bluuebunny/crossref_metadata_2025 huggingface dataset:
Horizontal cell sensitivity in the cat retina during prolonged dark adaptation
Authors: Lankheet M. J. M. , Rowe M. H. , van Wezel R. J. A. , van de Grind W. A.
Published: June 2009

The effects of dark adaptation on the response properties of ganglion cells have been documented extensively in the cat retina. To pinpoint the different retinal mechanisms that underlie these effects, we studied the response characteristics of cat horizontal (H) cells during prolonged dark adaptation. H-cell responses were recorded intracellularly in the optically intact,in vivoeye. To disentangle rod and cone contributions, sensitivity changes during dark adaptation were tracked with white light and with monochromatic lights that favored either rod or cone excitation. Stable, long-lasting recordings allowed us to measure changes of sensitivity for adaptation periods up to 45 min. Thresholds for white light and 503-nm monochromatic light decreased steadily and in parallel. The maximum increase of sensitivity, after extinguishing a photopic adaptation light, was 1.8 log units only, reached after about 35 min. Sensitivity for 581-nm lights also increased steadily, but at a shallower slope. The steady increase of sensitivity was concomitant with a linear shift in resting membrane potential and with an increase in relative rod contribution to the threshold responses. Even though small-amplitude responses were rod dominated after prolonged dark adaptation, sensitivity to rod signals remained relatively low, compared to sensitivity of cone responses or to the absolute sensitivity of ganglion cells. This suggests that the cone-H-cell pathway plays no role in the dark-adapted cat retina.
Differential effects ofninaCproteins (p132 and p174) on light-activated currents and pupil mechanism inDrosophilaphotoreceptors
Authors: Hofstee Cornelia A. , Henderson Stephen , Hardie Roger C. , Stavenga Doekele G.
Published: June 2009

TheDrosophila ninaClocus encodes two retinal specific proteins (p132 and p174) both consisting of a protein kinase joined to a myosin head domain and a C terminal with a calmodulin-binding domain. The role of p132 and p174 was studiedviawhole-cell recording and through measurements of the pupil mechanism, i.e. the pigment migration in the photoreceptor cells, in theninaCmutants, P[ninaCΔ132] (p132 absent), P[ninaCΔ174] (p174 absent), andninaCp235(null mutant). Voltage-clamped flash responses in P[ninaCΔ174] andninaCp235showed delayed response termination. In response to steady light, plateau responses in both P[ninaCΔ174] andninaCp235were also large. In both cases the defect was significantly more severe inninaCp235. Responses in P[ninaCΔ132] were apparently normal. P[ninaCΔ174] andninaCP235were also characterized by spontaneous quantum bump-like activity in the dark and by larger and longer light-induced quantum bumps. The turn-off of the pupil mechanism in P\ninaCΔ174] andninaCp235was also defective, although in this case the rate of return to baseline in both mutants was more or less the same. In allninaCmutants, the amplitudes of the pupillary pigment migration were distinctly smaller than that in the wild type. The reduction of the amplitude was largest in P[ninaCΔ174]. The light sensitivity of the pupil mechanism of P[ninaCΔ174] compared to that of wild type was reduced by 1.3 log units. Remarkably, the light sensitivity of P[ninaCΔ132] andninaCP235wasca. 0.5 log units higher than that of the wild type. The results suggest that the p174 protein is required for normal termination of the transduction cascade. The diverse phenotypes observed may suggest multiple roles for calmodulin distribution for controlling response termination and regulating pigment migration inDrosophilaphotoreceptors.
The pigeon optokinetic system: Visual input in extraocular muscle coordinates
Authors: Wylie Douglas R. W. , Frost Barrie J.
Published: June 2009

The generation of compensatory eye movements in response to rotational head movements involves the transformation of visual-optokinetic and vestibular signals into commands controlling the appropriate eye muscles. Previously, it has been shown that the three systems (optokinetic, vestibular, and eye muscle) share asimilarthree-dimensional reference frame. In this report, we suggest that a peculiarity in the structure of the horizontal recti in pigeons demonstrates that the optokinetic system is organized with respect to the eye muscles rather than the vestibular canals. Measurements of the orientation of the plane for each of the lateral and medial recti were obtained. These were compared with the direction preferences of optokinetic neurons responsive to horizontal motion, namely “back” units in the nucleus of the basal optic root (nBOR), “forward” units in the pretectal nucleus lentiformis mesencephali (LM), and “vertical axis” (VA) Purkinje cells in the flocculus. The average direction preference of LM neurons excited in response to forward (temporal to nasal) visual motion, andVAPurkinje cells in response to optokinetic motion in the ipsilateral visual field was approximately parallel to the visual horizontal. This corresponded to the orientation of the medial rectus, which was also approximately parallel to the visual horizontal. The average direction preference of nBOR neurons excited in response to backward (nasal to temporal) visual motion, andVAPurkinje cells in response to optokinetic motion in the contralateral visual field was approximately 20–30 deg down from the visual horizontal. The orientation of the lateral rectus was also approximately 20–30 deg down from the visual horizontal. These data suggest that the incoming optokinetic signals are organized with respect to the outgoing extraocular muscle commands.
GABAA receptors in neurons of the nerve fiber layer in rabbit retina
Authors: Ehinger B. , Zucker C. L.
Published: June 2009

Two synapse-rich layers are well recognized in the mammalian retina, the inner and outer plexiform layers. However, synapses occur also in other layers, particularly in the innermost nerve fiber layer. These synapses form a tenuous layer at times referred to as the superficial plexiform layer. We have found that staining for GABAA receptors in whole-mounted rabbit retina demonstrates this layer. It is most well developed in the region of the visual streak 2–4 mm below the center of the myelinated streak and is very sparse in other parts. Most or all of the processes in the plexus originate from cells in the ganglion cell layer.
Are there separate ON and OFF channels in fly motion vision?
Authors: Egelhaaf Martin , Borst Alexander
Published: June 2009

Visual information is processed in a series of subsequent steps. The performance of each of these steps depends not only on the computations it performs itself but also on the representation of the visual surround on which it operates. Here we investigate the consequences of signal preprocessing for the performance of the motion-detection system of the fly. In particular, we analyze whether the retinal input signals are rectified and segregate into separate ON and OFF channels, which then feed independent parallel motion-detection pathways. We recorded the activity of an identified directionally selective interneuron (HI-cell) in response to apparent motion stimuli, i.e. sequential brightness changes at two neighboring locations in the visual field, as well as to brightness changes at only a single location. For apparent motion stimuli, the motion-dependent response component was determined by subtracting from the overall response the responses to the individual stimulus components when presented alone. The following conclusions could be derived: (1) Apparent motion consisting of a sequence of increased or decreased brightness at two locations in the visual field have the same optimum interstimulus time interval (Fig. 3). (2) Sequences of brightness steps of like polarity (either increments or decrements) elicit positive and negative motion-dependent response components when mimicking motion in the cell's preferred and null direction, respectively. The motion-dependent response components are inverted in sign when the brightness steps of a stimulus sequence have a different polarity (Fig. 7). (3) The responses to the beginning and the end of a brightness pulse depend on the pulse duration. For pulse durations of less than 2 s, both events interact with each other (Fig. 9). All of these results do not provide any indication that the fly processes motion information in independent ON and OFF motion detectors. Brightness changes of both signs are rather represented at the input of the same movement detectors, and interactions between signals resulting from both brightness increments and decrements take their sign into account. This type of preprocessing of the retinal input is argued to render a motion-detection system particularly robust against noise.
Volume transmission of dopamine may modulate light-adaptive plasticity of horizontal cell dendrites in the recovery phase following dopamine depletion in goldfish retina
Authors: Yazulla Stephen , Studholme Keith M.
Published: June 2009

We investigated the recovery of light-adaptive spinule formation following dopamine depletion with intraocular injection of 6-hydroxydopamine (6-OHDA) and subsequent neogeneration of dopamine interplexiform cells (DA-IPC) at the marginal zone. DA-IPCs were gone by 2 weeks postinjection and appeared at the marginal zone by 6 weeks postinjection, at which time DA-IPC neurites grew toward the central retina, reaching within 0.5 mm of the central retina by 1 year. Retinas from day time, light-adapted fish at 2 weeks, 4 weeks, 3 months, and 1 year postinjection with 6-OHDA were processed for pre-embedding tyrosine hydroxylase immunoreactivity (TOH-IR) and compared to sham-injected and control retinas at the electron-microscopical (EM) level. Only 6-OHDA fish that tilted markedly toward the injected eye were used for these experiments. The tilt mimics the dorsal light reaction, indicating a 2–2.5 log unit increase in the photopic sensitivity of the 6-OHDA eye. Spinule formation was reduced by about 60% in the 2- and 4-week 6-OHDA retinas, but returned to control levels throughout the entire retina of 3-month and 1 year 6-OHDA retinas even though the central region of these retinas contained no detectable TOH-IR. Intraocular injection with 10 μM SCH 23390 (a Dl antagonist) reduced light-adaptive spinule formation by 50% both in control eyes as well as those eyes that were 3 months post 6-OHDA injected. The full return of spinule formation with only partial reinnervation of the retina with DA-IPC processes and their subsequent inhibition by SCH 23390 indicates that dopamine diffused large distances within the retina to regulate this synaptic plasticity (i.e. displayed volume transmission). Also, since all 6-OHDA injected fish displayed an increased photopic sensitivity in the injected eye when sacrificed, we suggest that horizontal cell spinules are not required for photopic luminosity coding in the outer retina.
Differential intertectal delay between Rana pipiens and Xenopus laevis: Implications for species-specific visual plasticity
Authors: Scherer Warren J. , Udin Susan B.
Published: June 2009

In the frog Xenopus laevis, the isthmotectal projection, which relays input from the ipsilateral eye, exhibits anatomical reorganization following surgical eye rotation performed during tadpole stages while the isthmotectal projection in the frog Rana pipiens fails to show reorganization. This plasticity has been shown to be dependent upon activation of the N-methyl-D-aspartate (NMDA) receptor located on tectal cell dendrites. The reorganization process in Xenopus is hypothesized to employ a Hebbian mechanism requiring correlated firing of ipsilateral and contralateral inputs to a given tectal cell; when an ipsilateral axon synapses onto a tectal cell that receives input from a contralateral axon with a matching receptive-field location, the correlation in activity triggers stabilization of the ipsilateral synapse. However, in neither Xenopus nor Rana do ipsilateral and contralateral inputs begin to fire simultaneously in response to a given visual stimulus; the ipsilateral input is delayed because it reaches the tectum indirectly, through a polysynaptic relay via the opposite tectum and nucleus isthmi. The objective of this experiment was to test whether there is a significant difference in this intertectal delay between Xenopus laevis and Rana pipiens in order to determine whether intertectal delay could be a contributing factor in this species-specific ability to exhibit visual plasticity. We have found that intertectal delay is 26.16 ms longer in Rana pipiens (36.53 ms) than in Xenopus laevis (10.37 ms).
Evoked potential and psychophysical analysis of Fourier and non-Fourier motion mechanisms
Authors: Victor Jonathan D. , Conte Mary M.
Published: June 2009

Some visual stimuli produce a strong percept of motion, even though they fail to excite motion detectors based on Fourier energy or cross correlation. Models which suffice to explain the motion percept in these non-Fourier motion (NFM) stimuli include linear spatiotemporal filtering, followed by rectification, followed by standard motion analysis (Chubb & Sperling 1988). We used the human “motion-onset” evoked potential, which has been assigned to area 17 on the basis of work in the macaque (van Dijk et al., 1986; van Dijk & Spekreijse, 1989), to investigate the neural substrate of the processing stages postulated in the above models. Motion-onset VEPs elicited by FM and NFM matched for spatial and temporal characteristics were indistinguishable in temporal characteristics and scalp topography at a transverse chain of electrodes. Addition of textural cues (granularity and higher-order form) did not influence the response dynamics or scalp topography of NFM responses. However, comparison of responses to NFM stimuli and related stimuli without coherent motion but similar spatial and temporal properties showed that the motion-onset responses were distinct from responses to the onset of fixed flicker-defined contours not undergoing coherent motion. We discuss the implications of these results for computational models of motion analysis.
A breakdown of the blood-brain barrier is associated with optic nerve regeneration in the frog
Authors: Tennant M. , Beazley L. D.
Published: June 2009

We have examined the integrity of the blood-brain barrier during optic nerve regeneration in the frog Liloria (Hyla) moorei using rhodamine B-labeled bovine serum albumin (RBA). A transient localized breakdown of the blood-brain barrier was observed between 1 and 5 weeks after extracranial optic nerve crush. The zone of breakdown progressed along the experimental optic nerve, ascended the opposite optic tract, and swept rostro-caudally across the tectum contralateral to the crushed nerve. By 7 weeks, the blood-brain barrier was once again intact along the length of the optic pathway. In a concurrent series of frogs, regenerating optic axons were visualized by anterograde transport of horseradish peroxidase (HRP). At each stage examined, the region reached by the front of regenerating axons corresponded to that in which the blood-brain barrier had been shown to break down.

In contrast to the results after nerve crush, the blood-brain barrier remained intact along the length of the optic pathway following optic nerve ligation to prevent regeneration. We conclude that the breakdown of the blood-brain barrier which occurs during optic nerve regeneration in the frog is triggered by the regenerating axons.
Visual deprivation fails to reduce calbindin 28kD or GABA immunoreactivity in the Rhesus monkey superior colliculus
Authors: Mize R. Ranney , Luo Qian
Published: June 2009

Antibody labeling of the calcium-binding protein calbindin 28kD (CaBP) and gamma-aminobutyric acid (GABA) is altered by short-term monocular deprivation in the lateral geniculate nucleus and visual cortex of adult primates. It is not known whether these alterations occur in other subcortical visual structures. We therefore have examined antibody labeling to CaBP and GABA in the superior colliculus (SC) of visually deprived Rhesus monkeys. One group was monocularly enucleated as adults. The other monkeys experienced different types of monocular and binocular deprivation from birth, including occlusion of one eye, and/or surgically induced aphakia, optically corrected with extended-wear contact lenses, or an intraocular lens implant. Some of these monkeys also had one eye enucleated prior to perfusion.

In the SC of normal monkeys, CaBP-immunoreactive neurons formed three laminar tiers within SC, one within the zonal layer (ZL) and upper superficial gray layer (SGL), another bridging the optic and intermediate gray layers, and a third within the deep gray layer. CaBP neurons within the upper tier had small pyriform or stellate morphologies while those in the deeper tiers were slightly larger neurons, most with a stellate morphology. GABA-immunoreactive neurons were densely distributed within the SGL and more sparsely distributed within the deeper layers. These cells were mostly small neurons with horizontal, pyriform, or stellate morphologies.

Neither monocular enucleation nor occlusion nor aphakia combined with continuous occlusion of the fellow eye produced any visible reduction in antibody labeling in cells or neuropil within the SC. Full-field measures of labeling intensity (optical density) within the ZL and upper SGL revealed no consistent differences between the SC contralateral or ipsilateral to the affected eye in either CaBP- or GABA-labeled sections. Measures of the optical density, number, and size of labeled neurons also showed no consistent effects of enucleation and/or occlusion. We therefore conclude that the retino-geniculostriate and retino-collicular systems differ in their response to deprivation which is likely due to the significant overlap of retinal axons from the two eyes that occurs in the SC of the Rhesus monkey.
Metastable motion anisotropy
Authors: Chaudhuri Avi , Glaser Donald A.
Published: June 2009

The phenomenon of apparent motion can arise when two spatially separated visual tokens are presented in temporal sequence. If tokens at opposite corners of a hypothetical square are presented simultaneously followed by simultaneous presentation of tokens at the remaining two corners, an apparent motion percept may occur along either the vertical or horizontal axis. The display is perceptually metastable since most observers will perceive motion along only one axis at a time. The metastable display, however, produces anisotropic results, in that with central fixation, vertical motion is seen more frequently than horizontal motion. The ratio of the vertical to horizontal length of the sides of a rectangle needed to achieve equal frequencies of motion judgments along the respective axes falls in the range of 1.18–1.92 for different observers in our experiments. It appears that signal transmission across the vertical midline is a major determinant of the vertical bias, since the anisotropic effects disappear when the fixation point is sufficiently offset along the horizontal meridian so as to cause a fully homonymous representation of all of the metastable tokens. One of the factors may be signal degradation or delay in callosal transmission which could reduce the strength of the motion signal along the horizontal axis. In addition, there appears to be a strip along the vertical midline with a width of 30–50 min are within which reduced levels of anisotropy are found. The possibility that this strip is a consequence of a zone of naso-temporal overlap in the projection of the retina to the brain along the vertical meridian will be discussed.
Effects of synaptic drugs on turtle optokinetic nystagmus and the spike responses of the basal optic nucleus
Authors: Ariel M. , Rosenberg A.F.
Published: June 2009

Behavioral and electrophysiological measures were used to elucidate the retinal modulation of oculomotor control in the turtle. Eye movements were recorded following intravitreal applications of 2-amino-4-phosphonobutyrate (APB) and the GABA antagonists picrotoxin and bicuculline. Visual responses of single basal optic nucleus (BON) neurons of the accessory optic system were studied in parallel experiments. The effectiveness of APB, a glutamate analog thought to act selectively on the retinal ON pathway, was assessed independently by recording electroretinograms or ganglion cell activity.

Injections of APB into the turtle's eye reduced or blocked the injected eye's ability to drive horizontal optokinetic nystagmus, as also observed in rabbit and cat (Knapp et al., 1988; Yucel et al., 1989). Single-unit recordings from the BON during APB superfusion (50–200 μM APB) of the contralateral retina demonstrated that these cells, which are direction-sensitive and respond to the offset of light flashes, have their responses to moving stimuli blocked by APB.

During the APB effect, GABA antagonists were applied to the same eye. Although moderate doses of APB were sufficient to block optokinetic or BON light responses, the addition of GABA blockers still elicited a spontaneous temporal-to-nasal nystagmus (Ariel, 1989) or visually responsive yet direction-insensitive responses from BON cells (Schuerger et al., 1990). These results are discussed in terms of the retinal output to pathways involved in oculomotor control of optokinetic nystagmus.
Dim background light and Cerenkov radiation from32P block reversal of rhodopsin phosphorylation in intact frog retinal rods
Authors: Biernbaum Michael S. , Binder Brad M. , Bownds M. Deric
Published: June 2009

The phosphorylation of photoexcited rhodopsin (Rho*) is thought to inactivate this receptor by inhibiting its interaction with the GTP-binding protein transducin (Gt). Here we report that the time course of phosphorylation-dephosphorylation after bright illumination of intact rod outer and inner segments (ROS-RIS) incubated in33Pican be altered if the ROS-RIS are first exposed to levels of dim illumination that cause light adaptation in these ROS-RIS. The dephosphorylation of >107phosphorylated rhodopsin molecules/ROS following a bright flash can be blocked by prior dim continuous illumination (generating 103Rho*/ROS/s) that cumulatively bleaches ≍ 105rhodopsin molecules/ROS. The phenomenon has not been previously noted because these low levels of light are emitted as a result of Cerenkov radiation from the32P isotope that is usually employed to monitor rhodopsin phosphorylation. The inhibition of rhodopsin dephosphorylation by dim conditioning illumination is observed in intact ROS-RIS but is lost when ROS-RIS are electropermeabilized or fragmented.
Changing distribution of GABA-like immunoreactivity in pigeon visual areas during the early posthatching period and effects of retinal removal on tectal GABAergic systems
Authors: Bagnoli Paola , Fontanesi Gigliola , Streit Peter , Domenici Luciano , Alesci Roberto
Published: June 2009

The distribution of GABA-like immunoreactivity in the pigeon visual system was studied during the first 9 days after hatching using a mouse monoclonal antibody, mAb 3A12, to glutaraldehyde linked GABA (Matute & Streit, 1986). GABA-like immunoreactivity was seen in cell bodies as well as in neuropil at the level of both the retina and central visual regions at any posthatching age. However, the distribution of putative GABAergic cells and processes varied with age reaching the adult pattern at around 9 days. As a general observation, almost no cell bodies in the retina (except for some perikarya in the ganglion cell layer) were labeled at hatching but densely packed immunostained processes were present in the inner plexiform layer. During the next few days, GABA-immunoreactive amacrine and horizontal cells appeared and the adult distribution of GABA-like immunoreactivity was reached at around 9 days. In the other visual regions examined, the general trend in the variation of GABA-like immunoreactivity included: (1) a progressive decrease in the density of immunostained cell bodies and (2) an almost parallel increase in the concentration of stained neuropil. Since in pigeons the adult organization of visual pathways and the final distribution putative GABAergic systems are reached at around the same age, we suggest the possibility that incoming ganglion cell axons play a role in regulating the distribution of GABA-like immunoreactivity in Visual areas. This hypothesis is supported by the fact that the distribution of GABA-like immunoreactivity in the superficial layers of the optic tectum was altered following ablation of the contralateral retina immediately after hatching.
Retinal projections in the ground squirrel (Citellus tridecemlineatus)
Authors: Agarwala Seema , Petry Heywood M. , May Jack G.
Published: June 2009

The retinal projections of the thirteen-lined ground squirrel were determined by tracing anterograde transport of intravitreally injected horseradish peroxidase (HRP) or wheat-germ conjugated horseradish peroxidase (WGA-HRP). Label was seen in the suprachiasmatic nucleus and adjacent anterior hypothalamic area, the accessory optic system (the medial, dorsal, and lateral terminal nuclei), the dorsal and ventral lateral geniculate nuclei, the intergeniculate leaflet, the pretectal nuclei (the anterior, posterior, and olivary pretectal nuclei and the nucleus of optic tract), and the superior colliculus. Most of these structures were labeled bilaterally, with dense contralateral label and sparse ipsilateral label, a pattern typical for animals with laterally placed eyes. However, the suprachiasmatic nucleus and the nucleus of the optic tract received input only from the contralateral eye. In contrast to previous degeneration studies, the sensitive HRP tracers (in conjunction with cytochrome-oxidase reactivity) revealed an elaborate organization within the lateral geniculate nucleus (dorsal LGN, ventral LGN, and intergeniculate leaflet) that is consistent with existing organizational schemes for other mammalian species.
Mechanism and site of action of a dopamine D1antagonist in the rabbit retina
Authors: Jesen Ralph J.
Published: June 2009

Dopamine D1antagonists have been shown to alter drastically the spontaneous and light-evoked activity of ganglion cells in the rabbit retina (Jensen & Daw, 1984, 1986). A major target of dopaminergic neurons in mammalian retinas appears to be rod All amacrine cells (Pourcho, 1982; Voigt & Wässle, 1987). In the present study, the following questions were addressed: (1) Do dopamine D1antagonists alter the activity of ganglion cells through actions primarily on rod All amacrine cells? (2) Are the effects of dopamine D1antagonists on ganglion cells due to an inhibition of dopamine-stimulated adenylate cyclase activity?

Using an isolated, superfused retinal preparation, the ability of several pharmacological agents to counteract the physiological effects of the dopamine D1antagonist (+)-SCH 23390 on rabbit ganglion cells was examined. The glycine antagonist strychnine abolished the effects of (+)-SCH 23390 on the spontaneous and light-evoked activity of OFF-center ganglion cells, whereas the excitatory amino-acid antagonist kynurenic acid abolished the effects of (+)-SCH 23390 on the spontaneous and light-evoked activity of ON-center ganglion cells. The findings obtained with these antagonists can be explained in terms of the known synaptic connections of All amacrine cells.

Both 8-(4-chlorophenylthio) cyclic AMP, a membrane-permeable cAMP analog, and forskolin, an activator of adenylate cyclase, reversed the effects of (+)-SCH 23390 on the spontaneous and light-evoked activity of OFF-center ganglion cells but not ON-center ganglion cells. These findings suggest that the effects of dopamine D1antagonists on OFF-center ganglion cells are due to an inhibition of dopamine-stimulated adenylate cyclase, with the ensuing lowering of cellular cAMP levels. The effects of dopamine D1antagonists on ON-center ganglion cells appear, however, to be independent of intracellular cAMP levels.
Neural differentiation in the retina of the larval sea lamprey (Petromyzon marinus)
Authors: Rubinson Kalman , Cain Hilary
Published: June 2009

The peripheral retina of the sea lamprey develops in a 5-year-long process in which only certain neurons differentiate each year. The growth of cell layers, the differentiation of the neurons, and the morphology of their dendrites and axons were studied with normal, HRP, and Golgi preparations. Ganglion cells are differentiated in 3-year-old larvae, amacrine and horizontal cells in 4-year-old larvae, photoreceptor cells in stage I transformers, and bipolar cells in stage III transformers. Each new development is expressed as a radial gradient of differentiation. As a result of this protracted and stepped process, lamprey retinal neurons, particularly ganglion cells, differentiate in the absence of other cells to which they will ultimately be connected and may express their individual genetic programs more fully than in other vertebrate retinas. This could account for the unusual relationship of the ganglion cell, inner plexiform, and optic nerve layers and for the very high ratio of displaced to orthotopic ganglion cells.
Pharmacological separation of mechanisms contributing to human contrast sensitivity
Authors: Smith A. T. , Baker-Short C. M.
Published: June 2009

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

In in-vitro preparations of both macaque and human retina, intracellular injections of Neurobiotin and horseradish peroxidase were used to characterize the morphology, depth of stratification, and mosaic organization of a type of bistratified ganglion cell. This cell type, here called the small bistratified cell, has been shown to project to the parvocellular layers of the dorsal lateral geniculate nucleus (Rodieck, 1991) and is therefore likely to show color-opponent response properties.

In both human and macaque, the two dendritic tiers of the bistratified cell are narrowly stratified close to the inner and outer borders of the inner plexiform layer. The inner tier is larger in diameter and more densely branched than the outer tier and gives rise to distinct spine-like branchlets bearing large, often lobulated heads. By contrast the smaller, outer tier is sparsely branched and relatively spine-free.

In human retina, the small bistratified cells range in dendritic field diameter from ∼50 µm in central retina to ∼400 µm in the far periphery. The human small bistratified cells are about 20% larger in dendritic-field diameter than their counterparts in the macaque. However, when the difference in retinal magnification between human and macaque is taken into account, the small bistratified cells are similar in size in both species. In macaque, the small bistratified cell has a dendritic-field size that is ~10% larger than that of the magnocellular-projecting parasol ganglion cell. Human small bistratified ganglion cells tend to have smaller dendritic-field diameters than parasol cells. This is because parasol ganglion cells are larger in human than in macaque retina (Dacey & Petersen, 1992).

In macaque retina, intracellular injections of Neurobiotin revealed heterotypic tracer coupling to a distinct mosaic of amacrine cells and probable homotypic coupling to an array of neighboring ganglion cells around the perimeter of the injected cell's dendritic tree. The amacrine cell mosaic had a density of 1700 cells/mm2 in peripheral retina. Individual amacrines had small, densely branched and bistratified dendritic fields. From the homotypic coupling, it was possible to estimate for the small bistratified cell a coverage factor of ~1.8, and a density of ~1% of the total ganglion cells in central retina, increasing to ~6–10% in the retinal periphery.

The estimated density, dendritic-field size, and depth of stratification all suggest that the small bistratified ganglion cell type is the morphological counterpart of the common short-wavelength sensitive or ‘blue-ON’ physiological type.
Color-reversal learning: Effects after lesions of thalamic visual structures in pigeons
Authors: Chaves Lin M. , Hodos William , Güntürkün Onur
Published: June 2009

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

Immunocytochemical techniques have been used to examine the distribution of substance-P (SP)-labeled neurons in the superior colliculus of rats from birth to adulthood. At birth, there are almost no SP-immunopositive neurons in the tectum. A small number of SP neurons appear over the next several days. However, the vast majority of SP neurons appear between P9 and P10, and by P12 have attained adult-like numbers and distribution. Neurons are confined to the superficial layers of the colliculus, specifically the upper two-thirds of the stratum griseum superficiale (SGS). There is no indication of a differential developmental sequence along rostrocaudal or mediolateral axes. Neuronal types can be distinguished as early as P6 and include horizontal, vertical, and multipolar cells.

Substance-P-immunoreactive axons and boutons are also present in the superior colliculus at birth, and are for the most part confined to the deep layers. Boutons are generally of the en-passant type. The density of labeled axons and boutons increases progressively, and by P10 there is an almost adult-like lamination and patchiness. In the adult, labeled axons and boutons are most dense in the stratum opticum and stratum griseum intermedium. Bridges of dorsoventrally oriented labeled axons span the relatively label-poor stratum album intermedium. SP label in the stratum griseum profundum is dense and patchy, and there is also dense label in the stratum album profundum bordering the periaqueductal grey.

The role of substance-P-labeled neurons in the superior colliculus is still a matter of speculation. The findings of this study indicate that SP neurons may play a role in intrinsic collicular circuitry.
Contrast adaptation in striate cortical neurons of the nocturnal primate bush baby (Galago crassicaudatus)
Authors: Allison John D. , Casagrande Vivien A. , Debruyn Edward J. , Bonds A. B.
Published: June 2009

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

The pattern of dendritic stratification of retinal ganglion cells in the fetal monkey (Macaca mulatta) was examined using horseradish peroxidase and retinal explants. Ganglion cells in the rhesus monkey are born between embryonic day (E) 30–70 (La Vail et al., 1983). At E60, E67, and E68, approximately 50% of all ganglion cells within the central 3.0 mm of the retina had dendritic arbors that were unistratified within the inner plexiform layer (IPL), while the remaining 50% had bistratified arbors. Unistratified cells had relatively flat arbors that ramified within a restricted portion of the IPL. In contrast, bistratified cells had one portion of the arbor that branched in the inner half of the IPL and a second portion that branched in the outer half of the IPL. Relatively few bistratified cells were encountered in the central 1.0 mm of the retina but were more numerous with increasing eccentricity. At E81, E90, and E110, the dendritic arbors of ganglion cells increased in both area and complexity, but occupied a relatively small percentage of the total depth of the IPL. The bistratified cells encountered at these fetal ages were typically located in the far retinal periphery. Between E125-E140, the dendritic arbors of individual ganglion cells increased in area and depth to occupy a greater proportion of the total IPL than at earlier fetal ages.

These observations suggest that ganglion cells in the macaque undergo at least three stages of dendritic stratification: (1) an initial period of dendritic growth during which the cells have either unistratified or bistratified dendritic arbors; (2) a loss of the majority of bistratified cells through cell death or remodeling of the arbor; and (3) growth or expansion of the arbor to occupy a greater percentage of the total depth of the IPL. The first two stages are similar to recent observations in the fetal cat (Maslim & Stone, 1988) with the exception that dendritic development in the primate lacks an initial diffuse ingrowth to the IPL. Additionally, primate ganglion cells undergo a third stage of dendritic growth in late fetal development during which the arbor occupies a greater proportion of the depth of the IPL.
Light-induced GTPase activity and GTP[γS] binding in squid retinal photoreceptors
Authors: Brown Joel E. , Combs Anthony , Ackermann Karen , Malbon Craig C.
Published: June 2009

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

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

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

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