bluuebunny/crossref_metadata_2025_split huggingface dataset:
Binocular interaction in the optokinetic system of the crabCarcinus maenas(L.): Optokinetic gain modified by bilateral image flow
Authors: Nalbach Hans-Ortwin , Thier Peter , Varjú Dezsö 
Published: June 2009

AbstractWe recorded optokinetic eye movements of the crab,Carcinus maenas, in split-drum experiments. The patterns were either oscillated in antiphase on both sides mimicking translational image flow or they were oscillated in phase producing rotational image flow. Eye movements elicited by the rotational stimulus were larger than those produced by the pseudotranslational pattern movements. The smaller response to the latter is mainly a consequence of binocular interaction, the strength of which depends on both the phase-shift and amplitude of pattern oscillation. We develop two hypotheses to explain our results: either (1) signals from each eye modify the gain of the linkage signals coming from the other eye, or (2) the signals coming from the other eye modify the gain of the control loop itself. Quantitative evaluation of the data favors the second of these two hypotheses, which comprises the models of Barnes and Horridge (1969) and Nalbach et al. (1985). In addition, we found that it is the signals from the two slow channels of the crab's movement-detecting system that are transferred from one eye to the other, while signals of the fastest channel act almost exclusively ipsilaterally. We discuss our results as an adaptation by which an animal with panoramic vision compensates exclusively the rotational component of image flow during locomotion. The fact that freely walking crabs distinguish the two components of image flow better than restrained crabs indicates that further visual and nonvisual signals help to disentangle image flow.
Colocalization of glycine in substance P-amacrine cells of the larval tiger salamander retina
Authors: Watt Carl B. , Florack Valarie J. 
Published: June 2009

AbstractThe present study was performed as part of a systematic examination of glycine's coexistence with other classical transmitters and neuropeptides in neuronal populations of the larval tiger salamander retina. Substance P immunocytochemistry was combined with either glycine immunocytochemistry or autoradiography of glycine high-affinity uptake to examine whether tiger salamander substance P-amacrine cells express these glycine markers. Double-label analyses revealed two populations of substance P-amacrine cells that express glycine immunoreactivity and glycine high-affinity uptake. The large majority of double-labeled cells were situated in the innermost cell row of the inner nuclear layer, while a smaller number were located in the inner nuclear layer in the second cell row distal to the inner plexiform layer. Double-label immunocytochemistry revealed that these double-labeled cells accounted for 91.7% of substance P-immunoreactive amacrine cells. A slightly lower percentage (90.1%) of substance P-amacrine cells were found to exhibit a glycine high-affinity uptake mechanism. Substance P-amacrine cells that did not co-label for markers of glycine activity were situated in the innermost cell row of the inner nuclear layer. Substance P-immunoreactive displaced amacrine cells were not observed to co-label for either glycine immunoreactivity or glycine high-affinity uptake.The present study reveals that the large majority of substance P-amacrine cells in the larval tiger salamander retina co-express markers of glycine activity. This finding suggests a functional diversity in the population of tiger salamander substance P-amacrine cells relative to their coexisting relationship with a major inhibitory neurotransmitter.
Concentrations of phosphatidylinositol 4,5-bisphosphate and inositol 1,4,5-trisphosphate within the distal segment of squid photoreceptors
Authors: Szuts Ete Z. 
Published: June 2009

AbstractAlthough inositol trisphosphate (InsP3) is a key substance in phototransduction of invertebrate photoreceptors, its intracellular concentration remains unknown. The purpose of this study was to assay its concentration and the concentration of its precursor, phosphatidylinositol bisphosphate (PtdInsP2), within squid photoreceptors. Rhabdomeric membranes were purified and their PtdInsP2content measured with a phosphate assay after the extracted phospholipids were deacylated and separated by ion-exchange chromatography. At least 75% of the total PtdInsP2found in the retinal homogenate was associated with the plasma membranes of the rhabdomeric microvilli, where PtdInsP2was 3.1 ± 0.7% of the total phospholipids, a level comparable to values published for rat brain. In terms of rhodopsin, microvillar membranes contained 3.7 ± 0.9 mol PtdInsP2/mol rho. The InsP3content of living retinas was measured with a radioreceptor assay. The basal content of dark-adapted retinas was 0.15 ± 0.05 InsP3/rho, equivalent to 30 ± 9 nmol/g tissue that is about twice that of rat brains. Flash illumination (≈lms in duration) that photoactivated 1% of rhodopsin increased the level about fivefold to 0.68 ± 0.22 lnsP3/rho. Corresponding decrease in PtdInsP2was undetectable as it was within measurement errors. For PtdInsP2, the measured content corresponds to 5.6 ± 1.4 mM within the volume of rhabdomere. Maximal light-induced concentration of InsP3is calculated to be 1.2 ± 0.4 mM within the cytoplasm of the distal segment. Each photoactivated rhodopsin leads to the formation of 500 InsP3molecules when measured 15 s after the flash. Thus, high concentration of InsP3in these cells is primarily due to restricted intracellular volumes rather than to high amplification by the enzyme cascade. The InsP3concentration within squid photoreceptors is the highest yet reported for any transducing cell and may indicate the involvement of relatively low affinity receptors or channels during invertebrate phototransduction.
Nonlinearity of the inhibition underlying retinal directional selectivity
Authors: Amthor Franklin R. , Grzywacz Norberto M. 
Published: June 2009

AbstractAn important mechanism for the discrimination of direction of motion in the retina is a spatially asymmetric inhibition. This inhibition has been postulated to operate either as a subtraction, like in difference-of-Gaussians' models, or as a division, like in shunting-inhibition models of directional selectivity. The latter, but not the former, is nonlinear. This raises the question of whether the inhibitory mechanism involved in directional selectivity is nonlinear. To investigate this issue, we studied the linearity of the contrast dependence of the extracellularly recorded responses to apparent motions in ON-OFF directionally selective ganglion cells of the rabbit retina. The results show that the inhibition underlying directional selectivity is nonlinear and fits shunting-inhibition models well. Other biophysical mechanisms that might account for the type of nonlinearity observed in the data are also considered.
Spectral sensitivity of ON and OFF responses from the optic nerve of goldfish
Authors: DeMarco Paul J. , Powers Maureen K. 
Published: June 2009

AbstractThe vertebrate retina processes visual information in parallel neural pathways known as the ON and OFF pathways. These pathways encode increments and decrements of light independently as excitatory responses. We examined the photopic spectral response of ON and OFF mechanisms in goldfish by measuring the sensitivity of optic nerve responses to the onset and termination of stimuli of various wavelengths. Using various adapting backgrounds, we found that the ON and OFF responses have different spectral sensitivities. The weighting of the cone inputs to the responses was estimated by an algebraic summation model. This model suggests that for the ON response, input from S-cones is stronger and more independent than for the OFF response, and M- and L-cones show stronger antagonism in the ON response than in the OFF response. The OFF response probably receives input from all cone types, but spectral antagonism is weak and its dominant input is from L-cones.
Synaptic organization of two types of amacrine cells with CRF-like immunoreactivity in the turtle retina
Authors: Williamson Douglas E. , Eldred William D. 
Published: June 2009

AbstractThe ultrastructural features and synaptic contacts of two amacrine cell types with corticotropin-releasing factor-like immunoreactivity in the turtle retina were examined using electron immunocytochemistry. Type A cells were found only in the visual streak and had elongated dendritic arborizations that ran parallel to the visual streak. These cells arborized primarily in stratum 1 and near the border of strata 2 and 3 of the inner plexiform layer, with some processes extending into stratum 5. Type B cells were found only ventral to the visual streak and arborized primarily in a wide band in strata 4 and 5, with sparse dendritic arborizations in stratum 1.There was a diffuse cytoplasmic reaction product within each cell type; however, large labeled vesicles were rarely observed. Type A amacrine cells received many conventional synaptic contacts from amacrine cells in stratum 1 and at the border of strata 2 and 3, but only a small number of contacts in stratum 5. Bipolar synaptic contacts onto type A amacrine cells were observed in strata 1 and at the border of strata 2 and 3. The only positively identified synaptic outputs of type A cells were conventional synapses onto amacrine cells in strata 1 and at the border of 2 and 3. Type B amacrine cells received synaptic contacts from amacrine cells in strata 1 and 5, and bipolar cell synaptic input in stratum 5. They made conventional synapses onto amacrine cells in strata 1 and 5, and onto bipolar cells in stratum 5. We also found conventional synaptic contacts between unlabeled amacrine cells and type B amacrine cells outside of the primary layers of stratification. In addition, there were specialized junctions observed between type A cell profiles in stratum 1 and between type B cell profiles in stratum 5. The unique regional distributions of the type A and B cells, as well as their differences in synaptic connectivity, suggested that these amacrine cells play distinct physiological roles although they contain the same neuropeptide.
Topographic organization, number, and laminar distribution of callosal cells connecting visual cortical areas 17 and 18 of normally pigmented and Siamese cats
Authors: Berman Nancy E. J. , Grant Simon 
Published: June 2009

AbstractThe callosal connections between visual cortical areas 17 and 18 in adult normally pigmented and “Boston” Siamese cats were studied using degeneration methods, and by transport of WGA-HRP combined with electrophysiological mapping. In normal cats, over 90% of callosal neurons were located in the supragranular layers. The supragranular callosal cell zone spanned the area 17/18 border and extended, on average, some 2–3 mm into both areas to occupy a territory which was roughly co-extensive with the distribution of callosal terminations in these areas. The region of the visual field adjoining the vertical meridian that was represented by neurons in the supragranular callosal cell zone was shown to increase systematically with decreasing visual elevation. Thus, close to the area centralis, receptive-field centers recorded from within this zone extended only up to 5 deg into the contralateral hemifield but at elevations of -10 deg and -40 deg they extended as far as 8 deg and 14 deg, respectively, into this hemifield. This suggests an element of visual non-correspondence in the callosal pathway between these cortical areas, which may be an essential substrate for “coarse” stereopsis at the visual midline.In the Siamese cats, the callosal cell and termination zones in areas 17 and 18 were expanded in width compared to the normal animals, but the major components were less robust. The area 17/18 border was often devoid of callosal axons and, in particular, the number of supragranular layer neurons participating in the pathway were drastically reduced, to only about 25% of those found in the normally pigmented adults. The callosal zones contained representations of the contralateral and ipsilateral hemifields that were roughly mirror-symmetric about the vertical meridian, and both hemifield representations increased with decreasing visual elevation. The extent and severity of the anomalies observed were similar across individual cats, regardless of whether a strabismus was also present. The callosal pathway between these visual cortical areas in the Siamese cat has been considered “silent,” since nearly all neurons within its territory are activated only by the contralateral eye. The paucity of supragranular pyramidal neurons involved in the pathway may explain this silence.
Effects of selective pressure block of Y-type optic nerve fibers on the receptive-field properties of neurons in the striate cortex of the cat
Authors: Burke W. , Dreher B. , Michalski A. , Cleland B. G. , Rowe M. H. 
Published: June 2009

AbstractIn an aseptic operation under surgical anesthesia, one optic nerve of a cat was exposed and subjected to pressure by means of a special cuff. The conduction of impulses through the pressurized region was monitored by means of electrodes which remained in the animal after the operation. The pressure was adjusted to selectively eliminate conduction in the largest fibers (Y-type) but not in the medium-size fibers (X-type). The conduction block is probably due to a demyelination and remains complete for about 3 weeks. Within 2 weeks after the pressure-block operation, recordings were made from single neurons in the striate cortex (area 17, area VI) of the cat anesthetized with N2O/O2mixture supplemented by continuous intravenous infusion of barbiturate. Neurons were activated visuallyviathe normal eye andviathe eye with the pressure-blocked optic nerve (“Y-blocked eye”). Several properties of the receptive fields of single neurons in area 17 such as S (simple) or C (complex) type of receptive-field organization, size of discharge fields, orientation tuning, direction-selectivity indices, and end-zone inhibition appear to be unaffected by removal of the Y-type input. On the other hand, the peak discharge rates to stimuli presentedviathe Y-blocked eye were significantly lower than those to stimuli presentedviathe normal eye. As a result, the eye-dominance histogram was shifted markedly towards the normal eye implying that there is a significant excitatory Y-type input to area 17. In a substantial proportion of area 17 neurons, this input converges onto the cells which receive also non-Y-type inputs. In one respect, velocity sensitivity, removal of the Y input had a weak but significant effect. In particular, C (but not S) cells when activatedviathe normal eye responded optimally at slightly higher stimulus velocities than when activatedviathe Y-blocked eye. These results suggest that the Y input makes a distinct contribution to velocity sensitivity in area 17 but only in C-type neurons. Overall, our results lead us to the conclusion that the Y-type input to the striate cortex of the cat makes a significant contribution to the strength of the excitatory response of many neurons in this area. However, the contributions of Y-type input to the mechanism(s) underlying many of the receptive-field properties of neurons in this area are not distinguishable from those of the non-Y-type visual inputs.
A psychophysically motivated model for two-dimensional motion perception
Authors: Wilson Hugh R. , Ferrera Vincent P. , Yo Christopher 
Published: June 2009

AbstractA quantitative model is developed to predict the perceived direction of moving two-dimensional patterns. The model incorporates both a simple motion energy pathway and a “texture boundary motion” pathway that incorporates response squaring before the extraction of motion energy. These pathways correspond to Fourier and non-Fourier motion pathways and are hypothesized to reflect processing in the VI-MT and V1-V2-MT pathway, respectively. A cosine-weighted sum of these pathways followed by competitive feedback inhibition accurately predicts the perceived direction for patterns composed of two cosine gratings at different orientations (“plaids”). The model also predicts direction discrimination, differences between foveal and peripheral viewing, changes in perceived direction with exposure duration, motion masking, and motion transparency.
Visual callosal projections in the adult ferret
Authors: Grigonis Antony M. , Rayos Del Sol-Padua Rosemary B. , Murphy E. Hazel 
Published: June 2009

AbstractThe laminar and tangential organization of visual callosal projections of areas 17 and 18 were investigated in the adult ferret, using histochemical methods to visualize axonally transported horseradish peroxidase (HRP). Normal adult ferrets were given injections of HRP throughout one visual cortex or had gelfoam soaked in HRP applied to the transected corpus callosum. The ferret callosal cell distribution has a greater tangential extent in area 18 than in area 17. In addition, the radial organization of callosal cells in areas 17 and 18 differs: three times as many infragranular cells are present in area 18 than in area 17, although the number of supragranular cells is similar for both areas 17 and 18. Since the projections of alpha retinal ganglion cells are reported to be exclusively contralateral in the ferret (Vitek et al., 1985), callosal projections may make a major contribution to the binocularity of neurons in area 18.
Light-dependent delay in the falling phase of the retinal rod photoresponse
Authors: Pepperberg David R. , Cornwall M. Carter , Kahlert Martina , Hofmann Klaus Peter , Jin Jing , Jones Gregor J. , Ripps Harris 
Published: June 2009

AbstractUsing suction electrodes, photocurrent responses to 100-ms saturating flashes were recorded from isolated retinal rods of the larval-stage tiger salamander (Ambystoma tigrinum). The delay period (Te) that preceded recovery of the dark current by a criterion amount (3 pA) was analyzed in relation to the flash intensity (If), and to the corresponding fractional bleach (R*0/Rtot) of the visual pigment;R*0/Rtotwas compared withR*s/Rtotthe fractional bleach at which the peak level of activated transducin approaches saturation. Over an approximately 8 In unit range ofIfthat included the predicted value ofR*s/Rtot, Teincreased linearly with InIf. Within the linear range, the slope of the function yielded an apparent exponential time constant (TC) of 1.7 ± 0.2 s (mean ± S.D.). Background light reduced the value ofTcmeasured at a given flash intensity but preserved a range over whichTcincreased linearly with InIf; the linear-range slope was similar to that measured in the absence of background light. The intensity dependence ofTcresembles that of a delay (Td) seen in light-scattering experiments on bovine retinas, which describes the period of essentially complete activation of transducin following a bright flash; the slope of the function relatingTdand In flash intensity is thought to reflect the lifetime of photoactivated visual pigment (R*) (Pepperberg et al., 1988; Kahlert et al., 1990). The present data suggest that the electrophysiological delay has a similar basis in the deactivation kinetics ofR*, and thatTcrepresentsTR* the lifetime ofR* in the phototransduction process. The results furthermore suggest a preservation of the “dark-adapted” value ofTR* within the investigated range of background intensity.
Localization of phototransduction in Limulus ventral photoreceptors: A demonstration using cell-free rhabdomeric vesicles
Authors: Bacigalupo Juan , Johnson Edwin C. 
Published: June 2009

AbstractSecond messengers are involved in a number of cellular responses to a variety of stimuli. Diffusion of these second messengers likely will determine the speed and efficiency of such responses. Localization, particularly in large cells, would enhance the efficiency of such transduction systems by restricting the volume in which this diffusion takes place and thereby limiting the diffusion of soluble messengers. Phototransduction in Limulus ventral photoreceptors involves second-messenger systems; the volume of this cell is quite large, but the effect of a single photoexcited rhodopsin molecule is exerted over light-dependent channels localized within a very small area of the plasma membrane. In order to investigate localization of phototransduction in these photoreceptors, we have compared the light responses of small vesicles (photoballs) excised from these cells with those of the intact photoreceptors. We found that the basic kinetics of excitation and adaptation of the photoballs are essentially identical to those of the intact cell. This indicates that all of the necessary machinery for phototransduction is present and intact in the photoball and that any diffusion of second messengers that affect the normal light response of the cell must occur within a region at least as small as our photoballs (on the order of 1 μm3).
Localization of GABAAreceptor subtypes in the tiger salamander retina
Authors: Yang Chen-YU , Lin Zhen-Shi , Yazulla Stephen 
Published: June 2009

AbstractDry autoradiography was used to determine the distribution of GABAAbinding sites in tiger salamander retina. High-affinity binding of [3H]-flunitrazepam ([3H]-FNZ) was used to localize benzodiazepine receptors (BZR) and [3H]-muscimol was used to localize the GABAArecognition site. Specific [3H]-FNZ binding was present only in the inner retina, primarily in the inner plexiform layer (IPL). Co-incubation with GABA enhanced [3H]-FNZ binding by 20–50%. [3H]-muscimol binding was found throughout the IPL and in the outer plexiform layer (OPL). Mouse monoclonal antibodies 62–3G1 and BD-17, that recognize the GABAAβ2, β3polypeptides, and BD-24, that recognizes the GABAAα1, polypeptide, did not label either the OPL or IPL, despite numerous variations in the fixation and immunoprocessing methods. GABAAreceptor location, as revealed by [3H]-muscimol binding, matches the distribution of presumed GABAergic terminals in the OPL and IPL. We suggest that there are at least two subtypes of GABAAreceptor in the tiger salamander retina: one type is present only in the inner retina, primarily in the IPL and is functionally coupled to BZRs; the other type is located in the OPL and is not coupled to the BZRs. Furthermore, GABAAreceptors in the tiger salamander retina appear to be of a different epitope than GABAAreceptors in numerous other preparations that are recognized by mAbs 62–3G1, BD-17, and BD-24.
Transfer of contrast sensitivity in linear visual networks
Authors: Watson Andrew B. 
Published: June 2009

AbstractContrast sensitivity is a useful measure of the ability of an observer to distinguish contrast signals from noise. Although usually applied to human observers, contrast sensitivity can also be defined operationally for individual visual neurons. In a model linear neuron consisting of a filter and noise source, this operational measure is a function of filter gain, noise power spectrum, signal duration, and a performance criterion. This definition allows one to relate the sensitivities of linear neurons at different levels in the visual pathway. Mathematical formulae describing these relationships are derived, and the general model is applied to the specific problem of relating the sensitivities of parvocellular LGN neurons and cortical simple cells in the primate.