bluuebunny/crossref_metadata_2025_split huggingface dataset:
Behavioral and electrophysiological sensitivity to temporally modulated visual stimuli in the ground squirrel
Authors: Crognale Michael A. , Jacobs Gerald H. 
Published: June 2009

AbstractBehavioral and electrophysiological methods were used to measure sensitivity to flickering lights in a dichromatic species, the California ground squirrel (Spermophilus beecheyi). Discrimination tests were used to determine spectral sensitivity at stimulus frequencies from 5–50 Hz and increment threshold spectral sensitivity. The contributions of retinal mechanisms to these capacities were assessed by recording the responses of optic nerve fibers to temporally modulated monochromatic lights. In the ground squirrel, as in the human, the shape of the spectral-sensitivity function depends on the temporal frequency of the stimulus. Results from single-unit recording show that all of the classes of optic nerve fibers in the ground squirrel are highly phase-locked to the stimulus for modulation rates as high as 50 Hz. Neither the responses of photoreceptors nor any class of optic nerve fiber can singly account for the behavioral results. The electrophysiological results are also counter to models which propose that temporally dependent changes in the spectral sensitivity of spectrally opponent fibers account for the behavior. The temporal resolution of the optic nerve fibers exceeds that of the behaving animal suggesting that retinal mechanisms do not limit behavioral temporal resolution.
The perihypoglossal projection to the superior colliculus in the rhesus monkey
Authors: Hartwich-Young Rosi , Nelson Jon S. , Sparks David L. 
Published: June 2009

AbstractThe projection of the perihypoglossal (PH) complex to the superior colliculus (SC) in the rhesus monkey was investigated using the retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Following physiological identification by electrical stimulation and multiunit recording, small injections of the tracer were placed within the SC of three monkeys. The largest numbers of retrogradely labeled neurons within the PH complex were found in the contralateral nucleus prepositus hypoglossi (NPH), in the laterally adjacent medial vestibular nucleus, and in the ventrally adjacent reticular formation (the nucleus reticularis supragigantocellularis). These labeled neurons are strikingly heterogeneous in size and morphology. The nuclei supragenualis and intercalatus also contain numerous labeled neurons in the 2 cases in which the injections involve the caudal SC. Large numbers of retrogradely labeled neurons as well as anterogradely transported WGA-HRP are observed alo throughout the pontine and medullary reticular formation, including the midline raphe. The PH complex, particularly the NPH, is known to be involved in the coding of eye position and has been hypothesized to be a critical component of the “neural integrator.” Our data demonstrate the existence of a robust projection from the PH complex to the contralateral SC in the rhesus monkey. This projection may serve as the anatomical substrate by which a corollary of eye position could reach the SC. Such a signal is a prerequisite for the computation, at the collicular level, of saccadic motor error signals observed in the SC of rhesus monkeys.
Dopamine and its agonists reduce a light-sensitive poor of cyclic AMP in mouse photoreceptors
Authors: Cohen Adolph I. , Blazynski Christine 
Published: June 2009

AbstractThe exposure to bright light of dark-adapted (DKA) mouse retinas incubated in the dark (DI) in IBMX-containing medium causes a marked loss of cyclic AMP. This light response also occurs if the medium contains 10 mM aspartate or cobaltous ion, agents believed to confine the effects of light to photoreceptors. Thus, the action of light in the presence of either of these agents defines a light-sensitive pool of cyclic AMP in photoreceptors. This pool could also be reduced or eliminated in DKA-DI retinas by nanomolar to micromolar levels of dopamine (if the medium contained SCH23390, a potent antagonist of Dl receptors), thus indicating an agonistic action of dopamine at D2 receptors. The D2 agonists LY171555 (EC5010 nM) or (+)-3-PPP also reduced the cyclic AMP level in the dark. Of the D2 antagonists tested, the butyrophenone spiperone (in the presence of the 5HT-2 blocker ketanserin) countered the action of the D2 agonists but substituted benzamides were ineffective. Consistently, the D2 agonists had no effect on cyclic AMP levels of mutant retinas lacking photoreceptors (rd'rd), but reduced cyclic AMP in DKA-Dl glutamate-modified retinas which exhibit a major loss of inner retinal neurons without apparent loss of photoreceptors. The Dl antagonist SCH23390 only reduced cyclic AMP levels of DKA-DI retinas when cyclic AMP levels had been elevated by adding dopamine to the incubation medium.
Light-dependent hydration of the space surrounding photoreceptors in the cat retina
Authors: Li Jian-Dong , Govardovskii Victor I. , Steinberg Roy H. 
Published: June 2009

AbstractWe have studied the effect of retinal illumination on the concentration of the extracellular space marker tetramethylammonium (TMA+) in the dark-adapted cat retina using double-barreled ion-selective microelectrodes. The retina was loaded with TMA+ by a single intravitreal injection. Retinal illumination produced a slow decrease in , which was maximal in amplitude in the most distal portion of the space surrounding photoreceptors, the subretinal space. The light-evoked decrease in was considerably slower and of a different overall time course than the light-evoked decrease in , also recorded in the subretinal space. decreased to a peak at 38 s after the onset of illumination, then slowly recovered towards the baseline, and transiently increased following the offset of illumination. It resembled the light-evoked decreases previously recorded in the in vitro preparations of frog (Huang & Karwoski, 1990, 1992) and chick (Li et al., 1992, 1994) but was considerably larger in amplitude, 22% compared with 7%. As in frog, where it was first recorded, the light-evoked decrease is considered to originate from a light-evoked increase in the volume of the subretinal space (or subretinal hydration). A mathematical model accounting for diffusion predicted that the volume increase underlying the response was 63% on average and could be as large as 95% and last for minutes. The estimated volume increase was then used to examine its effect on K+ concentration in the subretinal space. We conclude that a light-dependent hydration of the subretinal space represents a significant physiological event in the intact cat eye, which should affect the organization of the interphotoreceptor matrix, and the concentrations of all ions and metabolites located in the subretinal space.
Psychophysical evidence for area V2 involvement in the reduction of subjective contour tilt aftereffects by binocular rivalry
Authors: van der Zwan Rick , Wenderoth Peter 
Published: June 2009

AbstractPrevious research suggests binocular rivalry disrupts extrastriate, but not striate processes, although the locus along the visual pathway at which such disruption first occurs is uncertain. It has been argued that subjective contours arise via a two-stage process in which end-stopped cells feed into orientation-sensitive neurones in V2, and that orientation aftereffects induced with subjective contours are the product of mechanisms similar to those giving rise to real contour aftereffects. If binocular rivalry disrupts the acquisition of subjective contour aftereffects, then it follows from this model that rivalry disrupts processing in V2. Experiments reported here confirm this and provide evidence which suggests binocular rivalry arises through interactions between binocular neurones, rather than via some type of specialized binocular rivalry mechanism.
Processing of form and motion in area 21a of cat visual cortex
Authors: Dreher B. , Michalski A. , Ho R. H. T. , Lee C. W. F. , Burke W. 
Published: June 2009

AbstractExtracellular recordings from single neurons have been made from presumed area 21a of the cerebral cortex of the cat, anesthetized with N2O/O2/sodium pentobarbitone mixture. Area 21a contains mainly a representation of a central horizontal strip of contralateral visual field about 5 deg above and below the horizontal meridian.Excitatory discharge fields of area 21a neurons were substantially (or slightly but significantly) larger than those of neurons at corresponding eccentricities in areas 17, 19, or 18, respectively. About 95% of area 21a neurons could be activated through either eye and the input from the ipsilateral eye was commonly dominant. Over 90% and less than 10% of neurons had, respectively, C-type and S-type receptive-field organization. Virtually all neurons were orientation-selective and the mean width at half-height of the orientation tuning curves at 52.9 deg was not significantly different from that of neurons in areas 17 and 18. About 30% of area 21a neurons had preferred orientations within 15 deg of the vertical.The mean direction-selectivity index (32.8%) of area 21a neurons was substantially lower than the indices for neurons in areas 17 or 18. Only a few neurons exhibited moderately strong end-zone inhibition. Area 21a neurons responded poorly to fast-moving stimuli and the mean preferred velocity at about 12.5 deg/s was not significantly different from that for area 17 neurons.Selective pressure block of Y fibers in contralateral optic nerve resulted in a small but significant reduction in the preferred velocities of neurons activated via the Y-blocked eye. By contrast, removal of the Y input did not produce significant changes in the spatial organization of receptive fields (S or C type), the size of the discharge fields, the width of orientation tuning curves, or direction-selectivity indices.Our results are consistent with the idea that area 21a receives its principal excitatory input from area 17 and is involved mainly in form rather than motion analysis.
A reassessment of the lower visual field map in striate-recipient lateral suprasylvian cortex
Authors: Sherk Helen , Mulligan Kathleen A. 
Published: June 2009

AbstractLateral suprasylvian visual cortex in the cat has been studied extensively, but its retinotopic organization remains controversial. Although some investigators have divided this region into many distinct areas, others have argued for a simpler organization. A clear understanding of the region’s retinotopic organization is important in order to define distinct areas that are likely to subserve unique visual functions. We therefore reexamined the map of the lower visual field in the striate-recipient region of lateral suprasylvian cortex, a region we refer to as the lateral suprasylvian area, LS.A dual mapping approach was used. First, receptive fields were plotted at numerous locations along closely spaced electrode penetrations; second, different anterograde tracers were injected at retinotopically identified sites in area 17, yielding patches of label in LS. To visualize the resulting data, suprasylvian cortex was flattened with the aid of a computer.Global features of the map reported in many earlier studies were confirmed. Central visual field was represented posteriorly, and elevations generally shifted downward as one moved anteriorly. Often (though not always) there was a progression from peripheral locations towards the vertical meridian as the electrode moved down the medial suprasylvian bank.The map had some remarkable characteristics not previously reported in any map in the cat. The vertical meridian’s representation was split into two pieces, separated by a gap, and both pieces were partially internalized within the map. Horizontal meridian occupied the gap. Thearea centralisusually had a dual representation along the posterior boundary of the lower field representation, and other fragments of visual field were duplicated as well. Finally, magnification appeared to change abruptly and unexpectedly, so that compressed regions of representation adjoined expanded regions. Despite its complexity, we found the map to be more orderly than previously thought. There was no clearcut retinotopic basis on which to subdivide LS’s lower field representation into distinct areas.
Light-induced retinal degeneration inrdgB(retinal degeneration B) mutant ofDrosophila: Electrophysiological and morphological manifestations of degeneration
Authors: Rubinstein Chaim T. , Bar-Nachum Shoshana , Selinger Zvi , Minke Baruch 
Published: June 2009

AbstractQuantitative light and electron microscopy was used to monitor the extent of retinal degeneration as a function of age and temperature in the white-eyedrdgBKS222mutant ofDrosophila melanogaster. Parallel measurements of the electroretinogram (ERG) of the degenerating retina reveal a new phenomenon – the appearance of spike potentials following illumination with bright light. These spikes, which do not appear in the normal fly retina, have a relatively long duration (20–50 ms), regenerative properties, and a rate of occurrence which increases with increasing light intensity. The spikes differed from the light response in being more susceptible to CO2and to cuts in the eye. The spikes completely disappeared at low extracellular Ca2+levels which did not reduce the amplitude of the light response. The spike potentials become triphasic when the recording electrode is advanced to the level of the basement membrane. This suggests that the spike potentials originate from the photoreceptor axons as a result of synchronous opening of voltage-dependent channels in a large number of photoreceptor cells. The occurrence of spike potentials during the process of degeneration was studied. Two phases can be distinguished: (1) Spike potentials appear in retinae of 2–3-day-old flies which display few morphological signs of degeneration. The frequency of appearance of spike potentials decreases in retinae of 14–16-day-old flies which show extensive degeneration of the R1–6 photoreceptor cells but no degeneration of the central R7,8 cells. (2) Spike potentials appear more frequently again in flies of 22–24 d of age. This is probably a consequence of degeneration of the remaining R7,8 photoreceptor cells. Temperature and the light-dark cycle had a critical effect on degeneration. Eight-day-old mutants raised at 19°C in a normal light-dark cycle showed only little degeneration. Eight-day-old mutants raised at 24°C showed only a slight degeneration when raised in the dark. However, the degree of degeneration was greatly enhanced in the mutants raised at 24°C under a light-dark cycle regime.The combined electrophysiological and morphological study of the degeneration, as a function of age and temperature, revealed that (1) the degeneration process takes place even in darkness, but at a slow rate, while light greatly accelerates the degeneration. (2) The degeneration is negligible at 19°C, even during light, in the first week after eclosion. (3) The appearance of spike potentials at an early stage of the degeneration suggests that changes in the plasma membrane of the photoreceptor cells manifest at an initial stage of the degeneration process.
Packaging of rhodopsin and porphyropsin in the compound eye of the crayfish
Authors: Zeiger Joel , Goldsmith Timothy H. 
Published: June 2009

AbstractThe distribution of 3-dehydroretinal (Ral2) in dorsal, middle, and ventral slices of eyes of the crayfishProcambarus clarkiiwas examined by HPLC. No pronounced differences were found. Similar results were obtained when the eyes were cut into anterior, intermediate, and posterior portions.Dichroic difference spectra were measured in single halves of microvillar layers of isolated rhabdoms and the proportions of rhodopsin (P1) and porphyropsin (P2) estimated by comparison with computer-generated mixtures of these pigments, whose spectra are known from previous work. The fraction of visual pigment that is porphyropsin appears to be uniform throughout individual retinular cells and among the retinular cells of individual rhabdoms, but various substantially among different rhabdoms from the same eye.The interommatidial variation in the amount of P2greatly exceeds the gross regional variation in Ral2. This means there is an intermingling of ommatidia with different levels of P2. The variability in P2among ommatidia is not likely to have important implications for the vision of the crayfish but suggests that in the metabolism of retinoids, individual ommatidia are quasi-independent metabolic units. The results are compatible with a single opsin for both crayfish rhodopsin and porphyropsin.
Currents in the presynaptic terminal arbors of barnacle photoreceptors
Authors: Hayashi Jon H. , Stuart Ann E. 
Published: June 2009

AbstractWe have described the currents flowing across the presynaptic membranes of the four median photoreceptors of the giant barnacle,Balanus nubilus, using a quasi-voltage clamp arrangement. Membrane potential, measured in the terminal region of one photoreceptor, was controlled in all four terminals by feedback current supplied through the nerve containing the photoreceptors’ axons. The [Ca2+]∘in the saline was reduced to decrease the Ca2+current, enabling better voltage control, and tetraethylammonium ion (TEA, 20 mM) was added to block a fast voltage-dependent K+conductance.Depolarizing voltage steps from the resting potential in the dark (−60 mV) evoked slow, inward Ca2+-dependent currents which could be blocked by Co2+, Mg2+, or Cd2+. The Ca2+currents were followed by large outward currents that persisted for many seconds after the offset of moderate or large pulses. These tail currents increased in magnitude and duration with pulse duration and reversed at about −80 mV, consistent with previous evidence for a Ca2+-activated K+conductance in this membrane. When the Ca2+-activated outward current was reduced to zero by increasing the [K+]∘so as to setEKat −20 mV, and then stepping the voltage to this value, the step evoked a steady inward Ca2+current. Thus, the Ca2+current did not show voltage- or Ca2+-dependent inactivation. When Ba2+was substituted for Ca2+, 500-ms depolarizing steps evoked steady inward currents but no outward currents. In any given experiment, the activation voltage of the Ca2+or Ba2+current did not depend on holding potential.At the barnacle photoreceptor’s synapse, the postsynaptic cell adapts to maintained presynaptic voltage by a mechanism that is not understood. We conclude that neither Ca2+current inactivation nor a shift in activation voltage with holding potential can account for this adaptation.
Brain-stem influence on visual response of lagged and nonlagged cells in the cat lateral geniculate nucleus
Authors: Hartveit E. , Heggelund P. 
Published: June 2009

AbstractThis study examined the influence of the pontomesencephalic peribrachial region (PBR) on the visual response properties of cells in the dorsal lateral geniculate nucleus (LGN). The response of single cells to a stationary flashing light spot was recorded with accompanying electrical stimulation of the PBR. The major objectives were to compare the effects of PBR stimulation on lagged and nonlagged cells, to examine how the visual response pattern of lagged cells could be modified by PBR stimulation and to examine whether the physiological criteria used to classify lagged and nonlagged cells are applicable during increased PBR input to the LGN. During PBR stimulation, the visual response was enhanced to a similar degree for lagged and nonlagged cells and the latency to half-rise of the visual response was reduced, particularly for the lagged X cells. The latency to half-fall of the visual response of lagged cells was not changed by PBR stimulation. Accordingly, the division of LGN cells into lagged and nonlagged cells based on visual response latencies was maintained during PBR stimulation. The initial suppression that a visual stimulus evokes in lagged cells was resistant to the effects of PBR stimulation. For the lagged cells, the largest response increase occurred for the initial part of the visual response. For the nonlagged cells, the largest increase occurred for the tonic part of the response. The results support the hypothesis that the differences in temporal response properties between lagged and nonlagged cells belong to the basic distinctions between these cell classes.
Stimulus dependence of orientation and direction sensitivity of cat LGNd relay cells without cortical inputs: A comparison with area 17 cells
Authors: Thompson Kirk G. , Leventhal Audie G. , Zhou Yifeng , Liu Dan 
Published: June 2009

AbstractThe cortical contribution to the orientation and direction sensitivity of LGNd relay cells was investigated by recording the responses of relay cells to drifting sinusoidal gratings of varying spatial frequencies, moving bars, and moving spots in cats in which the visual cortex (areas 17, 18, 19, and LS) was ablated. For comparison, the spatial-frequency dependence of orientation and direction tuning of striate cortical cells was investigated employing the same quantitative techniques used to test LGNd cells. There are no significant differences in the orientation and direction tuning to relay cells in the LGNd of normal and decorticate cats. The orientation and direction sensitivities of cortical cells are dependent on stimulus parameters in a fashion qualitatively similar to that of LGNd cells. The differences in the spatial-frequency bandwidths of LGNd cells and cortical cells may explain many of their differences in orientation and direction tuning. Although factors beyond narrowness of spatial-frequency tuning must exist to account for the much stronger orientation and direction preferences of cells in area 17 when compared to LGNd cells, the evidence suggests that the orientation and direction biases present in the afferents to the visual cortex may contribute to the orientation and direction selectivities found in cortical cells.
Directional hyperacuity in ganglion cells of the rabbit retina
Authors: Grzywacz Norberto M. , Amthor Franklin R. , Merwine David K. 
Published: June 2009

AbstractBiological visual systems can detect positional changes that are finer than these systems' acuity to sine-wave gratings, a property known as hyperacuity. Some systems can even detect changes finer that the photoreceptor spacing. We report here that rabbit's directionally selective ganglion cells not only detect positional changes in the hyperacuity range, but also discriminate the direction of their motion. Our experiments show that directional selectivity occurs for edges of light moving as little as 1.1 μm (26” of visual angle) across the retina. This distance corresponds to a hyperacuity, since the acuity to sine-wave gratings of rabbit's On-Off DS ganglion cells is about 125 μm (50′). In addition, this distance is smaller than the minimal spacing between rabbit photoreceptors (1.9 μm or 46”), as estimated from cell-density studies (Young & Vaney, 1991). Such a hyperacuity suggests low-noise high-gain signal transmission from photoreceptors to ganglion cells and that directional selectivity can arise in small portions of retinal dendritic processes.