bluuebunny/crossref_metadata_2025 huggingface dataset:
Immunohistochemical analysis of the neurotrophins BDNF and NT-3 and their receptors trk B, trk C, and p75 in the developing chick retina
Authors: Das Indranil , Hempstead Barbara L. , Macleish Peter R. , Sparrow Janet R.
Published: June 2009

The neurotrophins are trophic and mitogenic factors critical for the development of specific classes of neurons in the central and peripheral nervous systems. In the retina, BDNF and NT-3 have been shown to promote the survival of differentiated ganglion cells (Rodriguez-Tebar et al., 1989; De La Rosa et al., 1994). NT-3 has also been demonstrated to support the survival of amacrine cells and facilitates the differentiation of retinal neurons in culture (De La Rosa et al., 1994). Here, we examine immunohistochemically the expression of BDNF and NT-3 proteins, their cognate receptors, trk B and trk C, respectively, and the p75 neurotrophin receptor in the developing chick retina. At E8, the earliest stage of retinal development examined, all of these proteins exhibit diffuse expression throughout the width of the retina, with the strongest reactivity in the innermost layers. A gradual restriction in expression to ganglion cells and amacrine cells, the staining of which is most prominent at E15, is followed by a downregulation of expression with the strongest immunoreactivity persisting in the ganglion cell layer. Overlapping patterns of expression throughout embryonic development indicate a colocalization of the neurotrophins and their receptors, although NT-3 and p75 alone are present in the inner plexiform layer and only p75 is observed in the outer plexiform layer. Although some of the immunoreactivity for BDNF, NT-3, and their receptors in retina may reflect trophic mechanisms operating in association with the optic tectum and isthmo-optic nucleus, the colocalization of ligands and receptors in retina strengthens the assertion that these neurotrophins function locally during development.
Neuronal responses in extrastriate cortex to objects in optic flow fields
Authors: Sherk Helen , Mulligan Kathleen , Kim Jong-Nam
Published: June 2009

During locomotion, observers respond to objects in the environment that may represent obstacles to avoid or landmarks for navigation. Although much is known about how visual cortical neurons respond to stimulus objects moving against a blank background, nothing is known about their responses when objects are embedded in optic flow fields (the patterns of motion seen during locomotion). We recorded from cells in the lateral suprasylvian visual area (LS) of the cat, an area probably analogous to area MT. In our first experiments, optic flow simulations mimicked the view of a cat trotting across a plain covered with small balls; a black bar lying on the balls served as a target object. In subsequent experiments, optic flow simulations were composed of natural elements, with target objects representing bushes, rocks, and variants of these. Cells did not respond to the target bar in the presence of optic flow backgrounds, although they did respond to it in the absence of a background. However, 273/423 cells responded to at least one of the taller, naturalistic objects embedded in optic flow simulations. These responses might represent a form of image segmentation, in that cells detected objects against a complex background. Surprisingly, the responsiveness of cells to objects in optic flow fields was not correlated with preferred direction as measured with a moving bar or whole-field texture. Because the direction of object motion was determined solely by receptive-field location, it often differed considerably from a cell's preferred direction. About a quarter of the cells responded well to objects in optic flow movies but more weakly or not at all to bars moving in the same direction as the object, suggesting that the optic flow background modified or suppressed direction selectivity.
Visual cortex neurons in monkeys and cats: Detection, discrimination, and identification
Authors: Geisler Wilson S. , Albrecht Duane G.
Published: June 2009

A descriptive function method was used to measure the detection, discrimination, and identification performance of a large population of single neurons recorded from within the primary visual cortex of the monkey and the cat, along six stimulus dimensions: contrast, spatial position, orientation, spatial frequency, temporal frequency, and direction of motion. First, the responses of single neurons were measured along each stimulus dimension, using analysis intervals comparable to a normal fixation interval (200 ms). Second, the measured responses of each neuron were fitted with simple descriptive functions, containing a few free parameters, for each stimulus dimension. These functions were found to account for approximately 90% of the variance in the measured response means and response standard deviations. (A detailed analysis of the relationship between the mean and the variance showed that the variance is proportional to the mean.) Third, the parameters of the best-fitting descriptive functions were utilized in conjunction with Bayesian (optimal) decision theory to determine the detection, discrimination, and identification performance for each neuron, along each stimulus dimension. For some of the cells in monkey, discrimination performance was comparable to behavioral performance; for most of the cells in cat, discrimination performance was better than behavioral performance. The behavioral contrast and spatial-frequency discrimination functions were similar in shape to the envelope of the most sensitive cells; they were also similar to the discrimination functions obtained by optimal pooling of the entire population of cells. The statistics which summarize the parameters of the descriptive functions were used to estimate the response of the visual cortex as a whole to a complex natural image. The analysis suggests that individual cortical neurons can reliably signal precise information about the location, size, and orientation of local image features.
Callosally projecting neurons in the macaque monkey V1/V2 border are enriched in nonphosphorylated neurofilament protein
Authors: Hof Patrick R. , Ungerleider Leslie G. , Adams Michelle M. , Webster Maree J. , Gattass Ricardo , Blumberg Dana M. , Morrison John H.
Published: June 2009

Previous immunohistochemical studies combined with retrograde tracing in macaque monkeys have demonstrated that corticocortical projections can be differentiated by their content of neurofilament protein. The present study analyzed the distribution of nonphosphorylated neurofilament protein in callosally projecting neurons located at the V1/V2 border. All of the retrogradely labeled neurons were located in layer III at the V1/V2 border and at an immediately adjacent zone of area V2. A quantitative analysis showed that the vast majority (almost 95%) of these interhemispheric projection neurons contain neurofilament protein immunoreactivity. This observation differs from data obtained in other sets of callosal connections, including homotypical interhemispheric projections in the prefrontal, temporal, and parietal association cortices, that were found to contain uniformly low proportions of neurofilament protein-immunoreactive neurons. Comparably, highly variable proportions of neurofilament protein-containing neurons have been reported in intrahemispheric corticocortical pathways, including feedforward and feedback visual connections. These results indicate that neurofilament protein is a prominent neurochemical feature that identifies a particular population of interhemispheric projection neurons at the V1/V2 border, and suggest that this biochemical attribute may be critical for the function of this subset of callosal neurons.
Architectonic subdivisions of the inferior pulvinar in New World and Old World monkeys
Authors: Stepniewska Iwona , Kaas Jon H.
Published: June 2009

Architectonic subdivisions of the inferior pulvinar (PI) complex were delineated in New World owl and squirrel monkeys and Old World macaque monkeys. Brain sections were processed for Nissl substance, myelin, cytochrome oxidase (CO), acetylcholinesterase (AChE), calbindin-D28K (Cb), or with the monoclonal antibody Cat-301. In all three primates, we identified the posterior nucleus (PIp) and the medial nucleus (PIm) of previous reports, and divided the previously recognized central nucleus (PIc) into two subdivisions, medial (PIcm) and lateral (PIcl). Each nucleus had several features that allowed it to be readily distinguished. (1) PIp was dark in Cb, and moderately dark in AChE and CO preparations. (2) PIm was Cb light, and AChE and CO dark. (3) PIcm was Cb dark, and AChE and CO light. (4) PIcl was Cb moderate with a scattering of dark neurons, and moderately dark for AChE and CO. (5) In sections processed for Cat-301, PIm in macaque monkeys and PIcm and PIp in squirrel monkeys stained darkly, while little staining was apparent in owl monkeys. The results allowed subdivisions of the inferior pulvinar to be more clearly defined, homologized, and compared across taxa. All monkeys appear to have the same four subdivisions of the PI, although properties vary.
Synaptic inputs to retrogradely labeled ganglion cells in the retina of the cane toad, Bufo marinus
Authors: Zhu Bao-Song , Gibbins Ian L.
Published: June 2009

The entire population of ganglion cells in the retina of the toad Bufo marinus was labeled by retrograde transport of a lysine-fixable biotinylated dextran amine of 3000 molecular weight. Synaptic connections between bipolar, amacrine, and ganglion cells in the inner plexiform layer were quantitatively analyzed, with emphasis on synaptic inputs to labeled ganglion cell dendrites. Synapses onto ganglion cell dendrites comprised 47% of a total of 1234 identified synapses in the inner plexiform layer. Approximately half of the bipolar or amacrine cell synapses were directed onto ganglion cell dendrites, while the rest were made mainly onto amacrine cell dendrites. Most of the synaptic inputs to ganglion cell dendrites derived from amacrine cell dendrites (84%), with the rest from bipolar cell terminals. Synaptic inputs to ganglion cell dendrites were distributed relatively uniformly throughout all sublaminae of the inner plexiform layer. The present study provides unambiguous identification of ganglion cell dendrites including very fine processes, enabling a detailed analysis of the types and distribution of synaptic inputs from the bipolar and amacrine cell to the ganglion cells. The retrograde tracing technique used in the present study will prove to be a useful tool for identifying synaptic inputs to ganglion cell dendrites from neurochemically identified bipolar and amacrine cell types in the retina.
Immunocytochemical localization of GABA, GABAAreceptors, and synapse-associated proteins in the developing and adult ferret retina
Authors: Karne A. , Oakley D. M. , Wong G. K. , Wong R. O. L.
Published: June 2009

Gamma-aminobutyric acid (GABA) modulates the pattern of correlated spontaneous bursting activity between amacrine cells and ganglion cells of the ferret retina during the first postnatal month. Here, we demonstrate the presence of an anatomical network which may underlie these interactions throughout the period when correlated bursting activity is observed, by immunolabelling the neonatal ferret retina for GABA, GABAAreceptors, and synapse-associated proteins. GABA immunoreactivity was detected in cell somata in the ganglion cell layer (GCL), in amacrine cells, and in the inner plexiform layer (IPL) by embryonic day 38. This pattern remained largely unchanged throughout neonatal development and in the adult. By contrast to other mammals, the outer plexiform layer (OPL) was only very weakly labelled for GABA, at all ages studied. Strong, punctate, immunolabelling for the β2/3 subunit of the GABAAreceptor was apparent in the IPL by birth, and appeared in the OPL by the second postnatal week. The possibility that synaptic interactions in the IPL occur during bursting activity was examined by immunolabelling for synapse-associated proteins. Strong immunoreactivity for synaptic vesicle proteins, Synapsin I and II, and synaptic vesicle-2 (SV2), a synaptic vesicle transporter protein, was observed in the IPL by birth. Immunoreactivity for SNAP-25, a protein associated with vesicle fusion, was also intense at the level of the IPL and in the nerve fiber layer of the retina at birth. Taken together, these patterns of immunoreactivity suggest the presence of a GABAergic network in the IPL of the ferret retina by birth, coinciding with the appearance of correlated bursting activity in the inner retina.
A comparison of receptive-field and tracer-coupling size of amacrine and ganglion cells in the rabbit retina
Authors: Bloomfield Stewart A. , Xin Daiyan
Published: June 2009

Recent studies have shown that amacrine and ganglion cells in the mammalian retina are extensively coupled as revealed by the intercellular movement of the biotinylated tracers biocytin and Neurobiotin. These demonstrations of tracer coupling suggest that electrical networks formed by proximal neurons (i.e. amacrine and ganglion cells) may underlie the lateral propagation of signals across the inner retina. We studied this question by comparing the receptive-field size, dendritic-field size, and extent of tracer coupling of amacrine and ganglion cells in the dark-adapted, supervised, isolated retina eyecup of the rabbit. Our results indicate that while the center-receptive fields of proximal neurons are approximately 15% larger than their corresponding dendritic diameters, this slight difference can be explained by factors other than electrical coupling such as tissue shrinkage associated with histological processing. However, the extent of tracer coupling of amacrine and ganglion cells was, on average, about twice the size of the corresponding receptive fields. Thus, the receptive field of an individual proximal neuron matched far more closely to its dendritic diameter than to the size of the tracer-coupled network of cells to which it belonged. The exception to this rule was the AII amacrine cells for which center-receptive fields were 2–3 times the size of their dendritic diameters but matched closely to the size of the tracer-coupled arrays. Thus, with the exception of AII cells, our data indicate that tracer coupling between proximal neurons is not associated with an enlargement of their receptive fields. Our results, then, provide no evidence for electrical coupling or, at least, indicate that extensive lateral spread of visual signals does not occur in the proximal mammalian retina.
Intracortical connections are not required for oscillatory activity in the visual cortex
Authors: Ghose Geoffrey M. , Freeman Ralph D.
Published: June 2009

arises from the integration of signals from strongly oscillatory cells within the LGN. The model also predicts the incidence of 50-Hz oscillatory cells within the cortex. Oscillatory discharge around 30 Hz is explained in a second model by the presence of intrinsically oscillatory cells within cortical layer 5. Both models generate spike trains whose power spectra and mean firing rates are in close agreement with experimental observations of simple and complex cells. Considered together, the two models can largely account for the nature and incidence of oscillatory discharge in the cat's visual cortex. The validity of these models is consistent with the possibility that oscillations are generated independently of intracortical interactions. Because these models rely on intrinsic stimulus-independent oscillators within the retina and cortex, the results further suggest that oscillatory activity within the cortex is not necessarily associated with the processing of high-order visual information.
Effect of guanine nucleotides on the dark voltage of single frog rods
Authors: Schmidt Karl-Friedrich , Nöll Gottfried N. , Baumann Christian
Published: June 2009

Single frog rods consisting of the outer segment and the ellipsoid were investigated by the whole-cell patch-clamp technique. When the recording pipette was filled with a simple intracellular medium containing potassium as the principal cation, a slow increase in dark voltage (hyperpolarization) associated with a decay of the photoresponses was observed. The hyperpolarization started at a dark voltage of −27 ± 8 mV, followed an exponential course, and leveled out at −52 ± 6 mV. The time constant was proportional to the access resistance of the preparations. With a pipette medium containing a 0.5 or 1.0 μM cGMP, the initial dark voltage was shifted to more positive values and the tendency of hyperpolarization was clearly attenuated. Similar results were obtained with 1 mM GTP. The effects of GDP and of ATP were less significant. In experiments with 1 mM GTPplus1 mM ATP, the dark voltage behaved as in experiments with only GTP. The stabilizing action of GTP was amplified by EGTA so that with 1 mM GTP plus 1 mM free EGTA the dark voltage was stable at a level of −15 mV. It is concluded that the preparations lose intracellular components such as cGMP and GTP by diffusion into the recording pipette and that the losses are prevented or reduced when the pipette medium contains these nucleotides in nearly physiological concentrations. For the internal transmitter cGMP, the results suggest that its free concentration does not exceed 1 μM.
Comparison of adenosine uptake and endogenous adenosine-containing cells in mammalian retina
Authors: Blazynski Christine , Mosinger Judith L. , Cohen Adolph I.
Published: June 2009

Autoradiographic techniques were used to label [3H]-adenosine and [3H]-cyclohexyladenosine accumulating cells in rabbit, mouse, and ground squirrel retinas. Immunohistochemical methods revealed the distribution of cells that stained for endogenous adenosine. Comparisons of these two markers revealed for all three species that the distribution of specific subpopulations of retinal cells that store or accumulate the purine nucleoside, adenosine, is similar. For all three species, cells localized in the ganglion cell layer accumulated adenosine and exhibited adenosine-like immunoreactivity (ALIR). A smaller proportion of cells localized in the inner nuclear layer were labeled for ALIR, while a larger proportion of cells in this layer accumulated adenosine. Subtle differences between species are presented. However, the general similarities of the distribution of these two putative purinergic markers supports the evidence that a discrete adenosinergic neurotransmitter/modulatory system is present in the retina.
Differential elasticity of the immature retina: A contribution to the development of the area centralis?
Authors: Kelling Steven T. , Sengelaub Dale R. , Wikler Kenneth C. , Finlay Barbara L.
Published: June 2009

Differential stretch of a retinal surface with an initially uniform cell density has been repeatedly implicated as one of the developmental mechanisms that produces the topographic organization of cell density in the adult retina, notably the area centralis or visual streak versus peripheral regions. It is known that intraocular pressure is required to produce the normal conformation and thinning of the retina during development. We tested the possibility that the retina has elastic properties that might permit differential stretch in conjunction with intraocular pressure. The relative deformation of the retina containing the presumptive area centralis was compared to the deformation of peripheral retina at equivalent applied fluid displacements in 7–12-day-old cats. The peripheral retina deformed significantly more, consistent with the hypothesis that differences in the local elasticities of the developing neural retina contribute to its characteristic topographic changes. Thus, a biomechanical property of the growing eye may contribute to the mechanism by which the pattern of the visual array is sampled.
Evoked responses to sinusoidal gratings in the pigeon optic tectum
Authors: Porciatti V. , Alesci R. , Bagnoli P.
Published: June 2009

Tectal evoked potentials (TEPs) in response to sinusoidal gratings of different contrast, spatial and temporal frequency have been recorded from the tectal surface of the pigeon. Responses have been digitally filtered in order to isolate transient oscillatory (fast) potentials (50–150 Hz), transient slow potentials (1–50 Hz), and the steady-state second-harmonic component (16.6 Hz). Transient slow potentials, as well as the steady-state second-harmonic component, are band-pass spatially tuned with a maximum at 0.5 cycles/deg and attenuation at higher and lower spatial frequencies. The high spatial frequency cutoff is 4–5 cycles/deg. Both transient slow potentials and the steady-state second-harmonic component increase in amplitude as a function of log contrast and saturate at about 20% contrast. The contrast sensitivity, as determined by extrapolating TEP amplitude to 0 V is 0.1–0.2%. These characteristics of spatial-frequency selectivity and contrast sensitivity are similar to those reported for single tectal cells. Unlike slow potentials, oscillatory potentials are not band-pass spatially tuned. In addition, their contrast response function does not saturate at moderate contrast. These differences suggest that tectal evoked slow and fast potentials reflect the activity of different neuronal mechanisms.
p-Chloroamphetamine treatment modifies evoked responses to sinusoidal gratings in the pigeon optic tectum
Authors: Alesci R. , Porciatti V. , Sebastiani L. , Bagnoli P.
Published: June 2009

This study was performed in order to establish whether selective depletion of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the pigeon optic tectum (TeO) induced byp-chloroamphetamine (p-CA) modified tectal evoked potentials (TEPs). TEPs in response to sinusoidal gratings of different contrast, spatial and temporal frequency were recorded in control pigeons and in pigeons intraperitoneally injected withp-CA (10 mg/kg; two administrations in consecutive days). TEPs ofp-CA treated pigeons, as compared to those of control pigeons, were reduced in amplitude as a function of contrast, spatial and temporal frequency. In addition, TEPs ofp-CA treated pigeons differed from those recorded in controls in their transfer characteristics of contrast and spatial frequency. In particular, TEPs ofp-CA treated pigeons did not saturate at moderate contrast, unlike those of controls. Furthermore, the TEP spatial tuning inp-CA treated pigeons is broader than that in controls; it thus suggests a reduction of spatial-frequency selectivity. These findings indicate that a selective neurotoxin for serotonergic systems, such asp-CA, can serve as a useful denervation tool for the study of the serotonergic function in the pigeon TeO. In addition, selective changes of TEP properties suggest the possibility that serotonergic afferents play a modulatory role on the receptive-field characteristics of tectal neurons.
Development of the nucleus isthmi in Xenopus, II: Branching patterns of contralaterally projecting isthmotectal axons during maturation of binocular maps
Authors: Udin Susan B.
Published: June 2009

The tectum of Xenopus frogs receives input from both eyes. The contralateral eye's projection reaches the tectum directly, via the optic nerve, and the ipsilateral eye's projection reaches the tectum indirectly, via the nucleus isthmi. Under normal conditions, the topography of the ipsilateral map relayed from the nucleus isthmi is in register with the topography of the retinotectal map from the contralateral eye. During development, the process of aligning the two maps is complicated by the dramatic changes in binocular overlap of the two eyes' visual fields which take place during late tadpole and juvenile stages. The goal of this study is to determine the branching patterns of contralaterally projecting isthmotectal axons before, during, and after the period of rapid eye migration.

Isthmotectal axons were filled by anterograde transport of horseradish peroxidase (HRP) from the nucleus isthmi. The results show that crossed isthmotectal axons enter the entire extent of the tectum before binocular overlap begins to increase. Therefore, binocular overlap is not necessary for the initial isthmotectal projection to span the tectum. The density of isthmotectal branches rises dramatically at the same time that the eyes begin to shift. During the period when eye migration is most rapid, many isthmotectal axons form arbors which resemble adult arbors but which extend over greater proportions of the tectal surface.

The axons appear to be directed toward appropriate mediolateral positions as they enter the tectum. Their trajectories are roughly rostocaudal, with relatively little change along the mediolateral dimension. These data, when combined with available physiological data, suggest that mediolateral order is initially established by vision-independent mechanisms but can be altered by vision-dependent mechanisms. Rostrocaudal order becomes discernable only at the time when binocular visual cues become available and appears to be established primarily on the basis of the activity of the retinotectal and isthmotectal axons.
A neural model of foveal light adaptation and afterimage formation
Authors: Wilson Hugh R.
Published: June 2009

Psychophysical research has documented the existence of three processes in light adaptation: a fast subtractive process, a divisive process that is fast at light onset and slower at light offset, and a very slow subtractive process (Hayhoe et al., 1987). In the neural model developed here, the fast subtractive process is identified with horizontal cell feedback onto cones and the divisive process with amacrine cell feedback onto bipolar cells. The very slow subtractive process is identified with the modulatory feedback circuit from amacrines via interplexiform cells to horizontal cells. A nonlinear dynamical model is developed incorporating these aspects of retinal circuitry along with both ON- and OFF-center M and P pathways. This model is shown to account for many aspects of foveal light adaptation, including negative afterimage formation, and to explain a number of the physiological differences between M and P ganglion cells, including their differing contrast-response functions.
The DAPI-3 amacrine cells of the rabbit retina
Authors: Wright Layne L. , Macqueen Colin L. , Elston Guy N. , Young Heather M. , Pow David V. , Vaney David I.
Published: June 2009

In the rabbit retina, the nuclear dye, 4,6, diarnidino-2-phenylindole (DAPI), selectively labels a third type of amacrine cell, in addition to the previously characterized type a and type b cholinergic amacrine cells. In this study, these “DAPI-3” amacrine cells have been characterized with respect to their somatic distribution, dendritic morphology, and neurotransmitter content by combining intracellular injection of biotinylated tracers with wholemount immunocytochemistry. There are about 100,000 DAPI-3 amacrine cells in total, accounting for 2% of all amacrine cells in the rabbit retina, and their cell density ranges from about 130 cells/mm2 in far-peripheral retina to 770 cells/mm2 in the visual streak. The thin varicose dendrites of the DAPI-3 amacrine cells form a convoluted dendritic tree that is symmetrically bistratified in S1/S2 and S4 of the inner plexiform layer. Tracer coupling shows that the DAPI-3 amacrine cells have a fivefold dendritic-field overlap in each sublamina, with the gaps in the arborization of each cell being occupied by dendrites from neighboring cells. The DAPI-3 amacrine cells consistently show the strongest glycine immunoreactivity in the rabbit retina and they also accumulate exogenous [3H]-glycine to a high level. By contrast, the All amacrine cells, which are the best characterized glycinergic cells in the retina, are amongst the most weakly labelled of the glycine-immunopositive amacrine cells. The DAPI-3 amacrine cells costratify narrowly with the cholinergic amacrine cells and the On-Off direction-selective ganglion cells, suggesting that they may play an important role in movement detection.
Concentrations of biogenic amines in fundal layers in chickens with normal visual experience, deprivation, and after reserpine application
Authors: Ohngemach Sibylle , Hagel Gabi , Schaeffel Frank
Published: June 2009

Previous experiments in chickens have shown that dopamine released from the retina may be one of the messengers controlling the growth of the underlying sclera. It is also possible, however, that the apparent relationship between dopamine and myopia is secondary and artifactual. We have done experiments to assess this hypothesis. Using High Pressure Liquid Chromatography with electrochemical detection (HPLC-ED), we have asked whether changes in dopamine metabolism are restricted to the local retinal regions in which myopia was locally induced. Furthermore, we have measured the concentrations of biogenic amines separately in different fundal layers (vitreous, retina, choroid, and sclera) to find out how changes induced by “deprivation” (= removal of high spatial frequencies from the retinal image by translucent eye occluders which produce “deprivation myopia”) are transmitted through these layers. Finally, we have repeated the deprivation experiments after intravitreal application of the irreversible dopamine re-uptake blocker reserpine to see how suppression of dopaminergic transmission affects these changes. We found that (1) Alterations in retinal dopamine metabolism were indeed restricted to the retinal areas in which myopia was induced. (2) The retina was the major source of dopamine release with a steep gradient both to the vitreal and choroidal side. Vitreal content was about one-tenth, choroidal content about one-third, and scleral content about one-twentieth of that of the retina. (3) There was a drop by about 40% in vitreal dopamine, DOPAC (3,4-dihydroxyphenylacetic acid) and HVA (homovanilic acid) concentrations following deprivation which occurred already at a time where little changes could yet be seen in their total retinal contents. (4) Choroidal and scleral dopamine levels were not affected by deprivation, indicating that other messengers must relay the information to the sclera. (5) A single intravitreal injection of reserpine lowered dopamine and HVA levels in retina and vitreous for at least 10 days in a dose-dependent fashion and diminished or suppressed further effects of deprivation on these compounds. DOPAC levels continued to change upon deprivation even after reserpine injection (Fig. 3). Our results suggest that the release rates of dopamine from retinal amacrine cells can be estimated from vitreal dopamine concentrations; furthermore, they are in line with the hypothesis that there is an inverse relationship between dopamine release and axial eye growth rates. Although our experiments do not ultimately prove that dopamine has a functional role in the visual control of eye growth, they are in line with this notion.
Depth perception and evoked brain activity: The influence of horizontal disparity and visual field location
Authors: Skrandies Wolfgang
Published: June 2009

The perception of dynamic random-dot stereograms (RDS) depends on the physiological fusion of horizontally disparate binocular visual input. Thus, the use of RDS offers the possibility to study selectively cortical processing of visual information in man. We investigated the influence of horizontal disparity on the scalp topography of RDS evoked brain activity in 33 healthy subjects. Stereoscopic checkerboard patterns were presented in the center or lateralized in the left or right visual field with horizontal disparities changing at temporal frequencies of six or eight depth reversals/s using different disparity values ranging from 3.5 to 28 min of arc. In 11 subjects evoked potential fields were recorded from 16 electrodes, and 21 subjects participated in 30-channel recordings with electrodes located over the parietal and occipital brain areas. Stimulation frequency-related brain activity was obtained with all disparity values; however, with large or small disparities the potential field strength decreased significantly while largest responses were obtained with intermediate disparities. Significant differences were observed in RDS evoked brain activity when central and lateralized stimulus locations were compared. With lateral stimuli (extending from the fovea to 17.1-deg eccentricity) maximal amplitudes were obtained at larger disparities than with central stimuli. In addition there were pronounced differences between brain activity evoked with stimuli presented in the left or right visual field; however, there were very similar evoked potential signals recorded from electrodes located over the left and right hemispheres. Our findings indicate that the processing of disparity information with lateralized stimuli is different from the processing in the center of the visual field. In addition, lateralized stimulation yields a significant disparity tuning mainly with stereoscopic targets occurring to the right from the fixation point (but not with stimuli to the left) suggesting a functional difference between the visual half-fields.
Serial inhibitory synapses in retina
Authors: Zhang Jian , Jung Chang-Sub , Slaughter Malcolm M.
Published: June 2009

Whole-cell voltage clamp in the retinal slice and intracellular current clamp in the intact retina were used to study inhibitory interactions in the inner plexiform layer. Picrotoxin or strychnine reduced inhibitory, light-evoked currents in a majority of ganglion cells. However, in nearly a third of the ganglion cells, each of these antagonists enhanced the inhibitory synaptic current. All inhibitory current was blocked by the addition of the other antagonist. This indicates a cross-inhibition between GABAergic and glycinergic feedforward pathways. Blocking of GABAARs with SR95531 shortened the time course of both excitatory and inhibitory synaptic currents in ganglion cells. Application of picrotoxin, which blocked both GABAARs and GABACRs, produced the opposite effect. Recordings in the intact retina indicated that the light responses of ON bipolar cells, sustained ON, and transient ON-OFF third-order neurons were all made more transient by SR95531 and made more sustained by picrotoxin. The data suggest that a GABACfeedback pathway to bipolar cells makes light responses more phasic and that this feedback is inhibited through a GABAAR pathway. Consequently, the balance between GABAAR and GABACR inhibition regulates the time course of inputs to ganglion cells.
Light-induced modulation of coupling between AII amacrine cells in the rabbit retina
Authors: Bloomfield Stewart A. , Xin Daiyan , Osborne Tristan
Published: June 2009

The rod-driven, AII amacrine cells in the mammalian retina maintain homologous gap junctions with one another as well as heterologous gap junctions withon-cone bipolar cells. We used background illumination to study whether changes in the adaptational state of the retina affected the permeabilities of these two sets of gap junctions. To access changes in permeability, we injected single AII amacrine cells with the biotinylated tracer, Neurobiotin, and measured the extent of tracer coupling to neighboring AII cells and neighboring cone bipolar cells. We also measured the center-receptive field size of All cells to assess concomitant changes in electrical coupling. Our results indicate that in well dark-adapted retinas, AII cells form relatively small networks averaging 20 amacrine cells and covering about 75 μm. The size of these networks matched closely to the size of AII cellon-center receptive fields. However, over most of their operating range, AII cells formed dramatically larger networks, averaging 326 amacrine cells, which corresponded to an increased receptive-field size. As the retina was light adapted beyond the operating range of the AII cells, they uncoupled to form networks comparable in size to those seen in well dark-adapted retinas. Our results, then, indicate that the adaptational state of the retina has a profound effect on the extent of electrical coupling between AII amacrine cells. Although we observed light-induced changes in the number of tracer-coupled cone bipolar cells, these appeared to be an epiphenomenon of changes in homologous coupling between AII amacrine cells. Therefore, in contrast to the robust changes in AII–AII coupling produced by background illumination, our data provided no evidence of a light-induced modulation of coupling between AII cells andon-cone bipolar cells.
Dynamic shifts of the contrast-response function
Authors: Victor Jonathan D. , Conte Mary M. , Purpura Keith P.
Published: June 2009

We recorded visual evoked potentials in response to square-wave contrast-reversal checkerboards undergoing a transition in the mean contrast level. Checkerboards were modulated at 4.22 Hz (8.45-Hz reversal rate). After each set of 16 cycles of reversals, stimulus contrast abruptly switched between a “high” contrast level (0.06 to 1.0) to a “low” contrast level (0.03 to 0.5). Higher contrasts attenuated responses to lower contrasts by up to a factor of 2 during the period immediately following the contrast change. Contrast-response functions derived from the initial second following a conditioning contrast shifted by a factor of 2–4 along the contrast axis. For low-contrast stimuli, response phase was an advancing function of the contrast level in the immediately preceding second. For high-contrast stimuli, response phase was independent of the prior contrast history. Steady stimulation for periods as long as 1 min produced only minor effects on response amplitude, and no detectable effects on response phase. These observations delineate the dynamics of a contrast gain control in human vision.
Solar pruning of retinal rods in albino rainbow trout
Authors: Allen Donald M. , Hallows Ted E.
Published: June 2009

Morphology of the central retina and scotopic visual sensitivity were compared in juvenile albino and normally pigmented rainbow trout living under natural and reduced daylight. Outdoor albinos avoided exposing their eyes to direct sunlight, whereas normals were indifferent to it. After 4 months outdoors (Σ10,000 lux in albinos, Σ100,000 lux in normals), albinos had severely truncated or missing rod outer segments (ROS) and some missing rod ellipsoids, but normal numbers of photoreceptor nuclei and fully intact cones. Albino estimated ROS volume was only 7.1% of normal in July, but increased to 20% by the following February, mainlyviaan increase in numbers of ROS. However, in albinos moved indoors October 7 and exposed to 10–30 lux ambient daylight, both the number and length of ROS increased significantly, with estimated ROS volume reaching 95% of normal by 34 days. Albinos generally had more phagosomes (Σ3 X normal) and more macrophages (Σ2 X normal) in their outer retina. An optomotor reflex was used to define the effect of ROS volume on the ability to respond visually during dark adaptation. In July, albinos and normals from outdoor raceways (3 months) or indoor raceways (35 days) showed equal sensitivity after first being placed in darkness, but after 1 h in darkness, outdoor albinos with 6% of normal ROS volume were 2.0 log units less sensitive than indoor or outdoor normals, whereas indoor albinos with 53% of normal ROS volume were only 0.7 log units less sensitive. This verifies that most rod cell bodies of albino trout can persist without functional ROS in indirect sunlight, and can regrow functional outer segments in dim daylight. This finding is distinct from the extensive retinal light damage observed in albino rats exposed to more moderate cyclic light, in which entire rod cells degenerate early on.
Characterization of aldehyde dehydrogenase-positive amacrine cells restricted in distribution to the dorsal retina
Authors: Milam Ann H. , Possin Daniel E. , Huang Jing , Fariss Robert N. , Flannery John G. , Saari John C.
Published: June 2009

A class 1 aldehyde dehydrogenase (ALDH) catalyzes oxidation of retinaldehyde to retinoic acid in bovine retina. We used immunocytochemistry andin situhybridization to localize this enzyme in adult and fetal bovine retinas. Specific ALDH immunoreactivity was present in the cytoplasm of wide-field amacrine cells restricted in distribution to the dorsal part of the adult retina. The somata diameters ranged from ∼8 μ to ∼15 μ, and the cells increased in density from ∼125 cells/mm2near the horizontal meridian to ∼425 cells/mm2in the superior far periphery. The ALDH-positive cells had somata on both sides of the inner plexiform layer (IPL) and processes in two IPL strata. The majority of ALDH-positive cells were unreactive with antibodies against known amacrine cell enzymes and neurotransmitters, including GABA and glycine. The ALDH-positive amacrine cells also did not react with anti-cellular retinoic acid-binding protein, which was present in a subset of GABA-positive amacrine cells. In flat-mounted retinas processed byin situhybridization, the larger ALDH-positive amacrine cells tended to be more heavily labeled. In addition to amacrine cells, Müller cell processes in the inner retina were weakly immunoreactive for ALDH; however, these glial cells did not contain ALDH mRNA. The pattern of ALDH expression in fetal bovine retinas was documented by immunocytochemistry. No ALDH reactivity was found before 5.5 months; for the remainder of the fetal period, ALDH immunoreactivity was present in amacrine cells similar to those in adult retina. The ALDH-positive amacrine cells in bovine retina are novel, being limited in distribution to the dorsal retina and unlabeled with other amacrine cell-specific markers. Identification of ALDH in amacrine cells provides additional evidence that cells of the inner retina are involved in retinoid metabolism.
Evidence for only depolarizing rod bipolar cells in the primate retina
Authors: Dolan Robert P. , Schiller Peter H.
Published: June 2009

The mammalian rod bipolar, for which only one class has been identified, has been described as being hyperpolarizing by some investigators and depolarizing by others. We now report the effects of 2-amino-4-phosphonobutyrate (APB), a potent blocker of depolarizing bipolar cells, on visual behavior in the dark-adapted monkey. While in mesopic and photopic conditions only the monkeys' ability to detect incremental stimuli is impaired, under scotopic conditions all light mediated response in the monkey is eliminated. Assuming APB is acting on rod bipolars in the same fashion as it does on cone bipolars, we conclude that the primate rod bipolars all depolarize to light and that the ON and OFF channels are formed by the amacrine cell network.
Quantitative stimulus-response studies on sustained ganglion cells in the frog retina
Authors: Garcia Rene , Gaillard Frederic
Published: June 2009

“Sustained” visual units, i.e. nonerasable (R1) and erasable (R2) units as commonly described, were recorded in the superficial layers of the rostral optic tectum of Rana esculenta and their neuronal activity (expressed as the mean firing frequency ) was quantitatively analyzed The mean value of the exponent α of the velocity function of the erasable R1 units was found to be 0.46 and the constant k to be about 24.7. The optimal stimulus diameter was equal to 2.6 deg. For the whole population of the erasable units, the exponent α was found to be between 0.36–0.75 (mean value ≈ 0.56, i.e. largely different from the values currently reported for such units) and was independent of the stimulus diameter (D = 0.6–6 deg). However, the constant k of the velocity function (range: 8.2–37.7) varied with D. Most of the erasable units (called “mixed R1-R2” units) therefore showed an R1-type velocity function with an exponent α ≈ 0.5 and a constant k ≈ 25 but reacted to other parameters as did “typical” R2 units: (i) their neuronal response was related to the stimulus diameter by a logarithmic function with a maximum obtained for D = 2.4 deg; and (ii) a variation of about 4–17% on either side of the average value of was observed, independent either of the stimulus velocity or of the diameter of the stimulus. Results are compared to known quantitative data, and the use of stimulus-response relationships as a tool for classification is discussed.
Integration regions for vernier acuity in the cat: Comparative aspects of cortical scaling
Authors: Berkley M. A.
Published: June 2009

The spatial region involved in vernier acuity (integration region) was behaviorally determined in cats and compared with published human data and cortical scaling parameters for the two species. Integration region was estimated from vernier thresholds obtained with: (1) gaps of various sizes between the contiguous ends of the offset contours (gap effects); and (2) irrelevant contours placed at various distances from the vernier offset (interference effects). The gap studies showed that thresholds decreased as the gap grew from 0 to 4–7 min but then increased progressively with separations greater than 7 min. In the interference studies, thresholds were increased 2–6 times when the irrelevant contours were located within 40 min of the offset. Comparing these data with available human measures showed large species differences. Converting the interference distances for both species into cortical distances using published estimates of cortical magnification factor did not resolve the discrepancy. However, a comparison of the cat data with published human data, taken at an eccentricity at which the estimated human cortical magnification factor equals that of the cat, i.e. 7 deg, showed the effects of gap size and interference distance on vernier thresholds to be remarkably similar between the two species. This similarity supports the hypothesis that positional acuity depends upon mechanisms in striate cortex, and also suggests that such acuity may be mediated by a generic neural mechanism common to mammals.
Effect of retinal impulse blockage on cytochrome oxidase-rich zones in the macaque striate cortex: I. Quantitative electron-microscopic (EM) analysis of neurons
Authors: Wong-Riley Margaret T. T. , Tripathi Satish C. , Trusk Thomas C. , Hoppe Daniel A.
Published: June 2009

Our previous light-microscopic study indicates that unilateral retinal impulse blockage with tetrodotoxin (TTX) causes a reversible decrease of cytochrome oxidase (CO) in alternating rows of metabolically active zones (puffs) in the adult macaque striate cortex (Wong-Riley & Carroll, 1984b). The goal of the present study was to determine if TTX blockade adversely affects all neurons or only a subpopulation of neurons within the puffs. Three major neuronal types were identified based on mitochondrial CO activities and morphological characteristics. Type A neurons were the most prevalent, consisting of small pyramidal and nonpyramidal neurons that received only symmetrical axosomatic synapses. They had little cytoplasm and relatively low levels of CO activity, and showed the least change with TTX treatment. Type B cells were medium-to-large pyramidal neurons that received exclusively symmetrical axosomatic synapses and were moderately reactive for CO. Impulse blockage caused a decrease in mitochondrial size and packing density, but somal size remained within the control range. Type C cells were medium-sized nonpyramidal neurons contacted by both asymmetrical and symmetrical axosomatic synapses. They contained abundant darkly reactive mitochondria and presumably are metabolically the most active. This cell type suffered the greatest decrease in somal size and packing density of mitochondria, particularly the darkly reactive ones. A rare fourth cell type, type D, was a small, darkly reactive nonpyramidal variety that gave rise to somatodendritic synapses. Their low occurrence prevented statistical analysis under normal and TTX-treated conditions. These data indicate that retinal impulse blockade is most detrimental to the metabolically most active neurons in the adult primate cortical puffs. The alterations are not permanent, because the effects of TTX are fully reversible (Carroll & Wong-Riley, 1987).