bluuebunny/crossref_metadata_2025 huggingface dataset:
Survival of ganglion cells which form the retino-retinal projection during optic nerve regeneration in the frog
Authors: Tennant M. , Bruce S. R. , Beazley L. D.
Published: June 2009

During optic nerve regeneration in the frog, axons transiently grow along the opposite optic nerve forming a retino-retinal projection. In the present study, we crushed the left optic nerve in the frogLitoria (Hyla) mooreiand later applied horseradish peroxidase (HRP) or diamidino yellow (DY) to the right optic nerve. In one series, retinae were examined 3 days after application of the tracer. The retino-retinal projection was found to be maximal at 5 weeks, fell significantly by 7 weeks, and returned to close-to-normal levels by 24 weeks. In a second series, we applied DY at 5 weeks as before but did not sacrifice the frogs until 7 weeks. Numbers of labeled ganglion cells were not significantly different from those frogs in the first series labeled and examined at 5 weeks. We conclude that ganglion cells giving rise to the retino-retinal projection had not died in appreciable numbers, presumably being sustained by collateral axons in the brain.
Light-evoked changes in near-infrared transmission by the ON and OFF channels of the anuran retina
Authors: Dawis Stevan M. , Rossetto Michelangelo
Published: June 2009

We have developed an optical method to monitor the activity of the ON and OFF channels in the anuran retina. The change in the fraction of near infrared that is transmitted transversely through the retina in an eyecup slice is monitored during stimulation by visible, green light. Near-infrared transmission increases both at the onset and at the termination of a step stimulus. This “ON/OFF” response is maximal in the neural retina. Sodium L-aspartate, which blocks the light-evoked activity of post-photoreceptor neurons, abolishes the “ON/OFF” response. L-AP4, used as a selective blocker of the ON channel, reduces the “ON” component and has little or no effect on the “OFF” component. The “ON” and “OFF” processes observed optically are distinct from those that generate the b– and d–waves of the electroretinogram, and the “ON” and “OFF” components may be superior to the b– and d–waves as indicators of ON and OFF channel activity. The optical method is almost as simple as electroretinography and has the advantage that responses can be spatially localized with ease.
Reduction of a pattern-induced motion aftereffect by binocular rivalry suggests the involvement of extrastriate mechanisms
Authors: Van Der Zwan Rick , Wenderoth Peter , Alais David
Published: June 2009

Previous research suggests that plaid-induced motion aftereffects (MAEs) involve extrastriate mechanisms (Wenderoth et al., 1988). There is evidence also that binocular rivalry occurs beyond VI and that it disrupts the processing of MAEs which are believed to be based upon extrastriate mechanisms (e.g. the spiral MAE) but not MAEs, such as linear MAE induced by a drifting grating, which are thought to arise in striate cortex (Wiesenfelder & Blake, 1990). The logical inference is that binocular rivalry during drifting plaid-induced adaptation should reduce the MAEs which result. We report experiments which confirm this prediction.
Comparison of the responses to light and to GABA of cells postsynaptic to barnacle photoreceptors (I-cells)
Authors: Callaway Joseph C. , Stuart Ann E.
Published: June 2009

We tested the hypothesis that gamma-aminobutyric acid (GABA) is the transmitter released by barnacle photoreceptors onto postsynaptic cells (I-cells). GABA was applied to I-cells either by superfusion or by ejecting it with pressure from a pipette positioned close to the I-cell's soma. The I-cell's response to GABA was compared with its response to light (i.e. to the photoreceptors' transmitter) by recording intracellularly from its soma. Bath-applied (100 µm to 10 mM) and pressure-applied GABA (10 mM in pipette) hyperpolarizes I-cells by increasing their conductance, as does the photoreceptors' transmitter. The response to pressure-applied GABA consists of two components; both persist when Co2+ or Cd2+ are added to the saline to block synaptic transmission in the preparation, indicating that GABA affects the I-cell directly rather than affecting a presynaptic cell. GABA hyperpolarizes the I-cell when applied to the cell over the soma and ipsilateral arbor or over the contralateral arbor. The I-cells' responses to GABA and to light both depend on extracellular K+ and are affected by changes in intracellular and extracellular Cl−. However, picrotoxin and β-guanidinopropionic acid block the response to pressure-applied GABA but do not block the response to light even at an order of magnitude higher concentration. Thus, GABA is not likely to be the transmitter that causes the hyperpolarizing response of the I-cell. It may be a neuromodulator or the transmitter of an unknown input to the I-cell.
Retinal projections in quail (Coturnix coturnix)
Authors: Norren Robert B. , Silver Rae
Published: June 2009

The trajectory of retinal projections and the location of retinorecipient nuclei in the quail brain was examined after application of horseradish peroxidase (HRP) either to the cut end of the optic nerve or following intraocular injection of HRP. Retinal projections to the hypothalamus, dorsalateral anterior thalamus (rostralateral part, magnocellular part, and lateral part), lateral anterior thalamus, lateroventral geniculate nucleus, lateral geniculate intercalated nuclei (rostral and caudal parts), ventrolateral thalamus, superficial synencephalic nucleus, external nucleus, tectal gray, diffuse pretectal area, pretectal optic area, ectomammillary nucleus, and optic tectum were revealed. Retinal projections observed in quail were compared with results obtained in other avian species and considered in relation to possible anatomic pathways underlying photoperiodism and circadian rhythms.
Retinogeniculate EPSPs recorded intracellularly in the ferret lateral geniculate nucleus in vitro: Role of NMDA receptors
Authors: Esguerra Manuel , Kwon Young H. , Sur Mriganka
Published: June 2009

We used an in vitro preparation of the ferret lateral geniculate nucleus (LGN) to examine the role of the NMDA class of excitatory amino acid (EAA) receptors in retinogeniculate transmission. Intracellular recordings revealed that blockade of NMDA receptors both shortened the time course and reduced the amplitude of fast and slow components of excitatory postsynaptic potentials (EPSPs) evoked by optic tract stimulation. The amplitude and width of the EPSPs mediated by NMDA receptors increased as membrane potential was depolarized towards spike threshold. Individual LGN cells were influenced to varying extents by blockade of NMDA receptors; NMDA and non-NMDA receptor blockade together attenuated severely the entire retinogeniculate EPSP. The dependence of all components of retinogeniculate EPSPs (and action potentials) on NMDA receptor activation supports the hypothesis that the NMDA receptor participates in fast (<10 ms) synaptic events underlying conventional retinogeniculate transmission. The voltage dependence of the NMDA receptor-gated conductance suggests strongly that the transmission of retinal information through the LGN is subject to modulation by extraretinal inputs that affect the membrane potential of LGN neurons.
Binocular interactions in the cat's dorsal lateral geniculate nucleus, II: Effects on dominant-eye spatial-frequency and contrast processing
Authors: Tong Lillian , Guido William , Tumosa Nina , Spear Peter D. , Heidenreich Susan
Published: June 2009

The present study tested the hypothesis that nondominant-eye influences on lateral geniculate nucleus (LGN) neurons affect the processing of spatial and contrast information from the dominant eye. To do this, we determined the effects of stimulating the nondominant eye at its optimal spatial frequency on the responses of LGN cells to sine-wave gratings of different spatial frequency and contrast presented to the dominant eye. Detailed testing was carried out on 49 cells that had statistically significant responses to stimulation of the nondominant eye alone.

Spatial-frequency response functions to nondominant-eye stimulation indicated that the responses were spatially tuned, as reported previously (Guido et al., 1989). Optimal spatial frequencies through the nondominant eye were significantly correlated with the optimal spatial frequencies through the dominant eye (r = 0.54; P < 0.0001), and the optimal spatial frequencies were fairly similar for the two eyes.

Nondominant-eye stimulation changed the maximal amplitude of the fundamental (Fl) response to dominant-eye stimulation for only about 45% (22 of 49) of the cells that responded to nondominant-eye stimulation alone. The response vs. contrast function through the dominant eye was altered for 73% of the cells (51% independent of spatial frequency). Three types of effects were observed: a change in the initial slope of the response vs. contrast function (contrast gain), a change in the response amplitude at which saturation occurred, or an overall change in response at all contrasts. The incidence of these changes was similar for X and Y cells in LGN layers A, Al, and C (only four W cells were tested).

Nondominant-eye stimulation had little or no effect on the sizes or sensitivities of the receptive-field centers or surrounds for the dominant eye. In addition, nondominant-eye stimulation had little or no effect on optimal spatial frequency, spatial resolution, or the bandwidth of spatial-frequency contrast sensitivity curves for the dominant eye.

Possible functions of binocular interactions in the LGN are considered. The present results suggest a role in interocular contrast-gain control. Interocular contrast differences can occur before the acquisition of binocular fusion, when the two eyes are viewing different aspects of a visual stimulus. Psychophysical and physiological studies suggest that an interocular mechanism exists to maintain relatively constant binocular interactions despite differences in interocular contrast. The present results suggest that at least part of this mechanism occurs in the LGN.
N-methyl-D-aspartate-induced neurotoxicity in the adult rat retina
Authors: Siliprandi Renata , Canella Roberto , Carmignoto Giorgio , Schiavo Nicola , Zanellato Anna , Zanoni Renzo , Vantini Guido
Published: June 2009

The present study provides evidence that the adult mammalian retina is highly sensitive to the excitotoxic action of NMDA. In particular, we have investigated the effects of a single intravitreal injection of different doses of N-methyl-D-aspartate (NMDA) (2–200 nmoles) on the adult rat retina. Morphological evaluation of transverse sections of retinae demonstrated a dose-dependent loss of cells in the ganglion cell layer (GCL) and a reduction in the thickness of the inner plexiform layer. No obvious alterations were noted in the more distal retinal layers. Quantitative analyses of Nissl-stained whole-mounted retinae revealed that administration of 20 nmoles of NMDA resulted in a 70% loss of cells with a soma diameter greater than 8 μm (presumed retinal ganglion cells); a 20% loss of cells with a soma diameter smaller than 8 μm (presumed displaced amacrine cells) was also observed. In addition, NMDA produced a dose-dependent decrease of retinal choline acetyltransferase (ChAT) activity, suggesting that NMDA affects cholinergic amacrine cells as well. MK-801, a non-competitive NMDA antagonist, completely prevented the NMDA-induced loss of cells in the GCL and blocked, in a dose-dependent manner, the NMDA-induced decrease of ChAT activity. The excitotoxic action of NMDA observed in these experiments is thus likely mediated through the NMDA receptor subtype. This ”in vivo” model may be utilized to identify potential drugs that antagonize or limit the deleterious effects consequent to NMDA receptor overstimulation in the central nervous system.
Visual effects of damage to P ganglion cells in macaques
Authors: Lynch James J. , Silveira Luiz C. L. , Perry V. Hugh , Merigan William H.
Published: June 2009

Four indices of visual performance were measured in control macaques and in macaques that had been exposed to monomeric acrylamide, a neurotoxicant that preferentially damages P retinal ganglion cells. Morphological examination of the retina and visual pathways of these monkeys showed virtually complete loss of P ganglion cells over a region extending to at least 40 deg from the fovea, and relative sparing of M ganglion cells. The four tests examined visual functions for which the visual pathway from P ganglion cells might be of great importance: visual acuity, contrast discrimination, hyperacuity, and shape discrimination.

In the acrylamide-dosed monkeys, visual acuity was reduced slightly more than fourfold, a somewhat larger reduction than that seen previously after ibotenic-acid lesions of the P pathway in the geniculate. The residual acuity was in good agreement with the Nyquist frequency calculated from the density of ON or OFF M ganglion cells. Contrast increment thresholds were elevated for the dosed monkeys only in one of the two conditions tested. The elevation was found only under those spatiotemporal conditions for which we have previously shown that contrast thresholds are increased by acrylamide exposure, and was most marked at low background contrasts. Vernier acuity was elevated in one dosed monkey, but not affected in a second monkey that also had severe loss of P ganglion cells. Finally, we found no effect of acrylamide exposure on the number of training trials required to learn simple or complex shape discriminations. These results support previous findings in showing that the P pathway mediates visual acuity, and they show that several other important aspects of visual perception are not exclusively dependent on the P pathway.
The effect of threshold on the relationship between the receptive-field profile and the spatial-frequency tuning cure in simple cells of the cat's striate cortex
Authors: Tadmor Y. , Tolhurst D. J.
Published: June 2009

It is believed that spatial summation in most simple cells is a linear process. If this were so, then the Fourier transform of a simple cell's line weighting function should predict the cell's spatial frequency tuning curve. We have compared such predictions with experimental measurements and have found a consistent discrepancy: the predicted tuning curve is much too broad. We show qualitatively that this kind of discrepancy is consistent with the well-known threshold nonlinearity shown by most cortical cells. We have tested quantitatively whether a response threshold could explain the observed disagreements between predictions and measurements: a least-squares minimization routine was used to fit the inverse Fourier Transform of the measured frequency tuning curve to the measured line weighting function. The fitting procedure permitted us to introduce a threshold to the reconstructed line weighting function. The results of the analysis show that, for all of the cells tested, the Fourier transforms produced better predictions when a response threshold was included in the model. For some cells, the actual magnitude of the response threshold was measured independently and found to be compatible with that suggested by the model. The effects of nonlinearities of spatial summation are considered.
Neurotransmitters, receptors, and neuropeptides in the accessory optic system: An immunohistochemical survey in the pigeon (Columba livia)
Authors: Britto Luiz R. G. , Hamassaki Dania E. , Keyser Kent T. , Karten Harvey J.
Published: June 2009

Immunohistochemical techiniques were used to survey the distribution of several conventional transmitters, receptors, and neuropeptides in the pigeon nucleus of the basal optic root (nBOR), a component of the accessory optic ststem. Amongst the conventional neurotransmitts'modulators, the most intense labeling of fibers/terminals within the nBOR was obtained with antisera directed against glutamic acid decarboxylase (GAD) and serotonin (5-HT). Moderately dense fiber plexuses were seen to label with antibodies directed against tyrosine hydroxylase (TH) and choline acetltransferase (ChAT). GAD-like immunoractivity (GAD-L1) was found in many small and medium-size perikarya within the nBOR. Some of the medium-sized cells were occasionally positive for ChAT-L1. Cell body and dendritic staining was also commonly seen with the two tested antisera against receptors–anti-GABA-A receptor and anti-nicotinic acetylcholine receptor.

The antisera directed against various neuropetides produced only fiber labelling within the nBOR. The densest fiber plexus staining was observed with antiserum against neuropeptide Y (NPY-L1), while intermediate fiber densities were seen for substance P (SP-L1) and cholecystokinin (CCK-L1). A few varicose fibers were labeled with antisera against neurotensin (NT), leucine-enkephalin (L-KNK), and the vasoactive intestinal polypeptide (VIP).

Unilateral enucleation produced an almost complete elimination of TH-L1 in the contralateral nBOR. SP-L1 and CCK-L1 were also decreased after enucleation. No apparent changes were seen for all other substances.

These results indicate that a wide variety of chemically-specific systems arborize within the nBOR. Three of the immunohistochemically defined fiber systems (TH-LI, SP-LI, and CCK-LI fibers) were reduced after removal of the retina, which may indicate the presence of these substances in retinal ganglion cells. In contrast, the fibers exhibiting ChAT-LI, GAD-LI, 5-HT-Ll, NPY-Ll, NT-LI, L-ENK-LI, and VIP-LI appear to be of nonretinal origin. Two different populations of nBOR neurons exhibited GAD-LI and ChAT-LI. However, these two populations together constituted only about 20% of the nBOR neurons.
Displaced horizontal cells and biplexiform horizontal cells in the mammalian retina
Authors: Silveira L. C. L. , Yamada E. S. , Picanço-Diniz C. W.
Published: June 2009

We have used the neurofibrillar method of Gros-Schultze to stain the axonless horizontal cells of capybara, agouti, cat, and rabbit retinae. In all of these species, we have found two unusual horizontal cell morphologies: displaced horizontal cells and biplexiform horizontal cells. The displaced horizontal cells have perikarya located in the ganglion cell layer and dendrites branching in the inner plexiform layer. Many dendrites take an ascending trajectory to branch in the outer plexiform layer. The biplexiform horizontal cells are normally placed horizontal cells with descending processes that branch in the inner plexiform layer. Both cell types occur mainly in the retinal periphery, near the ora serrata. They are more numerous in the capybara retina, where they represent as much as 50% of the axonless horizontal cells of the retinal periphery.
Cortical afferents of visual area MT in the Cebus monkey: Possible homologies between New and old World monkeys
Authors: Rosa Marcello G. P. , Soares Juliana G. M. , Fiorani Mario , Gattass Ricardo
Published: June 2009

Cortical projections to the middle temporal (MT) visual area were studied by injecting the retrogradely transported fluorescent tracer Fast Blue into MT in adult New World monkeys (Cebus apella). Injection sites were selected based on electrophysiological recordings, and covered eccentricities from 2–70 deg, in both the upper and lower visual fields. The position and laminar distribution of labeled cell bodies were correlated with myeloarchitectonic boundaries and displayed in flat reconstructions of the neocortex. Topographically organized projections were found to arise mainly from the primary, second, third, and fourth visual areas (V1, V2, V3, and V4). Coarsely topographic patterns were observed in transitional V4 (V4t), in the parieto-occipital and parieto-occipital medial areas (PO and POm), and in the temporal ventral posterior area (TVP). In addition, widespread or nontopographic label was found in visual areas of the superior temporal sulcus (medial superior temporal, MST, and fundus of superior temporal, FST), annectent gyrus (dorsointermediate area, DI; and dorsomedial area, DM), intraparietal sulcus (lateral intraparietal, LIP; posterior intraparietal, PIP; and ventral intraparietal, VIP), and in the frontal eye field (FEF). Label in PO, POm, and PIP was found only after injections in the representation of the peripheral visual field (>10 deg), and label in V4 and FST was more extensive after injections in the central representation. The projections from V1 and V2 originated predominantly from neurons in supragranular layers, whereas those from V3, V4t, DM, DI, POm, and FEF consisted of intermixed patches with either supragranular or infragranular predominance. All of the other projections were predominantly infragranular. Invasion of area MST by the injection site led to the labeling of further pathways, including substantial projections from the dorsal prelunate area (DP) and from an ensemble of areas located along the medial wall of the hemisphere. In addition, weaker projections were observed from the parieto-occipital dorsal area (POd), area 7a, area prostriata, the posterior bank of the arcuate sulcus, and areas in the anterior part of the lateral sulcus. Despite the different nomenclatures and areal boundaries recognized by different models of simian cortical organization, the pattern of projections to area MT is remarkably similar among primates. Our results provide evidence for the existence of many homologous areas in the extrastriate visual cortex of New and Old World monkeys.
The retinal ganglion cell distribution and the representation of the visual field in area 17 of the owl monkey, Aotus trivirgatus
Authors: Silveira L. C. L. , Perry V. H. , Yamada E. S.
Published: June 2009

The distribution of ganglion cells and displaced amacrine cells was determined in whole-mounted Aotus retinae. In contrast to diurnal simians, Aotus has only a rudimentary fovea. Ganglion cell density decreases towards the periphery at approximately the same rate along all meridians, but is 1.2–1.8 times higher in the nasal periphery when compared to temporal region at the same eccentricities. The total number of ganglion cells varied from 421,500 to 508,700. Ganglion cell density peaked at 15,000/mm2 at 0.25 mm dorsal to the fovea. The displaced amacrine cells have a shallow density gradient, their peak density in the central region is about 1500–2000/mm2 and their total number varied from 315,900 to 482,800. Comparison between ganglion cell density and areal cortical magnification factor for the primary visual cortex, area 17, shows that there is not a simple proportional representation of the ganglion cell distribution. There is an overrepresentation of the central 10 deg of the visual field in the visual cortex. The present results for Aotus and the results of a similar analysis of data from other primates indicate that the overrepresentation of the central visual field is a general feature of the visual system of primates.
Synaptic connections involving immunoreactive glycine receptors in the turtle retina
Authors: Zucker Charles L. , Ehinger Berndt
Published: June 2009

The distribution of glycine receptors in the turtle retina was studied with the aid of a monoclonal antibody that detects the 93-kD protein associated with the strychnine-sensitive glycine receptor. Light microscopically, receptors were found in the inner plexiform layer and, more sparsely, in the innermost parts of the inner nuclear layer. No receptors were seen to be associated with photoreceptor cells, horizontal cells, or any other structures in the distal inner nuclear layer or outer plexiform layer. Ultrastructurally, glycine receptors were found on the inner face of postsynaptic membranes of processes from amacrine and presumed ganglion cells and always involved amacrine cell processes as the presynaptic element. Such glycine receptor immunoreactive synapses onto amacrine cell processes were distributed throughout the inner plexiform layer with a peak density near the middle. On the other hand, output synapses onto ganglion cell processes displaying immunoreactive glycine receptor sites showed a bimodal distribution in the inner plexiform layer. Glycine receptor immunoreactivity was not detected on bipolar cells, but presumed glycine-utilizing processes (i.e. those presynaptic to immunoreactive glycine receptors) were occasionally found to be postsynaptic in bipolar cell dyads. The majority of the synaptic input to the presumed glycine-utilizing amacrine cell processes was from other amacrine processes, some of which were themselves glycine utilizing. The observations suggest that glycinergic synapses in the turtle retina are, to a large extent, engaged in processing interamacrine signals.
Complex transcallosal interactions in visual cortex
Authors: Payne B.R. , Siwek D.R. , Lomber S.G.
Published: June 2009

Reversible inactivation by cooling of the transcallosal projecting neurons in areas 17 and 18 of one hemisphere bring about complex changes in the spontaneous and evoked activity of neurons in the callosal receiving zone of the opposite hemisphere. These changes include increase and decreases in evoked and spotaneous activities. Overall, 90% of neurons in alyers II and III, 50% in layer IV, and 100% in layers V and VI were affected by the block of transcallosal input. The complexity of the changes was greatest in layers II and III, which are the major callosal recipient layers. The results indicate that many excitatory and inhibitory circuits are under the direct control of transcallosal fibers in the normally fuctioning brain.
Foveal dark adaptation, photopigment regeneration, and aging
Authors: Coile D. Caroline , Baker Howard D.
Published: June 2009

Foveal dark adaptation in 58 subjects and photopigment regeneration in 60 subjects from 10–78 years of age exhibit parallel slowing of recovery rate with increasing age, with significant correlation of the two functions among individuals. The data are suggestive of an initial slight decline in rate before age 50, followed by a greater decline occuring at different ages in different ages in different individuals. Longitudinal data for one subject from age 40–65 show an increase in pigment regeneration time constant consistent with this idea. Foveal sensitivity and photopigment density both decrease with increasing age and are significantly correlated among individuals, although sensitivity declines more with age than does photopigment density. In contrast to earlier proposals based upon the Rushton-Dowling equation, we found no universal constant of proportionality to relate log relative threshold to photopigment within our population.
Light-adaptation properties of the ultraviolet-sensitive cone mechanism in comparison to the other receptor mechanisms of goldfish
Authors: Hawryshyn Craig W.
Published: June 2009

The light-adaptation properties of goldfish photoreceptor mechanisms were examined using Stiles' two-color threshold technique. Thresholdvs. background intensity (TVI) curves were determined for isolated cone and rod mechanisms using the heart-rate conditioning technique. The principal aim of this study was to compare the light-adaptation properties of the ultraviolet (UV)-sensitive cone mechanism to the other receptor mechanisms of goldfish. This examination revealed several striking functional differences: (1) The UV-sensitive cone mechanism thresholdvs. background intensity (TVI) exhibited a slope of 0.65 (compared to the approximate 1.0 for the other cone mechanisms on a log/log plot) and thus was not in accordance with Weber's law. This may in part be related to the intrusion of the blue-sensitive mechanism at the upper radiance range. (2) The operation of the UV-sensitive cone mechanism was limited to intermediate intensities (i.e. not very dim or bright). (3) The UV-sensitive cone mechanism exhibited a Weber fraction or luminance contrast threshold of 0.316 that was approximately six times larger than the other cone mechanisms but comparable to the rod mechanism. This indicates that the UV-sensitive cone mechanism performs relatively poorly in terms of brightness contrast detection.
Transmitter-gated currents of GABAergic amacrine-like cells in chick retinal cultures
Authors: huba Reiner , Hofmann Hans-Dieter
Published: June 2009

A subpopulation of cells developing in dissociated neuronal cultures prepared from 8-day-old embryonic chick retinae can be identified as putative in vitro counterparts of GABAergic amacrine cells by immunocytochemical and autoradiographic markers and by their electrophysiological responses to transmitter agonists. In the present study, transmitter-gated conductances expressed by these neurons were examined using the whole-cell patch-clamp technique. At negative holding potentials, the excitatory amino acid agonists N-methyl-D-aspartate (NMDA), kainate quisqualate, and glutamate induced inward currents with reversal potentials close to 0 mV in most of the cells selected for recording. NMDA-evoked responses were selectively blocked by the noncompetitive inhibitor MK 801 and by Mg2+ (in a voltage-dependent manner) and were potentiated in the presence of submicromolar concentrations of glycine. Glutamate apparently interacted with both NMDA and non-NMDA type receptors. All cells tested responded to the inhibitory transmitters GABA and glycine. Both inhibitory agonists could be shown to activate chloride conductances. Responses to GABA and glycine were specifically inhibited in the presence of bicuculline and strychnine, respectively. Thus, GABAergic neurons in retinal cultures express at least two different excitatory amino acid receptors–NMDA and non-NMDA–and two different inhibitory amino acid receptors–the GABAA and the glycine receptor. The results demonstrate the ability of the cultured neurons to develop an apparently mature phenotype and contribute to the understanding of the functional properties of GABAergic amacrine cells in the vertebrate retina.
Organization of reciprocal connections between area 17 and the lateral suprasylvian area of cat visual cortex
Authors: Shipp Stewart , Grant Simon
Published: June 2009

The lateral suprasylvian (LS) area (or Clare-Bishop area) is a region of visual cortex in the cat which has been defined as an isolated projection zone of area 17 (VI or striate cortex) within the suprasylvian sulcus. We have studied the overall topography and detailed pattern of connection between these two visual areas following injections of WGA-HRP into one or the other.

The projection from area 17 to LS is formed largely (-90%) from supragranular layer neurons that are distributed, in the coronal plane, in multiple regularly spaced patches. These patches are especially prominent in regions of area 17 representing central vision along and around the horizontal meridian. In reconstructions of serial coronal sections, and in flatmounts of the same region, the patches are seen to align so that in the plane tangential to the cortical surface they appear as a system of parallel bands whose main axis of elongation is rostro-ventral to caudo-dorsal, or near parallel to the area 17/18 border. The mean periodicity of the bands is about 1.0 mm.

The projection from area 17 terminates mainly in layers 4, 3, and 2 of area LS, and also appears patchy in the coronal plane. Reconstruction of the cortical surface view again reveals a system of rostrocaudal bands, but with a mean periodicity of 2 mm. The back projection is less periodically organized, arising predominantly (-80%) from a continuous sheet of infragranular neurons in area LS and terminating mainly in layer 1 of area 17, across the underlying patch and interpatch zones of the supragranular projection cells. However, neurons in layers 2 and upper 3 of area LS, which form the minority origin of the back projection, are mostly located in columnar registration with the patches of area 17 terminals.

The bands of supragranular layer neurons projecting to area LS are aligned obliquely to the iso-orientation domains of area 17, indicating a further component to its organization. It is suggested that this may correspond to a segregation of the X and Y channels in area 17, with outputs to area LS selectively arising from the Y pathway, in accordance with previous reports.
Background contrast modulates kinetics and lateral spread of responses to superimposed stimuli in outer retina
Authors: Reifsnider Eric S. , Tranchina Daniel
Published: June 2009

Surround enhancement (sensitization) is a poorly understood form of network adaptation in which the kinetics of the responses of retinal neurons to test stimuli become faster, and absolute sensitivity of the responses increases with increasing level of steady, surrounding light. Surround enhancement has been observed in all classes of retinal neurons in lower vertebrates except cones, in some primate retinal ganglion cells, and in human psychophysical studies. In theory, surround enhancement could be mediated by two broad classes of mechanisms, which are not mutually exclusive: one in which the kinetics of the transduction linking cone voltage to postsynaptic current in second-order neurons is modulated, and another in which the transformation of postsynaptic current to membrane voltage is modulated. We report here that both classes of mechanism play a role in surround enhancement measured in turtle horizontal cells (HCs). We stimulated the retina by modulating sinusoidally the illuminance of a bar placed at various positions in the HC receptive field. The bar was surrounded by either equally luminant or dim, steady light. Interpretation of responses in the context of a model for the cone-HC network led to the conclusion that the speeding up of response kinetics —due to selective increase in response gain at high temporal frequencies — by surround illuminance is almost completely accounted for by the change in the kinetics of the transduction linking cone membrane potential to HC postsynaptic current. However, surround illuminance also had an additional, surprising effect on the transformation between postsynaptic current and voltage: the space constant for signal spread in the HC network for the dim-surround condition was roughly twice as large as that for the bright-surround condition. Thus, increasing surround illuminance had analogous effects in the spatial and temporal domains: it restricted the time course and the spatial spread of signal. Both effects were dependent on the contrast between the mean bar illuminance and that of the surround, rather than on overall light level. When the stimulus with the bright surround was dimmed uniformly by a neutral density filter, the space constant did not increase, and response gain at high temporal frequencies did not decrease. Pharmacological experiments performed with dopamine and various agonists and antagonists indicated that, although exogenous dopamine can influence surround enhancement, endogenous dopamine does not play an important role in surround enhancement. We conclude that contrast in background light modulates the spatiotemporal properties of signal processing in the outer retina, and does so by a non-dopaminergic mechanism.
The pupillary response to light in the turtle
Authors: Granda A. M. , Dearworth J. R. , Kittila C. A. , Boyd W. D.
Published: June 2009

When intense adapting lights are turned off, the pupil of the turtle, Pseudemys scripta elegans, enlarges. The recovery functions for pupillary dilation have different time constants that are defined by red- and green-sensitive cones and rods as they are affected by prior light adaptation and time in the dark. Pupillary area related to dilation responds over at least a three- to four-fold range. Following white-light adaptation, the course of pupil dilation in the dark shows a three-legged curve of differing time constants. With spectral-light adaptations, the contributions of separate classes of photoreceptors can be isolated. Red- and green-sensitive cones contribute shorter time constants of 3.31 and 3.65 min to prior white-light adaptation—4.81 and 4.18 min to prior spectral-light adaptations. Rods contribute a much longer time constant of 6.69 min to prior white-light adaptation—7.60 min to prior spectral-light adaptation. The ratios are in keeping with the flash sensitivities of photoreceptors in this same animal, as well as with psychophysical visual threshold mechanisms of color sensitivity.
A sustained input to the direction-selective mechanism in cat striate cortex neurons
Authors: Baker Curtis L. , Cynader Max S.
Published: June 2009

Direction-selective neurons in cat striate cortex were tested with bar-shaped stimuli, sequentially flashed at spatially displaced positions chosen to elicit maximal direction selectivity. Temporally overlapping flash exposures of prolonged duration (400–1000 ms) were employed at a series of onset asynchronies to explore the nature of temporal tuning of the direction-selective mechanism. In most neurons studied, direction selectivity was found to be supported by a surprisingly broad range of stimulus onset asynchronies, which was greater for longer exposure durations. These findings imply the existence of a sustained input to the direction-selective mechanism, in spite of the relatively transient nature of most cortical neurons' step responses. A model is described to illustrate how different front-end temporal filters can affect the dependence of two-flash direction selectivity on stimulus onset asynchrony. The versions of the model which successfully predict the form of the observed responses are those which combine inputs from sustained and transient filters.
Identification of cone classes in Xenopus retina by immunocytochemistry and staining with lectins and vital dyes
Authors: Zhang Jie , Kleinschmidt Jochen , Sun Paranee , Witkovsky Paul
Published: June 2009

The aim of the present study was to determine the number of cone classes in the Xenopus retina. We examined the dimensions and staining properties of cones, utilizing two monoclonal antibodies, COS-1 and OS-2, developed by Szel and Rohlich (1985). Living cones also were reacted with the plant lectins peanut agglutinin (PNA) and wheat germ agglutinin (WGA) and with a fluorescent stilbene dye, DIDS, which binds selectively to red-sensitive cones (Kleinschmidt, 1991; Kleinschmidt & Harosi, 1992a, b). Three cone populations were distinguished based on differences in size and staining properties. Eighty-eight percent of all cones were stained strongly by COS-1, PNA, and DIDS, but weakly by OS-2. The group of cones stained by COS-1 had the largest mean dimensions of outer segment length, width, and oil droplet diameter. COS-1 negative cones were divisible into two groups: a subclass of miniature cones (approximately 4% total cones) was stained strongly by OS-2, PNA, and DIDS. The balance, constituting approximately 9% total cones, were of intermediate size, were not stained by PNA and reacted weakly to OS-2 and DIDS. WGA stained all cones. Large, COS-1 + cones appear to be red-sensitive and belong to the class of anion-tunable cone pigments. We suggest that the intermediate size, COS-1 negative cones are blue-sensitive based on the finding that blue-sensitive chromatic horizontal cells connect to them preferentially (Witkovsky et al., work in progress). The remaining class of miniature cones may be UV-sensitive, since another amphibian, the salamander, has been shown to possess red-, blue-, and UV-sensitive cones (Perry & McNaughton, 1991).
The role of light scatter in the residual visual sensitivity of patients with complete cerebral hemispherectomy
Authors: King Sheila M. , Azzopardi Paul , Cowey Alan , Oxbury John , Oxbury Susan
Published: June 2009

Various residual visual capacities have been reported for the phenomenally blind field of hemispherectomized patients, providing evidence for the relative roles of cortical and subcortical pathways in vision. We attempted to characterize these functions by examining the ability of five patients to detect, localize, and discriminate high-contrast flashed, flickering and moving targets. Dependent measures were verbal, manual, and oculomotor responses. As a control for light scatter, intensity thresholds for monocular detection of targets in the hemianopic field were compared with thresholds obtained when using an additional half eyepatch to occlude the blind hemiretina of the tested eye. One unilaterally destriate patient was tested on the same tasks. In photopic conditions, none of the hemispherectomized patients could respond to visual cues in their impaired fields, whereas the destriate patient could detect, discriminate, and point to targets, and appreciate the apparent motion of stimuli across his midline. Under reduced lighting, the threshold luminance required by hemispherectomized patients to detect stimuli presented monocularly was similar to that required for their detection when all visual information was occluded in the blind field, and only available to the visual system indirectly via light scatter. In contrast, the destriate patient's monocular threshold in his blind field was substantially lower than that for stimuli directly occluded in the blind field. As we found no range of stimuli which the hemispherectomized patients could detect or discriminate that was not also associated with discriminable scattered light, we conclude that the subcortical pathways which survive hemispherectomy cannot mediate voluntary behavioural responses to visual information in the hemianopic field.
Characterization of protein phosphatases type 1 and type 2A inLimulusnervous tissue: Their light regulation in the lateral eye and evidence of involvement in the photoresponse
Authors: Edwards Samuel C. , O'Day Peter M. , Herrera Desiree C.
Published: June 2009

The activities of both protein phosphatases and protein kinases are responsible for the transient changes in the levels of phosphorylation and probably the functions of protein intermediates involved in the biochemical and physiological mechanisms underlying the photoresponse in photoreceptor cells from both vertebrate and invertebrate organisms. Of the known protein serine/threonine phosphatases, various forms of type I (PP 1) and type 2A (PP 2A) protein phosphatases are responsible for dephosphorylating many of the known phosphoproteins including those involved in photoreceptor cell function. In this report, we provide biochemical evidence for both PP 1– and PP 2A-like activities in the visual and nonvisual tissue of the horseshoe crab,Limulus polyphemus, that membrane and soluble forms of both enzymes are present, and that the activities of both enzymes are greater in light- than in dark-adapted lateral eyes. These activities were characterized using glycogen phosphorylasea, a substrate for both PP 1 and PP 2A, and various protein phosphatase inhibitors, including okadaic acid. We also report that okadaic acid, at concentrations required to inhibit PP 1, inhibited physiological functions of photoreceptor cells from the ventral eye, causing a delayed reduction of the resting membrane, and slowing and reducing light responses.
Functional architecture of area 17 in normal and monocularly deprived marmosets (Callithrix jacchus)
Authors: Sengpiel Frank , Troilo David , Kind Peter C. , Graham Bryan , Blakemore Colin
Published: June 2009

The organization of the primary visual cortex (VI) of the common marmoset (Callithrix jacchus) was studied both physiologically and by means of transneuronal labelling of geniculocortical afferents. We addressed the question whether monocular deprivation (MD) could stabilize segregation into ocular dominance (OD) columns, which are not seen in normal adult marmosets but are present in juvenile animals (Spatz, 1979, 1989). Properties of neurons in normal marmosets closely resembled those of other New-World and Old-World monkeys and orderly tangential progressions of preferred orientation were observed. However, in contrast to species that display well-defined OD columns, neurons of layer 4 in VI of normal adult marmosets received balanced inputs from the two eyes. Early MD (even though followed by prolonged binocular experience into adulthood) resulted in a reduction of cell size in laminae of the lateral geniculate nucleus with input from the deprived eye and a dramatic overall shift in ocular dominance towards the non-deprived eye in the cortex. However, isolated clusters of cells dominated by the deprived eye were found in both layers 4 and 6. Injection of lectin-conjugated horseradish peroxidase (WGA-HRP) into the deprived eye revealed elongated patches of terminal label, about 350 μm wide, in flat-mounted sections through layer 4. Afferent segregation was sharper and more regular in the region of VI representing parafoveal visual space than in that representing the fovea. Our findings support the notion that all Old-World and New-World monkeys possess the capacity for segregation of geniculocortical afferents into OD columns.
Relationship between numbers of retinal ganglion cells and lateral geniculate neurons in the rhesus monkey
Authors: Spear Peter D. , Kim Charlene B. Y. , Ahmad Aneeq , Tom Bryony W.
Published: June 2009

Studies of the numbers of retinal ganglion cells and lateral geniculate nucleus (LGN) neurons in primates suggest that the numbers of both types of neurons may vary over a two-fold range from one individual to another. This raises the question of whether the numbers of ganglion cells and LGN neurons are related or vary independently from individual to individual. We used stereological procedures to obtain unbiased estimates of the numbers of both cell types in seven rhesus monkeys. We found no significant correlation (rs. = −0.21) between the numbers of retinal and LGN cells in the same animals. In agreement with previous studies, the average ratio of the number of retinal ganglion cells that project to the LGN and the number of LGN cells was approximately 1:1. However, this ratio varied over a two-fold range, from 0.78:1 to 1.64:1, in individual animals. These results have important implications for understanding the mechanisms of retino-geniculate development and for understanding the connectional wiring between the retina and LGN.
Neuropeptide Y immunoreactivity of a projection from the lateral thalamic nucleus to the optic tectum of the leopard frog
Authors: Chapman Angela M. , Debski Elizabeth A.
Published: June 2009

Using rhodamine-labelled latex beads as a retrograde tracer, we have shown that a subset of the neurons projecting from the lateral thalamic nucleus to the optic tectum of the leopard frog are neuropeptide Y-like immunoreactive (NPY-IR). In juvenile frogs, approximately twice as many lateral thalamic nucleus cells from this area project to the ipsilateral tectum as project to the contralateral tectum. NPY-IR cells make up 25% of the projection to the ipsilateral tectum and 13% of the projection to the contralateral tectum. The ipsilateral NPY-IR projection from the lateral nucleus was present in tadpoles and was similar in its characteristics to that found in the juvenile frog. However, the contralateral tectal projection was virtually nonexistent in these animals. The results of these experiments suggest that NPY from the lateral nucleus is released into the ipsilateral tectal neuropil in both the developing and adult frog.