimuli that moved less than ≈83 deg through their visual field even if the stimuli moved through the visual-field center.
ON and OFF activity gradients in the lateral geniculate nucleus of the cat: A combined 14C 2-deoxyglucose and D, L-2-amino-4-phosphonobutyric acid study
Authors: Thurlow G. A. , Bowling D. B. , Cooper R. M.
Published: June 2009

Experiments on the lateral geniculate nucleus (LGN) of the cat based on 14C 2-deoxyglucose (2-DG) autoradiography and intraocular injections of 2-amino-4-phosphonobutyric acid (APB) provided evidence for gradients of metabolic activity in the ON and OFF pathways in layer A, but only very weakly, if at all, in layer Al. Alert and freely moving cats were exposed to square-wave gratings over a 45-min period after injection of the 2-DG. When one eye had been treated previously with APB, contralateral layer A showed a clear gradient of 2-DG label indicating that the remaining OFF pathway was most active ventrally in the layer and, by implication, that the ON pathway is normally most active dorsally. No gradient was apparent in layer Al ipsilateral to the APB eye. Control experiments based on binocular injections of tetrodotoxin (TTX) demonstrated that no gradients were present in the baseline activity within the layers. Finally, monocular injections of TTX provided evidence for gradients of nondominant eye activity in layers A and Al that were maximal near the interlaminar zone between layers A and A1 and declined in mirror-symmetric fashion toward the dorsal border of A and the ventral border of A1.

Combined with earlier anatomical studies showing depth-dependent patterns of geniculo-cortical projection, these results indicate that in the cat, as in several other species, the visual input to striate cortex is partly organized around ON and OFF pathways. In addition, the results suggest that a systematic variation of binocular interaction, perhaps related to ocular dominance, exists through the depths of the geniculate layers. Understanding how the ON and OFF pathways, and binocular interactions, are organized in the thalamus may provide insight into the functional merging of these systems in the cortex.
Parvalbumin immunoreactivity in the lateral geniculate nucleus of rhesus monkeys raised under monocular and binocular deprivation conditions
Authors: Tigges Margarete , Tigges Johannes
Published: June 2009

Newborn rhesus monkeys were raised under monocular (lid suture, aphakia, aphakia corrected optically with contact lenses, and occlusion with opaque occluder lenses) and under binocular visual deprivation conditions (aphakia combined with occlusion or optical undercorrection of the fellow eye). Routine immunohistochemical methods with an antibody to the calcium-binding protein parvalbumin (PV) were used to examine the distribution of PV+ neurons and PV+ processes in the LGN of these monkeys. Under all rearing conditions, we found no obvious difference in PV density in neurons in any lamina, although in all monocularly deprived and in two of the three binocularly deprived monkeys neurons connected to the deprived eye were of reduced size. Furthermore, PV-immunoreactive processes in the neuropil of deprived laminae were as numerous and of the same morphologies as those in nondeprived laminae or as in normal controls. Thus, in the LGN of rhesus monkeys, the calcium-binding protein parvalbumin is resistant to monocular as well as binocular visual deprivation during the postnatal maturation process of the visual system.
Retinal transformation at metamorphosis in the winter flounder (Pseudopleuronectes americanus)
Authors: Evans Barbara I. , Fernald Russell D.
Published: June 2009

Winter flounder (Pseudopleuronectes americanus) are hatched as bilaterally symmetric larvae which live near the ocean surface. At metamorphosis, they become laterally compressed, one eye migrates to the opposite side of the head, and they live the remainder of their lives lying on their blind side on the ocean floor. The present study characterizes and quantifies retinal cell distribution throughout the larval period and contrasts it with the adult retina. Based on light- and electron-microscopic analyses, retinas of larval flounder contain only a single cone-like photoreceptor type, arranged in a hexagonal array. In contrast, after metamorphosis, the adult retina has three types of photoreceptors: rods, single cones, and double cones. Rod photoreceptors are numerous in the ventral retina and decrease in density dorsad. The cone photoreceptor density, in contrast to rods, is higher in the dorsal retina decreasing ventrad. Adult cone photoreceptors are arranged in a square mosaic with four double cones surrounding one single cone. The differences in larval and adult retinal morphology reflect the distinctly different habitat each occupies.