bluuebunny/crossref_metadata_2025_split huggingface dataset:
Background contrast modulates kinetics and lateral spread of responses to superimposed stimuli in outer retina
Authors: Reifsnider Eric S. , Tranchina Daniel 
Published: June 2009

AbstractSurround enhancement (sensitization) is a poorly understood form of network adaptation in which the kinetics of the responses of retinal neurons to test stimuli become faster, and absolute sensitivity of the responses increases with increasing level of steady, surrounding light. Surround enhancement has been observed in all classes of retinal neurons in lower vertebrates except cones, in some primate retinal ganglion cells, and in human psychophysical studies. In theory, surround enhancement could be mediated by two broad classes of mechanisms, which are not mutually exclusive: one in which the kinetics of the transduction linking cone voltage to postsynaptic current in second-order neurons is modulated, and another in which the transformation of postsynaptic current to membrane voltage is modulated. We report here that both classes of mechanism play a role in surround enhancement measured in turtle horizontal cells (HCs). We stimulated the retina by modulating sinusoidally the illuminance of a bar placed at various positions in the HC receptive field. The bar was surrounded by either equally luminant or dim, steady light. Interpretation of responses in the context of a model for the cone-HC network led to the conclusion that the speeding up of response kinetics —due to selective increase in response gain at high temporal frequencies — by surround illuminance is almost completely accounted for by the change in the kinetics of the transduction linking cone membrane potential to HC postsynaptic current. However, surround illuminance also had an additional, surprising effect on the transformation between postsynaptic current and voltage: the space constant for signal spread in the HC network for the dim-surround condition was roughly twice as large as that for the bright-surround condition. Thus, increasing surround illuminance had analogous effects in the spatial and temporal domains: it restricted the time course and the spatial spread of signal. Both effects were dependent on the contrast between the mean bar illuminance and that of the surround, rather than on overall light level. When the stimulus with the bright surround was dimmed uniformly by a neutral density filter, the space constant did not increase, and response gain at high temporal frequencies did not decrease. Pharmacological experiments performed with dopamine and various agonists and antagonists indicated that, although exogenous dopamine can influence surround enhancement, endogenous dopamine does not play an important role in surround enhancement. We conclude that contrast in background light modulates the spatiotemporal properties of signal processing in the outer retina, and does so by a non-dopaminergic mechanism.
The pupillary response to light in the turtle
Authors: Granda A. M. , Dearworth J. R. , Kittila C. A. , Boyd W. D. 
Published: June 2009

AbstractWhen intense adapting lights are turned off, the pupil of the turtle, Pseudemys scripta elegans, enlarges. The recovery functions for pupillary dilation have different time constants that are defined by red- and green-sensitive cones and rods as they are affected by prior light adaptation and time in the dark. Pupillary area related to dilation responds over at least a three- to four-fold range. Following white-light adaptation, the course of pupil dilation in the dark shows a three-legged curve of differing time constants. With spectral-light adaptations, the contributions of separate classes of photoreceptors can be isolated. Red- and green-sensitive cones contribute shorter time constants of 3.31 and 3.65 min to prior white-light adaptation—4.81 and 4.18 min to prior spectral-light adaptations. Rods contribute a much longer time constant of 6.69 min to prior white-light adaptation—7.60 min to prior spectral-light adaptation. The ratios are in keeping with the flash sensitivities of photoreceptors in this same animal, as well as with psychophysical visual threshold mechanisms of color sensitivity.
A sustained input to the direction-selective mechanism in cat striate cortex neurons
Authors: Baker Curtis L. , Cynader Max S. 
Published: June 2009

AbstractDirection-selective neurons in cat striate cortex were tested with bar-shaped stimuli, sequentially flashed at spatially displaced positions chosen to elicit maximal direction selectivity. Temporally overlapping flash exposures of prolonged duration (400–1000 ms) were employed at a series of onset asynchronies to explore the nature of temporal tuning of the direction-selective mechanism. In most neurons studied, direction selectivity was found to be supported by a surprisingly broad range of stimulus onset asynchronies, which was greater for longer exposure durations. These findings imply the existence of a sustained input to the direction-selective mechanism, in spite of the relatively transient nature of most cortical neurons' step responses. A model is described to illustrate how different front-end temporal filters can affect the dependence of two-flash direction selectivity on stimulus onset asynchrony. The versions of the model which successfully predict the form of the observed responses are those which combine inputs from sustained and transient filters.
Identification of cone classes in Xenopus retina by immunocytochemistry and staining with lectins and vital dyes
Authors: Zhang Jie , Kleinschmidt Jochen , Sun Paranee , Witkovsky Paul 
Published: June 2009

AbstractThe aim of the present study was to determine the number of cone classes in the Xenopus retina. We examined the dimensions and staining properties of cones, utilizing two monoclonal antibodies, COS-1 and OS-2, developed by Szel and Rohlich (1985). Living cones also were reacted with the plant lectins peanut agglutinin (PNA) and wheat germ agglutinin (WGA) and with a fluorescent stilbene dye, DIDS, which binds selectively to red-sensitive cones (Kleinschmidt, 1991; Kleinschmidt & Harosi, 1992a, b). Three cone populations were distinguished based on differences in size and staining properties. Eighty-eight percent of all cones were stained strongly by COS-1, PNA, and DIDS, but weakly by OS-2. The group of cones stained by COS-1 had the largest mean dimensions of outer segment length, width, and oil droplet diameter. COS-1 negative cones were divisible into two groups: a subclass of miniature cones (approximately 4% total cones) was stained strongly by OS-2, PNA, and DIDS. The balance, constituting approximately 9% total cones, were of intermediate size, were not stained by PNA and reacted weakly to OS-2 and DIDS. WGA stained all cones. Large, COS-1 + cones appear to be red-sensitive and belong to the class of anion-tunable cone pigments. We suggest that the intermediate size, COS-1 negative cones are blue-sensitive based on the finding that blue-sensitive chromatic horizontal cells connect to them preferentially (Witkovsky et al., work in progress). The remaining class of miniature cones may be UV-sensitive, since another amphibian, the salamander, has been shown to possess red-, blue-, and UV-sensitive cones (Perry & McNaughton, 1991).
The role of light scatter in the residual visual sensitivity of patients with complete cerebral hemispherectomy
Authors: King Sheila M. , Azzopardi Paul , Cowey Alan , Oxbury John , Oxbury Susan 
Published: June 2009

AbstractVarious residual visual capacities have been reported for the phenomenally blind field of hemispherectomized patients, providing evidence for the relative roles of cortical and subcortical pathways in vision. We attempted to characterize these functions by examining the ability of five patients to detect, localize, and discriminate high-contrast flashed, flickering and moving targets. Dependent measures were verbal, manual, and oculomotor responses. As a control for light scatter, intensity thresholds for monocular detection of targets in the hemianopic field were compared with thresholds obtained when using an additional half eyepatch to occlude the blind hemiretina of the tested eye. One unilaterally destriate patient was tested on the same tasks. In photopic conditions, none of the hemispherectomized patients could respond to visual cues in their impaired fields, whereas the destriate patient could detect, discriminate, and point to targets, and appreciate the apparent motion of stimuli across his midline. Under reduced lighting, the threshold luminance required by hemispherectomized patients to detect stimuli presented monocularly was similar to that required for their detection when all visual information was occluded in the blind field, and only available to the visual system indirectly via light scatter. In contrast, the destriate patient's monocular threshold in his blind field was substantially lower than that for stimuli directly occluded in the blind field. As we found no range of stimuli which the hemispherectomized patients could detect or discriminate that was not also associated with discriminable scattered light, we conclude that the subcortical pathways which survive hemispherectomy cannot mediate voluntary behavioural responses to visual information in the hemianopic field.
Characterization of protein phosphatases type 1 and type 2A inLimulusnervous tissue: Their light regulation in the lateral eye and evidence of involvement in the photoresponse
Authors: Edwards Samuel C. , O'Day Peter M. , Herrera Desiree C. 
Published: June 2009

AbstractThe activities of both protein phosphatases and protein kinases are responsible for the transient changes in the levels of phosphorylation and probably the functions of protein intermediates involved in the biochemical and physiological mechanisms underlying the photoresponse in photoreceptor cells from both vertebrate and invertebrate organisms. Of the known protein serine/threonine phosphatases, various forms of type I (PP 1) and type 2A (PP 2A) protein phosphatases are responsible for dephosphorylating many of the known phosphoproteins including those involved in photoreceptor cell function. In this report, we provide biochemical evidence for both PP 1– and PP 2A-like activities in the visual and nonvisual tissue of the horseshoe crab,Limulus polyphemus, that membrane and soluble forms of both enzymes are present, and that the activities of both enzymes are greater in light- than in dark-adapted lateral eyes. These activities were characterized using glycogen phosphorylasea, a substrate for both PP 1 and PP 2A, and various protein phosphatase inhibitors, including okadaic acid. We also report that okadaic acid, at concentrations required to inhibit PP 1, inhibited physiological functions of photoreceptor cells from the ventral eye, causing a delayed reduction of the resting membrane, and slowing and reducing light responses.
Functional architecture of area 17 in normal and monocularly deprived marmosets (Callithrix jacchus)
Authors: Sengpiel Frank , Troilo David , Kind Peter C. , Graham Bryan , Blakemore Colin 
Published: June 2009

AbstractThe organization of the primary visual cortex (VI) of the common marmoset (Callithrix jacchus) was studied both physiologically and by means of transneuronal labelling of geniculocortical afferents. We addressed the question whether monocular deprivation (MD) could stabilize segregation into ocular dominance (OD) columns, which are not seen in normal adult marmosets but are present in juvenile animals (Spatz, 1979, 1989). Properties of neurons in normal marmosets closely resembled those of other New-World and Old-World monkeys and orderly tangential progressions of preferred orientation were observed. However, in contrast to species that display well-defined OD columns, neurons of layer 4 in VI of normal adult marmosets received balanced inputs from the two eyes. Early MD (even though followed by prolonged binocular experience into adulthood) resulted in a reduction of cell size in laminae of the lateral geniculate nucleus with input from the deprived eye and a dramatic overall shift in ocular dominance towards the non-deprived eye in the cortex. However, isolated clusters of cells dominated by the deprived eye were found in both layers 4 and 6. Injection of lectin-conjugated horseradish peroxidase (WGA-HRP) into the deprived eye revealed elongated patches of terminal label, about 350 μm wide, in flat-mounted sections through layer 4. Afferent segregation was sharper and more regular in the region of VI representing parafoveal visual space than in that representing the fovea. Our findings support the notion that all Old-World and New-World monkeys possess the capacity for segregation of geniculocortical afferents into OD columns.
Relationship between numbers of retinal ganglion cells and lateral geniculate neurons in the rhesus monkey
Authors: Spear Peter D. , Kim Charlene B. Y. , Ahmad Aneeq , Tom Bryony W. 
Published: June 2009

AbstractStudies of the numbers of retinal ganglion cells and lateral geniculate nucleus (LGN) neurons in primates suggest that the numbers of both types of neurons may vary over a two-fold range from one individual to another. This raises the question of whether the numbers of ganglion cells and LGN neurons are related or vary independently from individual to individual. We used stereological procedures to obtain unbiased estimates of the numbers of both cell types in seven rhesus monkeys. We found no significant correlation (rs. = −0.21) between the numbers of retinal and LGN cells in the same animals. In agreement with previous studies, the average ratio of the number of retinal ganglion cells that project to the LGN and the number of LGN cells was approximately 1:1. However, this ratio varied over a two-fold range, from 0.78:1 to 1.64:1, in individual animals. These results have important implications for understanding the mechanisms of retino-geniculate development and for understanding the connectional wiring between the retina and LGN.
Neuropeptide Y immunoreactivity of a projection from the lateral thalamic nucleus to the optic tectum of the leopard frog
Authors: Chapman Angela M. , Debski Elizabeth A. 
Published: June 2009

AbstractUsing rhodamine-labelled latex beads as a retrograde tracer, we have shown that a subset of the neurons projecting from the lateral thalamic nucleus to the optic tectum of the leopard frog are neuropeptide Y-like immunoreactive (NPY-IR). In juvenile frogs, approximately twice as many lateral thalamic nucleus cells from this area project to the ipsilateral tectum as project to the contralateral tectum. NPY-IR cells make up 25% of the projection to the ipsilateral tectum and 13% of the projection to the contralateral tectum. The ipsilateral NPY-IR projection from the lateral nucleus was present in tadpoles and was similar in its characteristics to that found in the juvenile frog. However, the contralateral tectal projection was virtually nonexistent in these animals. The results of these experiments suggest that NPY from the lateral nucleus is released into the ipsilateral tectal neuropil in both the developing and adult frog.
Contrast coding by cells in the cat's striate cortex: Monocular vs. binocular detection
Authors: Anzai Akiyuki , Bearse Marcus A. , Freeman Ralph D. , Cai Daqing 
Published: June 2009

AbstractMany psychophysical studies of various visual tasks show that performance is generally better for binocular than for monocular observation. To investigate the physiological basis of this binocular advantage, we have recorded, under monocular and binocular stimulation, contrast response functions for single cells in the striate cortex of anesthetized and paralyzed cats. We applied receiver operating characteristic analysis to our data to obtain monocular and binocular neurometric functions for each cell. A contrast threshold and a slope were extracted from each neurometric function and were compared for monocular and binocular stimulation. We found that contrast thresholds and slopes varied from cell to cell but, in general, binocular contrast thresholds were lower, and binocular slopes were steeper, than their monocular counterparts. The binocular advantage ratio, the ratio of monocular to binocular thresholds for individual cells, was, on average, slightly higher than the typical ratios reported in human psychophysics. No single rule appeared to account for the various degrees of binocular summation seen in individual cells. We also found that the proportion of cells likely to contribute to contrast detection increased with stimulus contrast. Less contrast was required under binocular than under monocular stimulation to obtain the same proportion of cells that contribute to contrast detection. Based on these results, we suggest that behavioral contrast detection is carried out by a small proportion of cells that are relatively sensitive to near-threshold contrasts. Contrast sensitivity functions (CSFs) for the cell population, estimated from this hypothesis, agree well with behavioral data in both the shape of the CSF and the ratio of binocular to monocular sensitivities. We conclude that binocular summation in behavioral contrast detection may be attributed to the binocular superiority in contrast sensitivity of a small proportion of cells which are responsible for threshold contrast detection.
Receptive-field properties of displaced starburst amacrine cells change following axotomy-induced degeneration of ganglion cells
Authors: Jensen Ralph J. 
Published: June 2009

AbstractStarburst amacrine cells in the rabbit retina were labeled following an intraocular injection of the fluorescent dye, 4, 6, diamidino-2-phenylindole (DAPI). From each eye a strip of retina was removed, mounted on a platform beneath an epifluorescence microscope, and superfused with a physiological solution. The tip of a tungsten microelectrode (for extracellular recording) was visually positioned near the cell body of a DAPI-labeled starburst amacrine cell that was located in the ganglion cell layer. Light-evoked responses from the displaced starburst amacrine cells were studied in normal retinas and in retinas that had received a small electrolytic lesion near the optic disk 5–9 months beforehand. In normal retinas, a small spot of light centered over the receptive field of a displaced starburst amacrine cell in nearly all cases evoked a brief burst of spikes only at light onset. When stimulated with a large spot or an annulus of light, many cells gave a small burst of spikes at light offset. In lesioned retinas, the light responses of displaced starburst amacrine cells were recorded in areas of the retina where ganglion cells had degenerated. All cells responded with a large burst of spikes at the onset and offset of a small, centered spot of light. Large spots and annuli of light also evoked robust ON/OFF responses from these cells. The results from this study show that the receptive-field properties of displaced starburst amacrine cells change following axotomy-induced degeneration of ganglion cells. This finding indicates that changes in either synaptic transmission or the membrane properties of neurons occur in the retina following degeneration of ganglion cells.
Preproenkephalin messenger RNA-containing amacrine cells in the chicken retina identified with in situ hybridization histochemistry
Authors: Molnar Margherita , Casini Giovanni , Davis Brian M. , Brecha Nicholas C. , Bagnoli Paola 
Published: June 2009

AbstractEnkephalin peptides are present in the retina of several vertebrate species. In the avian retina, enkephalin immunoreactivity is primarily localized to a population of amacrine cells. In the present study, we determined the localization of cells expressing preproenkephalin (PPE) mRNA, which encodes the precursor of enkephalin peptides, in adult as well as in embryonic chicken retinas. The localization of PPE mRNA-expressing cells to the proximal inner nuclear layer (INL) in the adult chicken retina is similar to that of enkephalin-immunoreactive cells observed in previous studies, indicating that amacrine cells expressing PPE mRNA synthesize Met5- and Leu5-enkephalin peptides and related extended forms. Specific hybridization signal is absent in retinas at embryonic day (E) 11, but it is detected in retinas at E 15 and at hatching. PPE mRNA-expressing cells at these ages are located in the proximal INL, and they can be classified as amacrine cells on the basis of their soma size and laminar position. These findings confirm and extend previous observations on the presence of opioid peptides in amacrine cells of the chicken retina. The presence of PPE mRNA at embryonic ages, together with the evidence that enkephalins influence developmental processes, suggests that these peptides modulate retinal maturation in birds.
Effects of neurotensin on visual neurons in the superficial laminae of the hamster's superior colliculus
Authors: Zhang Yi , D. Richard , Bennett-Clarke Carol A. , Rhoades Robert W. 
Published: June 2009

AbstractAutoradiography with 125I-neurotensin in normal and enucleated hamsters was used to define the distribution of receptors for this peptide in the superficial layers of the superior colliculus (SC). Neurotensin binding sites were densely distributed in the stratum griseum superficiale (SGS), and results from the enucleated animals indicated that they were not located on retinal axons. The effects of neurotensin on individual superficial layer cells were tested in single-unit recording experiments. Neurotensin was delivered via micropressure ejection during visual stimulation (n = 75 cells), or during electrical stimulation of either the optic chiasm (OX; n = 47 cells) or visual cortex (CTX; n = 29 cells). In comparison with control values, application of neurotensin decreased visual responses of all SC cells tested to 54.1 ± 34.9% (mean ± standard deviation; range of decrement 7.5 to 100%; nine cells showed no effect or an increase in visual activity, which for four of these was ≥30%). Neurotensin application also reduced responses to electrical stimulation of either OX or CTX, respectively, to 65.8 ± 36.5% of control values (range of decrement 2.6 to 97.4%; 12 neurons showed a weak increment ≤ 30%) and 68.0 ± 38.5% (range of decrement 3.3 to 100%; five cells showed no effect or an increment, in one case ≥ 30%). Of the 25 neurons tested with both OX and CTX stimulation, the correlation of evoked response suppression by neurotensin was highly significant (r = 0.70; P < 0.001). This suggests that the suppressive effects of neurotensin were common to both pathways. To test whether the inhibitory effects of neurotensin were presynaptic or postsynaptic, Mg2+ ions were ejected iontophoretically to abolish synaptic responses, and the neurons (n = 16) were activated by iontophoresis of glutamate and then tested with neurotensin. Neurotensin reduced the glutamate-evoked responses to an average 59.3 ± 37.9% of control values (range 2.3 to 92.5%; one cell showed an increment >30%). This result suggests that the site of action of neurotensin is most likely postsynaptic.