bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of the nucleus isthmi in Xenopus, II: Branching patterns of contralaterally projecting isthmotectal axons during maturation of binocular maps
Authors: Udin Susan B. 
Published: June 2009

AbstractThe tectum of Xenopus frogs receives input from both eyes. The contralateral eye's projection reaches the tectum directly, via the optic nerve, and the ipsilateral eye's projection reaches the tectum indirectly, via the nucleus isthmi. Under normal conditions, the topography of the ipsilateral map relayed from the nucleus isthmi is in register with the topography of the retinotectal map from the contralateral eye. During development, the process of aligning the two maps is complicated by the dramatic changes in binocular overlap of the two eyes' visual fields which take place during late tadpole and juvenile stages. The goal of this study is to determine the branching patterns of contralaterally projecting isthmotectal axons before, during, and after the period of rapid eye migration.Isthmotectal axons were filled by anterograde transport of horseradish peroxidase (HRP) from the nucleus isthmi. The results show that crossed isthmotectal axons enter the entire extent of the tectum before binocular overlap begins to increase. Therefore, binocular overlap is not necessary for the initial isthmotectal projection to span the tectum. The density of isthmotectal branches rises dramatically at the same time that the eyes begin to shift. During the period when eye migration is most rapid, many isthmotectal axons form arbors which resemble adult arbors but which extend over greater proportions of the tectal surface.The axons appear to be directed toward appropriate mediolateral positions as they enter the tectum. Their trajectories are roughly rostocaudal, with relatively little change along the mediolateral dimension. These data, when combined with available physiological data, suggest that mediolateral order is initially established by vision-independent mechanisms but can be altered by vision-dependent mechanisms. Rostrocaudal order becomes discernable only at the time when binocular visual cues become available and appears to be established primarily on the basis of the activity of the retinotectal and isthmotectal axons.
A neural model of foveal light adaptation and afterimage formation
Authors: Wilson Hugh R. 
Published: June 2009

AbstractPsychophysical research has documented the existence of three processes in light adaptation: a fast subtractive process, a divisive process that is fast at light onset and slower at light offset, and a very slow subtractive process (Hayhoe et al., 1987). In the neural model developed here, the fast subtractive process is identified with horizontal cell feedback onto cones and the divisive process with amacrine cell feedback onto bipolar cells. The very slow subtractive process is identified with the modulatory feedback circuit from amacrines via interplexiform cells to horizontal cells. A nonlinear dynamical model is developed incorporating these aspects of retinal circuitry along with both ON- and OFF-center M and P pathways. This model is shown to account for many aspects of foveal light adaptation, including negative afterimage formation, and to explain a number of the physiological differences between M and P ganglion cells, including their differing contrast-response functions.
The DAPI-3 amacrine cells of the rabbit retina
Authors: Wright Layne L. , Macqueen Colin L. , Elston Guy N. , Young Heather M. , Pow David V. , Vaney David I. 
Published: June 2009

AbstractIn the rabbit retina, the nuclear dye, 4,6, diarnidino-2-phenylindole (DAPI), selectively labels a third type of amacrine cell, in addition to the previously characterized type a and type b cholinergic amacrine cells. In this study, these “DAPI-3” amacrine cells have been characterized with respect to their somatic distribution, dendritic morphology, and neurotransmitter content by combining intracellular injection of biotinylated tracers with wholemount immunocytochemistry. There are about 100,000 DAPI-3 amacrine cells in total, accounting for 2% of all amacrine cells in the rabbit retina, and their cell density ranges from about 130 cells/mm2 in far-peripheral retina to 770 cells/mm2 in the visual streak. The thin varicose dendrites of the DAPI-3 amacrine cells form a convoluted dendritic tree that is symmetrically bistratified in S1/S2 and S4 of the inner plexiform layer. Tracer coupling shows that the DAPI-3 amacrine cells have a fivefold dendritic-field overlap in each sublamina, with the gaps in the arborization of each cell being occupied by dendrites from neighboring cells. The DAPI-3 amacrine cells consistently show the strongest glycine immunoreactivity in the rabbit retina and they also accumulate exogenous [3H]-glycine to a high level. By contrast, the All amacrine cells, which are the best characterized glycinergic cells in the retina, are amongst the most weakly labelled of the glycine-immunopositive amacrine cells. The DAPI-3 amacrine cells costratify narrowly with the cholinergic amacrine cells and the On-Off direction-selective ganglion cells, suggesting that they may play an important role in movement detection.
Concentrations of biogenic amines in fundal layers in chickens with normal visual experience, deprivation, and after reserpine application
Authors: Ohngemach Sibylle , Hagel Gabi , Schaeffel Frank 
Published: June 2009

AbstractPrevious experiments in chickens have shown that dopamine released from the retina may be one of the messengers controlling the growth of the underlying sclera. It is also possible, however, that the apparent relationship between dopamine and myopia is secondary and artifactual. We have done experiments to assess this hypothesis. Using High Pressure Liquid Chromatography with electrochemical detection (HPLC-ED), we have asked whether changes in dopamine metabolism are restricted to the local retinal regions in which myopia was locally induced. Furthermore, we have measured the concentrations of biogenic amines separately in different fundal layers (vitreous, retina, choroid, and sclera) to find out how changes induced by “deprivation” (= removal of high spatial frequencies from the retinal image by translucent eye occluders which produce “deprivation myopia”) are transmitted through these layers. Finally, we have repeated the deprivation experiments after intravitreal application of the irreversible dopamine re-uptake blocker reserpine to see how suppression of dopaminergic transmission affects these changes. We found that (1) Alterations in retinal dopamine metabolism were indeed restricted to the retinal areas in which myopia was induced. (2) The retina was the major source of dopamine release with a steep gradient both to the vitreal and choroidal side. Vitreal content was about one-tenth, choroidal content about one-third, and scleral content about one-twentieth of that of the retina. (3) There was a drop by about 40% in vitreal dopamine, DOPAC (3,4-dihydroxyphenylacetic acid) and HVA (homovanilic acid) concentrations following deprivation which occurred already at a time where little changes could yet be seen in their total retinal contents. (4) Choroidal and scleral dopamine levels were not affected by deprivation, indicating that other messengers must relay the information to the sclera. (5) A single intravitreal injection of reserpine lowered dopamine and HVA levels in retina and vitreous for at least 10 days in a dose-dependent fashion and diminished or suppressed further effects of deprivation on these compounds. DOPAC levels continued to change upon deprivation even after reserpine injection (Fig. 3). Our results suggest that the release rates of dopamine from retinal amacrine cells can be estimated from vitreal dopamine concentrations; furthermore, they are in line with the hypothesis that there is an inverse relationship between dopamine release and axial eye growth rates. Although our experiments do not ultimately prove that dopamine has a functional role in the visual control of eye growth, they are in line with this notion.
Depth perception and evoked brain activity: The influence of horizontal disparity and visual field location
Authors: Skrandies Wolfgang 
Published: June 2009

AbstractThe perception of dynamic random-dot stereograms (RDS) depends on the physiological fusion of horizontally disparate binocular visual input. Thus, the use of RDS offers the possibility to study selectively cortical processing of visual information in man. We investigated the influence of horizontal disparity on the scalp topography of RDS evoked brain activity in 33 healthy subjects. Stereoscopic checkerboard patterns were presented in the center or lateralized in the left or right visual field with horizontal disparities changing at temporal frequencies of six or eight depth reversals/s using different disparity values ranging from 3.5 to 28 min of arc. In 11 subjects evoked potential fields were recorded from 16 electrodes, and 21 subjects participated in 30-channel recordings with electrodes located over the parietal and occipital brain areas. Stimulation frequency-related brain activity was obtained with all disparity values; however, with large or small disparities the potential field strength decreased significantly while largest responses were obtained with intermediate disparities. Significant differences were observed in RDS evoked brain activity when central and lateralized stimulus locations were compared. With lateral stimuli (extending from the fovea to 17.1-deg eccentricity) maximal amplitudes were obtained at larger disparities than with central stimuli. In addition there were pronounced differences between brain activity evoked with stimuli presented in the left or right visual field; however, there were very similar evoked potential signals recorded from electrodes located over the left and right hemispheres. Our findings indicate that the processing of disparity information with lateralized stimuli is different from the processing in the center of the visual field. In addition, lateralized stimulation yields a significant disparity tuning mainly with stereoscopic targets occurring to the right from the fixation point (but not with stimuli to the left) suggesting a functional difference between the visual half-fields.
Serial inhibitory synapses in retina
Authors: Zhang Jian , Jung Chang-Sub , Slaughter Malcolm M. 
Published: June 2009

AbstractWhole-cell voltage clamp in the retinal slice and intracellular current clamp in the intact retina were used to study inhibitory interactions in the inner plexiform layer. Picrotoxin or strychnine reduced inhibitory, light-evoked currents in a majority of ganglion cells. However, in nearly a third of the ganglion cells, each of these antagonists enhanced the inhibitory synaptic current. All inhibitory current was blocked by the addition of the other antagonist. This indicates a cross-inhibition between GABAergic and glycinergic feedforward pathways. Blocking of GABAARs with SR95531 shortened the time course of both excitatory and inhibitory synaptic currents in ganglion cells. Application of picrotoxin, which blocked both GABAARs and GABACRs, produced the opposite effect. Recordings in the intact retina indicated that the light responses of ON bipolar cells, sustained ON, and transient ON-OFF third-order neurons were all made more transient by SR95531 and made more sustained by picrotoxin. The data suggest that a GABACfeedback pathway to bipolar cells makes light responses more phasic and that this feedback is inhibited through a GABAAR pathway. Consequently, the balance between GABAAR and GABACR inhibition regulates the time course of inputs to ganglion cells.
Light-induced modulation of coupling between AII amacrine cells in the rabbit retina
Authors: Bloomfield Stewart A. , Xin Daiyan , Osborne Tristan 
Published: June 2009

AbstractThe rod-driven, AII amacrine cells in the mammalian retina maintain homologous gap junctions with one another as well as heterologous gap junctions withon-cone bipolar cells. We used background illumination to study whether changes in the adaptational state of the retina affected the permeabilities of these two sets of gap junctions. To access changes in permeability, we injected single AII amacrine cells with the biotinylated tracer, Neurobiotin, and measured the extent of tracer coupling to neighboring AII cells and neighboring cone bipolar cells. We also measured the center-receptive field size of All cells to assess concomitant changes in electrical coupling. Our results indicate that in well dark-adapted retinas, AII cells form relatively small networks averaging 20 amacrine cells and covering about 75 μm. The size of these networks matched closely to the size of AII cellon-center receptive fields. However, over most of their operating range, AII cells formed dramatically larger networks, averaging 326 amacrine cells, which corresponded to an increased receptive-field size. As the retina was light adapted beyond the operating range of the AII cells, they uncoupled to form networks comparable in size to those seen in well dark-adapted retinas. Our results, then, indicate that the adaptational state of the retina has a profound effect on the extent of electrical coupling between AII amacrine cells. Although we observed light-induced changes in the number of tracer-coupled cone bipolar cells, these appeared to be an epiphenomenon of changes in homologous coupling between AII amacrine cells. Therefore, in contrast to the robust changes in AII–AII coupling produced by background illumination, our data provided no evidence of a light-induced modulation of coupling between AII cells andon-cone bipolar cells.
Dynamic shifts of the contrast-response function
Authors: Victor Jonathan D. , Conte Mary M. , Purpura Keith P. 
Published: June 2009

AbstractWe recorded visual evoked potentials in response to square-wave contrast-reversal checkerboards undergoing a transition in the mean contrast level. Checkerboards were modulated at 4.22 Hz (8.45-Hz reversal rate). After each set of 16 cycles of reversals, stimulus contrast abruptly switched between a “high” contrast level (0.06 to 1.0) to a “low” contrast level (0.03 to 0.5). Higher contrasts attenuated responses to lower contrasts by up to a factor of 2 during the period immediately following the contrast change. Contrast-response functions derived from the initial second following a conditioning contrast shifted by a factor of 2–4 along the contrast axis. For low-contrast stimuli, response phase was an advancing function of the contrast level in the immediately preceding second. For high-contrast stimuli, response phase was independent of the prior contrast history. Steady stimulation for periods as long as 1 min produced only minor effects on response amplitude, and no detectable effects on response phase. These observations delineate the dynamics of a contrast gain control in human vision.
Solar pruning of retinal rods in albino rainbow trout
Authors: Allen Donald M. , Hallows Ted E. 
Published: June 2009

AbstractMorphology of the central retina and scotopic visual sensitivity were compared in juvenile albino and normally pigmented rainbow trout living under natural and reduced daylight. Outdoor albinos avoided exposing their eyes to direct sunlight, whereas normals were indifferent to it. After 4 months outdoors (Σ10,000 lux in albinos, Σ100,000 lux in normals), albinos had severely truncated or missing rod outer segments (ROS) and some missing rod ellipsoids, but normal numbers of photoreceptor nuclei and fully intact cones. Albino estimated ROS volume was only 7.1% of normal in July, but increased to 20% by the following February, mainlyviaan increase in numbers of ROS. However, in albinos moved indoors October 7 and exposed to 10–30 lux ambient daylight, both the number and length of ROS increased significantly, with estimated ROS volume reaching 95% of normal by 34 days. Albinos generally had more phagosomes (Σ3 X normal) and more macrophages (Σ2 X normal) in their outer retina. An optomotor reflex was used to define the effect of ROS volume on the ability to respond visually during dark adaptation. In July, albinos and normals from outdoor raceways (3 months) or indoor raceways (35 days) showed equal sensitivity after first being placed in darkness, but after 1 h in darkness, outdoor albinos with 6% of normal ROS volume were 2.0 log units less sensitive than indoor or outdoor normals, whereas indoor albinos with 53% of normal ROS volume were only 0.7 log units less sensitive. This verifies that most rod cell bodies of albino trout can persist without functional ROS in indirect sunlight, and can regrow functional outer segments in dim daylight. This finding is distinct from the extensive retinal light damage observed in albino rats exposed to more moderate cyclic light, in which entire rod cells degenerate early on.
Characterization of aldehyde dehydrogenase-positive amacrine cells restricted in distribution to the dorsal retina
Authors: Milam Ann H. , Possin Daniel E. , Huang Jing , Fariss Robert N. , Flannery John G. , Saari John C. 
Published: June 2009

AbstractA class 1 aldehyde dehydrogenase (ALDH) catalyzes oxidation of retinaldehyde to retinoic acid in bovine retina. We used immunocytochemistry andin situhybridization to localize this enzyme in adult and fetal bovine retinas. Specific ALDH immunoreactivity was present in the cytoplasm of wide-field amacrine cells restricted in distribution to the dorsal part of the adult retina. The somata diameters ranged from ∼8 μ to ∼15 μ, and the cells increased in density from ∼125 cells/mm2near the horizontal meridian to ∼425 cells/mm2in the superior far periphery. The ALDH-positive cells had somata on both sides of the inner plexiform layer (IPL) and processes in two IPL strata. The majority of ALDH-positive cells were unreactive with antibodies against known amacrine cell enzymes and neurotransmitters, including GABA and glycine. The ALDH-positive amacrine cells also did not react with anti-cellular retinoic acid-binding protein, which was present in a subset of GABA-positive amacrine cells. In flat-mounted retinas processed byin situhybridization, the larger ALDH-positive amacrine cells tended to be more heavily labeled. In addition to amacrine cells, Müller cell processes in the inner retina were weakly immunoreactive for ALDH; however, these glial cells did not contain ALDH mRNA. The pattern of ALDH expression in fetal bovine retinas was documented by immunocytochemistry. No ALDH reactivity was found before 5.5 months; for the remainder of the fetal period, ALDH immunoreactivity was present in amacrine cells similar to those in adult retina. The ALDH-positive amacrine cells in bovine retina are novel, being limited in distribution to the dorsal retina and unlabeled with other amacrine cell-specific markers. Identification of ALDH in amacrine cells provides additional evidence that cells of the inner retina are involved in retinoid metabolism.
Evidence for only depolarizing rod bipolar cells in the primate retina
Authors: Dolan Robert P. , Schiller Peter H. 
Published: June 2009

AbstractThe mammalian rod bipolar, for which only one class has been identified, has been described as being hyperpolarizing by some investigators and depolarizing by others. We now report the effects of 2-amino-4-phosphonobutyrate (APB), a potent blocker of depolarizing bipolar cells, on visual behavior in the dark-adapted monkey. While in mesopic and photopic conditions only the monkeys' ability to detect incremental stimuli is impaired, under scotopic conditions all light mediated response in the monkey is eliminated. Assuming APB is acting on rod bipolars in the same fashion as it does on cone bipolars, we conclude that the primate rod bipolars all depolarize to light and that the ON and OFF channels are formed by the amacrine cell network.
Quantitative stimulus-response studies on sustained ganglion cells in the frog retina
Authors: Garcia Rene , Gaillard Frederic 
Published: June 2009

Abstract“Sustained” visual units, i.e. nonerasable (R1) and erasable (R2) units as commonly described, were recorded in the superficial layers of the rostral optic tectum of Rana esculenta and their neuronal activity (expressed as the mean firing frequency ) was quantitatively analyzed The mean value of the exponent α of the velocity function of the erasable R1 units was found to be 0.46 and the constant k to be about 24.7. The optimal stimulus diameter was equal to 2.6 deg. For the whole population of the erasable units, the exponent α was found to be between 0.36–0.75 (mean value ≈ 0.56, i.e. largely different from the values currently reported for such units) and was independent of the stimulus diameter (D = 0.6–6 deg). However, the constant k of the velocity function (range: 8.2–37.7) varied with D. Most of the erasable units (called “mixed R1-R2” units) therefore showed an R1-type velocity function with an exponent α ≈ 0.5 and a constant k ≈ 25 but reacted to other parameters as did “typical” R2 units: (i) their neuronal response was related to the stimulus diameter by a logarithmic function with a maximum obtained for D = 2.4 deg; and (ii) a variation of about 4–17% on either side of the average value of was observed, independent either of the stimulus velocity or of the diameter of the stimulus. Results are compared to known quantitative data, and the use of stimulus-response relationships as a tool for classification is discussed.
Integration regions for vernier acuity in the cat: Comparative aspects of cortical scaling
Authors: Berkley M. A. 
Published: June 2009

AbstractThe spatial region involved in vernier acuity (integration region) was behaviorally determined in cats and compared with published human data and cortical scaling parameters for the two species. Integration region was estimated from vernier thresholds obtained with: (1) gaps of various sizes between the contiguous ends of the offset contours (gap effects); and (2) irrelevant contours placed at various distances from the vernier offset (interference effects). The gap studies showed that thresholds decreased as the gap grew from 0 to 4–7 min but then increased progressively with separations greater than 7 min. In the interference studies, thresholds were increased 2–6 times when the irrelevant contours were located within 40 min of the offset. Comparing these data with available human measures showed large species differences. Converting the interference distances for both species into cortical distances using published estimates of cortical magnification factor did not resolve the discrepancy. However, a comparison of the cat data with published human data, taken at an eccentricity at which the estimated human cortical magnification factor equals that of the cat, i.e. 7 deg, showed the effects of gap size and interference distance on vernier thresholds to be remarkably similar between the two species. This similarity supports the hypothesis that positional acuity depends upon mechanisms in striate cortex, and also suggests that such acuity may be mediated by a generic neural mechanism common to mammals.