bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThe 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

AbstractFour 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

AbstractIt 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

AbstractImmunohistochemical 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

AbstractWe 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

AbstractCortical 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

AbstractThe 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

AbstractThe 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

AbstractReversible 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

AbstractFoveal 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

AbstractThe 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

AbstractA 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

AbstractThe 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.