bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of contrast on the visual response of lagged and nonlagged cells in the cat lateral geniculate nucleus
Authors: Hartveit E. , Heggelund P.
Published: June 2009

The response vs. contrast characteristics of different cell classes in the dorsal lateral geniculate nucleus (LGN) were compared. The luminance of a stationary flashing light spot was varied stepwise while the background luminance was constant. Lagged X cells had lower slope of the response vs. contrast curve (contrast gain), and they reached the midpoint of the response range over which the cells' response varied (dynamic response range) at higher contrasts than nonlagged X cells. These results indicated that nonlagged cells are well suited for detection of small contrasts, whereas lagged cells may discriminate between contrasts over a larger range. The contrast gain and the contrast corresponding to the midpoint of the dynamic response range were similar for X and Y cells. The latency to onset and to half-rise of the visual response decreased with increasing contrast, most pronounced for lagged cells. Even at the highest contrasts, the latency of lagged cells remained longer than for nonlagged cells. For many lagged cells, the latency to half-fall decreased with increasing contrast. It is shown that the differences in the response vs. contrast characteristics between lagged and nonlagged X cells in the cat are similar to the differences between the parvocellular and magnocellular neurones in the monkey.
Molecular cloning and localization of rhodopsin kinase in the mammalian pineal
Authors: Zhao Xinyu , Haeseleer Françoise , Fariss Robert N. , Huang Jing , Baehr Wolfgang , Milam Ann H. , Palczewski Krzysztof
Published: June 2009

Several retinal photoreceptor proteins involved in phototransduction have also been found in the mammalian pineal. This study demonstrates that rat and human pineals express protein kinases that are identical to the corresponding rod photoreceptor rhodopsin kinases. The deduced amino acid sequence of rat and human rhodopsin kinases have 84% sequence similarity to the earlier reported sequence of the bovine retinal enzyme, with complete conservation of the topological regions containing the position of the catalytic domain and sites of posttranslational modifications. Rat pineal also expresses rod opsin and putative blue cone opsin. Using immunocytochemistry, rod opsin and rhodopsin kinase were found to be co-localized in pinealocytes in the human tissue. These data demonstrate that the mammalian pineal contains light-sensitive opsins and a kinase involved in their inactivation. These findings correlate with an earlier report that neonatal rats show extraretinal light sensitivity, and suggest that a functional photoreceptive system may be present in the adult mammalian pineal.
Modulation of endogenous dopamine release in the fish retina by light and prolonged darkness
Authors: Weiler Reto , Baldridge William H. , Mangel Stuart C. , Dowling John E.
Published: June 2009

The effect of light stimuli and prolonged darkness on the release of endogenous dopamine was measured in the white perch and hybrid bass retinas. Isolated retinas were superfused and released dopamine was measured using extraction and high-pressure liquid chromatography separation techniques. Potassium-induced release did not depend on the background illumination nor on the period of previous darkness. Steady white light did not affect release, but flickering light of 2 Hz increased release about two-fold. During prolonged darkness, the release of dopamine increased steadily over the test period of 2 h, but only if the experiments were performed at night. During the day such an increase was not observed. The increased release during prolonged darkness at night was turned off by a short period of steady white light. The release patterns obtained from the white perch and the hybrid bass were similar. However, the hybrid bass retina showed much lower levels of dopamine than did the white perch retina.
Glutamate containing neurons in the cat superior colliculus revealed by immunocytochemistry
Authors: Jeon Chang-Jin , Gurski Michael R. , Mize R. Ranney
Published: June 2009

Glutamate is the probable neurotransmitter of both retinal and cortical afferents to the cat superior colliculus (SC). The present study shows that glutamate is also contained in many postsynaptic neurons in SC. The distribution, morphology, and ultrastructure of neurons in SC were examined using glutamate antibody immunocytochemistry. Labeled cells were widely distributed throughout, but a specific laminar pattern was evident. Relatively few cells were found in the zonal and upper superficial gray layers (SGL). A dense band of intensely labeled neurons was found within the deep superficial gray and upper optic layers. Many cells were also labeled in the deeper layers. Labeled cells had varied sizes and morphologies. Soma diameters ranged from 9–67 μm, with a mean of 22 μm. Cells with stellate, vertical fusiform, and multipolar morphologies were labeled. Cells in the deep subdivision all had morphologies and sizes typical of projection neurons. To determine if labeled cells in the dense band were also projection neurons, WGA-HRP was injected into the lateral posterior nucleus and these sections were double-labeled with the glutamate antibody. Over one-half of cells in the dense band that were labeled by HRP were also obviously labeled by antibody. At the electron-microscope level, both medium- and large-sized neurons were also labeled by glutamate antibodies. These cells had different but characteristic morphologies.
Endogenous opiates in the chick retina and their role in form-deprivation myopia
Authors: Seltner Ruth L. Pickett , Rohrer Baerbel , Grant Vincent , Stell William K.
Published: June 2009

In this study, the possible role of the retinal enkephalin system in form-deprivation myopia (FDM) in the chick eye was investigated. Daily intravitreal injection of the nonspecific opiate antagonist naloxone blocked development of FDM in a dose-dependent manner, while injection of the opiate agonist morphine had no effect at any dose tested. TheED50for naloxone (calculated maximum concentration in the vitreous) was found to be in the low picomolar range. The results using receptor-subtype-specific drugs were contradictory. Drugs specific for μ and δ receptors had no effect on FDM. The κ-specific antagonist nor-binaltorphimine (nor-BNI) reduced FDM by about 50% at maximum daily retinal doses ranging between 4 X 10-10and 4 X 10-7M, while the κ-specific agonist U50488 blocked FDM in a dose-dependent manner with anED50between 5 X 10-8and 5 X 10-7M. Met-enkephalin immunoreactivity (ME-IR) was localized immunocytochemically to a subset of amacrine cells (ENSLI cells) and their neurites in the inner plexiform layer (IPL). As reported previously, ENSLI cells from untreated chick retinas showed a cyclical pattern of immunoreactivity, with increased immunoreactivity in the light compared to the dark. Form-deprivation did not appear to change this pattern. Amounts of preproenkephalin mRNA from normal or form-deprived eyes were approximately the same under all conditions. Daily injection of naloxone, however, did increase ME-IR in the dark. These results suggest that naloxone may affect release of enkephalin from the ENSLI cells. The results as presented are inconclusive with regards to the role of the enkephalin system in FDM. While the κ receptor may participate, there is no conclusive evidence here for a direct effect of opiate receptors. The effect of naloxone on form-deprived eyes may be due to its effect on release of peptides from the ENSLI cells.
A comparison of GABACand ρ subunit receptors from the white perch retina
Authors: Qian Aohua , Hyatt George , Schanzer Andres , Hazra Rohan , Hackam Abigail S. , Cutting Garry R. , Dowling John E.
Published: June 2009

There is increasing evidence that GABACreceptors are composed of GABA ρ subunits. In this study, we compared the properties of native GABACreceptors with those of receptors composed of a GABA ρ subunit. A homologue of the GABA ρ gene was cloned from a white perch (Roccus americana) retinal cDNA library. The clone (perch-s) has an open reading frame of 1422 nucleotide base pairs and encodes a predicted protein of 473 amino acids. It is highly homologous to GABA ρ subunits cloned from human and rat retinas. The receptors (perch-s receptor) expressed by this gene inXenopusoocytes show properties similar to those of the GABACreceptors present on white perch retinal neurons. GABA induced a sustained response that had a reversal potential of –27.1 +minus; 3.6 mV. TheEC50for the response was 1.74 +− 1.25 μM, a value similar to that reported for GABACreceptors. Pharmacologically, the responses were bicuculline insensitive and not modulated by either diazepam or pentobarbital as is the case for GABAc receptors. There were, however, some distinct differences between native GABAc and perch-s receptors. I4AA acts as a partial agonist on perch-s receptors whereas it is strictly an antagonist on native GABACreceptors. Picrotoxin inhibition is noncompetitive on perch-s receptors, but both competitive and noncompetitive on GABACreceptors. We conclude that GABACreceptors are formed by GABApsubunits but that native GABAc receptors probably consist of a mixture of GABA ρ subunits.
Specialized neuropeptide Y- and glucagon-like immunoreactive amacrine cells in the peripheral retina of the turtle
Authors: Wetzel Randall K. , Eldred William D.
Published: June 2009

There are many regional differences in cell morphology and neurochemistry in the retina. This study examined a specialized population of neuropeptide Y- and glucagon-like immunoreactive amacrine cells in the peripheral retina of the turtle. Some of the dendritic processes from these peptidergic amacrine cells formed a dense circumferentially oriented nerve fiber plexus which ran parallel to the ora serrata. Collaterals from this plexus projected into and innervated the nonpigmented ciliary epithelium in the pars plana region of the ciliary body. Electron microscopy revealed that the neuropeptide Y- and glucagon-like immunoreactive processes in the ciliary epithelium contained many labeled, large dense-cored vesicles. Small crystals of lipid-soluble fluorescent dye were implanted in the retina near the ora serrata in fixed retinal tissue to search for other peripheral retinal specializations. Numerous thick and thin cell processes oriented parallel to the ora serrata were labeled in the retina by the dye. In addition, many dye-labeled somata with circumferentially oriented dendritic arborizations were seen in the extreme periphery of the retina. Many of these dye-labeled cells and processes were clearly not associated with the neuropeptide Y- and glucagon-like immunoreactive cells described above. This study has shown that some peptidergic neurons in the peripheral retina have a unique morphology in comparison to more centrally located cells. The function of these specialized peripheral cells is not established, but the innervation of the ciliary epithelium by peptidergic amacrine cells suggests that they may be involved in control of aqueous inflow.
Alternating monocular exposure increases the spacing of ocularity domains in area 17 of cats
Authors: Tieman Suzannah Bliss , Tumosa Nina
Published: June 2009

Goodhill (1993) has recently suggested that the spacing of ocularity domains in visual cortex is not solely an intrinsic property of cortex, but is determined, at least in part, by the degree of correlation in the activity of the two eyes. In support of this model, Löwel (1994) has shown that strabismus, which decorrelates the activity of the two eyes, increases the spacing of ocular dominance columns in area 17, but not area 18, of the cat. As a further test of Goodhill's model, in this paper we examine the effects of another rearing procedure that decorrelates the activity of the two eyes, namely alternating monocular exposure (AME). Cats were reared either normally (9 cats) or with AME (21 cats). We labeled their ocularity domains by one of three methods: ocular dominance columns by 2-deoxyglucose (14 cats), and ocular dominance patches by transneuronal transport (14 cats), or by injections of tracer into single layers of the lateral geniculate nucleus (LGN; 2 cats). The spacing of ocular dominance was 11% greater in the AME cats than in the normal cats (0.976vs.0.877 mm). These results are similar to those previously reported for strabismic cats, although the effect is less striking. We thus confirm that decorrelating the activity of the two eyes increases the spacing of cortical ocularity domains. Our results further suggest that the degree of decorrelation affects the extent of that increase.
Estimating the contributions of NMDA and non-NMDA currents to EPSPs in retinal ganglion cells
Authors: Velte T. J. , Yu W. , Miller R. F.
Published: June 2009

Whole-cell recordings were obtained from retinal ganglion cells of the tiger salamander (Ambystoma tigrinum) in a superfused slice preparation to evaluate contributions of NMDA (N-methyl-D-aspartate) and KA/AMPA (kainate/α-amino-3-hydroxy-5-methyl-4-isoxalone propionic acid) receptors to excitatory postsynaptic potentials (EPSPs) of retinal ganglion cells. Synaptic activation of retinal ganglion cells was achieved through the use of a brief pressure pulse of hyperosmotic Ringer (Ringer + sucrose) delivered through a microelectrode visually placed in the inner plexiform layer while whole-cell recordings were obtained from adjacent cells in the ganglion cell layer. Separation of NMDA and KA/AMPA excitatory postsynaptic currents (EPSCs) was achieved through the application of the antagonists NBQX and D-AP7, while inhibitory currents were blocked by strychnine and picrotoxin. Simple addition of the two independent EPSCs showed, most often, that the sum of the KA/AMPA and NMDA currents was less than the control response, but in some cases the sum of the two currents exceeded the magnitude of the control response. Neither result was consistent with expectations based on voltage-clamp principles and the assumption that the two currents were independent; for this reason, we considered the possibility of nonlinear interactions between KA/AMPA and NMDA receptors. Computer simulations were carried out to evaluate the summation experiments. We used both an equivalent cylinder model and a more realistic, compartmental model of a ganglion cell constrained by a passive leakage conductance, a linear KA/AMPA synaptic current, and a nonlinear NMDA current based on the well-known, voltage-sensitive Mg2+ block. Computer simulation studies suggest that the hypo- and hyper-summation of NMDA and KA/AMPA currents, observed physiologically, can be accounted for by a failure to adequately space clamp the neuron. Clamp failure leads to enhanced NMDA currents as the ion channels are relieved of the Mg2+ block; their contribution is thus exaggerated depending on the magnitude of the conductance change and the spatial location of the synaptic input.
The use of m-sequences in the analysis of visual neurons: Linear receptive field properties
Authors: Reid R. C. , Victor J. D. , Shapley R. M.
Published: June 2009

We have used Sutter's (1987) spatiotemporal m-sequence method to map the receptive fields of neurons in the visual system of the cat. The stimulus consisted of a grid of 16 X 16 square regions, each of which was modulated in time by a pseudorandom binary signal, known as an m-sequence. Several strategies for displaying the m-sequence stimulus are presented. The results of the method are illustrated with two examples. For both geniculate neurons and cortical simple cells, the measurement of first-order response properties with the m-sequence method provided a detailed characterization of classical receptive-field structures. First, we measured a spatiotemporal map of both the center and surround of a Y-cell in the lateral geniculate nucleus (LGN). The time courses of the center responses was biphasic: OFF at short latencies, ON at longer latencies. The surround was also biphasic—ON then OFF—but somewhat slower. Second, we mapped the response properties of an area 17 directional simple cell. The response dynamics of the ON and OFF subregions varied considerably; the time to peak ranged over more than a factor of two. This spatiotemporal inseparability is related to the cell's directional selectivity (Reid et al., 1987, 1991; McLean & Palmer, 1989; McLean et al., 1994). The detail with which the time course of response can be measured at many different positions is one of the strengths of the m-sequence method.
Spiking and nonspiking models of starburst amacrine cells in the rabbit retina
Authors: Velte T. J. , Miller R. F.
Published: June 2009

The integrative properties of starburst amacrine cells in the rabbit retina were studied with compartmental models and computer-simulation techniques. The anatomical basis for these simulations was provided by computer reconstructions of intracellularly stained starburst amacrine cells and published data on dendritic diameter and biophysical properties. Passive and active membrane properties were included to simulate spiking and nonspiking behavior. Simulated synaptic inputs into one or more compartments consisted of a bipolar-like conductance change with peak and steady-state components provided by the sum of two Gaussian responses. Simulated impulse generation was achieved by using a model of impulse generation that included five nonlinear channels (INa, ICa, Ia,. Ik. Ik.Ca). The magnitude of the sodium channel conductance change was altered to meet several different types of impulse generation and propagation behaviors. We studied a range of model constraints which included variations in membrane resistance (Rm) from 4,000 Ω.cm2 to 100,000 Ω.cm2, and dendritic diameter from 0.1 to 0.3 μm. In a separate series of simulations, we studied the feasibility of voltage-clamping starburst amacrine cells using a soma-applied, single-electrode voltage clamp, based on models with and without dendritic and somatic spiking behavior. Our simulation studies suggest that single dendrites of starburst amacrine cells can behave as independent functional subunits when the Rm is high, provided that one or a small number of dendrites is synaptically co-activated. However, as the number of co-activated dendrites increases, the starburst cell behavior becomes more uniform and independent dendritic function is less prevalent. The presence of impulse activity in the dendrites raises new questions about dendritic function. However, dendritic impulses do not necessarily eliminate independent dendritic function, because dendritic impulses commonly fail as they propagate toward the soma, where they contribute EPSP-like responses which summate with conventional synaptic currents.
Large retinal ganglion cells that form independent, regular mosaics in the ranid frogs Rana esculenta and Rana pipiens
Authors: Shamim K. M. , Scalia F. , Tóth P. , Cook J. E.
Published: June 2009

Population-based studies of ganglion cells in retinal flatmounts have helped to reveal some of their natural types in mammals, teleost fish and, recently, the aquatic mesobatrachian frog Xenopus laevis. Here, ganglion cells of the semiterrestrial neobatrachian frogs Rana esculenta and Rana pipiens have been studied similarly. Ganglion cells with large somata and thick dendrites could again be divided into three mosaic-forming types with distinctive stratification patterns. Cell dimensions correlated inversely with density, being smallest in the visual streak. Cells of the αa mosaic (<0.2% of all ganglion cells) had the largest somata at each location (often displaced) and their trees were confined to one shallow plane within sublamina a of the inner plexiform layer. In regions of high regularity, many trees were symmetric. Elsewhere, asymmetric, irregular trees predominated and their dendrites, although sparsely branched, achieved consistent coverage by intersecting in complex ways. Cells of the αab mosaic were more numerous (≈0.7%) and had large somata, smaller (but still large) trees, and dendrites that branched extensively in two separate shallow planes in sublaminae a and b. The subtrees did not always match in symmetry, and each subtree tessellated independently with its neighbors. Cells of the αc mosaic (≈0.1%) had large, orthotopic somata and large, sparse trees (often asymmetric and irregular) close to the ganglion cell layer. Nearest-neighbor analyses and spatial correlograms confirmed that each mosaic was regular and independent. Densities, proportions, sizes, and mosaic statistics are tabulated for all three types, which are compared with types defined by size and symmetry in R. pipiens, by discriminant analysis in R. temporaria, by physiological response in both, and by mosaic analysis in Xenopus and several teleosts. The variable stratification of these otherwise similar types across species is consistent with other evidence that stratification may be determined, in part, by functional interactions.
The role of GABA in modulating theXenopuselectroretinogram
Authors: Arnarsson Arsaell , Eysteinsson Thor
Published: June 2009

We have recorded the electroretinogram (ERG) from the superfused eyecup of theXenopusretina in order to assess the effects of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA), and its agonists and antagonists, on individual ERG components. We found that GABA (0.5–10 mM) reduced the amplitudes of both theb-andd-waves of theXenopusERG. The GABA uptake blocker nipecotic acid (1 mM) had similar effects onb-andd-waves. GABA at 5 mM and 10 mM also caused an increase in thea-wave. The GABA antagonist picrotoxin (0.1–2 mM) and the GABA/a antagonist bicuculline (0.2 mM) both increased the amplitude of theb-andd-waves of the ERG. The GABA/b agonist baclofen (0.3 mM) reduced the amplitude of the ERGb-wave, enhanced the amplitude of thea-wave, and slightly reduced the amplitude and increased the peak time of thed-wave. The GABA/b antagonists phaclofen and saclofen had no reliable effects on theXenopusERG. Glutamate analogs known to affect specific types of retinal neurons were applied to modify the retinal circuitry and then the effects of GABA and its antagonists were examined under these modified conditions. 2-amino-4-phosphonobutyric acid (APB) increased thed-wave, and blocked theb-wave and the effect of GABA on the ERG, but not the antagonist-induced increase in thed-wave. KYN blocked the antagonist-induced increase in theb-wave, while GABA increases the amplitude of theb-wave if thed-wave has been removed by prior superfusion with kynurenic acid (KYN). N-methyl-DL-aspartate (NMDLA), which acts only in the proximal retina, reduced the amplitude of the ERG and blocked the effect of GABA and the antagonist-induced increase in ERGb-andd-waves amplitude. These results suggest that GABAergic mechanisms related to both A and B receptor types can influence the amplitude and light sensitivity of all the components of theXenopusERG. Since GABA is found in greatest abundance in the proximal retina, and B type of receptors are present almost exclusively there, the data suggests that most of the effects of GABA agonists and antagonists observed are dependent on proximal retinal mechanisms, and that there are separate mechanisms in the proximal retina related to theb-and thed-waves.
Characteristics of cervico-ocular responses in the chameleon
Authors: Gioanni Henri , Sansonetti Annie , Bennis Mohamed
Published: June 2009

The cervico-ocular reflex (COR) was investigated in the chameleon. Two kinds of responses were observed by oscillating the body (sine-wave stimuli) in the fixed-head animal: a "smooth response" of very low gain (around 0.08) and a saccadic response composed of 1–12 saccades per cycle of stimulation (depending on the stimulation frequency). Both responses were elicited in the compensatory direction (same direction as the stimulation) and exhibited a frequency dependence with low-pass properties. The saccadic response was especially developed and displayed a higher gain (up to 0.4) than the smooth response. In darkness, the saccades were triggered near the zero point (head-body alignment), whereas in the presence of a fixed visual surround they were elicited more regularly throughout the stimulation cycle. The amplitude of saccades was increased in the light. Consequently, the gain and the phase lag of the saccadic reponse were enhanced by the visual input. No visuo-cervical interaction was observed for the smooth response. Oscillating the body at a constant velocity (seesaw or ramp stimuli) revealed a frequency effect on the number of saccades (during a cycle of stimulation), but not on the gain of the response. Increasing the amplitude of oscillations augmented only very slightly the amplitude of saccades and consequently decreased the gain. Hence, the best working range of the saccadic response corresponds to body or head movements of low amplitude (up to ±20 deg) and low frequency (up to 0.25 Hz), and is improved by a visual input. These properties are discussed on a comparative point of view. It is proposed that, in chameleons, the saccadic response could contribute to gaze stabilization and add to the vestibulo-ocular and the optokinetic responses.
Spectral sensitivity of cones in an ungulate
Authors: Neitz Jay , Jacobs Gerald H.
Published: June 2009

Ungulates have been classified as having arrhythmic eyes in the sense that they contain features appropriate both to diurnal and nocturnal life. The former is typically associated with multiple classes of cones and a color-vision capacity. To see if an arrhythmic animal has these features, the number of cone classes was determined and the spectra of these cones were measured in a common ungulate, the domestic pig (Sus scrofa). Examination with electroretinogram (ERG) flicker photometry revealed the presence of two classes of cones in the pig's eye having average maximum sensitivity (λmax) at 439 nm and 556 nm, respectively. This ungulate thus has the requisite retinal basis for dichromatic color vision.
Centrifugal directional bias in the middle temporal visual area (MT) of the macaque
Authors: Albright Thomas D.
Published: June 2009

We have examined the distribution of preferred directions of motion for neurons in the middle temporal visual area (MT) of the macaque. We found a marked anisotropy favoring directions that are oriented away from the center of gaze. This anisotropy is present only among neurons with peripherally located receptive fields. This peripheral centrifugal directionality bias corresponds well to the biased distribution of motions characteristic of optic flow fields, which are generated by displacement of the visual world during forward locomotion. The bias may facilitate the processing of this common form of visual stimulation and could underlie previously observed perceptual anisotropies favoring centrifugal motion. We suggest that the bias could arise from exposure of modifiable cortical circuitry to a naturally occurring form of selective visual experience.
Expression of GABA in the fetal, postnatal, and adult human retinas: An immunohistochemical study
Authors: Nag T. C. , Wadhwa S.
Published: June 2009

The expression of GABA in the human fetal (12–25 weeks of gestation), postnatal (five-month-old), and adult (35-year-old) retinas was investigated by immunohistochemistry. GABA expression was seen as early as 12 weeks in the undifferentiated cells of the inner neuroblast zone; a few optic nerve fiber layer axons were clearly labeled, suggesting that some of the stained cell bodies were prospective ganglion cells, others could be displaced amacrine cells. From 16–17 to 24–25 weeks, intense labeling was found in the amacrine, displaced amacrine, and some ganglion cells. During this time period, horizontal cells (identified by calbindin immunohistochemistry), undergoing migration (periphery) and differentiation (center), expressed GABA prominently. In the postnatal retina, some horizontal cells were moderately labeled, but very weakly in a few cells, in the adult. The Müller cells developed immunoreactivity first weakly at 12 weeks and then moderately from 16–17 weeks onward. The staining was also evident in the postnatal and adult retinas, showing labeled processes of these glial cells. Virtually no axons in the adult optic nerve and nerve fiber layer were stained; the staining was restricted to a few, large ganglion cells and displaced amacrine cells. Some amacrines were also labeled. The possibility that GABA might play a role in horizontal cell differentiation and maturation is highlighted. Other evidences suggest that GABA might play a role in metabolism during retinal development.
Immunocytochemical localization of dopamine D1 receptors in the retina of mammals
Authors: Nguyen-Legros J. , Simon A. , Caillé I. , Bloch B.
Published: June 2009

Dopamine is one of the major neurotransmitters in the retina. It is released from amacrine and interplexiform cells into both inner (IPL) and outer (OPL) plexiform layers. Several dopaminergic actions are known to occur through D1 receptors (D1R) but the precise location of these receptors has not been established. An antibody that recognizes the intracytoplasmic C-terminal of the rat D1R was used to detect D1R, immunohistochemically, in rats (Wistar and RCS), mouse, hamster, and macaque monkey retinas. The OPL was heavily stained in each species, consistent with the known actions of dopamine on horizontal cells. Three to five bands were observed in the IPL, depending on species. Three were in the a sublayer, the outermost of which was close to the amacrine cell layer, and may represent the massive dopamine input to the AII rod-amacrine cells. As observed in mice, where bipolar cells are D1-immunoreactive, the band located in sublayer 3 of the IPL may contain cone-bipolar cell terminals. A band of D1R-immunoreactivity in the b sublayer of the IPL contains ON-bipolar cell terminals and a second site of interaction between dopaminergic cells and the AII amacrine cells. This sublayer was absent from the RCS rat retina, suggesting a severe impairment of the rod-driven pathway following rod degeneration in these mutant rats. Cells in the ganglion cell layer exhibited relatively heavy staining, and may be ganglion cells or displaced amacrine cells. Some extrasynaptic localizations of D1R in the retina are suggested.
The appearance and distribution of microglia in the developing retina of the rat
Authors: Ashwell K. W. S. , Holländer H. , Streit W. , Stone J.
Published: June 2009

We have examined the development of microglia in the rat retina, using a peroxidase-conjugated lectin derived fromGriffonia simplicifolia. Retinas were studied from animals aged from E(embryonic day)12, just after the invagination of the optic cup and prior to the closure of the optic fissure, to adulthood. The lectin also proved a sensitive label for the endothelial cells of the developing retina. Our results provide some support for the view that microglia are derived from the monocyte-macrophage series of blood cells. At E12, most labeled cells were found at the vitreal surface, suggesting that they had come from the hyaloid circulation, while some had entered the retina and appeared to be migrating towards its ventricular surface. From E14 to early postnatal ages, most labeled cells had processes and resembled the amoeboid microglial cells described in silver carbonate staining studies (Ling, 1982). The number of labeled cells rose from about 700 to E14 to a peak of about 27,000 at P(postnatal day)7, and fell to about 19,600 by P12. As early as E16, a regularity was apparent in the distribution of microglial cells over the surface of the retina, the cells tending to avoid each other. Microglial cells are found throughout the thickness of the very young retina, but as the layers of the retina differentiate, they are increasingly restricted to the inner half of the retina. Our findings indicate that microglia enter the retina well before the period of neuronal death, making it unlikely that they invade the retina solely in response to cell death. Our results confirm however that, once in the retina, microglia become associated with, and appear to phagocytose, the pyknotic debris which appears during the period of neuronal death. They also become closely associated with the retinal vasculature. In the adult, the intensity of the labeling of microglia was much reduced. Those cells which were labeled appeared more differentiated, resembling the “resting microglia” described in earlier studies.
Dopamine synthesis and metabolism in rhesus monkey retina: Development, aging, and the effects of monocular visual deprivation
Authors: Iuvone P. Michael , Tigges Margarete , Fernandes Alcides , Tigges Johannes
Published: June 2009

The normal postnatal development, the influence of age, and the effects of visual deprivation on the dopamine system in the retina of rhesus monkeys were examined. The lowest level of retinal dopamine was found at birth. By 3–4 weeks of age, the dopamine concentration had more than doubled. This level remained relatively constant in the retinas of older infants and of adult monkeys up to 34 yr of age. The level of the dopamine metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) and the activity of tyrosine hydroxylase did not significantly change as a function of age during the postnatal life span.

Monocular occlusion of newborn or infant monkeys for 1–15 months with opaque contact lenses resulted in decreases in the retinal concentrations of dopamine and DOPAC relative to the concentrations in the same animals' unoccluded eyes. Occlusion also resulted in a lower level of tyrosine hydroxylase activity in the retina. Monocular eyelid suture from birth to 15 months of age resulted in less consistent alterations of retinal dopamine and DOPAC levels; tyrosine hydroxylase activity, however, was consistently reduced by lid suture. Thus, dopamine synthesis and metabolism, and the ontogenetic increase of the retinal dopamine level of rhesus monkey are reduced by light deprivation.
Identification and localization of 5-hydroxytryptamine receptor sites in macaque visual cortex
Authors: Parkinson David , Coscia Elizabeth C. , Daw Nigel W.
Published: June 2009

The two main receptor subtypes for 5-hydroxytryptamine (5HT) were measured and localized in visual cortical areas of macaque monkey. [3H]5HT was used to label all 5HT-1 receptor subtypes and [3H]ketanserin was used to label 5HT-2 receptors. Both receptor types could be demonstrated in membranes prepared from macaque primary visual cortex. The specificity of these ligands for 5HT-1 or 5HT-2 receptors was demonstrated by the pharmacological profile of inhibitors of the specific binding. 5HT-1A receptor sites were detected by displacement experiments and by direct labeling with [3H]8-hydroxy-2(di-n-propylamino) tetralin 8OH-DPAT. Receptor autoradiography showed that the distribution of these receptor subtypes varied from one part of visual cortex to another. 5HT-1 receptors, labeled with [3H]5HT were present in several bands through layer IV of primary visual cortex with the densest band seen in and above layer IVA: another band was in lower layer VI. The band in layer VI was predominantly 5HT-1A sites. There were two main bands of 5HT-2 receptor sites, the most prominent around the IV/V boundary, and the other extending from layer IVA upwards. Adjacent areas showed 5HT receptors in a broad band corresponding to layer IV. 5HT-1A sites were found in superficial layers of adjacent areas, except V2. These layering patterns did not correspond precisely with cytoarchitectonic layering, nor with the pattern of 5HT-containing presynaptic fibres in published reports. It is important, therefore, in considering the role of the 5HT-containing neurons in cortical function to take account not only of the anatomy of the presynaptic terminals, but also of the postsynaptic receptors upon which the released transmitter will act, and their location within the cortex.
Quantitative aspects of synaptic ribbon formation in the outer plexiform layer of the developing cat retina
Authors: Rapaport David H.
Published: June 2009

The development of synaptic ribbons in rod and cone photoreceptor terminals of the cat retina was studied using quantitative electron microscopy. At the region of the area centralis, synaptic ribbon profiles are initially recognized at PCD (postconception day) 59. Synaptic ribbon density increases rapidly, reaching a peak of 0.55 ribbons/μm3 at PCD 68 (postnatal day 3) and maintains approximately that value for an additional 8 d. Following PCD 76, ribbon density begins to decrease, to 0.37 ribbons/μm3 at PCD 82 and 0.25 ribbons/μm3 at PCD 102. Although ribbon density drops by approximately 50% during this 39-d period, the outer plexiform layer (OPL) volume at the area centralis increases by about 20%. Ribbon density continues to decrease gradually over a protracted period to reach a final adult value of 0.11–0.14 ribbons/μm3. During the period of high ribbon density, rod spherules with two, or even three ribbon profiles, were routinely observed. In contrast, in the adult, spherules with more than one ribbon profile are only rarely encountered. During development, the length of synaptic ribbon profiles increases from a mean of 0.22 μm at PCD 62 to the 0.47 μm mean length found in the adult.
Effects of dark maintenance on retinal biochemistry and function during taurine depletion in the adult rat
Authors: Cocker Susan E. , Lake Norma
Published: June 2009

Light dependence of the effects of taurine depletion on retinal function and biochemistry was examined in albino rats housed either in cyclic lighting or in continuous darkness. Measurements of retinal taurine, DNA, and rhodopsin contents, and electroretinogram amplitudes were made at weekly intervals. Naka-Rushton parameters were estimated for thebwave amplitude-intensity function. No significant effects of lighting regime were observed on retinal taurine levels in untreated rats, or on the time course or extent of taurine depletion in animals treated with guanidinoethyl sulfonate, an antagonist of taurine transport. In both lighting schemes, treatment led to a linear reduction of retinal taurine content which plateaued after 5–6 weeks at 50% of control despite continued treatment. DNA values did not differ among groups, whereas rhodopsin levels doubled in both groups of dark-maintained rats. For treated rats housed in cyclic lighting, the onset of electroretinogram deficits paralleled the loss of retinal taurine in the absence of changes in rhodopsin levels or cell death.Vmaxwas significantly reduced after 4 weeks of treatment. In contrast, for rats housed in continuous darkness, there were no significant differences in electroretinogram parameters between control and taurine-depleted rats until after 10–14 weeks of treatment. This implies that light exposure accelerates the appearance of functional changes associated with retinal taurine deficiency. The basis of the light dependence and the interpretation of related studies is discussed.
Sur la relation d'Élaboration: des approches intuitives aux approches formelles
Authors: KLEIBER GEORGES , VASSILIADOU HÉLÈNE
Published: June 2009

Le but de notre article est d'entreprendre une réflexion générale sur une des relations de discours parmi les plus importantes, la relation dite d’Élaboration. Il s'agit d'un terme technique pour désigner une relation sémantique ou conceptuelle entre des phrases ou propositions. Toutefois, le sens mondain (non technique) qu'elle a a des répercussions sur l'emploi technique. On constate alors que c'est bien souvent ce sens mondain ou courant, à savoir qu'élaborer c'est préparer, réaliser quelque chose, qui intervient dans la reconnaissance ou dans l'analyse des exemples. Notre propos se limitera ainsi à examiner les définitions du type intuitif qu'on a pu donner de la relation d’Élaboration. Chemin faisant, nous aborderons également la définition donnée dans le cadre de la RST de W. C. Mann et S. Thompson pour en arriver à des caractérisations plus formelles. Nous ouvrirons, enfin, des pistes qui donneront lieu ultérieurement à une analyse plus poussée qui nous aidera à comparer la relation d'Élaborationavec d'autres relations discursives.
h-COBORDISMS AND MAPPING CYLINDER OBSTRUCTIONS
Authors: VAJIAC BOGDAN
Published: June 2009

In this paper we prove a realizability theorem for Quinn’s mapping cylinder obstructions for stratified spaces. We prove a continuously controlled version of the s-cobordism theorem which we further use to prove the relation between the torsion of an h-cobordism and the mapping cylinder obstructions. This states that the image of the torsion of an h-cobordism is the mapping cylinder obstruction of the lower stratum of one end of the h-cobordism in the top filtration. These results are further used to prove a theorem about the realizability of end obstructions.
Omnipresent vertically coherent fluctuations in the ionosphere with a possible worldwide‐midlatitude extent
Authors: Livneh Dorey J. , Seker Ilgin , Djuth Frank T. , Mathews John D.
Published: June 2009

Incoherent Scatter Radar power profile observations at Arecibo, Millstone Hill, and the Poker Flat AMISR have revealed the continuous presence of Coherent Omnipresent Fluctuations in the Ionosphere (COFIs) with periods ranging from roughly 30 to 60 minutes and apparent vertical wavelengths increasing with altitude from tens to hundreds of kilometers. Upon high‐pass filtering of the Incoherent Scatter Radar power profile and electron concentration data, the COFIs are seen unambiguously and ubiquitously in Arecibo results from 22–23 March 2004, 5–6 June, 21–25 September, and 17–20 November 2005, as well as Millstone Hill results from 4 October to 4 November 2002. The COFIs are strong throughout the F region, often spanning altitudes of 160 km to above 500 km, and are detected day and night in the F2 layer. In fact, the COFIs are seen at every time and altitude that there is sufficient plasma to detect them. The COFIs are also observed at Poker Flat, although the poor signal‐to‐noise ratio over segments of the data makes it difficult to determine whether or not they are always present. The consistent detection of the COFIs, along with the longitudinal alignment and large latitudinal spread of the observation sites, suggests that these waves are always present over at least North America. This phenomenon appears to have been reported in Total Electron Concentration (TEC) maps of the ionosphere over much of North America Tsugawa et al. (2007b) as well as in airglow images from Arecibo and many other midlatitude sites around the world. These observations give us insight into the horizontal properties of the waves. While Medium‐Scale Ionospheric Disturbances (MSTIDs) are generally associated with aurorally generated acoustic gravity waves, the properties of the COFIs may suggest otherwise. We present other possible source mechanisms, notably a possible link to oscillations in the solar wind and magnetosphere. We have observed consistent fluctuations with periods of about an hour observed in magnetic field measurements taken at geosynchronous altitudes by the Geostationary Operational Environmental Satellites (GOES)‐10 and ‐12 satellites, which may be linked to the COFIs. We give corresponding solar wind results from ACE and discuss possible coupling mechanisms.
A 3‐D empirical model of F region Medium‐Scale Traveling Ionospheric Disturbance bands using incoherent scatter radar and all‐sky imaging at Arecibo
Authors: Seker Ilgin , Livneh Dorey J. , Mathews John D.
Published: June 2009

Perhaps the most persistent and prominent of the midlatitude nighttime F region phenomena observed with all‐sky imagers is the Medium‐Scale Traveling Ionospheric Disturbances (MSTID) that occur when the geomagnetic activity is low. We introduce a simple empirical 3‐D model of these bands, which was developed on the basis of an extension of results given by Seker et al. (2008). Seker et al. (2008) reported observational results on the 3‐D geometry of MSTID structures found using combined incoherent scatter radar (ISR) and all‐sky imager observations over the Arecibo Observatory in Puerto Rico. To confirm and further investigate these findings, a simple empirical 3‐D model of nighttime MSTID bands is constructed. We show ISR and all‐sky imager results derived from the model, compare them with the actual observations, and highlight the important findings. This model is intended to replicate both the azimuth‐scanning ISR and the all‐sky imager results and is especially useful in explaining how these complex structures appear in azimuth‐scanning ISR results. In addition, confidence in the empirical model allows us to know what to expect from the theory (of MSTID) and to assess how well geomagnetically quiet, nighttime, midlatitude, F region electrodynamics models succeed. Furthermore, the technique described in the paper is not limited to F region or midlatitudes only; it could be applied to any other phenomenon which can be observed by both radar and imager.
Instantaneous dynamics of the cratonic Congo basin
Authors: Downey Nathan J. , Gurnis Michael
Published: June 2009

Understanding the formation mechanisms of cratonic basins provides an examination of the rheological, compositional and thermal properties of continental cratons. However, these mechanisms are poorly understood because there are few currently active cratonic basins. One cratonic basin thought to be active is the Congo basin located in equatorial Africa. The Congo basin is coincident with a large negative free‐air gravity anomaly, an anomalous topographic depression, and a large positive upper mantle shear wave velocity anomaly. Localized admittance models show that the gravity anomaly cannot be explained by a flexural support of the topographic depression at the Congo. We analyze these data and show that they can be explained by the depression of the Congo basin by the action of a downward dynamic force on the lithosphere resulting from a high‐density object within the lithosphere. We formulate instantaneous dynamic models describing the action of this force on the lithosphere. These models show that the gravity and topography of the Congo basin are explained by viscous support of an anomalously dense region located at 100 km depth within the lithosphere. The density anomaly has a magnitude within the range of 27–60 kg m−3 and is most likely compositional in origin. Our models do not provide a constraint on the lithospheric viscosity of the Congo craton because the shallow location of the anomaly ensures strong coupling of the anomaly to the surface regardless of viscosity structure.