bluuebunny/crossref_metadata_2025 huggingface dataset:
Serotonin synthesis and accumulation by neurons of the anuran retina
Authors: Zhu Baosong , Gábriel Robert , Straznicky Charles
Published: June 2009

Serotonin-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

Mammalian 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

The 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

The 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.
Electrophysiological sensitivity of carotenoid deficient and replaced Drosophila
Authors: Chen De-Mao , Stark William S.
Published: June 2009

R1–6 dominated electroretinographic (ERG) spectral sensitivities were determined as a function of days posteclosion from carotenoid deprived and replaced white-eyed Drosophila. The sensitivity of flies deprived from egg to adult waxed (about 1.5 log units by day 3), and then waned gradually from 3–11 days (over 2 log units by day 11). Carotenoid replacement (feeding nothing but carrot juice) effected recovery to near the replete control' level in about 1 day throughout (tested at 0, 4, and 11 days). The normal yellow cornmeal-agar-molasses-brewers yeast fly food (in our laboratory, supplemented with β-carotene) renders a slower recovery (requiring 7–9 days) since it is a medium designed largely for larval growth. Placing replete adults on deprivational medium did not create a deprivational syndrome in over 11 days. At 3–7 days, deprived flies reared and maintained in constant darkness had substantially enhanced sensitivity, beyond the 1.5 log unit increment already described for cyclic light rearing conditions. All spectral analyses are consistent with the ultraviolet (UV) sensitization of the blue (480 nm) rhodopsin by a replacement-dependent retinoid including two unexpected findings: (1) sensitivity recovery with carrot juice was so fast that the UV peak was already high at 6 h; and (2) the waxing of the deprived fly's sensitivity in dark rearing was so great that the UV peak was present at 4–7 days.
Ocular dominance columns and local projections of layer 6 pyramidal neurons in macaque primary visual cortex
Authors: Wiser Anne K. , Callaway Edward M.
Published: June 2009

To study the relationship between ocular dominance columns (ODCs) and axonal projections of individual layer 6 pyramidal neurons in the primary visual cortex, neurons were intracellularly labeled with biocytin in live slices prepared from macaque monkeys that had received an intravitreal injection of tetrodotoxin (TTX). The TTX injection indirectly causes a decrease in cytochrome oxidase (CO) expression in the cortical ODCs corresponding to the treated eye (Wong-Riley & Carroll, 1984). Sections from slices with labeled layer 6 neurons were double stained for biocytin and CO, to allow visualization of neuronal processes as well as ODCs. Twenty-seven layer 6 pyramidal neurons in ODC-labeled slices were analyzed. These neurons were classified according to the criteria of Wiser and Callaway (1996). Eight of these are class I neurons, which have dense axonal projections to the monocular layer 4C. The remaining 19 are class II neurons which project primarily to the binocular layers outside 4C. Among class I neurons, two have dense axonal arbors in layer 4Cα (type Iα), one in layer 4Cβ (type Iβ), and two throughout the depth of layer 4C (type IC). None of these neurons have ODC-specific axonal arbors. The remaining three class I neurons have focused axonal projections in layers 4Cβ and 4A (type IβA). All three appear to have axonal arbors predominantly within their home ODC in layer 4C. The axonal arbors of class II neurons do not appear to relate to ODCs in any specific fashion.
Large retinal ganglion cells in the pipid frog Xenopus laevis form independent, regular mosaics resembling those of teleost fishes
Authors: Shamim K. M. , Tóth P. , Cook J. E.
Published: June 2009

Population-based studies of retinal neurons have helped to reveal their natural types in mammals and teleost fishes. In this, the first such study in a frog, labeled ganglion cells of the mesobatrachian Xenopus laevis were examined in flatmounts. Cells with large somata and thick dendrites could be divided into three mosaic-forming types, each with its own characteristic stratification pattern. These are named αa, αab, and αc, following a scheme recently used for teleosts. Cells of the αa mosaic (~0.4% of all ganglion cells) had very large somata and trees, arborizing diffusely within sublamina a (the most sclerad). Their distal dendrites were sparsely branched but achieved consistent coverage by intersecting those of their neighbors. Displaced and orthotopic cells belonged to the same mosaic, as did cells with symmetric and asymmetric trees. Cells of the αab mosaic (~1.2%) had large somata, somewhat smaller trees that appeared bistratified at low magnification, and dendrites that branched extensively. Their distal dendrites arborized throughout sublamina b and the vitread part of a, tessellating with their neighbors. All were orthotopic; most were symmetric. Cells of the αc mosaic (~0.5%) had large somata and very large, sparse, flat, overlapping trees, predominantly in sublamina c. All were orthotopic; some were asymmetric. Nearest-neighbor analyses and spatial correlograms confirmed that each mosaic was regular and independent, and that spacings were reduced in juvenile frogs. Densities, proportions, sizes, and mosaic statistics are tabulated for all three types, which are compared with types defined previously by size and symmetry in Xenopus and potentially homologous mosaic-forming types in teleosts. Our results reveal strong organizational similarities between the large ganglion cells of teleosts and frogs. They also demonstrate the value of introducing mosaic analysis at an early stage to help identify characters that are useful markers for natural types and that distinguish between within-type and between-type variation in neuronal populations.
The origin of slow PIII in frog retina: Current source density analysis in the eyecup and isolated retina
Authors: Xu Xijing , Karwoski Chester J.
Published: June 2009

The objective of this research was to determine the sources and sinks of current underlying the slow PIII component of the electroretinogram. Current source density analysis of the ERG evoked by diffuse light flashes was performed in eyecup and isolated retinas of frog. Blockade of synaptic transmission with aminophosphonobutyric + kynurenic acids simplified the CSD profiles through the retina. In addition to the photoreceptor source/sink pair, there was evidence for a major slow PIII source near the outer limiting membrane, a major sink near the inner limiting membrane, and a small source near the inner plexiform layer. Addition of Ba2+ abolished the slow PIII source/sinks, and it left only the photoreceptor source and sink. The results support the idea that slow PIII originates through K+ spatial buffering by Müller cells. Specifically, the light-evoked decrease in [K+]0 in the subretinal space causes a primary K+ efflux from Müller cells (current source) and a primary K+ influx at the Müller cell endfeet (current sink). A decrease in [K+]0 in the proximal retina, caused by diffusion of K+ to the subretinal space, results in K+ efflux (the current source) at the inner plexiform layer.
GABACreceptors on ferret retinal bipolar cells: A diversity of subtypes in mammals?
Authors: Lukasiewicz Peter D. , Wong Rachel O.L.
Published: June 2009

The GABACreceptor subtypes on bipolar cells of rats and cold-blooded vertebrates differ in their pharmacological properties and probably have different molecular compositions. With the exception of the rat, native GABACreceptors in mammals had not been studied. In ferret, whole-cell, voltage-clamp recordings were made from bipolar cells in the retinal slice preparation to determine which subtype of GABACreceptor predominated. Puff-evoked GABA currents in bipolar cells were partially reduced by the GABAAreceptor antagonist bicuculline, indicating that both GABAAand GABACreceptors mediated the responses. By contrast, GABA currents of ganglion cells were always completely blocked by bicuculline, indicating that GABAAreceptors predominated on these cells. Small-amplitude GABA currents of bipolar cells evoked by short-duration puffs were less sensitive to bicuculline than large-amplitude currents evoked by long-duration puffs. This indicates that GABAc receptors mediated proportionately more of the small-amplitude, puff-evoked responses and GABAAreceptors mediated more of the large-amplitude, puff-evoked responses. In bipolar cells, the bicuculline-resistant component of the GABA current was entirely blocked by 3-APMPA (3-aminopropyl-(methyl)phosphonic acid), a GABACreceptor antagonist. Picrotoxin, which is relatively ineffective at rat GABACreceptors, completely blocked GABA currents in ferret bipolar cells, indicating that GABACreceptors on ferret bipolar cells resemble those in lower vertebrates rather than those in the rat retina. These results suggest that there may be a diversity of GABAc receptor subtypes on mammalian bipolar cells.
Inhibition of phospholipase C by U-73122 blocks one component of the receptor current inLimulusphotoreceptor
Authors: Nagy Károly , Contzen Klaus
Published: June 2009

In the ventral nerve photoreceptor ofLimulusa short, intense flash evokes a receptor current consisting of three components. In contrast to other hypotheses, we suggested previously that only the second component of the current is activated by the phospholipase C pathway, which releases calcium from intracellular stores by inositol trisphosphate. The present paper gives further evidence to our suggestion. It is demonstrated that U-73122, a specific inhibitor for the phospholipase C, selectively blocks the second component. The first and third components are moderately affected and could still be activated after the complete block of the second one. Results support the idea that the first and third components areactivated by pathways operating independently of phospholipase C.
Chromatic properties of neurons in macaque area V2
Authors: Kiper Daniel C. , Fenstemaker Suzanne B. , Gegenfurtner Karl R.
Published: June 2009

We recorded from single cells in area V2 of cynomolgus monkeys using standard acute recording techniques. After measuring each cell's spatial and temporal properties, we performed several tests of its chromatic properties using sine-wave gratings modulated around a mean gray background. Most cells behaved like neurons in area V1 and their responses were adequately described by a model that assumes a linear combination of cone signals. Unlike in V1, we found a subpopulation of cells whose activity was increased or inhibited by stimuli within a narrow range of color combinations. No particular color directions were preferentially represented. V2 cells showing color specificity, including cells showing narrow chromatic tuning, were present in any of the stripe compartments, as defined by cytochrome-oxidase (CO) staining. An addition of chromatic contrast facilitated the responses of most neurons to gratings with various luminance contrasts. Neurons in all three CO compartments gave significant responses to isoluminant gratings. Receptive-field properties of cells were generally similar for luminance and chromatically defined stimuli. We found only a small number of cells with a clearly identifiable double-opponent receptive-field organization.
Developmental changes in the pattern of NADPH-diaphorase staining in the cat's lateral geniculate nucleus
Authors: Guido William , Scheiner Christopher A. , Mize R. Ranney , Kratz Kenneth E.
Published: June 2009

We examined the pattern of NADPH-diaphorase (NADPH-d) staining in the lateral geniculate nucleus (LGN) of dorsal thalamus in fetal and newborn kittens, and adult cats. This staining visualizes the synthesizing enzyme of nitric oxide (NO), a neuromodulator associated with central nervous system (CNS) development and synaptic plasticity. In the adult, very few LGN cells stained for NADPH-d, and these were restricted to interlaminar zones and ventral C layers. NADPH-d labeled a dense network of fibers and axon terminals throughout the LGN and adjacent thalamic nuclei. The source of such labelling has been reported to be cholinergic neurons from the parabrachial region of the brain stem (Bickford et al., 1993). A very different pattern of staining was observed in prenatal and early postnatal kittens. Between embryonic (E) day 46–57, lightly stained cells appeared throughout the LGN. From this age, through about the first month of life, the number of stained cells in the LGN rose rapidly. The density (cells/ mm2) of labeled cells peaked at postnatal day (P) 28 (P28), and was about 150 times greater than the level measured in the adult LGN. After P28, cell staining declined rapidly, and fell to adult levels at P41. The reduction in cell staining that occurred between P35–41 was accompanied by the appearance of fine-caliber fiber staining, similar to that observed in the adult LGN. NADPH-d staining, which reveals the presence of nitric oxide synthase (NOS), and thus NO activity, may reflect two processes. In the adult LGN, the labeling of cholinergic axons arising from the brain-stem parabrachial region coupled with a paucity of the LGN cellular staining suggests that NO operates in an orthograde manner, being co-released with ACh to influence the gain and efficacy of retinogeniculate transmission. By contrast, in developing kitten, NADPH-d staining of LGN cells suggests that NO acts in a retrograde fashion, perhaps playing a role in maintaining associative processes underlying activity-dependent refinement of retinogeniculate connections.
Accessibility of colloidal gold and horseradish peroxidase to cytosolic spaces in Limulus ventral photoreceptors
Authors: Rubin L. J. , Womble M. , Brown J. E. , Finger T. E.
Published: June 2009

Physiological studies of intracellular messengers frequently employ intracellular injections of large molecules that either monitor or modulate the metabolism of the messenger cascade. Injected molecules have unknown mobility in the cytosol and unknown accessibility to various cytosolic compartments, including those postulated to be traversed by intracellular messenger molecules. In order to determine whether injected molecules have access to the confined spaces through which messenger molecules must diffuse, we injected 5-nm colloidal gold or horseradish peroxidase, or both, into Limulus ventral photoreceptors. Injections were made by applying pressure pulses to the back of an intracellular micropipette that also monitored membrane voltage. The tissue was fixed at varying times after injection and processed for electron microscopy by conventional techniques. Cells fixed 1–3 min after injection contained HRP reaction product only in the cell body. HRP reaction product was found at varying distances down axons in direct relation to the interval between injection and fixation. Colloidal gold particles were found throughout the cell body but not in axons of tissue fixed 1–3 min after injection. Both HRP reaction product and 5-nm colloidal gold particles were observed within the microvillar projections of internal and external rhabdomere, as well as within the extracisternal spaces of endoplasmic reticulum. We conclude that large molecules injected from an intracellular micropipette into an arbitrary locus of ventral photoreceptor cells have access to all of the presumed sites of the phototransduction cascade.
Vernier acuities of neurons in area 17 of cat visual cortex: Their relation to stimulus length and velocity, orientation selectivity, and receptive-field structure
Authors: Swindale N. V. , Cynader M. S.
Published: June 2009

The sensitivity of neurons in area 17 of the cat's visual cortex to vernier offset was expressed as the percentage reduction in response caused by the introduction of a given offset into a bar stimulus moving across the receptive field. There was a wide variation in sensitivity: in some cells response could be halved by an offset equal to a fifth of receptive-field width (defined as twice the standard deviation of a Gaussian curve fitted to the response profile), while other cells showed no sensitivity. The highest absolute sensitivities of complex and simple cells were similar, although most cells with poor sensitivity were complex.

Sensitivity was largely unaffected by changes in stimulus velocity and stimulus length, although there was a tendency for sensitivity to increase with decreasing bar length.

Comparisons of orientation tuning curves with vernier tuning curves showed that the response to a vernier stimulus approximated the response to a single bar of the same overall length and an orientation equal to that of a line joining the midpoints of each bar. This was true for a wide range of sensitivity values.

Vernier sensitivity was correlated with a measure of length summation H, which is positive when there is net facilitation between the bars, and negative when there is net inhibition. Vernier sensitivity was highest in cells with large values of H, and least in cells where H was negative.

We examined a linear model of the simple cell receptive field which, together with a variable response threshold, was able to explain the correlation between vernier acuity and length summation. Although this model accounted qualitatively for many of our findings, the majority of simple cells had tuning curves that were sharper than the predicted ones. This suggests that there are nonlinearities in the behavior of many simple cells whose effect is to increase the sharpness of orientation tuning and consequently vernier sensitivity.
Changing topography of the RPE resulting from experimentally induced rapid eye growth
Authors: Fleming Patricia A. , Harman Alison M. , Beazley Lyn D.
Published: June 2009

The retinal pigment epithelium (RPE) of the quokka wallaby, Setonix brachyurus, grows and changes throughout life. To investigate factors that determine changes in the quokka RPE, we have examined topography of this tissue in experimentally enlarged eyes. Unilateral eyelid suture was conducted at the time of normal eye opening, postnatal day (P) 110, and animals were examined at 1 or 1½ years of age. The numbers and densities of RPE cells and the extent of multinucleation were compared with those in normal animals. Eyelid suture resulted in a 9.8% and 17.4% increase in retinal area at 1 and 1½ years, respectively; a significant degree of myopia was associated with this enlargement. Cell density topography in experimental eyes was not the same as in controls. Cells from central retina were disproportionately larger in the experimental than control eyes. However, the RPE cell topography in sutured eyes was not the same as that of aged retinae of a similar size. Notably, in sutured eyes there was no development of the high or highest cell densities seen in equatorial and temporal central RPE in aged retinae, respectively. Furthermore, the degree of cell enlargement in peripheral regions was slight compared with that observed in similar-sized, aged retinae. There was no increase in RPE cell number; rather, average cell area increased accompanied by no change or a slight decrease in RPE thickness. Consequently, overall volume of cells did not change significantly. The large number of multinucleate cells normally seen in aged animals was not observed in experimentally enlarged eyes, implying that an increase in cell volume may be the trigger for multinucleation.
Tracer coupling among regenerated amacrine cells in the retina of the goldfish
Authors: Hitchcock Peter F.
Published: June 2009

This study sought to characterize the tracer coupling of regenerated amacrine cells in the retina of the goldfish and assess the integration of regenerated neurons into existing retinal circuits. Regeneration of new neurons from injury-induced progenitors was stimulated by surgically excising a small rectangular piece of retina. Several months after regeneration was complete, intracellular injections of Neurobiotin, a gap junction-permeant tracer, were made into single regenerated amacrine cells or nonregenerated (extant) amacrine cells lying outside the regenerated patch. Two groups of amacrine cells were injected: those that in normal retina are tracer coupled and a single type (the radiate amacrine cell) that is not. The data show that regenerated amacrine cells are tracer coupled to each other and to their homologous counterparts outside the patch of regenerated retina. Regenerated radiate cells possess morphologically abnormal dendrites, but these processes can extend out of regenerated retina into surrounding normal retina. Similarly, the dendrites of extant radiate cells, severed by the original lesion, can regenerate into the patch of regenerated retina. These results indicate that in the goldfish retina the cell-specific junctional circuitry present in normal retina is re-created in the regenerated retina, and suggest that regenerated neurons are functionally integrated into the existing retina.
Effect of retinal impulse blockage on cytochrome oxidase-rich zones in the macaque striate cortex: II. Quantitative electron-microscopic (EM) analysis of neuropil
Authors: Wong-Riley Margaret T. T. , Trusk Thomas C. , Tripathi Satish C. , Hoppe Daniel A.
Published: June 2009

Unilateral retinal impulse blockage with tetrodotoxin (TTX) induces reversible shrinkage and decreased cytochrome oxidase (CO) activity in alternate rows of supragranular, CO-rich puffs in the adult macaque striate cortex (Wong-Riley & Carroll, 1984b: Carroll & Wong-Riley, 1987). The present study extended the findings to the electron-microscopic (EM) level to determine if various neuropil profiles in control puffs exhibit heterogeneous levels of CO activity, and whether specific processes were more susceptible to intravitreal TTX than others.

Within the neuropil of control puffs, 60% of the total mitochondrial population resided in dendrites, and the majority of dendritic mitochondria were highly reactive for CO. Axon terminals forming symmetrical synapses also contained darkly reactive mitochondria, whereas those forming asymmetrical synapses possessed very few and mainly lightly reactive mitochondria. Unmyelinated axon trunks, myelinated axons, and glia all exhibited low levels of CO activity. Synaptic count revealed a 3:1 ratio of asymmetrical to symmetrical synapses.

Intravitreal TTX for 2–4 weeks adversely affects dendrites and symmetrical terminals much more so than other neuropil processes. There was a general decrease in darkly and moderately reactive mitochondria and an increase in lightly reactive mitochondria throughout the puffs, especially in dendrites. This indicates that afferent blockade is more detrimental to processes of higher metabolic activity. Changes also differed between central and peripheral regions of puffs, and indications of axonal and synaptic reorganization were more evident in the latter. Thus, stabilization of neuronal structure and synapses appears to be activity-dependent even in the adult. A working model of these metabolic and morphological responses to chronic TTX is proposed.
Characterization of guanylate cyclase in squid photoreceptors
Authors: Robinson Phyllis R. , Cote Richard H.
Published: June 2009

Light causes a rapid, 1.7-fold increase in cyclic GMP concentration in intact squid retinas (Johnson et al. (1986)). To determine whether light-induced changes in cyclic GMP concentration result from activation of guanylate cyclase, we have studied the regulation of guanylate cyclase activity in squid (Loligo pealei) photoreceptors. The enzyme is membrane-associated and activity is enhanced by the detergents Triton X-100 or digitonin. The enzyme requires divalent cations, Mn2+being preferred over Mg2+. The dependence of enzyme activity on the MnGTP concentration deviates from simple Michaelis-Menten kinetics. Under conditions where a light-induced binding of GTP to the guanine nucleotide regulatory protein can be observed, no light-induced change in guanylate cyclase could be detected.
Visual latency and brightness: An interpretation based on the responses of rods and ganglion cells in the frog retina
Authors: Donner Kristian
Published: June 2009

Rod and cone photoresponses in a variety of species have been accurately described with linear multistage filter models. In this study, the response latency and initial coding of intensity at two higher levels of visual processing are related to such photoreceptor responses. One level is the retinal output (spiking discharges from frog ganglion cells, based on experimental data reported here), the other is the perceptual level in humans (psychophysical latency and brightness functions, based on data from the literature). Photoreceptor responses are described with the “independent activation” model of Baylor et al. (1974). The intensity dependence of the earlyganglion celldischarge, its latency and initial impulse frequency, is shown to follow from such a waveform, assuming that 1) latencyL = l + D, wherelis the time it takes for the rod response linearly summed over the ganglion cell's receptive field to reach a criterion amplitude, andDis a constant delay; and 2) the initial frequency (below saturation) is proportional to the steepness of rise of the summed rod response at timel. It is shown that the intensity dependences of 1) humanvisual latencyand 2)brightness sensation, including effects of stimulus area and duration, are accounted for by the same model. The predicted functions are not power functions of intensity, but approximate such over wide ranges. Thus, a large body of psychophysical data is explained simply by the waveform of photoreceptor responses.
Two opposite effects of ATP on the apparent sensitivity of the cGMP-gated channel of the carp retinal cone
Authors: Watanabe Shu-Ichi , Shen Jing
Published: June 2009

Effects of ATP on the activity of cGMP-gated channels from carp cone photoreceptors were studied. In 29% of the patches examined (N = 45), ATP (1 mM) enhanced a current evoked by cGMP (20 μM, up to about 100%), in 33%, ATP suppressed it by up to about 90%, and in the remaining 38%, ATP had no effect. ATP showed similar effects on a current evoked by 8-bromoguanosine 3′,5′-cyclic monophosphate (2 μM, enhancing in 42% of the patches, suppressing in 25%, no effect in 33%, N = 12), suggesting that the effects were not through modulation of the phosphodiesterase. Both of the effects, enhancement and suppression, were produced by a change in apparent affinity for cGMP, since (1) the maximum current evoked by cGMP of the saturating concentration (≥1 mM) was not affected, and (2) the A1/2 value decreased by approximately 45% (N = 2) or increased by approximately 25% (N = 2). A lower pH (approximately 6) facilitated the enhancing effect. ATP-γ-S (1 mM) showed a suppressing effect in 80% of the patches and no effect in 20% of the patches (N = 10). However, ATP-γ-S did not show an enhancing effect. Thus, ATP had two opposite effects through different mechanisms on the apparent sensitivity of the channel to cGMP; increasing and decreasing.
The monoclonal antibody H386F labels microglia in the retinal nerve fiber layer of several mammals
Authors: Tumosa Nina , Baker James R.
Published: June 2009

The antibody H386F revealed microglia in the retinae of several species: owl monkey, slow loris, galago, ferret, raccoon, and tree shrew. The shape, size, and density of labeled microglia were identical to those labeled by OX-42 and OX-41, two antibodies specific for microglia, in both galago and owl monkey. The labeled microglia varied little in retinal location. There was remarkably little variability in density, shape, number, and size of the abeled microglia between species. All labeled microglia were evenly distributed across, but restricted to, the nerve liber layer. Possible reasons for this restriction in location are discussed.
Pattern of ocular dominance columns and cytochrome oxidase activity in a macaque monkey with naturally occurring anisometropic amblyopia
Authors: Horton Jonathan C. , Hocking Davina R. , Kiorpes Lynne
Published: June 2009

Unilateral eyelid suture, a model for amblyopia induced by congenital cataract, produces shrinkage of the deprived eye's ocular dominance columns in the striate cortex. Loss of geniculocortical projections are thought to account for the poor vision in the amblyopic eye. It is uncertain whether ocular dominance columns become shrunken in other forms of amblyopia. We examined the striate cortex in a pigtailed macaque with natural anisometropia discovered at age 5 months. Amblyopia in the left eye was documented at 1 year by behavioral testing. At age 6 years, the left eye was injected with [3H]proline and the striate cortex was processed for autoradiography and cytochrome oxidase (CO). The ocular dominance columns in layer IVc labelled with [3H]proline were normal. CO staining showed a novel pattern of thin dark bands in layer IV. These bands occupied the core zones at the center of the ocular dominance columns. Their appearance resulted from relative loss of CO activity along the borders of the ocular dominance columns, regions specialized for binocular processing. These findings indicate that not all forms of amblyopia are accompanied by shrinkage of ocular dominance columns. The unusual pattern of CO staining in layer IVc reflected a subtle alteration in metabolic activity which may have resulted from impairment of binocular function in anisometropic amblyopia.
An analysis of the cross-correlation between ganglion cells in the retina of goldfish
Authors: Levine Michael W.
Published: June 2009

Neighboring ganglion cells in the retinae of vertebrates show cross-correlation between their impulse trains. Cross-correlation is found both in maintained discharges and during responses to visual stimulation. There has been speculation about the function of this statistical dependence, but little is known about its genesis. This study examines the statistics of the interimpulse intervals preceding and those following impulses that coincide with an impulse in the other train. Short intervals are rarer than expected preceding a coincidence, regardless of the form of the cross-correlation. Short intervals are more common than expected following a coincidence when the cross-correlation is positive, but rarer than expected following coincidences during negative cross-correlation. These results contradict the extant models for cross-correlation, but may be explained by the multiplicative combination of a variable common input and the variability within each cell. In addition, the lag (relative timing of coincident impulses in the two cells) is found to be related to the maintained discharge rates of the cells, implying that the lags may be explained without invoking specific delay circuits.
Analysis of the distribution of glycine and GABA in amacrine cells of the developing rabbit retina: A comparison with the ontogeny of a functional GABA transport system in retinal neurons
Authors: Crook Denise K. , Pow David V.
Published: June 2009

The objectives of this study were to (1) determine whether the glycinergic and GABAergic amacrine cells in the developing rabbit retina were neurochemically distinct at birth, (2) determine if the ratio of GABAergic to glycinergic amacrine cells was constant during development, (3) determine whether the capacity to take up a GABA analogue was restricted to GABAergic neurons, and (4) whether initiation of GABA transport into GABAergic neurons preceded the presence of a content of GABA in these neurons. We have used a novel strategy to immunolocalize a non-endogenous GABA analogue, γ-vinyl GABA, which is taken up into neurons by a GABA transporter. Examination of serial semithin resin-embedded sections of neonatal rabbit retinae that had been immunolabelled for glycine, GABA or γ-vinyl GABA revealed that at 1 day postnatum, 60% of amacrine cells contain glycine but not GABA and did not accumulate γ-vinyl GABA, which is similar to the percentage of glycinergic amacrine cells in the adult retina. The vast majority of the remaining amacrine cells contained GABA and many also transported γ-vinyl GABA; however, a significant number of GABA-containing cells failed to accumulate γ-vinyl GABA suggesting that possession of a content of GABA did not have to be preceded by, or be concomitant with, the presence of a GABA transport system. By 10 days postnatum, over 99% of GABA-containing amacrine cells also transported γ-vinyl GABA indicating their functional maturity. Analysis of the horizontal cells revealed no evidence for uptake of γ-vinyl GABA, but another GABA analogue, diaminobutyric acid, which is a substrate both for the neuron-associated GABA transporter and the glial GABA transporter, was accumulated into some horizontal cells at 21 days postnatum, a time point when these cells also contain endogenous GABA. We conclude that amacrine cells are committed to being GABAergic or glycinergic at, or prior to birth, and that in some amacrine cells, expression of a content of GABA may occur prior to the capacity to transport GABA. Conversely, in some ganglion cells transport of γ-vinyl GABA may precede a content of GABA.
ON cone bipolar cells in rat express the metabotropic receptor mGluR6
Authors: Vardi Noga , Morigiwa Katsuko
Published: June 2009

The rod bipolar cell and about five types of ON cone bipolar cells depolarize to light by employing a sign-reversing metabotropic glutamate receptor. Glutamate responses are similar in both rod bipolar and cone bipolar cells, but the receptor mediating this response (mGluRo) was so far demonstrated only in rod bipolar cells. To test if ON cone bipolar cells also express mGluR6, we immunoreacted rat retina with an antibody specific for mGluRo, and studied the staining from serial ultrathin sections. We demonstrate that mGluR6 is indeed expressed in the dendritic tips of cone bipolar cells, the majority of which receive a ribbon synapse, and thus probably are ON cone bipolar cells. We further show that half of the dendritic tips contacting the cones stain for mGluR6, thus implying that all ON cone bipolar cell types express mGluR6.
Une formalisation plus précise pour une annotation moins confuse: la relation d'Élaboration d'entité
Authors: PRÉVOT LAURENT , VIEU LAURE , ASHER NICHOLAS
Published: June 2009

Les théories cherchant à capturer la cohérence discursive (Mann & Thompson, 1987; Asher & Lascarides, 2003) offrent des cadres théoriques stimulants pour analyser de nombreux phénomènes discursifs. Ils peinent parfois cependant à fournir des définitions de relations combinant précision et robustesse pour des travaux d'annotation à grande échelle permettant, par exemple, de constituer des corpus annotés en relations discursives. Le cas des relations d'Élaborationet d'Arrière-planconstitue une parfaite illustration de ce problème. La plupart des théories discursives les incluent, parfois sous des noms différents, et l'on pourrait penser que leur définition et la manière de les reconnaître est maintenant établie. Cependant, en dépit du fait que ce sont les relations les plus courantes dans les corpus, c'est à leur sujet que les annotateurs ont le plus de problèmes. Elles sont souvent prises l'une pour l'autre. Dans cet article nous examinons la source de ces problèmes et nous proposons une solution basée sur la distinction d'une relation d'Élaboration d'entité, que nous formalisons en SDRT.
D'abordmarqueur de structuration du discours
Authors: BRAS MYRIAM , LE DRAOULEC ANNE
Published: June 2009

Dans les études sur les adverbes du français,d'aborda la particularité d'être considéré à la fois comme un adverbe conjonctif et comme un adverbe organisateur du discours. Dans la présente analyse, nous nous focalisons sur les relations ded'abordavec son contexte gauche, dans le cadre théorique de laSegmented Discourse Representation Theory. Nous montrons que le constituant contenantd'abordest attaché, par une relation de discours subordonnante, à un constituant considéré comme topique de discours. Les relations subordonnantes peuvent être des relations d’Elaboration, d’Explication, deRésultatou dePrécondition. A l'inverse, nous montrons qued'abordinterdit les relations coordonnantes pour le rattachement à son contexte gauche.
THE RATE OF INCREASE OF MEAN VALUES OF FUNCTIONS IN HARDY SPACES
Authors: MASHREGHI JAVAD
Published: June 2009

The norm of a function f in the Hardy space Hp(𝔻) is by definition the limit of $\|f_r\|_p$ as r→1. We show that $d \|f_r\|_p/dr$ grows at most like o(1/log r) as r→1.
THE DRAZIN INVERSES OF PRODUCTS AND DIFFERENCES OF PROJECTIONS IN A C*-ALGEBRA
Authors: LI YUAN
Published: June 2009

For two given projections p and q in a C*-algebra, we investigate how to express the Drazin inverses of the product pq and the difference p−q, and give applications. As a special case, we obtain the results of [C. Y. Deng, ‘The Drazin inverses of products and differences of orthogonal projections’, J. Math. Anal. Appl.335 (2007) 64–71], with considerably simpler proofs.
A NEW CONSTRUCTION FOR REGULAR SEMIGROUPS WITH QUASI-IDEAL ORTHODOX TRANSVERSALS
Authors: KONG XIANGJUN , ZHAO XIANZHONG
Published: June 2009

In any regular semigroup with an orthodox transversal, we define two sets R and L using Green’s relations and give necessary and sufficient conditions for them to be subsemigroups. By using R and L, some equivalent conditions for an orthodox transversal to be a quasi-ideal are obtained. Finally, we give a structure theorem for regular semigroups with quasi-ideal orthodox transversals by two orthodox semigroups R and L.
Modeling the modern marine δ30Si distribution
Authors: Reynolds B. C.
Published: June 2009

The silicon isotopic composition of opal sediments can be used as a proxy for past Si utilization, and hence paleoproductivity for a fixed ocean circulation. Interpretation of this Si utilization proxy is limited by our understanding of the present marine Si isotope distribution. Observations show significant isotopic variations is silicic acid between deep‐water masses that are not captured by a previous global climate model (GCM). Here, simple box models of the global oceans for the Si cycle are presented, which can account for the observed 0.3‰ difference between Atlantic and Pacific deep‐water δ30Si values, using typical opal export fluxes. The δ30Si gradient results from both a high δ30Si of dissolved Si overturning in the North Atlantic and the dissolution of low δ30Si of opal in the deep waters around the Southern Ocean that feed into the Pacific.
Combined effects of QBO and 11‐year solar cycle on the winter hemisphere in a stratosphere‐troposphere coupled system
Authors: Ito Kosuke , Naito Yoko , Yoden Shigeo
Published: June 2009

Combined effects of the quasi‐biennial oscillation (QBO) and the 11‐year solar cycle (SC) on the winter hemisphere are investigated with an idealized mechanistic circulation model of a stratosphere‐troposphere coupled system. A zonal momentum forcing is imposed to mimic a westerly or easterly phase of the QBO and a heating anomaly associated with the SC is introduced around the stratopause. A series of long time integrations of 39,600 days are performed to obtain statistically significant results for forty‐six combinations of these experimental parameters. The obtained dependence of the temperature response in the polar stratosphere on the combination of QBO and SC are qualitatively consistent with the observed responses. The difference in the winter polar stratosphere between the solar maximum and minimum phase is highly significant at above the 95% confidence level in many cases of the QBO westerly runs. The SC effect is, however, relatively small compared to the QBO effect.
Hybrid simulation of foreshock waves and ion spectra and their linkage to cusp energetic ions
Authors: Wang X. Y. , Lin Y. , Chang S.‐W.
Published: June 2009

A three‐dimensional global hybrid simulation is carried out to investigate energetic ions and electromagnetic waves in the quasi‐parallel (Q‐∥) bow shock and cusp for a typical interplanetary magnetic field configuration during the cusp energetic particle events. The bow shock, magnetosheath, and dayside magnetosphere form by interaction between the solar wind and geomagnetic dipole field. Ions of solar wind characteristics injected into the system evolve along with electromagnetic waves in a self‐consistent manner. Several important features are yielded from the simulation. Solar wind ions are accelerated by the waves and turbulence at the bow shock and foreshock as indicated by the ion distribution. The shock‐accelerated ions possess an exponential energy spectrum with their differential flux scaled by the field‐aligned distance to the bow shock, consistent with satellite observations. Second, the compressive and transversal waves in the foreshock are strongly correlated with the diffuse ion dynamics. Third, energetic ions in the magnetosheath and cusp downstream from the Q‐∥ shock also exhibit a spectrum similar to those at the shock. By tracing trajectories of cusp energetic ions in the simulation, the origin of these ions is revealed. Their source is predominantly associated with the Fermi acceleration at the Q‐∥ shock and foreshock. Waves in the magnetosheath and cusp, as well as magnetic reconnection at the high‐latitude magnetopause, are relatively insignificant in accelerating cusp energetic particles.