bluuebunny/crossref_metadata_2025_split huggingface dataset:
Glutamate containing neurons in the cat superior colliculus revealed by immunocytochemistry
Authors: Jeon Chang-Jin , Gurski Michael R. , Mize R. Ranney 
Published: June 2009

AbstractGlutamate 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

AbstractIn 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

AbstractThere 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

AbstractThere 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

AbstractGoodhill (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

AbstractWhole-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

AbstractWe 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

AbstractThe 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

AbstractPopulation-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

AbstractWe 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

AbstractThe 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

AbstractUngulates 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

AbstractWe 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.