bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of CNQX, APB, PDA, and kynurenate on horizontal cells of the tiger salamander retina
Authors: Yang Xiong-Li , Wu Samuel M. 
Published: June 2009

AbstractEffects of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), 2-amino-4-phosphonobutyrate (APB), cis-2,3-piperidine dicarboxylic acid (PDA), and kynurenate (KYN) on the depolarizing actions of glutamate and kainate on horizontal cells (HCs) were studied in the larval tiger salamander retina. APB, PDA, and KYN hyperpolarized the HCs, but they failed to block either the actions of glutamate and kainate, or the HC light responses. APB and PDA did not cause membrane polarizations in either rods or cones, suggesting that the HC hyperpolarizations were not mediated by presynaptic actions of these compounds. CNQX, the newly synthesized non-NMDA (N-Methyl-D-Aspartate) receptor antagonist, blocked the HC light responses and the action of kainate, but not that of glutamate. These results suggest that the synaptic receptors in the tiger salamander HCs are probably non-NMDA although extra-synaptic NMDA receptors may exist in these cells.
Responses to sinusoidal gratings of two types of very nonlinear retinal ganglion cells of cat
Authors: Troy J. B. , Einstein G. , Schuurmans R. P. , Robson J. G. , Enroth-Cugell Ch. 
Published: June 2009

AbstractPerhaps 35% of all of the ganglion cells of the cat do not have classical center-surround organized receptive fields. This paper describes, quantitatively, the responses of two such cell types to stimulation with sinusoidal luminance gratings, whose spatial frequency, mean luminance, contrast, and temporal frequency were varied independently. The patterns were well-focused on the retina of the anesthetized and paralyzed cat. In one type of cell, the maintained discharge was depressed or completely suppressed when a contrast pattern was imaged onto the receptive field (suppressed-by-contrast cell). In the other type of cell, the introduction of a pattern elicited a burst of spikes (impressed-by-contrast cell).When stimulated with drifting gratings, the cell's mean rate of discharge was reduced (suppressed-by-contrast cell) or elevated (impressed-by-contrast cell) over a limited band of spatial frequencies. There was no significant modulated component of response. The reduction in mean rate of suppressed-by-contrast cells caused by drifting gratings had a monotonic dependence on contrast, a relatively low-pass temporal-frequency characteristic and was greater under photopic than mesopic illuminance. If gratings of spatial frequency, that when drifted evoked a response from these cells, were instead held stationary and contrast-reversed, the mean rate of a suppressed-by-contrast cell was also reduced and that of an impressed-by-contrast cell increased. But, for contrast-reversed gratings, the discharge contained substantial modulation at even harmonic frequencies, the largest being the second harmonic. The amplitude of this second harmonic did not depend on the spatial phase of the grating, and its dependence on spatial frequency, at least for suppressed-by-contrast cells, was similar to that of the reduction in mean rate of discharge. Our results suggest that the receptive fields of suppressed-by-contrast and impressed-by-contrast cells can be modeled with the general form of the nonlinear subunit components of Hochstein and Shapley's (1976) Y cell model.
Strabismus does not prevent recovery from monocular deprivation: A challenge for simple Hebbian models of synaptic modification
Authors: Malach Rafael , Van Sluyters Richard C. 
Published: June 2009

AbstractIt has been suggested that development of central connections in the mammalian visual system is governed by a simple Hebbian rule of synaptic modifiability. Under such a rule, simultaneity of presynaptic and postsynaptic action potentials is a prerequisite for enhanced synaptic efficacy. The present paper reports the results of a study designed to test whether this hypothesis is applicable to the development of the thalamo-cortical visual pathway.In four-week-old kittens, exposure to a 2-d period of monocular deprivation was used to render the vast majority of cortical cells capable of being activated only by the nondeprived eye. During a subsequent 3–5 month recovery period, both eyes were open but surgically misaligned. This combination of conditions was chosen so that during the recovery period presynaptic activity originating from the initially deprived eye would be decorrelated from postsynaptic action potentials in cortical neurons. If synaptic modification is regulated by a simple Hebbian mechanism, then in this situation the deprived eye should be unable to recover control of cortical cells.In fact, the present results indicate that during the recovery period the proportion of cortical neurons dominated by the deprived eye rose to a level equal to that of the nondeprived eye – a result contrary to that predicted by a simple Hebbian rule of development. Histological analysis indicated that a similar level of recovery was present both within and outside of cortical layer IV, the main thalamo-recipient layer. As expected, the induced strabismus resulted in a failure of cortical binocularity to recover in these kittens.Although these results argue against a simple Hebbian mechanism of development, they are compatible with the hypothesis that synaptic modifiability is dependent upon correlations between presynaptic activity and local, subthreshold, postsynaptic changes. This alternative hypothesis has the advantage of allowing modification of local synaptic circuits within the dendritic arbors of a single neuron.
Comparison of human and monkey retinal photoreceptor sampling mosaics
Authors: Samy Chander N. , Hirsch Joy 
Published: June 2009

AbstractWe test the hypothesis that the diameters of foveal and near-foveal rods and cones for one well-studied human photoreceptor mosaic and one well-studied monkey photoreceptor mosaic (Macaca fascicularis) a scaled relative to focal length. We conclude that this hypothesis is not supported. Rather than being scali proportionally, the sizes of the rods and cones, respectively, are nearly equivalent for both the human ar monkey resulting in an effectively finer retinal grain for the larger human eye. Furthermore, the human density exceeds the monkey rod density beyond about 1 deg of retinal eccentricity. These results suggest variation across primate species is reflected in retinal sampling strategies.
Temporal frequency responsivity shows multiple maturational phases: State-dependent visual evoked potential luminance flicker fusion from birth to 9 months
Authors: Apkarian Patricia 
Published: June 2009

AbstractMaturation of temporal resolution was investigated in a visual evoked potential study in 77 infants from birth to 9 months of age. Luminance evoked potential measures in response to homogeneous sinusoidal flickering light (1–64 Hz) were recorded under behavioral state-defined conditions. Behavioral state was determined by direct observation and by polygraphic recording of the electroencephalogram (EEG), eye movements (EOG), muscle activity (EMG), heart rate (ECG), and respiration. Temporal-frequency functions of the amplitude of the fundamental response across the temporal-frequency range were recorded during sleep and wakefulness. The highest temporal-frequency response recorded during wakefulness was accepted as a measure for inclusion in a growth function of temporal-frequency responsiveness. The resulting temporal resolution frequencyvs. age function showed three separate maturational phases. Maturational phases were defined as (1) an initial slow phase from 1–32 days postnatal during which maturation of temporal vision is unremarkable; (2) an intermediate rapid phase of improvement from age 26 to 170 days; and (3) an overlapping but final slow phase from 151 to at least 270 days during which adult-like flicker resolution is approximated. This study suggests that the multiple maturational phases of the infant's responses to flickering light are due to maturational differences, which correspond with maturation of structural factors of brain function. Finally, across the age span tested, high-frequency responsivity was influenced significantly by the degree of infant arousal.
Direction selectivity and physiological compensation in the superior colliculus following removal of areas 17 and 18
Authors: Mendola Janine D. , Payne Bertram R. 
Published: June 2009

AbstractPrevious studies indicate that cortical areas 17 and 18 play a prominent role in generating the direction selectivities of neurons in the superior colliculus of the cat. This hypothesis was tested by quantifying the activities of neurons in the superficial collicular layers in intact cats and cats which incurred ablation of areas 17 and 18 and part of area 19. In addition, since behavioral and anatomical studies suggest a functional adjustment in the superior colliculus following removal of inputs from areas 17, 18, and 19 in the neonatal cat, we included a group of neonatally lesioned cats. Computation of an index of directionality indicated that the majority of neurons in intact cats preferred movement in one direction, thus confirming reports of others. Following ablation of areas 17 and 18 and part of area 19 in both groups of lesioned cats, only modest changes in the population indices were detected when poorly responsive neurons were eliminated from the analyses. Based upon levels of visually evoked neuronal activity, our data suggest a physiological compensation by neurons in stratum griseum superficiale following removal of areas 17, 18, and 19 inputs. In the intact and neonatally operated groups, activity in stratum griseum superficiale is high, whereas in the adult lesioned group activity is low. In stratum opticum, neuronal activity was similar in all three groups of cats. These results show that neurons in stratum griseum superficiale undergo a physiological compensation following removal of immature areas 17 and 18.
Modulation of endogenous dopamine release in the turtle retina: Effects of light, calcium, and neurotransmitters
Authors: Kolbinger Walter , Weiler Reto 
Published: June 2009

AbstractIn the turtle retina, dopamine has been observed in a small population of amacrine cells. Whereas the effect of dopamine has been intensively studied, knowledge about the release of this transmitter and the neuronal control of its release are still poorly understood. We therefore decided to study the release of endogenous dopamine. Isolated retinas were superfused with Ringer’s solutions and stimulated with increased potassium, light, or drugs which interfere with neurotransmitter systems. Dopamine was analyzed by using aluminum-oxide extraction and high-pressure liquid chromatography (HPLC) with electrochemical detection. Increased potassium (25 mM) caused a five-fold increase in the basal release. When calcium was replaced by cobalt, no increase was induced by 25 mM potassium. Flickering light increased the basal release of endogenous dopamine by a factor of three. The effect of flickering light was greater in the presence of additional steady background illumination. Kainate (10 μM), an agonist for excitatory amino acids, doubled the basal dopamine release. Bicuculline (10 μM), a γ-amino butyric acid (GABA) antagonist, increased the release to about six times the basal level. Naloxone (10 μM), an opiate antagonist, increased the release to eight times the basal level. These findings suggest that dopamine is released from amacrine cells in the turtle retina in a calcium-dependent manner, which is most likely a vesicular release. Dopamine release is induced by flickering light vs. darkness and vs. steady background illumination. A moderate background illumination alone does not significantly increase basal dopamine release. Drug treatment during the release experiments suggests that dopaminergic neurons receive an excitatory input either directly or indirectly from glutamatergic bipolar and/or amacrine cells and inhibitory inputs either directly or indirectly from GABAergic amacrine cells and from enkephalinergic amacrine cells or efferent fibers.
Photoreceptor spectral absorbance in larval and adult winter flounder (Pseudopleuronectes americanus)
Authors: Evans Barbara I. , Hárosi Ferenc I. , Fernald Russell D. 
Published: June 2009

AbstractThe habitat occupied by larval winter flounder (Pseudopleuronectes americanus) differs considerably in light regime from that of the adult. To understand how the visual system has adapted to such changes, photoreceptor spectral absorbance was measured microspectrophotometrically in premetamorphic and postmetamorphic specimens of winter flounder. Before metamorphosis, larval flounder retinas contain only one kind of photoreceptor which is morphologically cone-like with peak absorbance at 519 nm. After metamorphosis, the adult retina has three types of photoreceptors: single cones, double cones, and rods. The visual pigment in single cones has a peak absorbance at λmax= 457 nm, the double cones at λmax= 531 and 547 nm, and the rod photoreceptors at λmax= 506 nm. Double cones were morphologically identical, but the two members contained either different (531/547 nm) or identical pigments (531/531 nm). The latter type were found only in the dorsal retina. The measured spectral half-bandwidths (HBW) were typical of visual pigments with chromophores derived from vitamin A1with the possible exception of the long-wavelength absorbing pigment in double cones which appeared slightly broader. Because the premetamorphic pigment absorbance has a different λmaxthan those of the postmetamorphic pigments, different opsin genes must be expressed before and after metamorphosis.
Neurochemical compartmentation of monkey and human visual cortex: Similarities and variations in calbindin immunoreactivity across species
Authors: Hendry Stewart H. C. , Carder Renee K. 
Published: June 2009

AbstractThe compartmental organization of visual cortical neurons was examined across species of primates by directly comparing the pattern of immunoreactivity for the 28-kD vitamin D-dependent calcium-binding protein (calbindin) in area 17 of squirrel monkeys, macaques, and neurologically normal adult humans. Area 17 of macaques and squirrel monkeys was similar in that somata and processes intensely immunoreactive for calbindin were present in the same layers (II-III, IVB, and V) and in both species formed a well-stained matrix that surrounded the CO-rich puffs in layer III. These intensely calbindin-immunoreactive neurons were identified as subpopulations of GABA-immunoreactive neurons. Among the most obvious differences in the two monkey species was the distribution of calbindin-positive elements outside of layer III: a dense immunostained matrix surrounded the puffs in layers II, IVB, V, and VI of squirrel monkeys but the immunostained neurons adopted no regular pattern outside layer III in macaques. In addition, although somata lightly immunoreactive for calbindin were present in both species, they were much more abundant in squirrel monkeys than macaques. The pattern of calbindin immunostaining in human area 17 resembled that of macaques in forming an intense matrix that surrounded puffs only in layer III, yet also resembled that of squirrel monkeys by including large numbers of lightly immunoreactive somata. These lightly immunostained somata included a very dense population forming a prominent band in layer IVA of human visual cortex. We conclude that for layer III of primary visual cortex, a similar pattern of neuronal chemistry exists across species of primates which is related to this layer's compartmental organization. Yet for other layers, the expression of calbindin immunoreactivity varies from one species to the next, perhaps reflecting variations in other neuronal properties.
Spatial summation in blindsight
Authors: Stoerig Petra 
Published: June 2009

AbstractSpatial summation curves were determined in the circumscribed visual-field defects of five patients with blindsight. Under light-adapted conditions that favor the color-opponent system, increment thresholds for white and red targets presented on a white background were measured as a function of stimulus size which ranged from 9–110 min arc. In both normal and defective hemifields, summation was linear for the red stimuli. In contrast, the curves measured with the white stimuli showed some nonlinearity in the normal hemifield, and a pronounced eccentricity-dependent notch in the field defect. The results indicate that the neurons mediating sensitivity differ in their summation properties for wavelength and intensity information.
Catecholaminergic amacrine cells in the dog and wolf retina
Authors: Peichl Leo 
Published: June 2009

AbstractCatecholaminergic (presumed dopaminergic) amacrine cells in the retinae of Beagle dogs (canis lupus f. familiaris) and wolves (canis lupus) were visualized with an antiserum against tyrosine hydroxylase (TH). In both species, TH immunoreactivity is found in a population of amacrine cells with large somata (about 14 μm diameter) and large, moderately branched dendritic trees. Somata are located in the proximal inner nuclear layer (normal amacrines) or in the ganglion cell layer (displaced amacrines). Most dendrites stratify in a narrow band in the inner plexiform layer close to the inner nuclear layer, where they form a dense plexus with the characteristic pattern of “dendritic rings.” The displaced cells have some of their dendrites in a proximal stratum of the inner plexiform layer. A few immunopositive processes are found in the outer plexiform layer (interplexiform processes).In Beagle dogs, the cell density of catecholaminergic amacrines varies from less than 1/mm2 in far periphery to 40–55/mm2 in central retina (mean density 21/mm2). The proportion of displaced amacrines varies locally from 10 to 85% (overall proportion 41% in one retina). In the wolf, densities of catecholaminergic cells range between about 3/mm2 in peripheral and up to 35/mm2 in central retina. The proportion of displaced cells is somewhat lower than in dogs, varying between 11 and 31% across the retina.The morphology and density distribution of canine catecholaminergic amacrines resemble that of other mammalian retinae. A marked difference, however, is the high percentage of displaced cells in both dog and wolf retina; it is the highest found in any mammal so far. The displaced and normal cells appear to be members of a single functional population. A comparison of the topographic distributions of catecholaminergic amacrines, rods, and ganglion cells in the dog retina shows no consistent density correlations between these neurons that are all part of the rod pathway.
Ultrastructural and electrophysiological changes associated with K+-evoked release of neurotransmitter at the synaptic terminals of skate photoreceptors
Authors: Ripps Harris , Chappell Richard L. 
Published: June 2009

AbstractBathing the skate retina in a Ringer solution containing a high concentration (100 mM) of potassium ions depolarized the visual cells, depleted the receptor terminals of synaptic vesicles, and suppressed completely the b-wave of the ERG and the intracellularly recorded response of horizontal cells (the S-potential). The depletion of synaptic vesicles was accompanied by a large increase in the extent of the plasma membrane resulting in distortion of the normal terminal profile, i.e. distension of the basal surface and elaborate infolding of protoplasmic extensions. Morphometric analysis showed that despite the changes in vesicle content and terminal structure, the combined linear extent of the vesicular and plasma membranes was unchanged from control (superfusion with normal Ringer solution); the increase in plasma membrane was equivalent to the observed loss of vesicular membrane. When returned to a normal Ringer solution, the terminals rapidly began to reform, and in about 10 min they were morphologically indistinguishable from receptor terminals seen in control preparations. After 30 min in the normal Ringer solution, the amount of membrane associated with the vesicles and the plasma membrane had reverted to control values, and once again the total membrane estimated morphometrically remained essentially the same. Thus, there is an efficient mechanism at the photoreceptor terminal for the recycling of vesicle membrane following exocytosis.The K+-induced depletion of synaptic vesicles was paralleled by a precipitous loss of responsivity in both the b-wave of the ERG and the S-potential of the horizontal cells. However, after 30-min exposure to the high K+ and a return to normal Ringer solution, the recovery of electrophysiological activity followed a much slower time course from that associated with the structural changes; 60 min or longer were required for the potentials to exhibit maximum response amplitudes. It appears that the rate-limiting step in restoring normal synaptic function following massive depletion of vesicular stores is transmitter resynthesis and vesicle loading rather than vesicle recycling.
Ocular dimensions and schematic eyes of freshwater and sea turtles
Authors: Northmore D. P. M. , Granda A. M. 
Published: June 2009

AbstractMeasurements were made of the ocular dimensions from living and frozen eyes of one species of freshwater turtle, Pseudemys scripta elegans, and of three species of marine turtles, Chelonia mydas, Dermochelys cariacea, and Eretmochelys imbricata. Estimates of refractive error by retinoscopy were also obtained with eyes in air and under water. The results suggest that unaccommodated eyes of all four species are approximately emmetropic in air but strongly hyperopic in water. Schematic eyes were calculated for each species in both air and water.
The density recovery profile: A method for the analysis of points in the plane applicable to retinal studies
Authors: Rodieck R. W. 
Published: June 2009

AbstractThe density recovery profile is a plot of the spatial density of a set of points as a function of the distance of each of those points from all the others. It is based upon a two-dimensional point autocorrelogram. If the points are randomly distributed, then the profile is flat, with a value equal to the mean spatial density. Thus, any deviation from this value indicates that the presence of the object represented by the point alters the probability of encountering nearby objects of the same set. Increased value near an object indicates clustering, decreased value near an object indicates anticlustering. The method appears to be unique in its ability to provide quantitative measures of the anticlustered state. Two examples are presented. The first is based upon a sample of the distribution of the somata of starburst amacrine cells in the macaque retina; the second is based upon the distribution of the terminal enlargements on the dendrites of a single macaque ganglion cell that projects to the superior colliculus. In both cases, the density recovery profile is initially lower than the mean density, and increases up to the plateau at the value of the mean density. Two useful measures can be derived from this profile: an intensive parameter termed the effective radius, which quantifies the extent of the region of decreased probability and is insensitive to random undersampling of the underlying distribution, and an extensive parameter termed the packing factor, which quantifies the degree of packing possible for a given effective radius, and is insensitive to scaling. An extension of this method, applicable to correlations between two superimposed distributions, and based upon a two-dimensional point cross-correlogram, is also described.