bluuebunny/crossref_metadata_2025_split huggingface dataset:
Developmental expression of protein kinase C immunoreactivity in rod bipolar cells of the rabbit retina
Authors: Casini Giovanni , Grassi Achille , Trasarti Luigi , Bagnoli Paola 
Published: June 2009

AbstractRod bipolar cells constitute the second-order neuron in the rod pathway. Previous investigations of the rabbit retina have evaluated the development of other components of the rod pathway, namely the dopaminergic and All amacrine cell populations. To gain further insights into the maturation of this retinal circuitry, we studied the development of rod bipolar cells, identified with antibodies directed to the α isoform of protein kinase C (PKC), in the rabbit retina. Lightly immunostained PKC-immunoreactive (IR) somata are first observed at postnatal day (PND) 6 in the distal inner nuclear layer (INL). Immunostaining is also observed in the outer plexiform layer (OPL), indicating the presence of PKC-IR dendrites. PKC-IR axons are present in the INL oriented toward the inner plexiform layer (IPL). Several of them terminate with enlarged structures resembling growth cones. At PND 8, some immunostained terminal bulbs, characteristic of rod bipolar cells, are detected in the proximal IPL. PKC-IR cells at PND 11 (eye opening) display stronger immunostaining and more mature characteristics than at earlier ages. The dendritic arborizations of these cells in the OPL and their axon terminals in the IPL attain mature morphology at later ages (PND 30 or older). The density of PKC-IR cells shows a peak at PND 11 followed by a drastic decrease up to adulthood. The total number of PKC-IR cells increases from PND 6 to PND 11 and then it remains almost unchanged until adulthood. The mosaic of PKC-IR cells is nonrandom in some retinal locations at PND 6, but the overall regularity index at PND 6 is lower than at older ages. The present data provide a comprehensive evaluation of the development of rod bipolar cells in the postnatal rabbit retina and are consistent with those previously reported for dopaminergic and All amacrine cell populations, indicating that different components of the rod pathway follow a similar pattern of maturation, presumably allowing the rod pathway to be functional at eye opening.
NADPH diaphorase activity in mammalian retinas is modulated by the state of visual adaptation
Authors: Zemel Esther , Eyal Orly , Lei Bo , Perlman Ido 
Published: June 2009

AbstractNADPH diaphorase histochemistry is commonly used to identify cells containing nitric oxide synthase (NOS), the enzyme catalyzing the production of nitric oxide from L-arginine. NADPH diaphorase activity and NOS immunostaining was demonstrated in different cells of the vertebrate retina; photoreceptors, horizontal cells, amacrine cells, ganglion cells, and Müller cells. However, the physiological role of nitric oxide (NO) in the retina has yet to be elucidated. In this study, we tested the assumption that NADPH diaphorase activity in the retinas of rabbits and rats depended on the state of visual adaptation. In the rabbit, light adaptation enhanced NADPH diaphorase activity in amacrine cells and practically eliminated it in horizontal cells. Dark adaptation induced the opposite effects; the NADPH diaphorase activity was reduced in amacrine cells and enhanced in horizontal cells. Retinas from eyes that were injected intravitreally with L-glutamate exhibited a pattern of NADPH diaphorase activity that was similar to that seen in dark-adapted retinas. In rats, the NADPH diaphorase activity of amacrine and horizontal cells exhibited adaptation dependency similar to that of the rabbit retina. But, the most pronounced effect of dark adaptation in the rat's retina was an enhancement of NADPH diaphorase activity in Müller cells, especially of the endfoot region. Assuming that NADPH diaphorase activity is a marker for NOS, these findings suggest that NO production in the mammalian retina is modulated by the level of ambient illumination and support the notion that NO plays a physiological role in the retina.
Contrast discrimination: A model and a hypothesis concerning the role of cholinergic modulation in contrast perception
Authors: Smith Andrew T. 
Published: June 2009

AbstractA model of contrast discrimination performance in human observers is developed and then extended to cover effects on performance of anticholinergic drugs. It is shown that it is necessary to assume that neural noise increases at high spatial frequencies in order to provide a satisfactory model of variations in discrimination performance with spatial frequency. The model results are compared with the results of empirical studies in which the effects of the muscarinic antagonist scopolamine (hyoscine) on contrast discrimination performance in human observers are examined. The purpose of the pharmacological work is to test the hypothesis that the differential contrast gain found psychophysically at different spatial frequencies might reflect differential facilitation by extrinsic cholinergic neurons. Contrast discrimination and contrast increment detection are found to be impaired by scopolamine in a manner that depends on both spatial frequency and base contrast. By comparing the empirical data with the predictions of the model, it is concluded that contrast constancy may reflect differential cholinergic modulation.
Contributions of individual layer 2–5 spiny neurons to local circuits in macaque primary visual cortex
Authors: Callaway Edward M. , Wiser Anne K. 
Published: June 2009

AbstractWe studied excitatory local circuits in the macaque primary visual cortex (V1) to investigate their relationships to the magnocellular (M) and parvocellular (P) streams. Sixty-two intracellularly labeled spiny neurons in layers 2–5 were analyzed. We made detailed observations of the laminar and columnar specificity of axonal arbors and noted correlations with dendritic arbors. We find evidence for considerable mixing of M and P streams by the local circuitry in V1. Such mixing is provided by neurons in the primary geniculate recipient layer 4C, as well as by neurons in both the supragranular and infragranular layers. We were also interested in possible differences in the axonal projections of neurons with different dendritic morphologies. We found that layer 4B spiny stellate and pyramidal neurons have similar axonal arbors. However, we identified two types of layer 5 pyramidal neuron. The majority have a conventional pyramidal dendritic morphology, a dense axonal arbor in layers 2–4B, and do not project to the white matter. Layer 5 projection neurons have an unusual “backbranching” dendritic morphology (apical dendritic branches arc downward rather than upward) and weak or no axonal arborization in layers 2–4B, but have long horizontal axonal projections in layer 5B. We find no strong projection from layer 5 pyramidal neurons to layer 6. In macaque V1 there appears to be no single source of strong local input to layer 6; only a minority of cells in layers 2–5 have axonal branches in layer 6 and these are sparse. Our results suggest that local circuits in V1 mediate interactions between M and P input that are complex and not easily incorporated into a simple framework.
Similarities and differences among inner retinal neurons revealed by the expression of reporter transgenes controlled by Brn-3a, Brn-3b, and Brn-3c promotor sequences
Authors: Xiang Mengqing , Zhou Lijuan , Nathans Jeremy 
Published: June 2009

AbstractBrn-3a, Brn-3b, and Brn-3c are highly homologous POU-domain transcription factors that are expressed in subsets of retinal ganglion cells. From each of the mouse Brn-3 genes, a DNA segment ranging in size from 4.6 to 13.4 kb and located immediately upstream of the start site of translation was joined to a human placental alkaline phosphatase (AP) reporter cDNA. Following the introduction of each construct into the mouse germline, a total of 19 transgenic lines were obtained, of which 16 expressed the AP reporter in the retina. Unexpectedly, at least 14 of the 16 expressing lines showed AP activity in subsets of amacrine cells, and these subsets typically differed among mouse lines injected with the same construct. Transgene expression was also found in ganglion cells in four lines and bipolar cells in seven lines. In all cases AP activity was confined to cells in the inner nuclear layer and the ganglion cell layer. The expression of Brn-3 transgenes in multiple cell types in the inner retina is reminiscent of earlier experiments in which visual pigment transgenes were found to be expressed in multiple cell types in the outer retina. Taken together, these observations suggest that anatomically and/or functionally related retinal neurons contain partially overlapping transcriptional regulatory specificities.
Passive electrical cable properties and synaptic excitation of tiger salamander retinal ganglion cells
Authors: Taylor W. Rowland , Mittman Scott , Copenhagen David R. 
Published: June 2009

AbstractThe passive electrical properties of 17 ON-OFF retinal ganglion cells were derived from electrophysiological recordings. The parameters for each cells' equivalent model were obtained from the transient current responses to small step changes in clamp potential. Thirteen of the cells could be adequately approximated by a spherical soma connected to an equivalent dendritic cable. Estimates for the cell input conductance (GN), membrane time constant (τm), the dendritic-to-soma conductance ratio (ρ), and the normalized electrotonic length (L) were obtained (mean ± standard deviation,n= 13):GN= 580 ± 530 pS, τm= 97 ±72 ms, ρ = 2.8 ± 2.8, andL= 0.34 ± 0.13. Series resistance averaged 32 ± 11 MΩ The mean of the derived soma diameters was 18 ± 6 μm and the mean diameter and length of the equivalent cables were 1.4 ± 0.6 and 470 ± 90 μm, respectively. The average of the specific membrane conductances, 1.67 ± 1.08 S/cm2, corresponded to a membrane resistivity of 60 kΩ-cm2. Computer simulations of synaptic inputs were performed on a representative model, with an electrode at the soma and using the worst-case configuration, in which all synaptic inputs were confined to the tips of the dendrites. We draw three conclusions from the modeling: (1) Under voltage clamp, fast, spontaneous EPSCs would be significantly attenuated and slowed while the time course of the slower, light-evoked non-NMDA and NMDA EPSCs would be minimally distorted by dendritic filtering. (2) Excitatory synaptic reversal potentials can be accurately determined under voltage clamp. (3) In the absence of GABAergic and glycinergic inhibition, the efficacy at the soma of excitatory conductance changes is essentially independent of their dendritic location. The specific membrane resistivity appears to represent a good compromise between having a small membrane time constant and minimal EPSP attenuation.
Influence of rod adaptation upon cone responses to light offset in humans: I. Results in normal observers
Authors: Frumkes Thomas E. , Lange Gudrun , Denny Noreen , Beczkowska Iwona 
Published: June 2009

AbstractDark-adapted rods exert a tonic suppressive influence upon cone-mediated sensitivity to rapid flicker, a phenomenon called suppressive rod-cone interaction (SRC1). However, rod dark adaptation has negligible influence upon cone-mediated thresholds measured with more usual psychophysical procedures. The present study separately examined the influences of rod light and dark adaptation upon cone-mediated sensitivity to transient increases or decreases in illumination using sawtooth flicker with rapid-on (ramp-off) or rapid-off (ramp-on) waveforms. In the parafoveal retina, cones alone were stimulated with flicker by spatially superimposing longand short-wavelength stimuli presented in counterphase and matched in scotopic illuminance. Several different adaptation procedures were used. For higher (>4 Hz) frequencies, sensitivity of cones to both waveforms is nearly identical under any condition of adaptation; sensitivity decreases as rods progressively dark adapt. A considerably different situation exists for slower frequencies (1–4 Hz). Sensitivity of cones to rapid-off flicker is appreciably greater under light-adapted conditions confirming recent observations by Bowen et al. (1989). But as rods progressively dark adapt, sensitivity of cones to rapid-off waveforms decreases considerably while sensitivity to rapid-on waveforms is much less affected; in the totally dark-adapted eye, sensitivity to both waveforms is identical. These results confirm and extend recent physiological observations in amphibian retina (Frumkes & Wu, 1990) suggesting that SRCI specifically involves responses to transient decreases in illumination.
Electroretinograms (ERGs) and visual-evoked potentials (VEPs) elicited by pattern displacement
Authors: Wu Shuang , Armington John C. , Reeves Adam 
Published: June 2009

AbstractThe relation between the amplitude of visual responses to a checkerboard stimulus and the degree of lateral displacement of the checks was examined across different check sizes with simultaneously recorded electroretinograms (ERGs) and visual-evoked potentials (VEPs). The amplitudes of both the b–wave and the after-potential of the ERG increase linearly with pattern displacement. However, the major components of the VEP (N70 and P100) were smaller than expected from linearity for both small checks with small displacements (thresholding) and for large checks with large displacements (saturation). These results suggest that the ERG is proportional to the number of receptors stimulated, but the VEP reflects neural processes influenced by the spatial structure of the stimulus.
Peptidergic neurons of teleost retinas
Authors: Marshak David W. 
Published: June 2009

AbstractIn retinas of teleost fish, neuropeptides typically have subtle, modulatory actions. The peptide effects typically have long latencies and durations, and, in some instances, they are known to be mediated by second messengers. Peptidergic neurons in teleost retinas have certain morphological features in common that are consistent with their function. Most peptidergic neurons are stratified amacrine cells with long, varicose processes; the processes of peptidergic centrifugal axons are also narrowly stratified and ramify extensively in the retina. The peptidergic amacrine cells are relatively infrequent, and, likewise, the centrifugal axons originate from a small number of perikarya in the brain. Cells that are so sparsely distributed and whose processes overlap so extensively are better-suited for modulation than for conveying detailed representations of visual space.
Vertical disparity and binocular vision in the praying mantis
Authors: Rossel Samuel , Mathis Ute , Collett Thomas 
Published: June 2009

AbstractWe have investigated how the binocular control of prey capture in the praying mantis is affected by abnormally large vertical disparities, which were introduced by prisms placed in front of the eyes. The position of a target on the two retinae determines both the magnitude of head saccades made to fixate a target and its perceived distance. Over the wholerange of vertical disparities tested (up to at least 30 deg), the frequency of fixating saccades is normal while the amplitude of their vertical component is a compromise between the saccades specified by each eye individually. Distance measurements are not affected by imposed vertical disparities. But the larger the vertical disparity, the more reluctant the mantid is to strike at the target until disparities exceed 15 deg when no strikes are elicited at all.
A slowly inactivating K+ current in retinal ganglion cells from postnatal rat
Authors: Sucher Nikolaus J. , Lipton Stuart A. 
Published: June 2009

AbstractThe whole-cell configuration of the patch-clamp technique was used to study voltage-gated K+ conductances in retinal ganglion cells from postnatal rat. Retinal ganglion cells were fluorescently labeled in situ, dissociated from the retina, and maintained in culture. With physiological solutions in the bath and the pipette, depolarizing voltage steps from physiological holding potentials activated Na+-(INa), Ca2+ (ICa), and K+ -currents studied previously in retinal ganglion cells. Here we report on a slowly decaying K+ current, not heretofore reported in rat. With 4-AP, TEA, and Co2+ in the bath, to block IA, IK, and IK(Ca), respectively, a slowly decaying outward current was activated from —80 mV by steps positive to —40 mV. This current was present in 92% of all ganglion cells tested (n = 83). It activated within 10 ms and inactivated with a voltage-independent time constant of about 70 ms at 35°C. Inactivation was voltage-dependent, half-maximal at —55 mV, and almost complete at 0 mV. The current was blocked by internal Cs+ and TEA, or by external application of 1 mM Ba2+, but not by 3 mM extracellular Co2+. The biophysical and pharmacological properties of this current are distinctly different from those of slowly inactivating K+ currents studied in other rat neurons. It was very similar, however, to a slowly inactivating K+ current previously reported in ganglion cells of tiger salamander retina. This last finding indicates conservation of a defined K+ channel type in functionally related cells in both lower vertebrates and mammals.
Photoreceptors in a primitive mammal, the South American opossum, Didelphis marsupialis aurita: Characterization with anti-opsin immunolabeling
Authors: Ahnelt Peter K. , Hokoç Jan Nora , Röhlich Pal 
Published: June 2009

AbstractThe retinas of placental mammals appear to lack the large number and morphological diversity of cone subtypes found in diurnal reptiles. We have now studied the photoreceptor layer of a South American marsupial (Didelphis marsupialis aurita) by peanut agglutinin labeling of the cone sheath and by labeling of cone outer segments with monoclonal anti-visual pigment antibodies that have been proven to consistently label middle-to-long wavelength (COS-1) and short-wavelength (OS-2) cone subpopulations in placental mammals. Besides a dominant rod population (max. = 400,000/mm2) four subtypes of cones (max. = 3000/mm2) were identified. The outer segments of three cone subtypes were labeled by COS-1: a double cone with a principal cone containing a colorless oil droplet, a single cone with oil droplet, and another single cone. A second group of single cones lacking oil droplets was labeled by OS-2 antibody. The topography of these cone subtypes showed striking anisotropies. The COS-1 labeled single cones without oil droplets were found all over the retina and constituted the dominant population in the area centralis located in the temporal quadrant of the upper, tapetal hemisphere. The population of OS-2 labeled cones was also ubiquitous although slightly higher in the upper hemisphere (200/mm2). The COS-1 labeled cones bearing an oil droplet, including the principal member of double cones, were concentrated (800/mm2) in the inferior, non-tapetal half of the retina. The two spectral types of single cones resemble those of dichromatic photopic systems in most placental mammals. The additional set of COS-1 labeled cones is a distinct marsupial feature. The presence of oil droplets in this cone subpopulation, its absence in the area centralis, and the correlation with the non-tapetal inferior hemisphere suggest a functional specialization, possibly for mesopic conditions. Thus, sauropsid features have been retained but probably with a modified function.
Responses of neurons in cat striate cortex to vernier offsets in reverse contrast stimuli
Authors: Swindale N.v. 
Published: June 2009

AbstractThis paper examines how the responses of cells in area 17 of the cat vary as a function of the vernier offset between a bright and a dark bar. The study was prompted by the finding that human vernier acuity is reduced for bars or edges of opposite contrast sign (Mather & Morgan, 1986; O'Shea & Mitchell, 1990). Both simple and complex cells showed V-shaped tuning curves for reverse contrast stimuli: i.e. response was minimum at alignment, and increased with increasing vernier offset. For vernier bars with the same contrast sign, γ-shaped tuning curves were found, as reported earlier (Swindale & Cynader, 1986). Sensitivity to offset was inversely correlated in the two paradigms. However, complex cells with high sensitivity to offsets in a normal vernier stimulus were significantly less sensitive to offsets in reverse contrast stimuli. A cell's response to a vernier stimulus in which both bars are bright can be predicted by the shape of its orientation tuning curve, if the vernier stimulus is approximated by a single bar with an orientation equal to that of a line joining the midpoints of the two component bars (Swindale & Cynader, 1986). This approximation did not hold for the reverse contrast condition: orientation tuning curves for compound barswere broad and shallow, rather than bimodal, with peaks up to 40 deg from the preferred orientation. Results from simple cells were compared with predictions made by a linear model of the receptive field. The model predicted the V-shaped tuning curves found for reverse contrast stimuli. It also predicted that absolute values of tuning slopes for vernier offsets in reverse contrast stimuli might sometimes be higher than with normal stimuli. This was observed in some simple cells. The model was unable to explain the shape of orientation tuning curves for compound bars, nor could it explain the breakdown of the equivalent orientation approximation.
Excitatory and inhibitory neurotransmitters in the nucleus rotundus of pigeons
Authors: Gao Hong-Feng , Wu Gang-Yi , Frost Barrie J. , Wang Shu-Rong 
Published: June 2009

AbstractRotundal neurons in pigeons (Columba livia) were examined for the effects of glutamate and its agonists NMDA and AMPA, antagonists CPP and CNQX, as well as of GABA and its antagonist bicuculline, on visual and tectal stimulation-evoked responses. Glutamate applied by iontophoresis excited all 48 rotundal cells tested, and this excitation was blocked by CNQX but not by CPP in 98% of cases, with 2% of cells being blocked by either CNQX or CPP. Out of 21 cells excited by AMPA, 20 were also excited by NMDA, indicating that AMPA and NMDA receptors may coexist in most rotundal cells. Action potentials were evoked in 36 additional cells by electrical stimulation applied to the tectum and they were also blocked by CNQX but not CPP. Visual responses recorded from a further eight luminance units and 21 motion-sensitive units were also blocked by CNQX and not CPP. On the other hand, GABA inhibited visual responses as well as responses evoked by tectal stimulation. An inhibitory period following tectal stimulation was eliminated by bicuculline. Taken together, these results indicate that glutamate may be an excitatory transmitter acting predominantly through non-NMDA receptors (AMPA receptors) in tectorotundal transmission. Meanwhile, GABA may be an inhibitory transmitter in the pigeon nucleus rotundus.