bluuebunny/crossref_metadata_2025 huggingface dataset:
Independence and merger of thalamocortical channels within macaque monkey primary visual cortex: Anatomy of interlaminar projections
Authors: Yoshioka Takashi , Levitt Jonathan B. , Lund Jennifer S.
Published: June 2009

An important issue in understanding the function of primary visual cortex in the macaque monkey is how the several efferent neuron groups projecting to extrastriate cortex acquire their different response properties. To assist our understanding of this issue, we have compared the anatomical distribution of VI intrinsic relays that carry information derived from magno- (M) and parvocellular (P) divisions of the dorsal lateral geniculate nucleus between thalamic recipient neurons and interareal efferent neuron groups within area VI. We used small, iontophoretic injections of biocytin placed in individual cortical laminae of area VI to trace orthograde and retrograde inter- and intralaminar projections. In either the same or adjacent sections, the tissue was reacted for cytochrome oxidase (CO), which provides important landmarks for different efferent neuron populations located in CO rich blobs and CO poor interblobs in laminae ⅔, as well as defining clear boundaries for the populations of efferent neurons in laminae 4A and 4B. This study shows that the interblobs, but not the blobs, receive direct input from thalamic recipient 4C neurons; the interblobs receive relays from mid 4C neurons (believed to receive convergent M and P inputs), while blobs receive indirect inputs from either M or P (or both) pathways through layers 4B (which receives M relays from layer 4Cα) and 4A (which receives P relays directly from the thalamus as well as from layer 4Cβ). The property of orientation selectivity, most prominent in the interblob regions and in layer 4B, may have a common origin from oriented lateral projections made by mid 4C spiny stellate neurons. While layer 4B efferents may emphasize M characteristics and layer 4A efferents emphasize P characteristics, the dendrites of their constituent pyramidal neurons may provide anatomical access to the other channel since both blob and interblob regions in layers ⅔ have anatomical access to M and P driven relays, despite functional differences in the way these properties may be expressed in the two compartments.
Morphological types of horizontal cell in rodent retinae: A comparison of rat, mouse, gerbil, and guinea pig
Authors: Peichl Leo , González-Soriano Juncal
Published: June 2009

Retinal horizontal cells of four rodent species, rat, mouse, gerbil, and guinea pig were examined to determine whether they conform to the basic pattern of two horizontal cell types found in other mammalian orders. Intracellular injections of Lucifer-Yellow were made to reveal the morphologies of individual cells. Immunocytochemistry with antisera against the calcium-binding proteins calbindin D-28k and parvalbumin was used to assess population densities and mosaics.

Lucifer-Yellow injections showed axonless A-type and axon-bearing B-type horizontal cells in guinea pig, but revealed only B-type cells in rat and gerbil retinae. Calbindin immunocytochemistry labeled the A-and B-type populations in guinea pig, but only a homogeneous regular mosaic of cells with B-type features in rat, mouse, and gerbil. All calbindin-immunoreactive horizontal cells in the latter species were also parvalbumin-immunoreactive; comparison with Nissl-stained retinae showed that both antisera label all of the horizontal cells. Taken together, the data from cell injections and the population studies provide strong evidence that rat, mouse, and gerbil retinae have only one type of horizontal cell, the axon-bearing B-type, where as the guinea pig has both A-and B-type cells. Thus, at least three members of the family Muridae differ from other rodents and deviate from the proposed mammalian scheme of horizontal cell types.

The absence of A-type cells is apparently not linked to any peculiarities in the photoreceptor populations, and there is no consistent match between the topographic distributions of the horizontal cells and those of the cone photoreceptors or ganglion cells across the four rodent species. However, the cone to horizontal cell ratio is rather similar in the species with and without A-type cells.
Push–pull model of the primate photopic electroretinogram: A role for hyperpolarizing neurons in shaping the b-wave
Authors: Sieving Paul A. , Murayama Koichiro , Naarendorp Franklin
Published: June 2009

Existing models of the primate photopic electroretinogram (ERG) attribute the light-adapted b–wave to activity of depolarizing bipolar cells (DBCs), mediated through a release of potassium that is monitored by Müller cells. However, possible ERG contributions from OFF-bipolar cells (HBCs) and horizontal cells (HzCs) have not been explored. We examined the contribution of these hyperpolarizing second-order retinal cells to the photopic ERG of monkey by applying glutamate analogs to suppress photoreceptor transmission selectively to HBC/HzCs vs. DBCs.

ERGs of Macaca monkeys were recorded at the cornea before and after intravitreal injection of drugs. Photopic responses were elicited by bright 200–220 ms flashes on a steady background of 3.3 log scotopic troland to suppress rod ERG components.

2–amino-4–phosphonobutyric acid (APB), which blocks DBC light responses, abolished the photopic b–wave and indicated that DBC activity is requisite for photopic b–wave production.

However, applying cis–2,3–piperidine dicarboxylic acid (PDA) and kynurenic acid (KYN), to suppress HBCs/HzCs and third-order neurons, revealed a novel ERG response that was entirely positive and was sustained for the duration of the flash. The normally phasic b–wave was subsumed into this new response. Applying n–methyl-dl-aspartate (NMA) did not replicate the PDA+KYN effect, indicating that third-order retinal cells are not involved. This suggests that HBC/HzC activity is critical for shaping the phasic b–wave.

Components attributable to depolarizing vs. hyperpolarizing cells were separated by subtracting waveforms after each drug from responses immediately before. This analysis indicated that DBCs and HBC/HzCs each can produce large but opposing field potentials that nearly cancel and that normally leave only the residual phasic b–wave response in the photopic ERG.

Latency of the DBC component was 5–9 ms slower than the HBC/HzC component. However, once activated, the DBC component had a steeper slope. This resembles properties known for the two types of cone synapses in lower species, in which the sign-preserving HBC/HzC synapse has faster kinetics but probably lower gain than the slower sign-inverting G-protein coupled DBC synapse.

A human patient with “unilateral cone dystrophy” was found to have a positive and sustained ERG that mimicked the monkey ERG after PDA+KYN, indicating that these novel positive photopic responses can occur naturally even without drug application.

These results demonstrate that hyperpolarizing second-order neurons are important for the primate photopic ERG. A “Push-Pull Model” is proposed in which DBC activity is requisite for b–wave production but in which HBC/HzC activity limits the amplitude and controls the shape of the primate photopic b–wave.
Cortical feedback increases visual information transmitted by monkey parvocellular lateral geniculate nucleus neurons
Authors: McClurkin John W. , Optican Lance M. , Richmond Barry J.
Published: June 2009

We studied the effect of cooling the striate cortex on parvocellular lateral geniculate nucleus (PLGN) neurons in awake monkeys. Cooling the striate cortex produced both facilitation and inhibition of the responses of all neurons, depending on the stimulus presented. Cooling the striate cortex also altered the temporal distribution of spikes in the responses of PLGN neurons. Shannon's information measure revealed that cooling the striate cortex reduced the average stimulus-related information transmitted by all PLGN neurons. The reduction in transmitted information was associated with both facilitation and inhibition of the response. Cooling the striate cortex reduced the amount of information transmitted about all of the stimulus parameters tested: pattern, luminance, spatial contrast, and sequential contrast. The effect of cooling was nearly the same for codes based on the number of spikes in the response as for codes based on their temporal distribution. The reduction in transmitted information occurred because the differences among the responses to different stimuli (signal separation) were reduced, not because the variability of the responses to individual stimuli (noise) was increased. We conclude that one function of corticogeniculate feedback is to improve the ability of PLGN neurons to discriminate among stimuli by enhancing the differences among their responses.
Cholinergic amacrine neurons of the dogfish retina
Authors: Brandon Christopher
Published: June 2009

In the mammalian retina, the dendritic arbors of cholinergic amacrine neurons have a unique starburst shape; these arbors lie in narrow sublaminae within the inner plexiform layer, where they provide input to a wide variety of ganglion cell types. Immunocytochemistry has been used to identify cholinergic cells in one poikilotherm, the goldfish (Tumosa et al., 1984), but there has been no description of the detailed dendritic morphology of these cells in the lower vertebrates. In the present study, cholinergic neurons have been characterized, by immunocytochemistry and dye filling, in the retina of the Pacific Coast dogfish, Squalus acanthias.

The inner nuclear layer contained two populations of choline acetyltransferase-immunoreactive amacrine cells, of different sizes (average soma diameters 12.2 vs. 16.3 μm); 70% of the immunoreactive cells were of the smaller type. Cholinergic dendrites from these two cell populations formed two narrow strata within the inner plexiform layer, at depths of 14% and 31%. In the ganglion cell layer, 40% of the cells were immunoreactive for choline acetyltransferase (ChAT); these cells were very homogeneous in size, had an average diameter of 12.6 μm, and appeared to represent a single class of cholinergic amacrine. The dendrites of these cells formed a single, narrow stratum within the inner plexiform layer, at a depth of 59%.

In living preparations, the smallest cell bodies in the ganglion cell layer were filled iontophoretically with Lucifer Yellow, under microscopic control. Such cells invariably had a stellate morphology; in many cases, they appeared quite similar to the starburst cholinergic amacrine cells described in rabbit and rat (Vaney, 1984; Voigt, 1986). Although double-label experiments failed to demonstrate ChAT immunoreactivity in specific dye-filled cells, the dendritic arbors of individual dye-filled stellate dogfish amacrines did co-stratify precisely with the proximal ChAT-immunoreactive sublamina of the inner plexiform layer. In addition, dye injection and ChAT immunocytochemistry appeared to label the same population of dogfish neurons, as suggested by the close structural similarity, and similar numerical proportion, of the cells identified with these two techniques.

Similarities between the displaced cholinergic amacrine neurons of the dogfish retina, and the cholinergic, “starburst” amacrine neurons of the rabbit retina, are discussed.
Regenerating axons from adult chick retinal ganglion cells recognize topographic cues from embryonic central targets
Authors: Vanselow Jens , Müller Bernhard , Thanos Solon
Published: June 2009

We investigated whether regenerating mature axons recapitulate embryonic features essential to successful reconnectivity within the injured nervous system. Strips from embryonic and adult chick retinae were cultured, and outgrowing axons were examined morphometrically and immunohistochemically. In addition, the target-recognition properties of adult neurites were analyzed. Regenerating adult axons elongate on a poly-L-lysine/laminin substratum with a speed about one order of magnitude slower than that of embryonic axons. Morphologically, adult axonal tips differ dramatically from embryonic growth cones in that they possess only filopodial extensions whereas embryonic growth cones possess both lamellipodial and filopodial processes. Both embryonic and adult neurites express the growth-associated protein GAP-43. When cultured on alternating stripes of anterior and posterior embryonic tectal membranes, both adult and embryonic retinal axons distinguish between the two membrane preparations. Our results demonstrate that during axonal regeneration the mature neurons express embryonic properties that are involved in the recognition of tectal positional cues.
Prolonged depolarization in rods in situ
Authors: Burkhardt Dwight A. , Zhang Shaoqi , Gottesman Jon
Published: June 2009

Intracellular recordings were made from rods in the superfused retina of the marine toad (Bufo marinus). It was found that injection of a brief depolarizing current pulse (0.04–1 nA) evoked a distinctive, long-lasting response, here called “the prolonged depolarization.” The response appears to be regenerative, has a stereotypical waveform, is typically about 6 mV in &litude and 3 s in duration, and has a relatively long recovery period (10–60 s). As a rule, the response cannot be directly evoked by light but the current-evoked response is significantly enhanced in the presence of steady illumination. The light-evoked hyperpolarization and the depolarizing spikes of the rod are both attenuated in the presence of the prolonged depolarization. The prolonged depolarization is not an altered manifestation of the depolarizing spikes of toad rods since both can be recorded simultaneously and steady illumination suppresses the spikes while enhancing the prolonged depolarization. The response is enhanced in chloride-free superfusate and also appears to be enhanced by the use of electrodes containing chloride. The response is markedly shortened in superfusates that lack calcium or contain 1–5 mM cobalt. On this and other evidence, it is suggested that the response may be generated by the sequential action of calcium channels and calcium-activated chloride channels. Although rarely evoked by light, the prolonged depolarization of toad rods is otherwise remarkably similar to the prolonged depolarization of turtle cones. It is proposed that the prolonged depolarization, in contrast to the feedback depolarization of cones, arises from mechanisms common to both rods and cones.
Fine structure of receptive-field centers of X and Y cells of the cat
Authors: Soodak R. E. , Shapley R. M. , Kaplan E.
Published: June 2009

We investigated the fine structure of receptive field centers of X and Y cells of the retina and lateral geniculate nucleus of the cat using sinusoidal grating stimuli of high spatial frequency. By measuring orientation tuning and spatial-frequency tuning at multiple orientations, the two-dimensional sensitivity distribution was examined. We found that receptive-field centers typically have multiple sensitivity peaks that can be modeled as several spatially offset subunits. A subunit structure was found in both X and Y cells, with an average number of subunits per receptive-field center of approximately 2.9 in X cells and approximately 4.6 in Y cells. In X cells these subunits may correspond to individual cone bipolar inputs. In Y cells, the subunits may reflect the structure of the dendritic tree. The observation of the subunit structure of the receptive-field center, in conjunction with manipulation of the retinal wiring through pharmacological intervention, may provide a new tool for probing the circuitry of the retina.
Diurnal control of rod function in the chicken
Authors: Schaeffel Frank , Rohrer Baerbel , Zrenner Eberhart , Lemmer Thomas
Published: June 2009

We studied rod function in the chicken by recording corneal electroretinograms (ERGs). The following experiments were performed to demonstrate rod function during daytime: (1) determining the dark-adaptation function; (2) measuring the spectral sensitivity by a a–b-wave amplitude criterion in response to monochromatic flickering light of different frequencies ranging from 6.5–40.8 Hz (duty cycle 1: I); (3) analyzing the response vs. log stimulus intensity (V–log I) function in order to reveal a possible two phase process; and (4) determining the spectral sensitivity function either in a non-dark adapted state or after dark adaptation of the animals for I and 24 h. None of these experiments demonstrated clear evidence of rod function during daytime. On the other hand, we found rods histologically by light- and electron microscopy. Therefore, we repeated our ERG recordings during the night (between midnight and 3:00 A.M.). Without previous dark adaptation, rod function could be seen immediately in the same experiments described above. The result shows that, in the chicken, rods are turned on endogenously during the night but are scarcely functional during the day.
Effects of calcium ions on L-type horizontal cells in the isolated turtle retina
Authors: Perlman Ido , Normann Richard A. , Chandler John P. , Lipetz Leo E.
Published: June 2009

A technique by which the retina can be isolated from the turtle eye is described. Scanning electron microscopy revealed morphological variability between preparations and also between regions of the same one. Large areas were often totally free of any pigment epithelial cells, yet contained a high proportion of photoreceptors with complete outer segments. However, adjacent regions may contain photoreceptors without outer segments or with fragmented ones. The physiological properties of the horizontal cells also demonstrated large variability between different preparations. In all cases, lowering calcium concentration from 2 mM to 0.1−0.5 mM depolarized the horizontal cells and augmented the amplitude of the maximum photoresponses. However, these effects were accompanied by changes in the photoresponse kinetics and by a reduction in the horizontal cell sensitivity to light. Moreover, prolonged exposure to low calcium induced permanent damage to the retina as was indicated by the reduction in the response amplitude after superfusion with 2 mM calcium solution had been resumed. The toxic effects of low calcium were most apparent when superfusion with 0.1−1.0 μM calcium concentration was performed. These solutions induced complex time-dependent effects on the resting potential of horizontal cells and on the amplitude and kinetics of the photoresponses. We conclude from these observations that the normal concentration of extracellular calcium in the turtle retina is in the 2 mM range.
Light adaptation in the primate retina: Analysis of changes in gain and dynamics of monkey retinal ganglion cells
Authors: Purpura Keith , Tranchina Daniel , Kaplan Ehud , Shapley Robert M.
Published: June 2009

The responses of monkey retinal ganglion cells to sinusoidal stimuli of various temporal frequencies were measured and analyzed at a number of mean light levels. Temporal modulation tuning functions (TMTFs) were measured at each mean level by varying the drift rate of a sine-wave grating of fixed spatial frequency and contrast. The changes seen in ganglion cell temporal responses with changes in adaptation state were similar to those observed in human subjects and in turtle horizontal cells and cones tested with sinusoidally flickering stimuli; “Weber's Law” behavior was seen at low temporal frequencies but not at higher temporal frequencies. Temporal responses were analyzed in two ways: (1) at each light level, the TMTFs were fit by a model consisting of a cascade of low- and high-pass filters; (2) the family of TMTFs collected over a range of light levels for a given cell was fit by a linear negative feedback model in which the gain of the feedback was proportional to the mean light level. Analysis (1) revealed that the temporal responses of one class of monkey ganglion cells (M cells) were more phasic at both photopic and mesopic light levels than the responses of P ganglion cells. In analysis (2), the linear negative feedback model accounted reasonably well for changes in gain and dynamics seen in three P cells and one M cell. From the feedback model, it was possible to estimate the light level at which the dark-adapted gain of the cone pathways in the primate retina fell by a factor of two. This value was two to three orders of magnitude lower than the value estimated from recordings of isolated monkey cones. Thus, while a model which includes a single stage of negative feedback can account for the changes in gain and dynamics associated with light adaptation in the photopic and mesopic ranges of vision, the underlying physical mechanisms are unknown and may involve elements in the primate retina other than the cone.
The effects of serotonin drugs on horizontal and ganglion cells in the rabbit retina
Authors: Mangel Stuart C. , Brunken William J.
Published: June 2009

We have investigated the effects of a serotonin 5-HT2antagonist and a 5-HTIAagonist on horizontal and ganglion cells in the rabbit retina. Simultaneous intracellular horizontal cell and extracellular ganglion cell recordings were obtained from a superfusedin vitrorabbit eyecup preparation and the effects of bath applied drugs on these cells' light responses observed. Sinusoidally modulated current was also injected into horizontal cells while the extracellular spike activity of nearby, single-unit ganglion cells was monitored. Although the ON components of the light-evoked responses of ganglion cells were reduced by the 5-HT2antagonist or the 5-HTIAagonist, the membrane potential and the light responses of horizontal cells and the 6-wave of the ERG were simultaneously unaffected. However, the drugs blocked current-driven ganglion cell spike activity induced by current injections into nearby horizontal cells. These results are discussed with respect to the site of action of these serotonin drugs and with respect to the circuitry of serotonergic neurons.
Organization and development of horizontal cells in the goldfish retina, II: Use of monoclonal antibody MH1
Authors: Peng You-Wei , Lam Dominic Man-Kit
Published: June 2009

We have produced and characterized a monoclonal antibody, MH1, which selectively labels rod horizontal cells and Miiller cells in the goldfish retina. Biochemical and tissue distribution studies indicate that MH1 may recognize four out of five classes of intermediate filament proteins in goldfish: vimentin, desmin, glial fibrillary acidic protein (GFAP), and keratin, but not neurofilament. The intermediate filament which is labeled strongest in the retina is vimentin. In the goldfish retina, the only type of horizontal cells recognized by MH1 appear to be rod horizontal cells. This result suggests that the rod horizontal cell, an interneuron, and Miiller (glial) cells share a common antigen: vimentin, which is usually only expressed in mesenchymal origin cells.

The development of rod horizontal cells in the goldfish retina was also studied using MH1. The cells were not labeled by MH1 until 4–6 weeks posthatching, a stage in which the animals are already visually active. MH1 also did not label any horizontal cell in the region close to the ora terminalis in the goldfish retina. These results suggest that either the emergence and maturation of rod horizontal cells occur late during goldfish retinal development or the expression of vimentin itself occurs late in the development of rod horizontal cells.
Light-evoked contraction of red absorbing cones in the Xenopus retina is maximally sensitive to green light
Authors: Besharse Joseph C. , Witkovsky Paul
Published: June 2009

To test the hypothesis that light-evoked cone contraction in eye cups from Xenopus laevis is controlled through a direct mechanism initiated by the cone's own photopigment, we conducted spectral-sensitivity experiments. We estimate that initiation of contraction of red absorbing cones (611 nm) is 1.5 log units more sensitive to green (533 nm) than red (650 nm) light stimuli. The difference is comparable to that predicted from the spectral-sensitivity function of the green absorbing, principal rod (523 nm). Furthermore, 480-nm and 580-nm stimuli which are absorbed nearly equally by the principal rod have indistinguishable effects on cone contraction. We also found that light blockade of nighttime cone elongation is much more sensitive to green than to red light stimuli. Our observations are inconsistent with the hypothesis tested, and suggest that light-regulated cone motility is controlled through an indirect mechanism initiated primarily by the green absorbing, principal rod.
Variability of responses of cat retinal ganglion cells
Authors: Levine Michael W. , Cleland Brian G. , Zimmerman Roger P.
Published: June 2009

Previous studies of the varibility of firing of retinal ganglion cells have led to apparently contradictory conclusions. To a first approximation, the variance of rate of maintained discharges of ganglion cells in cat is independent of the mean firing rate. On the other hand, the variability of responses to abrupt changes in lighting of ganglion cells in goldfish increascs with increasing firing rate. To examine whether the difference is due to differences between species, we examined the variablility of responses of cat ganglion cells, and find it similar to that of goldfish ganglion cells. The variance of rate of ganglion cells is neither independent of mean rate, as might be expected from maintained dischargs, nor directly proportional to the mean rate, as it is for cat cortical cells. Rather, there is a monlinear relationship between varience of rate and mean rate.
Visual aftereffects and the consequences of visual system lesions on their perception in the rhesus monkey
Authors: Schiller Peter H. , Dolan Robert P.
Published: June 2009

This study examined the consequences of visual system lesions on visual aftereffects produced by achromatic stimuli of various luminance contrasts and chromatic stimuli of various wavelength compositions. The effects of repeated exposure to such adapting stimuli were assessed using probes whose luminance contrast and wavelength composition were systematically varied using both detection and discrimination paradigms. Interocular tests revealed that both peripheral and central mechanisms contribute to the visual aftereffects produced by the adapting stimulus arrays used in this study. Contrary to the hypothesis according to which the midget system of the retina is the conveyor of visual afterimages, we found that blocking this system with lesions of parvocellular lateral geniculate nucleus, through which the midget cells make their way to the striate cortex in primates, did not eliminate the visual aftereffects. It appears therefore that the parasol system of the retina, which courses through the magnocellular layers of the lateral geniculate nucleus to cortex, can convey the necessary signals for the generation of visual aftereffects. Lesions of areas V4 and MT did not have significant effects on the visual aftereffects studied suggesting that the central factors that contribute to the visual aftereffects occur either already in area VI or are conveyed to higher centers through regions other than areas V4 and MT.
The ‘OFF’ response of the human electroretinogram does not contribute to the brief flash ‘ b–wave’
Authors: Seiple William , Holopigian Karen
Published: June 2009

It has been assumed that the ‘ON’ and ‘OFF’ responses of the human electroretinogram (ERG) interact to produce a single waveform when brief flashes are used. To test this assumption, we examined the separate effects of stimulus intensity, the level of retinal illuminance and stimulus duration on the ERG. Both ‘ON’ and ‘OFF’ response amplitude decreased as stimulus intensity was decreased and as the level of retinal illumination was reduced. When stimulus duration was reduced, the amplitude of the ‘OFF’ response decreased; however, the amplitude of the ‘ON’ response increased. Summing of the ‘ON’ and ‘OFF’ response waveforms could not account for the increased amplitude in response to brief stimuli or for the changes in ERG wave shape. These results indicate that there is not a significant corneally recordable ‘OFF’ response elicited by brief stimuli, such as those commonly used to record the flash ERG.
Depletion of retinal dopamine increases brightness perception in goldfish
Authors: Lin Zheng-Shi , Yazulla Stephen
Published: June 2009

The effect of unilateral depletion of retinal dopamine on goldfish visual behavior was studied using a behavioral reflex, the dorsal light reaction (DLR). Retinal dopamine was depleted by intraocular injections of 6–hydroxydopamine (6–OHDA) on two successive days. By 2 weeks postinjection, dopamine interplexiform cells (DA-IPC) were not detected using tyrosine-hydroxylase immunoreactivity (TH-IR). By 6 weeks postinjection, generation of DA-IPC was observed at the marginal zone and by 9 months postinjection, 2–3 rows of DA-IPC were present at the marginal zone. Neurites extended several hundred micrometers toward the central retina. By 2 weeks postinjection, all 6–OHDA lesioned fish tilted 7–15 deg toward the injected eye under uniform overhead illumination. The tilting did not occur under scotopic illumination and reappeared within 1 min of light adaptation. Quantitation of the DLR showed that 6–OHDA lesioned fish behaved as if light were 2.4 log units more intense to the injected eye. Partial recovery was observed by 9 months postinjection, paralleling the reappearance of DA-IPC at the marginal zone. Tilting also was induced by unilateral intraocular injection with Dl and D2 dopamine receptor antagonists, SCH 23390 and S(—)-sulpiride, respectively. Fish did not tilt if they were light adapted at the time of injection. Tilting was observed if the animals were dark-adapted for 3 h and left in the dark for 1 h postinjection. Fish tilted toward the drug-injected eye within 2 min of light adaptation and gradually returned to vertical within 2 h. The tilting response to S(—)-sulpiride was stronger (˜20 degvs.˜5deg) and occurred at lower concentration (1 μMvs.10 μM)compared to SCH 23390. We conclude that dopamine depletion mimics the dorsal light reaction by increasing the luminosity output of the eye and that dopamine is directly involved in photopic luminosity function.
Depletion of retinal dopamine does not affect the ERG b-wave increment threshold function in goldfish in vivo
Authors: Lin Zheng-Shi , Yazulla Stephen
Published: June 2009

Increment threshold functions of the electroretinogram (ERG) b–wave were obtained from goldfish using an in vivo preparation to study intraretinal mechanisms underlying the increase in perceived brightness induced by depletion of retinal dopamine by 6–hydroxydopamine (6–OHDA). Goldfish received unilateral intraocular injections of 6–OHDA plus pargyline on successive days. Depletion of retinal dopamine was confirmed by the absence of tyrosine-hydroxylase immunoreactivity at 2 to 3 weeks postinjection as compared to sham-injected eyes from the same fish. There was no difference among normal, sham-injected or 6–OHDA-injected eyes with regard to ERG waveform, intensity-response functions or increment threshold functions. Dopamine-depleted eyes showed a Purkinje shift, that is, a transition from rod-to-cone dominated vision with increasing levels of adaptation. We conclude (1) dopamine-depleted eyes are capable of photopic vision; and (2) the ERG b–wave is not diagnostic for luminosity coding at photopic backgrounds. We also predict that (1) dopamine is not required for the transition from scotopic to photopic vision in goldfish; (2) the ERG b–wave in goldfish is influenced by chromatic interactions; (3) horizontal cell spinules, though correlated with photopic mechanisms in the fish retina, are not necessary for the transition from scotopic to photopic vision; and (4) the OFF pathway, not the ON pathway, is involved in the action of dopamine on luminosity coding in the retina.
Differential expression of glycine receptor subunits in the retina of the rat: A study using immunohistochemistry andin situhybridization
Authors: Greferath U. , Brandstätter J. H. , Wässle H. , Kirsch J. , Kuhse J. , Grünert U.
Published: June 2009

Immunohistochemistry andin situhybridization were used to study the distribution of glycine receptor (GlyR) subunits and the GlyR-associated protein gephyrin in the rat retina. Monoclonal antibodies against the α and β subunits of the GlyR and gephyrin showed a strong punctate labeling pattern in the inner plexiform layer. Glycine receptor mRNAs were found in the inner nuclear layer and the ganglion cell layer. The α 1 subunit mRNA is predominantly present in the outer half of the INL and on some but not all ganglion cells. GlyR α2 subunit mRNA is predominantly present in the inner half of the INL and on nearly all cells in the ganglion cell layer. GlyR α3–, GlyR β-, and gephyrin-mRNAs are present in the entire INL and in cells in the ganglion cell layer. The differential expression of glycine receptor subunits indicates a functional diversity of glycine receptors in the retina.
Subdivisions of the visual system labeled with the Cat-301 antibody in tree shrews
Authors: Jain Neeraj , Preuss Todd M. , Kaas Jon H.
Published: June 2009

The monoclonal antibody Cat-301 was used to stain neurons and neuropil in the visual thalamus and cortex of tree shrews —small, highly visual mammals that are closely related to primates. Previously, this antibody has been found to label neurons associated with the Y-cell stream of processing in cats and the magnocellular or M-cell stream in macaque monkeys. In tree shrews, the antibody selectively labeled layers 1, 2, 4, and 5 of the dorsal lateral geniculate nucleus, layers that are likely to contain neurons previously classified as Y-cells. Of the two layers that contain W-cells, layer 3 was unlabeled and layer 6 was lightly labeled. In area 17, layer 3c was densely stained, as in cats and macaque monkeys. The external half of layer 5 was also densely stained, in contrast to cats where the internal half of layer 5 is stained and macaques where layer 5 is sparsely stained. Area 18 was characterized by dense, uniform staining of inner layer 3 and outer layer 5, but no pattern of alternating light and dense bands crossed the width of area 18 as in macaques. Dense labeling of these same sublayers occurred in cortical areas TA and TD just lateral to area 18. Area TD may be the homologue of area MT of primates, which also stains densely with Cat-301 in macaques. These results indicate that Cat-301 differentially labels layers and areas in the visual system of tree shrews, and raise intriguing issues of comparison among tree shrews, primates, and cats.
Accumulation of calcium in degenerating photoreceptors of severalDrosophilamutants
Authors: Sahly Iman , Schröder Walter H. , Zierold Karl , Minke Baruch
Published: June 2009

The hypothesis that a large, possibly toxic, increase in cellular calcium accompanies photoreceptor cell degeneration in several differentDrosophilamutants was tested. The calcium content of wild type and mutant photoreceptors ofDrosophilawas measured using rapid freezing of the eyes and energy-dispersive x-ray analysis (e.d.x.) of cryosections and semithin sections of cryosubstituted material. Light- and dark-raised mutants of the following strains were studied: retinal degeneration B (rdgB);retinal degeneration C (rdgC);neither inactivation nor afterpotential C (ninaC), and no receptor potential A (norpA).These are light-dependent retinal degeneration mutants in which the affected gene products had been previously shown as myosin-kinase (ninaC), calcium-dependent phosphoprotein phosphatase (rdgC), phosphoinositide transfer protein (rdgB), and phospholipase C (norpA).In light-raised mutants, ommatidia of variable degrees of degeneration were observed. Mass-dense globular bodies of 200–500 nm diameter in relatively large quantities were found in the degenerating photoreceptor of all the mutants tested. These subcellular globules were found to have a very high calcium content, which was not found in wild type or in nondegenerating photoreceptors of the mutants. Nondegenerating photoreceptors were found not only in dark-raised mutants, but in smaller quantities also in light-raised mutants. Usually these globular structures contained high levels of phosphorus, indicating that at least part of the calcium in the mutant photoreceptors is precipitated as calcium phosphate. The results indicate that a large increase in cellular calcium accompanies light-induced photoreceptor degeneration in degeneratingDrosophilamutants even when induced by very different mutations, suggesting that the calcium accumulation is a secondary rather than a primary effect in the degeneration process.
A sequence upstream of the mouse blue visual pigment gene directs blue cone-specific transgene expression in mouse retinas
Authors: Chiu M. Isabel , Nathans Jeremy
Published: June 2009

A 6.4–kb sequence upstream of the mouse blue visual pigment gene has been assayed in transgenic mice for the ability to direct cell-type-specific expression of a linked β-galactosidase (lacZ) reporter. The construct is expressed specifically in cone photoreceptors in three independent lines. Transgene expression is found in the developing retina on the first postnatal day, increases rapidly in subsequent days, and persists through adulthood. A gradient of transgene expression is observed across the retina, with the transgene-expressing cones found almost exclusively in the lower retina and rarely in the upper retina, a pattern that parallels the distribution of blue cones in the mouse retina. Double-labeling with anti-cone pigment antibodies shows that transgene expression is confined to blue cones. These results imply that all of the sequence elements necessary for the control of blue cone-specific expression are encoded within the 6.4–kb DNA fragment tested.
Brain-stem modulation of the response properties of cells in the cat's perigeniculate nucleus
Authors: Murphy P. C. , Uhlrich D. J. , Tamamaki N. , Sherman S. Murray
Published: June 2009

Transmission through the lateral geniculate nucleus is facilitated following activation of the cholinergic input from the brain stem, which is thought to reflect activity patterns seen during arousal. One of the underlying mechanisms is the suppression of inhibitory circuits local to the lateral geniculate nucleus. However, evidence exists that some visually driven inhibitory inputs to geniculate relay cells may be preserved or even enhanced under conditions of arousal, and during electrical activation of the parabrachial region of the brain stem. We have therefore reexamined the effect of brain-stem activation on the visual responses of one group of local inhibitory inputs to geniculate relay cells, those emanating from the adjacent perigeniculate nucleus. We recorded single perigeniculate cells in anesthetized, paralyzed cats. Axons innervating the lateral geniculate and perigeniculate nuclei from the parabrachial region of the brain stem were electrically activated, and the effect of this activation was assessed on both spontaneous and visually evoked responses. Visual stimulation consisted of sinusoidally modulated sine–wave gratings of varying spatial and temporal frequency. For the great majority of perigeniculate cells (32 of 40), brain-stem activation inhibited spontaneous activity, while one cell was excited, three showed a mixed effect and four were unaffected. Nevertheless, the responses of most cells (30 of 40) were facilitated when brain-stem activation was paired with certain spatio-temporal patterns of visual stimulation. Spatial tuning curves were constructed for 17 cells and temporal tuning curves for 14, before and during parabrachial activation. The responses of any one cell could be facilitated, unchanged, or suppressed, depending on the visual stimulus used. In some cases, this substantially modified the cell’s spatial and temporal tuning properties. We conclude that activation of the brain stem disinhibits geniculate relay cells in the absence of visual stimulation, but it has the potential to enhance either the magnitude or specificity of visually driven inhibition arising from the perigeniculate nucleus.
Neurochemical signatures revealed by glutamine labeling in the chicken retina
Authors: Kalloniatis Michael , Tomisich Guido , Marc Robert E.
Published: June 2009

Postembedding immunocytochemistry was used to determine the retinal distribution of the amino acid glutamine, and characterize amino acid signatures in the avian retinal ganglion cell layer. Glutamine is a potential precursor of glutamate and some glutamatergic neurons may use this amino acid to sustain production of glutamate for neurotransmission. Ganglion cells, cells in the inner nuclear layer, and some photoreceptors exhibited glutamine immunoreactivity of varying intensity. Ganglion cells demonstrated the highest level of immunoreactivity which indicates either slow glutamine turnover or active maintenance of a large standing glutamine pool relative to other glutamatergic neurons. Müller's cells in the avian retina are involved in glutamate uptake and carbon recycling by the rapid conversion of glutamate to glutamine, thus explaining the low glutamate and high glutamine immunoreactivity found throughout Müller's cells. Most chicken retinal ganglion cells are glutamate (E) and glutamine (Q) immunoreactive but display diverse signatures with presumed functional subsets of cells displaying admixtures of E and Q with GABA (7) and/or glycine (G). The four major ganglion cell signatures are (1) EQ; (2) EQγ; (3) EQG; and (4) EQγG.
Recoverin immunoreactivity in mammalian cone bipolar cells
Authors: Milam Ann H. , Dacey Dennis M. , Dizhoor Alexander M.
Published: June 2009

Human, macaque monkey, and rat retinas were immunostained with a polyclonal antibody preparation against purified recoverin, a 23-kD calcium-binding protein isolated from bovine retina that localizes to rods and cones (Dizhoor et al., 1991). In addition to immunoreactive photoreceptors, we have identified subpopulations of recoverin-positive bipolar cells in all three species. Results from immunostaining with progressive dilutions of anti-recoverin and preadsorption of the antibody with a dilution series of purified recoverin showed that photoreceptors and bipolar cells had similar affinities for the antibody and suggested that the molecule recognized by the antibody in both cell types is recoverin. Immunoreactivity for recoverin and protein kinase C, a selective marker for all rod bipolar cells, was found in separate bipolar cell populations. Recoverin immunoreactivity is therefore a characteristic of certain cone bipolar cell types.

In rat retina, anti-recoverin labeled two morphologically distinct subpopulations of cone bipolar cells whose axonal arbors stratified at different depths in the inner plexiform layer (IPL). The bipolar cells labeled with anti-recoverin did not correspond to those that were reactive for calbindin, another cone bipolar cell marker.

Human and monkey retinas also had two populations of cone bipolar cells that were recoverin-positive. One population showed a distinct pattern of narrow bistratification at the outer border of the IPL and a regular mosaic arrangement of its axonal arbors, suggesting that the entire population of a single cone bipolar type was labeled. Cell density, dendritic morphology, and axonal-field size and stratification indicate that anti-recoverin selectively stains the flat midget (presumed OFF-center) cone bipolar cell type observed previously in Golgi preparations. By contrast the second bipolar cell population had axonal stratification in the inner half of the IPL and showed an unusual but consistent morphology and spatial distribution. Individual cells were intensely stained but were present at an extremely low density (~2−5 cells/mm2). These cells had multibranched dendritic trees characteristic of the diffuse bipolar cell class, but very small axonal fields in the size range of the midget bipolar class. Neither of the two recoverin-positive bipolar cell types in monkey was labeled with anti-calbindin or anti-cholecystokinin. An antibody preparation against bovine pineal hydroxyindole-O-methyltransferase (HIOMT) labeled photoreceptors and bipolar cells that closely resembled the recoverin-positive bipolar cells in human and rat retinas. Preadsorption of this antibody preparation with purified recoverin abolished immunostaining of the bipolar cells, suggesting that the anti-HIOMT preparation contains antibodies against recoverin, which is known to be present in the bovine pineal gland.
Temporal asynchrony interferes with vernier acuity
Authors: Wehrhahn Christian , Westheimer Gerald
Published: June 2009

Two dots may be aligned vertically with a precision much higher than that expected from two-point resolution provided they are separated by a visual angle of 3–5 min of arc. This precision suffers when the two dots are not exposed synchronously. Neither onset nor offset asynchronies can be tolerated; exposure differences of the two components of the vernier task as low as 30 ms can lead to a reduction in performance when the total exposure is below 90 ms. This effect cannot be compensated for by synchronizing the onset of one stimulus component with the offset of the other, even when the two are of opposite contrast. The data suggest that vernier acuity may be subserved by a dynamical linking of cortical excitation generated by the synchronous arrival of signals within a range of locations in the cortex whose spatial separation is critical for optimal hyperacuity performance. The evidence presented in this paper must be taken into account when a physiological substrate for hyperacuity is considered.
Visual processing in pigeon nucleus rotundus: Luminance, color, motion, and looming subdivisions
Authors: Wang Yong-Chang , Jiang Shiying , Frost Barrie J.
Published: June 2009

The responses of single cells to luminance, color and computer-generated spots, bars, kinematograms, and motion-in-depth stimuli were studied in the nucleus rotundus of pigeons. Systematic electrode penetrations revealed that there are several functionally distinct subdivisions within rotundus where six classes of visual-selective cells cluster. Cells in the dorsal-posterior zone of the nucleus respond selectively to motion in depth (i.e. an expanding or contracting figure in the visual field). Most cells recorded from the dorsal-anterior region responded selectively to the color of the stimulus. The firing rate of the cells in the anterior-central zone, however, is dramatically modulated by changing the level of illumination over the whole visual field. Cells in the ventral subdivision strongly respond to moving occlusion edges and very small moving objects, with either excitatory or inhibitory responses. These results indicate that visual information processing of color, ambient illumination, and motion in depth are segregated into different subdivisions at the level of nucleus rotundus in the avian brain.