bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pharmacological separation of mechanisms contributing to human contrast sensitivity
Authors: Smith A. T. , Baker-Short C. M. 
Published: June 2009

AbstractTwo basic types of cholinergic receptor have been identified in nervous systems: nicotinic and muscarinic. In the mammalian visual system, the balance of evidence suggests that nicotinic activity is associated primarily with transmission and processing of information while muscarinic activity reflects modulatory influences arising in the brainstem and basal forebrain. We have measured contrast sensitivity functions using a two-alternative forced-choice procedure in young human volunteers with and without administration of nicotine (1.5 mg by buccal absorption) or the muscarinic antagonist scopolamine (1.2 mg orally). Scopolamine elevates contrast-detection thresholds uniformly at all spatial frequencies, consistent with blocking of a nonspecific arousal system. Nicotine, in contrast, improves sensitivity at low spatial frequencies (below about 4 cycle/deg); at higher spatial frequencies sensitivity is, if anything, impaired. Using counterphase gratings, we find that scopolamine elevates thresholds uniformly at all temporal frequencies. Nicotine lowers thresholds at high but not low temporal frequencies. The results obtained with nicotine suggest that contrast sensitivity reflects the activity of two mechanisms, or sets of spatiotemporal filters, that are pharmacologically distinct, the contrast sensitivity function reflecting the envelope of their sensitivities.
Morphology of a small-field bistratified ganglion cell type in the macaque and human retina
Authors: Dacey Dennis M. 
Published: June 2009

AbstractIn in-vitro preparations of both macaque and human retina, intracellular injections of Neurobiotin and horseradish peroxidase were used to characterize the morphology, depth of stratification, and mosaic organization of a type of bistratified ganglion cell. This cell type, here called the small bistratified cell, has been shown to project to the parvocellular layers of the dorsal lateral geniculate nucleus (Rodieck, 1991) and is therefore likely to show color-opponent response properties.In both human and macaque, the two dendritic tiers of the bistratified cell are narrowly stratified close to the inner and outer borders of the inner plexiform layer. The inner tier is larger in diameter and more densely branched than the outer tier and gives rise to distinct spine-like branchlets bearing large, often lobulated heads. By contrast the smaller, outer tier is sparsely branched and relatively spine-free.In human retina, the small bistratified cells range in dendritic field diameter from ∼50 µm in central retina to ∼400 µm in the far periphery. The human small bistratified cells are about 20% larger in dendritic-field diameter than their counterparts in the macaque. However, when the difference in retinal magnification between human and macaque is taken into account, the small bistratified cells are similar in size in both species. In macaque, the small bistratified cell has a dendritic-field size that is ~10% larger than that of the magnocellular-projecting parasol ganglion cell. Human small bistratified ganglion cells tend to have smaller dendritic-field diameters than parasol cells. This is because parasol ganglion cells are larger in human than in macaque retina (Dacey & Petersen, 1992).In macaque retina, intracellular injections of Neurobiotin revealed heterotypic tracer coupling to a distinct mosaic of amacrine cells and probable homotypic coupling to an array of neighboring ganglion cells around the perimeter of the injected cell's dendritic tree. The amacrine cell mosaic had a density of 1700 cells/mm2 in peripheral retina. Individual amacrines had small, densely branched and bistratified dendritic fields. From the homotypic coupling, it was possible to estimate for the small bistratified cell a coverage factor of ~1.8, and a density of ~1% of the total ganglion cells in central retina, increasing to ~6–10% in the retinal periphery.The estimated density, dendritic-field size, and depth of stratification all suggest that the small bistratified ganglion cell type is the morphological counterpart of the common short-wavelength sensitive or ‘blue-ON’ physiological type.
Color-reversal learning: Effects after lesions of thalamic visual structures in pigeons
Authors: Chaves Lin M. , Hodos William , Güntürkün Onur 
Published: June 2009

AbstractThe performance of pigeons on a color-reversal learning task was assessed after thalamic lesions disrupting the thalamofugal and tectofugal visual pathways. Successful performance of a simultaneous color discrimination was accomplished after surgery, and a series of reversals of the original discrimination followed during which the positive and negative consequences associated with the stimuli were interchanged. Shimizu and Hodos (1989) had reported that lesions of two laminae in the visual wulst (IHA and HD), both targets of the avian thalamofugal pathway, resulted in increased errors in a color-reversal learning task in pigeons. This finding suggested that the thalamofugal pathway might play a role in visual discrimination involving stimulus context changes. In the present study, lesions of the OPT complex (the thalamic source of afferents to IHA and HD) were found to have no effect on color-reversal learning performance. Instead, we found that damage to nucleus rotundus (the thalamic component of the tectofugal pathway) resulted in deficits that were far in excess of those that had been obtained after IHA and HD lesions. We suggest that the color-reversal learning deficits after Wulst lesions are not due to the Wulst's connections with the thalamofugal pathway, but rather to its connections with the tectofugal pathway.
Postnatal development of substance-P immunoreactivity in the rat superior colliculus
Authors: Behan M. , Appell P. P. , Kime N. 
Published: June 2009

AbstractImmunocytochemical techniques have been used to examine the distribution of substance-P (SP)-labeled neurons in the superior colliculus of rats from birth to adulthood. At birth, there are almost no SP-immunopositive neurons in the tectum. A small number of SP neurons appear over the next several days. However, the vast majority of SP neurons appear between P9 and P10, and by P12 have attained adult-like numbers and distribution. Neurons are confined to the superficial layers of the colliculus, specifically the upper two-thirds of the stratum griseum superficiale (SGS). There is no indication of a differential developmental sequence along rostrocaudal or mediolateral axes. Neuronal types can be distinguished as early as P6 and include horizontal, vertical, and multipolar cells.Substance-P-immunoreactive axons and boutons are also present in the superior colliculus at birth, and are for the most part confined to the deep layers. Boutons are generally of the en-passant type. The density of labeled axons and boutons increases progressively, and by P10 there is an almost adult-like lamination and patchiness. In the adult, labeled axons and boutons are most dense in the stratum opticum and stratum griseum intermedium. Bridges of dorsoventrally oriented labeled axons span the relatively label-poor stratum album intermedium. SP label in the stratum griseum profundum is dense and patchy, and there is also dense label in the stratum album profundum bordering the periaqueductal grey.The role of substance-P-labeled neurons in the superior colliculus is still a matter of speculation. The findings of this study indicate that SP neurons may play a role in intrinsic collicular circuitry.
Contrast adaptation in striate cortical neurons of the nocturnal primate bush baby (Galago crassicaudatus)
Authors: Allison John D. , Casagrande Vivien A. , Debruyn Edward J. , Bonds A. B. 
Published: June 2009

AbstractIt has been argued that in order for the visual system to detect edges accurately under a range of conditions, the visual system needs to adapt to the local contrast level to preserve sensitivity (Blakemore & Campbell, 1969). Cells in the primary visual cortex of cats adapt to stimuli with low to moderate contrast. Curiously, macaque monkey neurons in primary visual cortex (V1) do not show evidence for similar adaptation. To address the question of whether this differential sensitivity in contrast adaptation might be due to phylogenetic variation between cats and primates or to specializations for visual niche (e.g. nocturnal vs. diurnal), contrast adaptation to temporally and spatially optimized gratings was examined in 30 V1 cells of three nocturnal primate bush babies (Galago crassicaudatus). A second objective was to examine the relationship between the degree of contrast adaptation and cell classification or cell location relative to cortical layers or compartments [i.e. cytochrome-oxidase (CO) blobs and interblobs]. All cells were classified (simple vs. complex) and anatomically localized relative to cortical layers and cytochrome-oxidase (CO) blob and interblob compartments. Two independent measures of contrast adaptation were used. In the first test, contrast was sequentially increased from 3–56% and then decreased. The contrast required to maintain a half-maximum response amplitude in the 30 cells tested increased an average of 0.24 (±0.12) log units during the sequential decrements in contrast. For the second test, four sets of five interleaved contrasts within ±1 octave of a central adapting contrast (10%, 14%, 20%, and 28%, respectively) were presented. The cells produced a mean adaptation index of 0.57 (±0.47) which is very similar to that exhibited by cat cortical neurons (0.54 ± 0.41). Interestingly, cells in interblobs showed a trend toward greater adaptation than did blob cells. Moreover, cells in the supragranular layers exhibited greater adaptation than cells in the infragranular layers. No significant differences in adaptation were found to correlate with other cell classification indices. Taken together, our results suggest that contrast adaptation may be more important for maintaining sensitivity in nocturnal species (primates or cats) than in diurnal species (macaque monkeys), and that in the nocturnal bush baby, cells in cortical layers and compartments may be differentially specialized for contrast adaptation.
Early dendritic outgrowth of primate retinal ganglion cells
Authors: Kirby Michael A. , Steineke Thomas C. 
Published: June 2009

AbstractThe pattern of dendritic stratification of retinal ganglion cells in the fetal monkey (Macaca mulatta) was examined using horseradish peroxidase and retinal explants. Ganglion cells in the rhesus monkey are born between embryonic day (E) 30–70 (La Vail et al., 1983). At E60, E67, and E68, approximately 50% of all ganglion cells within the central 3.0 mm of the retina had dendritic arbors that were unistratified within the inner plexiform layer (IPL), while the remaining 50% had bistratified arbors. Unistratified cells had relatively flat arbors that ramified within a restricted portion of the IPL. In contrast, bistratified cells had one portion of the arbor that branched in the inner half of the IPL and a second portion that branched in the outer half of the IPL. Relatively few bistratified cells were encountered in the central 1.0 mm of the retina but were more numerous with increasing eccentricity. At E81, E90, and E110, the dendritic arbors of ganglion cells increased in both area and complexity, but occupied a relatively small percentage of the total depth of the IPL. The bistratified cells encountered at these fetal ages were typically located in the far retinal periphery. Between E125-E140, the dendritic arbors of individual ganglion cells increased in area and depth to occupy a greater proportion of the total IPL than at earlier fetal ages.These observations suggest that ganglion cells in the macaque undergo at least three stages of dendritic stratification: (1) an initial period of dendritic growth during which the cells have either unistratified or bistratified dendritic arbors; (2) a loss of the majority of bistratified cells through cell death or remodeling of the arbor; and (3) growth or expansion of the arbor to occupy a greater percentage of the total depth of the IPL. The first two stages are similar to recent observations in the fetal cat (Maslim & Stone, 1988) with the exception that dendritic development in the primate lacks an initial diffuse ingrowth to the IPL. Additionally, primate ganglion cells undergo a third stage of dendritic growth in late fetal development during which the arbor occupies a greater proportion of the depth of the IPL.
Light-induced GTPase activity and GTP[γS] binding in squid retinal photoreceptors
Authors: Brown Joel E. , Combs Anthony , Ackermann Karen , Malbon Craig C. 
Published: June 2009

AbstractIllumination greatly increases the GTPase activity in homogenates of squid (Loligo) whole retinas or rhabdomeric membranes. Adenylylimidodiphosphate inhibits the light-insensitive (but not the light-sensitive) GTPase activity in these homogenates. Illumination also greatly increases the binding of GTP[γS] to the rhabdomeric membranes. This binding at saturating illuminations indicates that there are approximately 10–100 times more rhodopsin molecules than G-protein molecules in squid photoreceptors. Each light-activated rhodopsin molecule activates about 10 G-protein molecules which might provide amplification for the first stage of the phototransduction cascade.
Glycine receptor immunoreactivity is localized at amacrine synapses in cat retina
Authors: Pourcho Roberta G. , Owczarzak Michael T. 
Published: June 2009

AbstractImmunocytochemical techniques were used to localize strychnine-sensitive glycine receptors in cat retina. Light microscopy showed staining in processes ramifying throughout the inner plexiform layer and in cell bodies of both amacrine and ganglion cells. At the electron-microscopic level, receptor immunoreactivity was seen to be clustered at sites postsynaptic to amacrine cells. In contrast, bipolar cells were neither presynaptic nor postsynaptic elements at sites of glycine receptor staining. Double-label studies verified the presence of glycine immunoreactivity in amacrine terminals presynaptic to glycine receptors. These findings support a role for glycine as an inhibitory neurotransmitter in amacrine cells.
Spatial vision of the cat: Variation with eccentricity
Authors: Pasternak Tatiana , Horn Kris 
Published: June 2009

AbstractWe examined the grating acuity and contrast sensitivity of cats whose eye position was monitored with a scleral search-coil technique. During each trial, the cat was required to maintain fixation on a laser spot and respond to the presence or the absence of a grating by pressing a right or left pedal. With this procedure, acuity was measured along the horizontal and vertical meridian over a range of eccentricities in the nasal, temporal, superior, and inferior retina. In addition, contrast sensitivity for stationary and drifting gratings was measured for the temporal retina along the horizontal meridian. Acuity in area centralis reached about 3.5 cycle\deg and declined by 0.5 octaves at 4 deg and by about 1.3 octaves at 16-deg eccentricity in the nasal retina. The acuity was higher in the nasal than temporal retina. At all eccentricities, spatial resolution exceeded the resolution limit derived from Y (alpha)-cell properties. Contrast sensitivity also decreased as the eccentricity increased when the target size was held constant. The slope of sensitivity-eccentricity function was relatively shallow for a low spatial frequency (0.30 cycle\deg) with sensitivity decreasing by a factor of 1.5–2 at 8-deg eccentricity. The slope of the sensitivity falloff for high spatial-frequency gratings (1.2 cycle\deg) was steeper, with a 5–10-fold difference in sensitivity between 0 and 8 deg. By varying the target size, we determined that the summation area in the cat is about a factor of 3 smaller in area centralis than a 16-deg eccentricity. When the size of the centrally and peripherally viewed targets was scaled relative to visual acuity, the sensitivity was constant across the visual field.
The effect of dopamine depletion on light-evoked and circadian retinomotor movements in the teleost retina
Authors: Douglas R. H. , Wagner H.-J. , Zaunreiter M. , Behrens U. D. , Djamgoz M. B. A. 
Published: June 2009

AbstractThe retinae of lower vertebrates undergo a number of structural changes during light adaptation, including the photomechanical contraction of cone myoids and the dispersion of melanin granules within the epithelial pigment. Since the application of dopamine to dark-adapted retinae is known to produce morphological changes that are characteristic of light adaptation, dopamine is accepted as a causal mechanism for such retinomotor movements. However, we report here that in the teleost fish,Aequidens pulcher, the intraocular injection of 6-hydroxydopamine (6-OHDA), a substance known to destroy dopaminergic retinal cells, has no effect on the triggering of light-adaptive retinomotor movements of the cones and epithelial pigment and only slightly depresses the final level of light adaptation reached. Furthermore, the retina continues to show circadian retinomotor changes even after 48 h in continual darkness that are similar in both control and 6-OHDA injected fish. Biochemical assay and microscopic examination showed that 6-OHDA had destroyed dopaminergic retinal cells. We conclude, therefore, that although a dopaminergic mechanism is probably involved in the control of light-induced retinomotor movements, it cannot be the only control mechanism, nor can it be the cause of circadian retinomotor migrations. Interestingly, 6-OHDA injected eyes never reached full retinomotor dark adaptation, suggesting that dopamine has a role to play in the retina's response to darkness.
Serotonin synthesis and accumulation by neurons of the anuran retina
Authors: Zhu Baosong , Gábriel Robert , Straznicky Charles 
Published: June 2009

AbstractSerotonin-synthesizing and serotonin-accumulating neurons were studied in the retinas of Xenopus laevis and Bufo marinus. All previously identified cell types exhibiting serotonin-like immunoreactivity (SLI) were labeled by intravitreal injection of 5,7-dihydroxytryptamine (5,7-DHT). They included two amacrine cell types (large and small) in both species, and one bipolar cell type in Xenopus. Incubation of retinas in culture medium in the ambient light reduced SLI in amacrine cells and enhanced the labeling in bipolar cells. After incubation, some photoreceptor cell bodies and large numbers of outer segments also displayed SLI in both species. Incubation with the serotonin-uptake inhibitor, fluoxetine, reduced immunolabeling in bipolar cells and outer segments to the level in the untreated retinas.Both large SLI and 5,7-DHT-accumulating amacrine cells in Xenopus and Bufo were labeled with an antibody raised against phenylalanine hydroxylase (PH), which binds to tryptophan 5-hydroxylase, one of the synthesizing enzymes for serotonin. Small SLI and 5,7-DHT-accumulating amacrine cells in both species represented two populations, one with and the other without PH-like immunoreactivity (PH-LI). The anti-PH antibody failed to label any SLI or 5,7-DHT-accumulating bipolar cells in Xenopus.These observations indicate that all large and some small SLI amacrine cells in the retinas of Xenopus and Bufo synthesize serotonin, while other small SLI amacrine, bipolar and photoreceptor cell bodies, and outer segments only accumulate serotonin.
The rod circuit in the rabbit retina
Authors: Vaney David I. , Young Heather M. , Gynther Ian C. 
Published: June 2009

AbstractMammalian retinae have a well-defined neuronal pathway that serves rod vision. In rabbit retina, the different populations of interneurons in the rod pathway can be selectively labeled, either separately or in combination. The rod bipolar cells show protein kinase C immunoreactivity; the rod (An) amacrine cells can be distinguished in nuclear-yellow labeled retina; the rod reciprocal (S1 & S2) amacrine cells accumulate serotonin; and the dopaminergic amacrine cells show tyrosine-hydroxylase immunoreactivity. Furthermore, intracellular dye injection of the microscopically identified interneurons enables whole-population and single-cell studies to be combined in the same tissue. Using this approach, we have been able to analyze systematically the neuronal architecture of the rod circuit across the rabbit retina and compare its organization with that of the rod circuit in central cat retina. In rabbit retina, the rod interneurons are not organized in a uniform neuronal module that is simply scaled up from central to peripheral retina. Moreover, peripheral fields in superior and inferior retina that have equivalent densities of each neuronal type show markedly different rod bipolar to An amacrine convergence ratios, with the result that many more rod photoreceptors converge on an An amacrine cell in superior retina. In rabbit retina, much of the convergence in the rod circuit occurs in the outer retina whereas, in central cat retina, it is more evenly distributed between the inner and outer retina.
Modulation of transduction gain in light adaptation of retinal rods
Authors: Pepperberg David R. , Jin Jing , Jones Gregor J. 
Published: June 2009

AbstractThe effect of light adaptation on the period of photocurrent saturation induced by a bright stimulating flash was examined in rod photoreceptors of the larval-stage tiger salamander (Ambystoma tigrinum). Using suction electrodes, photocurrent responses to brief flashes were recorded from single, isolated rods in the presence and absence of steady background illumination. Background light decreased the saturation period (T) measured at fixed flash intensity (fixedIf) and in this respect light-adapted the saturating response. Effects of the background on responses to weak (i.e. subsaturating) and bright flashes were compared with changes in a parameter,where ΔTis the decrease in saturation period, and whereTR*is the slope of the line that relatesTand lnIfin a given state of adaptation. Dark- and light-adapted responses to flash intensitiesand, respectively, exhibited similar absolute peak photocurrent and falling-phase kinetics whenandsatisfied the relation,, whereIbis the background intensity. It is argued thatψapproximates the relativePDE*/R*gain of transduction, i.e. the relative peak level of activated cGMP phosphodiesterase (PDE*) produced by a given, small amount of photoactivated visual pigment (R*). Interpreted on this view, the results imply that light adaptation derives largely from a decrease inPDE*/R*gain, rather than from the stimulation of guanylate cyclase activity. The data are consistent with the possibility that modulation of the lifetime ofPDE*underlies the background dependence of ψ.
Horizontal cells in cat and monkey retina express different isoforms of glutamic acid decarboxylase
Authors: Vardi Noga , Kaufman Daniel L. , Sterling Peter 
Published: June 2009

AbstractThe neurotransmitter used by horizontal cells in mammals has not been identified. GABA has been the leading candidate, but doubt has remained because of failure to clearly demonstrate the GABA synthetic enzyme, glutamic acid decarboxylase (GAD) in these cells. Because GAD was recently shown to exist as two isoforms, 65 kDa and 67 kDa, we considered whether there might be a mismatch between the forms of GAD expressed in horizontal cells and the probes used to detect it. Accordingly, we stained sections of mammalian retina with antibodies specific for each isoform. Cat horizontal cells of both types (A and B) were immunoreactive for GAD67 but negative for GAD65; monkey horizontal cells of both types (H1 and H11) were positive for GAD65 and negative for GAD67. The findings reconcile previous, apparently conflicting, observations and strengthen considerably the hypothesis that mammalian horizontal cells are GABAergic.