bluuebunny/crossref_metadata_2025_split huggingface dataset:
Response linearity and kinetics of the cat retina: The bipolar cell component of the dark-adapted electroretinogram
Authors: Robson J. G. , Frishman L. J. 
Published: June 2009

AbstractThe electroretinogram (ERG) of the dark-adapted cat eye in response to brief ganzfeld flashes of a wide range of intensities was recorded after intravitreal injection of n-methyl dl aspartate (NMdlA, cumulative intravitreal concentration of 1.3–3.9 mM) to suppress inner-retinal components, and after intravitreal dl or L-2-amino-4-phosphonobutyric acid (dl-APB, 1–3 mM; l-APB, 1.2 mM) and 6-cyano-7-nitroquinoxaline-2, 3 dione (CNQX, 40–60 µM), to suppress all post-receptoral neuronal responses. Rod PII, the ERG component arising from rod bipolar cells, was derived by subtracting records obtained after APB and CNQX from post-NMDLA records. When we measured the derived response at fixed times after the stimulus, we found that PII initially increased in proportion to stimulus intensity without any sign of a threshold. The leading edge of PII at early times after the stimulus, when the response was still small, was well described byV(t) =kI(t −td)5wherekis a constant,Iis the intensity of the stimulus, andtdis a brief delay of about 3 ms. Correspondingly, the time for the response to rise to an arbitrary small criterion voltageVcritwas adequately fitted bytcrit=td+ (Vcrit/kI)1/5. The time course of the leading edge of the PII response can be interpreted to indicate that the mechanism generating PII introduces three stages of temporal integration in addition to the three stages that are provided by the mechanism of the rod photoreceptors. This finding is consistent with the operation within the rod bipolar cell of a G-protein cascade similar to that in the rods.
Simulation of the Aii amacrine cell of mammalian retina: Functional consequences of electrical coupling and regenerative membrane properties
Authors: Smith Robert G. , Vardi Noga 
Published: June 2009

AbstractThe Aii amacrine cell of mammalian retina collects signals from several hundred rods and is hypothesized to transmit quantal “single-photon” signals at scotopic (starlight) intensities. One problem for this theory is that the quantal signal from one rod when summed with noise from neighboring rods would be lost if some mechanism did not exist for removing the noise. Several features of the Aii might together accomplish such a noise removal operation: The Aii is interconnected into a syncytial network by gap junctions, suggesting a noise-averaging function, and a quantal signal from one rod appears in five Aii cells due to anatomical divergence. Furthermore, the Aii contains voltage-gated Na+ and K+ channels and fires slow action potentials in vitro, suggesting that it could selectively amplify quantal photon signals embedded in uncorrelated noise. To test this hypothesis, we simulated a square array of AII somas (Rm = 25,000 Ohm-cm2) interconnected by gap junctions using a compartmental model. Simulated noisy inputs to the Aii produced noise (3.5 mV) uncorrelated between adjacent cells, and a gap junction conductance of 200 pS reduced the noise by a factor of 2.5, consistent with theory. Voltage-gated Na+ and K+ channels (Na+: 4 nS, K+: 0.4 nS) produced slow action potentials similar to those found in vitro in the presence of noise. For a narrow range of Na+ and coupling conductance, quantal photon events (-5–10 mV) were amplified nonlinearly by subthreshold regenerative events in the presence of noise. A lower coupling conductance produced spurious action potentials, and a greater conductance reduced amplification. Since the presence of noise in the weakly coupled circuit readily initiates action potentials that tend to spread throughout the AII network, we speculate that this tendency might be controlled in a negative feedback loop by up-modulating coupling or other synaptic conductances in response to spiking activity.
The morphology of the dorsal eye of the hydrothermal vent shrimp,Rimicaris exoculata
Authors: O'Neill Patrick J. , Jinks Robert N. , Herzog Erik D. , Battelle Barbara-Anne , Kass Leonard , Renninger George H. , Chamberlain Steven C. 
Published: June 2009

AbstractThe bresiliid shrimp,Rimicaris exoculata, lives in large masses on the sides of hydrothermal vent chimneys at two sites on the Mid-Atlantic Ridge. Although essentially no daylight penetrates to depths of 3500 m, very dim light is emitted from the hydrothermal vents themselves. To exploit this light,R. exoculatahas evolved a modified compound eye on its dorsal surface that occupies about 0.5% of the animal's body volume. The eye's morphology suggests that it is extremely sensitive to light. The cornea of the dorsal eye is smooth with no dioptric apparatus. The retina consists of two wing-shaped lobes that are fused across the midline anteriorly. The rhabdomeral segments of the 7000 ommatidia form a compact layer of photosensitive membrane with an entrance aperture of more than 26 mm2. Within this layer, the volume density of rhabdom is more than 70%. Below the rhabdomeral segments, a thick layer of white diffusing cells scatters light upward into the photoreceptors. The arhabdomeral segments of the five to seven photoreceptors of each ommatidium are mere strands of cytoplasm that expand to accommodate the photoreceptor nuclei. The rhabdom is comprised of well-organized arrays of microvilli, each with a cytoskeletal core. The rhabdomeral segment cytoplasm contains mitochondria, but little else. The perikaryon contains a band of mitochondria, but has only small amounts of endoplasmic reticulum. There is no ultrastructural indication of photosensitive membrane cycling in these photoreceptors. Vestigial screening pigment cells and screening pigment granules within the photoreceptors are both restricted to the inner surface of the layer of the white diffusing cells. Below the retina, photoreceptor axons converge in a fan-shaped array to enter the dorsal surface of the brain. The eye's size and structure are consistent with a role for vision in shrimp living at abyssal hydrothermal vents.
The influence of center-surround antagonism on light adaptation in cones in the retina of the turtle
Authors: Burkhardt Dwight A. 
Published: June 2009

AbstractThe influence of center-surround antagonism on light adaptation in cone photoreceptors was investigated by intracellular recording from red-sensitive cones in the retina of the turtle, Pseudemys scripta elegans. Test flashes of 0.15-mm diameter were applied at the center of background fields of 0.25-mm or 2.2-mm diameter. Immediately upon expanding the background from 0.25 to 2.2 mm, the membrane potential depolarized by about 1–4 mV. The test flash response was enhanced if the depolarization was primarily due to synaptic feedback from horizontal cells, whereas the response was attenuated if the prolonged depolarization, an intrinsic response of the cone, was the dominant source of the depolarization. After several seconds, however, only the synaptic depolarization was maintained so maintained illumination of the large background field produced an enhancement of the cone's incremental sensitivity. The enhancement was examined in detail in steady-state conditions by obtaining amplitude-intensity measurements for centered test flashes on steady background fields over a large range of intensity. The effect of the large background field at any fixed intensity was fairly well described as a vertical (upward) shift of the amplitude-intensity curve obtained on the small field. This operation constitutes a quasi-subtractive mechanism of light adaptation and might provide a basis for the sort of subtractive mechanisms inferred from psychophysical studies of human vision. The enhancement was quantified by measuring the incremental sensitivity over four decades of background illumination. The magnitude of the enhancement increased with background intensity and then tended to stabilize at higher background intensities. The maximum difference in incremental sensitivity obtained on the large vs. small background field averaged 0.46 log unit (±0.12 s.d.). At higher background intensities, incremental sensitivity conformed to Weber's Law behavior about equally well for flashes applied on either small or large background fields. In sum, the present results provide evidence for an additional mechanism of light adaptation in cone photoreceptors by showing that the incremental light sensitivity, initially set by mechanisms in the outer segment, can be modulated some three-fold by synaptic feedback at the inner segment of the cone.
Are the preferred directions of neurons in cat extrastriate cortex related to optic flow?
Authors: Sherk Helen , Kim Jong-Nam , Mulligan Kathleen 
Published: June 2009

AbstractIt has been proposed that one area of extrastriate cortex in the cat, the lateral suprasylvian area (LS), plays an important role in visual analysis during locomotion (Rauschecker et al., 1987). Cells in LS reportedly tend to prefer directions along a trajectory originating at the center of gaze, and passing outward through the receptive-field center. Such directions coincide with the directions of image motion in an optic flow field, the pattern seen by locomoting observers when they fixate the point towards which they are heading (Gibson, 1950). We re-examined this issue for cells in LS with receptive fields in the lower visual field. Cells recorded posterior to Horsley-Clarke A2 showed a clear correlation between preferred direction and receptive-field location, but not that predicted: preferred directions were generally orthogonal to “optic flow” directions. Since these cells were all located posterior to those in studies showing a bias for “optic flow” directions, we hypothesized that there are two cell populations within LS, an anterior population that tends to prefer radial-outward directions, and a posterior population that tends to prefer directions orthogonal to radial. Data from earlier mapping experiments (Sherk & Mulligan, 1993) supported this idea.
Ontogeny of the opioid growth factor, [Met5]-enkephalin, and its binding activity in the rat retina
Authors: Isayama Tomoki , Hurst W. Jeffrey , McLaughlin Patricia J. , Zagon Ian S. 
Published: June 2009

AbstractThe endogenous opioid peptide [Met5]-enkephalin is a tonically active opioid growth factor (OGF) with an inhibitory action on DNA synthesis in the developing rat retina. In this study, the ontogeny of the spatial and temporal expression of OGF and its binding activity was examined. OGF-like immunoreactivity was detected in the retina at gestation day (E) 20, but not at E18, and was localized to ganglion cell and neuroblast layers; immunochemical reaction was no longer seen in the retina by postnatal day 6. Native OGF was further identified and characterized by high-performance liquid chromatography (HPLC) studies and immunodot assays, which revealed that [Met5]-enkephalin was present in the neonatal, but not adult, rat retina. OGF binding activity was detected as early as E18 using [125I]-[Met5]-enkephalin andin vitroreceptor autoradiography. Little OGF binding activity was noted for prenatal retinas, but appreciable activity was observed from birth to postnatal day 4; no OGF binding could be detected after postnatal day 5 or in the adult. These results reveal the transient appearance of the OGF, [Met5]-enkephalin, and its receptor binding activity in the developing mammalian retina, and show that their ontogeny coincides with the timetable of DNA synthesis of retinal neuroblasts.
A comparison of receptive field and tracer coupling size of horizontal cells in the rabbit retina
Authors: Bloomfield Stewart A. , Xin Daiyan , Persky Seth E. 
Published: June 2009

AbstractThe large receptive fields of retinal horizontal cells are thought to reflect extensive electrical coupling via gap junctions. It was shown recently that the biotinylated tracers, biocytin and Neurobiotin, provide remarkable images of coupling between many types of retinal neuron, including horizontal cells. Further, these demonstrations of tracer coupling between horizontal cells rivaled the size of their receptive fields, suggesting that the pattern of tracer coupling may provide some index of the extent of electrical coupling. We studied this question by comparing the receptive field and tracer coupling size of dark-adapted horizontal cells recorded in the superfused, isolated retina-eyecup of the rabbit. Both the edge-to-edge receptive field and space constants (λ) were computed for each cell using a long, narrow slit of light displaced across the retinal surface. Cells were subsequently labeled by iontophoretic injection of Neurobiotin. The axonless A-type horizontal cells showed extensive, homologous tracer coupling in groups greater than 1000 covering distances averaging about 2 mm. The axon-bearing B-type horizontal cells were less extensively tracer coupled, showing homologous coupling of the somatic endings in groups of about 100 cells spanning approximately 400 μm and a separate homologous coupling of the axon terminal endings covering only about 275 μm. Moreover, we observed a remarkable, linear relationship between the size of the receptive fields of each of the three horizontal cell endings and the magnitude of their tracer coupling. Our findings suggest that the extent of tracer coupling provides a strong, linear index of the magnitude of electrical current flow, as derived from receptive-field measures, across groups of coupled horizontal cells. These data thus provide the first direct evidence that the receptive-field size of horizontal cells is related to the extent of their coupling via gap junctions.
Identification of sodium channel subtypes induced in cultured retinal pigment epithelium cells
Authors: Dawes Heather , Mandel Gail , Matthews Gary 
Published: June 2009

AbstractRecent electrophysiological experiments have shown that retinal pigment epithelium (RPE) cells begin to produce neuronal-type voltage-dependent sodium currents when placed in dissociated cell culture. In this study, the sodium channel types induced in cultured rat RPE cells were identified. Sodium channel mRNAs encoding two distinct alpha subunits were detected in the cultured RPE cells, brain type II/IIA, and a novel rat mRNA which we have termed RET1. These two sodium channel types may correspond to the TTX-sensitive and TTX-insensitive components of sodium current reported previously in cultured rat RPE cells.
Visual receptor cycle in normal and period mutant Drosophila: Microspectrophotometry, electrophysiology, and ultrastructural morphometry
Authors: Chen De-Mao , Christianson J. Scott , Sapp Randall J. , Stark William S. 
Published: June 2009

AbstractVisual pigment, sensitivity, and rhabdomere size were measured throughout a 12-h light/12-h dark cycle in Drosophila. Visual pigment and sensitivity were measured during subsequent constant darkness [dark/dark (D/D)]. MSP (microspectrophotometry) and the ERG (electroretinogram) revealed a cycling of visual pigment and sensitivity, respectively. A visual pigment decrease of 40% was noted at 4 h after light onset that recovered 2–4 h later in white-eyed (otherwise wild-type, w per+) flies. The ERG sensitivity [in w per+ flies in light/dark (L/D)] decreased by 75% at 4 h after light onset, more than expected if mediated by visual pigment (MSP) changes alone. ERG sensitivity begins decreasing 8 h before light onset while decreases in visual pigment begin 2 h after light onset. These cycles continue in constant darkness (D/D), suggesting a circadian rhythm. White-eyed period (per) mutants show similar cycles of visual pigment level and sensitivity in L/D; per's alterations, if any on the D/D cycles were subtle. The cross-sectional areas of rhabdomeres in w per+ were measured using electron micrographic (EM) morphometry. Area changed little through the L/D cycle.
Microspectrophotometric determinations of rod visual pigments in some adult and larval Australian amphibians
Authors: Partridge J. C. , Speare P. , Shand J. , Muntz W. R. A. , Williams D. McB. 
Published: June 2009

AbstractVisual pigments from the red rods of adults of eight species of Australian anuran amphibians, from a variety of habitats, were analyzed by microspectrophotometry. The λmax in all cases fell between 502 nm and 506 nm, and the absorption spectra were well fitted by an A1-based visual pigment template curve. Red rod pigments were also analyzed for a number of tadpoles. In some cases the data were best fitted with an A1based visual pigment template, in other cases with an A2-based template, and finally some tadpoles appeared to have mixtures of the two pigments.
Background illumination reduces horizontal cell receptive-field size in both normal and 6-hydroxydopamine-lesioned goldfish retinas
Authors: Baldridge William H. , Ball Alexander K. 
Published: June 2009

AbstractThe effect of background illumination on horizontal cell receptive-field size and dye coupling was investigated in isolated superfused goldfish retinas. Background illumination reduced both horizontal cell receptive-field size and dye coupling. The effect of light on horizontal cell receptive-field size was mimicked by treating the retina with 20 μM dopamine. To test the hypothesis that the effects of light were due to endogenous dopamine release, the effect of light was studied in goldfish retinas in which dopaminergic interplexiform cells were lesioned using 6-hydroxydopamine treatment. In lesioned retinas, background illumination reduced both horizontal cell receptive-field size and dye coupling. Furthermore, the effect of background illumination on unlesioned animals could not be blocked by prior treatment with the D1 dopamine receptor antagonist SCH-23390. These results suggest that, in goldfish retina, dopamine release is not the only mechanism by which horizontal cell receptive-field size could be reduced by light.
Spatial geometry of the dopamine innervation in the avascular area of the human fovea
Authors: Savy Claudine , Simon Axelle , Nguyen-Legros Jeanine 
Published: June 2009

AbstractThe dopamine (DA) innervation, labeled by tyrosine hydroxylase immunohistochemistry in a wholemounted human retina, is described in the avascular area of the fovea. Eleven DA neurons give rise to this innervation, among which five are interplexiform cells, so that the DA innervation consists of two plexuses: one is internal and is formed by the dendrites of all of the DA cells, and the other is external and is formed by the scleral processes of the interplexiform cells. Five concentric zones are delineated according to the focal plane in which the internal DA plexus is observed. The central zone 1 contains DA processes crossing in all directions. Zones 2 and 3 do not contain any cell bodies. In zone 3 the internal plexus begins to undergo a concentric arrangement, which is clearly observed in zones 4 and 5. The external DA innervation displays a different appearance in zones 1, 2, and 3, in which it consists of vertically oriented thin processes and terminals penetrating the outer nuclear layer, vs. zones 4 and 5 in which it consists of both the same type and horizontal processes lying in the outer plexiform layer. On the basis of DA-innervation appearance and distribution of labeled and unlabeled cell somata, it was concluded that zones 1, 2, and 3 contained the DA innervation of the foveola. DA processes filtering between photoreceptor cells are particularly well-observed in this region. This anatomical study of the DA innervation in the human fovea leads to a better understanding of the important role of DA in primate central vision and can be used as a reference for an approach of macular pathology.
Topography and homogeneity of monkey VI studied through subdurally recorded pattern-evoked potentials
Authors: Dagnlie Gislin , Spekreijse Henk , van Dijk Bob 
Published: June 2009

AbstractUsing small checkerboard stimulus fields, we have recorded visually evoked potentials (VEPs) in an alert rhesus monkey from an array of 35 electrodes chronically implanted between dura and arachnoid to study mass neuronal activity in striate and peristriate visual cortex. Although the principal purpose of this work was to study in detail cortical mapping in this particular animal for future intracortical recordings, we report here the usefulness of our approach for the non-invasive study of cortical processing, in particular of cortical magnification and receptive-field properties over the central 6° of the visual field.The striate and extrastriate components in the pattern onset VEP both have a double negative-going waveform, with N–P–N peak latencies of 75–100–135 ms and 90–115–160 ms, respectively, for small element sizes and moderate contrasts; latencies may be 5 ms shorter for large element sizes and high contrast. We found little activity at electrode locations over visual areas beyond V2. The waveforms and timing permit some careful speculation concerning intracortical processing and VEP generation.The complex logarithmic form of the retinotopical projection provides a satisfactory model for our data, if a value of 1–1.2° is used for the offset parameter a. Our data suggest that the most abundant receptive-field size in foveal striate cortex has a center diameter of 12′. This size remains constant up to 2° eccentricity, and increases only slowly up to 4°. The smallest receptive-field sizes seem to be independent of eccentricity, throughout the central 4° of Vl, with a value of 4–8′, in agreement with single-cell data reported by Dow et al. (1981) and Van Essen et al. (1984).
Expression and cellular localization of substance P/neurokinin A and neurokinin B mRNAs in the rat retina
Authors: Brecha Nicholas C. , Sternini Catia , Anderson Karl , Krause James E. 
Published: June 2009

AbstractThe mammalian tachykinin peptides, substance P (SP), neurokinin A (NKA), and neurokinin B (NKB) are encoded by distinct mRNAs derived from separate preprotachykinin (PPT) genes. The SP/NKA-encoding PPT gene generates three mRNAs by alternative RNA processing: α-PPT mRNA, which encodes SP only, and β- and γ-PPT mRNAs, which encode both SP and NKA. The NKB-encoding PPT gene generates mRNAs that produce NKB. The distribution and cellular localization of SP, NKA and NKB mRNAs in the rat retina were studied by RNA blot andin situhybridization techniques. Blot hybridization analysis of retinal RNA extracts with [32P]-labeled RNA probes complementary to SP/NKA and NKB mRNAs demonstrated single bands of hybridization at 1300 and 900 bases, respectively. Solution hybridization-nuclease protection experiments showed multiple SP/NKA-encoding transcripts with relative levels of ρ-PPT mRNA > β-PPT mRNA ≫ α-PPT mRNA.In situhybridization histochemistry with [35S]-labeled antisense RNAs demonstrated thatSP/NKA-encoding transcripts are expressed in small-to-medium somata located in the proximal inner nuclear, inner plexiform, and ganglion cell layers, whereas NKB-encoding transcripts are expressed in small-to-medium somata located only in the ganglion cell layer. In this layer, cells containing NKB mRNAs are more numerous than those containing SP/NKA mRNAs. Only background labeling was observed in sections incubated with sense RNA probes, pretreated with RNase A prior to hybridization or incubated in hybridization buffer without the labeled probe. Immunohistochemical studies with a monoclonal antibody directed to the conserved COOH-terminal sequence of the tachykinin peptides revealed tachykinin-like immunoreactive somata with similar size and distribution to those containing SP/NKA- and NKB-encoding transcripts. These results indicate that both SP/NKA and NKB mRNAs are present in the rat retina and that the PPT genes are differentially expressed in specific cell populations. The size and distribution of these cells suggest that they are amacrine and displaced amacrine cells, however, the possibility that tachykinins are present also in ganglion cells in the rat retina cannot be ruled out.