bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deficits in speed discrimination following lesions of the lateral suprasylvian cortex in the cat
Authors: Pasternak Tatiana , Horn Kris M. , Maunsell John H.R. 
Published: June 2009

AbstractWe examined the role of the lateral suprasylvian (LS) cortex in motion perception by testing the ability of three cats to detect moving targets and to discriminate differences in stimulus direction and speed before and after making bilateral ibotenic acid lesions in LS. The lesions had little or no effect on contrast sensitivity for detecting moving sinusoidal gratings. Moreover, we found no deficits in discriminating opposite directions of motion: the cats discriminated grating directions at threshold contrasts. All three cats, however, showed permanent deficits in discriminating differences in speed and in flicker rate. The deficits were most pronounced at higher temporal and spatial frequencies and at lower contrasts. This result suggests that LS plays an important role in the analysis of stimulus speed. It appears that information needed for discriminating opposite directions of motion may be signalled by visual areas outside LS.
Development of synapses in macaque monkey striate cortex
Authors: Zielinski B. S. , Hendrickson A. E. 
Published: June 2009

AbstractA quantitative electron-microscopic (EM) analysis of the development of synaptic density (number of synapses/100 μm neuropil) has been done in primary visual cortex (striate, area 17) of the Old World monkey Macaca nemesthna. A comparative EM morphological study of developing synaptic contacts also was done in the same tissue. We find that a few immature synaptic contacts are present at fetal (F) 75 days either in the marginal zone, which becomes layer 1, or in the deepest portion of the cortical plate, the future layer 6. At F90–140 days synaptic contacts are found throughout the cortical plate, but their density remains higher in lower cortical layers. By F140 days synaptic density averaged for all layers (10.9) is three times higher than at F90 days. Just before and after birth, synaptic density rises very rapidly to peak at postnatal (P)12 weeks (63) and then declines slowly to reach adult values (37.7) between 2–6 years. This pattern was further tested by comparing synaptic density in layer 2 which contains the last cells generated in the striate cortex to that in layer 6 which contains the first cells generated in the striate cortex. Layer 6 contained the first synapses, and had a higher density up to F140 days (an “inside-to-outside” distribution). Synaptic density was equal in the two layers at F152 days and P2 days, but by P12 weeks synaptic density in layer 2 was 27% higher than that in layer 6 (an “outside-to-inside” distribution). After P12 weeks, the synaptic density declined 51% in layer 2 and 21% in layer 6 so that both layers achieved similar densities by P6 years.A light and EM comparison of neuropil and synaptic contact morphology finds that, at each age up to birth, synapses in layer 2 are generally less mature than those in layer 6, but these differences disappear shortly after birth. Between P6–24 weeks, synaptic contacts throughout the cortex acquire a mature morphology that clearly differentiates between asymmetric and symmetric types, although asymmetric contacts continue to acquire more postsynaptic density until adulthood.This complex developmental pattern suggests a sequence for synaptic developments which is more related to neuron birthdate than to the arrival of extrinsic pathways or developmental events occurring in specific laminae.
Neurotransmitter-specific identification and characterization of neurons in the all-cone retina of Anolis carolinensis, I: Gamma-aminobutyric acid
Authors: Sherry David M. , Ulshafer Robert J. 
Published: June 2009

AbstractThe inhibitory amino-acid neurotransmitter, gamma-aminobutyric acid (GABA), was localized in the pure cone retina of the lizard Anolis carolinensis by autoradiographic and immunocytochemical techniques. Uptake of [3H]-GABA labeled horizontal cells, amacrine cells, numerous cells in the ganglion cell layer, both plexiform layers, and the nerve fiber layer. Label in the inner plexiform layer showed distinct lamination.The pattern of GABA immunoreactivity was similar to the pattern of [3H]-GABA uptake, although some differences, particularly in labeling of amacrine and ganglion cells, were observed. Immunocytochemistry revealed endogenous stores of GABA in a set of horizontal cells, amacrine cells, and cells in the ganglion cell layer. Both plexiform layers were labeled by the GABA antisera. Labeling in the inner plexiform layer (IPL) was highly stratified and GABA-immunoreactive strata were present in both sublaminae a and b. Six subtypes of conventionally placed GABA-immunoreactive amacrine cells and one displaced amacrine cell subtype were identified. Three of the six conventional amacrine cell subtypes were of pyriform morphology and three subtypes were of multipolar morphology. GABA-immunoreactive interstitial cells also were observed.Under certain conditions the GABA antiserum labeled the cones. Etching the resin eliminated cone labeling, suggesting that GABA in the cones is present in a labile pool, unlike GABA in horizontal or amacrine cells, or the observed labeling was not due to endogenous GABA. Cones did not demonstrate [3H]-GABA uptake.
Immunocytochemical reactivity of rod and cone visual pigments in the sturgeon retina
Authors: Govardovskii Victor I. , Röhlich Pál , Szél Ágoston , Zueva Lida V. 
Published: June 2009

AbstractMicrospectrophotometry and immunocytochemistry with several antivisual pigment antibodies were used to study visual cells of the Siberian sturgeon, Acipenser baeri Brandt. The retina contained rods and three morphological types of cones: large cones with oil drops, small cones with oil drops, and cone-like cells without oil drops. Rods and cone-like drop-free cells were found to possess porphyropsin-549, while the large oil drop-bearing cones contained red-sensitive (P613), green-sensitive (P542), and blue-sensitive (P462) visual pigments. The immunocytochemical staining pattern with three antibodies to visual pigment proteins also revealed one visual pigment in rods and three visual pigments in cones. Rods were labeled with all three antibodies, while the majority of large cones (type I), presumably the red-sensitive ones, were negative with the polyclonal serum AO against bovine opsin. A less-frequently occurring large cone type (type II) was stained by all three antibodies including mAb COS-1 specific to middle-to-long-wave visual pigments in birds and mammals, and is thought to be green-sensitive. An even less-frequent large cone type (type III, probably the blue-sensitive one) did not bind COS-1. The small cones with oil droplets showed immunoreactivities similar to either type II or type III cones. The oil drop-free small photoreceptor exhibited a staining pattern identical with that of rods. These results indicate that the immunocytochemical approach can be used to reveal photoreceptor-specific neural connections in the sturgeon retina.
Substance P modulates calcium current in retinal bipolar neurons
Authors: Ayoub George S. , Matthews Gary 
Published: June 2009

AbstractRetinal bipolar cells are non-spiking interneurons that relay information from photoreceptors to amacrine and ganglion cells. In turn, bipolar cells receive extensive synaptic feedback from amacrine cells, some of which contain neuropeptides, including substance P. We have examined the effect of substance P on single bipolar neurons isolated from goldfish retina and find that substance P (0.1–1 nM) produced a voltage-dependent inhibition of calcium current in these cells. The inhibition was strongest at negative potentials, with the peak suppression occurring at –20 to –30 mV; at potentials positive to 0 mV, there was little effect on calcium current. Thus, the net effect was to shift the voltage range of activation of calcium current toward more positive potentials. The inhibition of calcium current by substance P required GTP in the patch pipette and was blocked by internal GDP-β-S. Similar effects on calcium current were observed with somatostatin and metenkephalin, which are also found in amacrine cells.
A light- and electron-microscopic investigation of the optic tectum of the frog, Rana pipiens, II: The neurons that give rise to the crossed tecto-bulbar pathway
Authors: Hughes Thomas E. 
Published: June 2009

AbstractThe superficial layers of the frog&apos;s optic tectum, Potter&apos;s (1969) layers A-G, comprise a complex neuropil made up of many afferent axons, the somata of a few neurons, and many dendrites from the neurons located in the deeper layers. Different types of retinal axons are believed to terminate in different layers (Maturana et al., 1960; Kuljis & Karten, 1988; Sargent et al., 1989), but little is known about the relationships between each type of input and the dendrites of the deep tectal neurons that extend into these superficial layers. The present study used the method of retrograde transport of horseradish peroxidase to study the synaptic contacts on the dendrites of the neurons that give rise to the crossed tecto-bulbar pathway. These cells have apical dendrites that ascend through the superficial retino-recipient layers.The somata of the cells that give rise to the crossed tecto-bulbar pathway are located in the superficial half of layer 6, preferentially clustered along the caudal, lateral, and rostral margins of the tectum. The somata of these cells range from 8−30 ¼m in diameter. Their axons are large (2−4 ¼m in diameter) myelinated fibers that arise from either their somata or proximal dendrites. Their axons travel within the deep medullary layer to leave the tectum at the lateral margin. Their dendritic arbors extend obliquely through the superficial layers to reach layer B where they turn and extend within the layer for up to 0.5 mm. The somata of these cells receive only a scant synaptic input. In contrast, their dendrites receive input in every layer, but the nature of this input varies from layer to layer. Synaptic terminals that resemble retinal ganglion cell boutons contact the labeled dendrites in layers B, F, and G. This indicates that the dendrites may receive monosynaptic input from several types of retinal ganglion cells. Terminals with small, flattened vesicles also contact the dendrites of these cells in each layer. In layer F and below, the terminals with flattened vesicles constitute 15% of the contacts; above layer F they constitute only 5−8% of the contacts. Terminals with medium-sized, flattened vesicles also contact the dendrites of these cells in every layer and constitute a large proportion of their input (33−95%). The latter terminals resemble those that are often postsynaptic to retinal terminals.
Sclerally directed processes of dopaminergic interplexiform cells reach the outer nuclear layer in rat and monkey retina
Authors: Nguyen-Legros Jeanine , Moussafi Fatima , Simon Axelle 
Published: June 2009

AbstractTyrosine hydroxylase-immunolabeled wholemounts and sections of rat and monkey retina were observed at both the light- and electron-microscopic level. Small processes derived from sclerally directed processes of dopaminergic interplexiform cells were observed ascending to the outer nuclear layer where they were distributed between photoreceptor cells. A role in the regulation of disc shedding and/or melatonin biosynthesis is proposed for dopamine released at this level.
NADPH-diaphorase neurones of human retinae have a uniform topographical distribution
Authors: Provis Jan M. , Mitrofanis John 
Published: June 2009

AbstractWe have examined the morphology and distribution of neurones that contain nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase in human retinae. NADPH-diaphorase reactivity was observed in three different classes of amacrine cells (ND1, ND2, ND3 cells) and in the cone photoreceptors. ND1 cells had relatively large somata (mean, 12.3 ¼m) located in the inner nuclear layer (INL) and in the ganglion cell layer (GCL). Their dendrites were often strongly labeled and spread into either the middle or outer strata of the inner plexiform layer (IPL). The somata of ND2 cells were medium-sized (mean, 8.2 ¼m) and located in the INL and in the GCL; their dendrites were usually beaded and often spread in either the middle or outer strata of the IPL. ND3 cells had small, round somata (mean, 5.2 ¼m) located in either the INL or GCL, and were without labeled processes. The total number of NADPH-diaphorase cells (all classes) was estimated at 118,000, with a mean density of about 100/mm2. The most striking fea ture of NADPH-diaphorase cells in humans was that their distribution was relatively uniform across the retina, with no evidence of a peak in density at the foveal rim.
Binocular convergence of excitatory and inhibitory synaptic pathways onto neurons of cat visual cortex
Authors: Ferster David 
Published: June 2009

AbstractWhen a cortical neuron receives synaptic input from both eyes, do the synaptic pathways that mediate the input from each eye match? In this study, inputs from the two eyes were compared by measuring the latencies of EPSPs and IPSPs evoked by electrical stimulation of the two optic nerves. For binocular neurons, these latencies invariably matched closely, indicating that the pathways from the two eyes contain the same number of synapses; monosynaptic input from lamina A of the lateral geniculate nucleus (LGN) is always matched by monosynaptic input from lamina A1. Conversely, polysynaptic input from one eye, either excitatory or inhibitory, is invariably accompanied by similar input from the other eye. In addition, the match between the two eyes in latency indicates that for each eye a synaptic potential is mediated by the same type of afferent, either X or Y.Judging from intracellular recording, 75% of the neurons studied were binocular, that is, EPSPs could be evoked from either eye. In the remaining 25%, EPSPs could be evoked from only one eye, in agreement with extracellular receptive field studies in which 30% of cortical neurons are monocular.
Darkness stimulates rapid synthesis and release of melatonin in rat retina
Authors: Redburn Dianna A. , Mitchell Cheryl K. 
Published: June 2009

AbstractThe presence of melatonin in retina has been widely reported for over two decades although studies of its functional importance within the retina have only recently been emphasized. We have analyzed the biochemical characteristics of melatonin synthesis and release, focusing on rapid changes in response to light/dark conditions. Our major findings are consistent with the following conclusions: (1) melatonin synthesis is stimulated within minutes after exposure to darkness, and may reflect an increase in N-acetyl transferase activity; (2) melatonin is not stored, but rather it diffuses freely throughout the retina immediately after it is synthesized; and (3) the dark-induced increase in retinal melatonin release is a synthesis-coupled response and does not involve separate secretion mechanisms. The characteristics of melatonin synthesis and release described herein would be consistent with the proposed role of melatonin as a local paracrine effector of dark-adaptive responses in retina.
Evolutionary remodeling in a visual system through extensive changes in the synaptic connectivity of homologous neurons
Authors: Shaw S. R. , Moore D. 
Published: June 2009

AbstractThe cellular mechanisms by which nervous systems evolve to match evolutionary changes occurring in the rest of the body remain largely unexplored. In a distal visual neuropil of a previously unexamined ancient dipteran family, Stratiomyidae, homologues of all of the periodic neurons known already from more recent Diptera can be recognized, occupying the same locations within the unit structure. This points to extreme developmental stasis for more than 200 million years, conserving both cell identity and position. The arborizations that some neurons make also have remained conservative, but others show marked differences between families in both size and branching patterns. At the electron-microscopical level, extensive differences in synaptic connectivity are found, some sufficient to radically redefine the systems roles of particular neurons. The findings bear out an earlier prediction that changes in the connectivity matrix linking conserved neurons may have been a major factor in implementing evolutionary change in the nervous system.
Enkephalinergic modulation of the dopamine system in the turtle retina
Authors: Weiler Reto , Ball Alexander K. 
Published: June 2009

AbstractOne subpopulation of amacrine in the turtle retina was shown to contain met-enkephalin by means of immunocytochemistry, and another was demonstrated to have a high-affinity uptake system for [3H]-dopamine by means of tutoradiography. Although the amacrine soma size, density, and distribution of their neurites in IPL substrata was similar in retinas in which met-enkephalin and dopamine were localized, combined light microscope immuncytochemistry-autoradiography demonstrated that these two neurotransmitter systems did not coexist in the same cells. Because the two amacrine cell subtypes ramify in the same IPL substrata, neuronal interaction between them is possible. Release experiments showed that the potassium-induced release of [3H]-dopamine from the superfused turtle retina was reduced by 40% when enkephlian was added to the superfusate. The inhibition of [3H]-dopamine release could be blocked by the addition of naloxone. The addition of enkephalin had no effect of the potassium-induced release of [3H]-GABA from the superfused retina. These findings suggest that an enkephalinergic modulation of the dopaminergic amacrine cell system exits in the turtle retina.
Sensitization and multiplicative noise in the descending contralateral movement detector (DCMD) of the locust
Authors: Barker Peter D.R. 
Published: June 2009

AbstractSpike discharges from the descending contralateral movement detector (DCMD) were recorded extracellularly from the ventral nerve cord of the locust in complete darkness, in response to dim flashes of constant-intensity light, and in response to pairs of identical flashes presented different intervals apart. Three phenomena were discovered: novel long-term sensitization which changes the DCMD's sensitivity to light, a multiplicative cascade process driven by shot events, and the suppression of the spike discharge shortly after a dim flash.The DCMD's spike discharge is stochastic. It can be considered as a two-stage cascade process producing intrinsic multiplicative noise. An effective photon, or thermal isomerization in complete darkness, produces an unseen shot event which in turn initiates a random number of DCMD spikes in a cluster. A shot initiates a variable number of spikes when it directs the rate of a Poisson process. The results of statistical analyses are consistent with this model when the amplitudes of shot events are variable. The transmission efficiency is low because at least 2.4–9.6 quantum bumps are required to produce one extra DCMD spike.The DCMD has a constant mean discharge rate of 0.25–1.5 spikes/s in complete darkness. Clustering about particular points in time (shots) leads to a lack of independence between interspike intervals, and the overdispersion of interspike interval and number distributions compared with those from a simple Poisson process. The mean cluster size is 1.3–1.6 spikes in darkness. Similar clustering was found in response to flashes of light.A dim flash changes the DCMD's sensitivity to light, even at threshold when no spike discharge results. Sensitization occurs because the average number of shot events produced by isoquantal flashes depends on the history of visual stimulation. This contributes to the nonlinear response-intensity function. The evolution of sensitization is roughly constant in different DCMD cells, lasting approximately 3 s after a flash. Sensitization was observed in response to light only, presumably because the intensity of dark-light is too low. It is proposed that sensitization is associated with a set of processes or molecular state in the presynaptic region of a chemical synapse.
Dynamics of orientation coding in area V1 of the awake primate
Authors: Celebrini Simona , Thorpe Simon , Trotter Yves , Imbert Michel 
Published: June 2009

AbstractTo investigate the importance of feedback loops in visual information processing, we have analyzed the dynamic aspects of neuronal responses to oriented gratings in cortical area V1 of the awake primate. If recurrent feedback is important in generating orientation selectivity, the initial part of the neuronal response should be relatively poorly selective, and full orientation selectivity should only appear after a delay. Thus, by examining the dynamics of the neuronal responses it should be possible to assess the importance of feedback processes in the development of orientation selectivity. The results were base on a sample of 259 cells recorded in two monkeys, of which 89% were visually responsive. Of these, approximately two-thirds were orientation selective. Response latency varied considerably between neurons, ranging from a minimum of 41 ms to over 150 ms, although most had latencies of 50–70 ms. Orientation tuning (defined as the bandwidth at half-height) ranged from 16 deg to over 90 deg, with a mean value of around 55 deg. By examining the selectivity of these different neurons by 10-ms time slices, starting at the onset of the neuronal response, we found that the orientation selectivity of virtually every neuron was fully developed at the very start of the neuronal response. Indeed, many neurons showed a marked tendency to respond at somewhat longer latencies to stimuli that were nonoptimally oriented, with the result that orientation selectivity was highest at the very start of the neuronal response. Furthermore, there was no evidence that the neurons with the shortest onset latencies were less selective. Such evidence is inconsistent with the hypothesis that recurrent intracortical feedback plays an important role in the generation of orientation selectivity. Instead, we suggest that orientation selectivity is primarily generated using feedforward mechanisms, including feedforward inhibition. Such a strategy has the advantage of allowing orientation to be computed rapidly, and avoids the initially poorly selective neuronal responses that characterize processing involving recurrent loops.