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At least 775 records · Page 43Linked to original sources
PubMed1991

Receptive field properties of somatosensory neurons in the cat superior colliculus.

In general, knowledge of the internal organization of receptive fields has played an important role in shaping current understanding of sensory physiology. Such knowledge is particularly important for understanding the function of the superior colliculus, since this structure is at once implicated in spatial localization and has relatively large receptive fields. While this issue has been addressed in the visual and auditory modalities represented in the superior colliculus, there are no previous studies of its somatosensory receptive field organization. Here, the properties of somatosensory receptive fields in the cat superior colliculus were studied quantitatively to determine whether they contain internal non-homogeneities that might aid in the determination of stimulus detail. Of special interest was the possibility that these comparatively large receptive fields would contain areas of differential excitability that could aid in spatial resolution, that within-field spatial summation and/or inhibition would be exhibited, and that the borders of the excitatory receptive field would be flanked by inhibitory regions. The data demonstrate that while inhibition beyond the receptive field borders is a rarity, these somatosensory receptive fields nearly always contain a well-defined area of maximal sensitivity within which the size of the stimulus is a critical feature in determining the magnitude of the response. These best areas are systematically distributed across receptive fields as a function of their location in the structure, and indicate that the resolution of stimulus location and size may be greater than expected on the basis of receptive field size alone.

Animals↗
PubMed2005

Mislocalization of flashes during smooth pursuit hardly depends on the lighting conditions.

Targets that are briefly flashed during smooth pursuit eye movements are mislocalized in the direction of motion (forward shift) and away from the fovea (spatial expansion). Hansen [Hansen, R. M. (1979). Spatial localization during pursuit eye movements. Vision Research 19(11), 1213-1221] reported that these errors are not present for fast motor responses in the dark, whereas Rotman et al. [Rotman, G., Brenner, E., Smeets, J. B. (2004). Quickly tapping targets that are flashed during smooth pursuit reveals perceptual mislocalizations. Experimental Brain Research 156(4), 409-414] reported that they are present for fast motor responses in the light. To evaluate whether the lighting conditions are the critical factor, we asked observers to point to the positions of flashed objects during smooth pursuit either in the dark or with the room lights on. In a first experiment, the flash, which could appear at 1 of 15 different positions, was always shown when the eye had reached a certain spatial position. We found a forward bias and spatial expansion that were independent of the target and ambient luminance. In a second experiment, the flash was always shown at the same retinal position, but the spatial position of the eye at the moment of flash presentation was varied. In this case we found differences between the luminance conditions, in terms of how the errors depended on the velocity and position on the trajectory. We also found specific conditions in which people did not mislocalize the target in the direction of pursuit at all. These findings may account for the above-mentioned discrepancy. We conclude that although the lighting conditions do influence the localization errors under some circumstances, it is certainly not so that such errors are absent whenever the experiment is conducted in the dark.

Humans↗
PubMed1997

Characterization and localization of profilin in pollen grains and tubes of Lilium longiflorum.

Pollen tubes show a rapid and dramatically polarized growth in which the actin cytoskeleton appears to play a central role. In order to understand the regulation of actin we characterized its associated protein, profilin, in pollen tubes of Lilium longiflorum. By using purified polyclonal antibodies prepared against bean root profilin [Vidali et al., 1995: Plant Physiol. 108:115-123] we detected in pollen grains and tubes two profilin polypeptides with molecular masses of 14.4 and 13.4 KDa, and an identical isoelectric point of 5.05. Profilin comprises approximately 0.47% of the total grain protein, with actin being approximately 1.4%. We were unable to detect a statistically significant profilin increase after germination, while the actin increased approximately 68%. We also spatially localized the distribution of profilin using immunocytochemistry of fixed cells at both the light and electron microscope level, and by fluorescent analog cytochemistry on live cells. The results show that profilin is evenly distributed throughout the cytoplasm and does not specifically associate with any cellular structure.

Actins↗
PubMed1985

Temporal properties of visual channels measured by masking.

Threshold elevations for spatially localized test stimuli were measured as a function of the temporal frequency of a sinusoidal mask grating. Ten of these temporal-masking curves were determined, each using a test stimulus of different temporal frequency. It was found that these data could be accounted for by four temporal-tuning curves: one low-pass curve with a corner frequency of 8.0 Hz and three bandpass curves with bandwidths of 2.0-2.5 octaves and peaks all within the region 4.0-8.0 Hz. In another set of experiments, a series of 1 spatial-masking curves was determined, each using a test stimulus of different spatial frequency. Measurement of the entire series was repeated using 1.0- and 8.0-Hz mask temporal modulations. Spatial-masking data collected under the two temporal conditions could both be accounted for by a single set of seven spatial-tuning curves, without changing the shape of any of these curves. The data are therefore compatible with spatiotemporal separability. Finally, a large set of contrast-response curves (threshold elevation as a function of mask contrast) was collected. These curves were found to follow a power law whose exponent varied with the spatiotemporal conditions of the experiment.

Form Perception↗
PubMed1988

Disparity range for binocular summation.

Binocular summation of contrast and stereopsis have been linked because they both disappear under certain pathological conditions. The dependence of stereopsis on spatial frequency prompted us to examine how binocular summation varies with both spatial frequency and binocular disparity. We therefore measured binocular summation at different disparities using spatially localized stimuli which were also restricted in their Fourier composition. Contrast thresholds were measured using three interleaved forced-choice staircases for left and right eye monocular stimuli and a binocular stimulus composed of the two monocular stimuli presented simultaneously. At zero disparity binocular thresholds were 1.4 to 1.6 times lower than monocular. As disparity was increased the ratio between the thresholds became smaller, such that at large disparities it was near 1.2, the value expected from probability summation. The range of disparities over which probability summation was exceeded varied with the spatial frequency of the stimulus. At 6.0 cpd the range was 2-3 deg, but at 2.0 cpd or 0.75 cpd the range increased to 4-6 deg. These values closely parallel the range of disparities over which stereoscopic depth sensations occur, but they exceed the limits within which disparate images of an object can be fused into a single percept. The results support the contentions that "neural" summation occurs in the mechanism for stereopsis, that this mechanism uses spatial frequency selective channels, and that this mechanism is separate from the mechanism which mediates fusion.

Adult↗
PubMed1998

Spatial organization, predictability, and determinism in ventricular fibrillation.

The degree of spatial organization of ventricular fibrillation (VF) is a fundamental dynamical property of the arrhythmia and may determine the success of proposed therapeutic approaches. Spatial organization is closely related to the dimension of VF, and hence to its predictability and controllability. We have explored several techniques to quantify spatial organization during VF, to predict patterns of activity, and to see how spatial organization and predictability change as the arrhythmia progresses. Epicardial electrograms recorded from pig hearts using rectangular arrays of unipolar extracellular electrodes (1 mm spacing) were analyzed. The correlation length of VF, the number of Karhunen-Loeve modes required to approximate data during VF, the number, size and recurrence of wavefronts, and the mean square error of epicardial potential fields predicted 0.256 seconds into the future were all estimated. The ability of regularly-timed pacing stimuli to capture areas of fibrillating myocardium during VF was confirmed by a significant increase in local spatial organization. Results indicate that VF is neither "low-dimensional chaos" (dimension <5) nor "random" behavior (dimension= infinity ), but is a high-dimensional response with a degree of spatial coherence that changes as the arrhythmia progresses. (c) 1998 American Institute of Physics.

Journal Article↗
PubMed1993

A processing stream in mammalian visual cortex neurons for non-Fourier responses.

Mammalian striate and circumstriate cortical neurons have long been understood as coding spatially localized retinal luminance variations, providing a basis for computing motion, stereopsis, and contours from the retinal image. However, such perceptual attributes do not always correspond to the retinal luminance variations in natural vision. Recordings from area 17 and 18 neurons of the cat revealed a specialized nonlinear processing stream that responds to stimulus attributes that have no corresponding luminance variations. This nonlinear stream acts in parallel to the conventional luminance processing of single cortical neurons. The two streams were consistent in their preference for orientation and direction of motion but distinct in processing spatial variations of the stimulus attributes.

Animals↗
PubMed2000

Revisiting spatial vision: toward a unifying model.

We report contrast detection, contrast increment, contrast masking, orientation discrimination, and spatial frequency discrimination thresholds for spatially localized stimuli at 4 degrees of eccentricity. Our stimulus geometry emphasizes interactions among overlapping visual filters and differs from that used in previous threshold measurements, which also admits interactions among distant filters. We quantitatively account for all measurements by simulating a small population of overlapping visual filters interacting through divisive inhibition. We depart from previous models of this kind in the parameters of divisive inhibition and in using a statistically efficient decision stage based on Fisher information. The success of this unified account suggests that, contrary to Bowne [Vision Res. 30, 449 (1990)], spatial vision thresholds reflect a single level of processing, perhaps as early as primary visual cortex.

Computer Simulation↗
PubMed1995

[Human folliculogenesis and local regulation].

It is well known that gonadotropin controls a major part of follicular development. However, the mechanism of local regulation under the control of gonadotropins in still unclear. In this study, we focused on the local regulation of steroidogenesis, growth factors and cell proliferation to evaluate the human follicular development. To assess steroidogenesis, it is important to detect the expression of steroidogenic enzymes in the granulosa and theca cells during folliculogenesis. We initially tried to find out the transcription factor Ad4BP that binds the Ad4 site and regulates the function of steroidogenic enzyme. By immunohistochemistry, the expression of Ad4BP was confirmed sporaf1p4lly in preantral granulosa cells. In the antral follicles, the expression of Ad4BP was observed both in the granulosa and theca cell. According steroidogenic enzyme, we evaluated temporal and spatial localization of cholesterol side chain cleavage (scc), 3 beta hydroxysteroid dehydrogenase (3 beta HSD), 17 alpha hydroxylase (17 alpha) and aromatase, and steroid receptors. In briefly, the localizations of scc, 3 beta HSD and 17 alpha were observed in preantral follicles and the mRNA expressions of these enzymes were confirmed in the theca cell by in situ hybridization method. Expression of aromatase was generally observed in only one follicle (antral or mature follicle) per case in mid proliferative to premenstrual phase. The localization of androgen and estrogen receptor was observed in the antral follicle granulosa cells, and estrogen receptor was detected only in aromatase positive follicles. These results suggested that Ad4BP initially controls the function of steroidogenic enzymes and steroidogenic enzymes gradually express from primary follicles to mature follicles. At antral follicle stage, steroid metabolism completes to produce testosterone. When aromatase and estrogen receptor express in antral follicle, this antral follicle develops as the dominant follicle and produces estradiol to promote follicle maturation. We therefore speculate that the expression of aromatase and estrogen receptor have an important role for the selection of dominant follicle in human. According growth factors for follicular development, it has been demonstrated to be important in the biological activity in the ovary. In this study, we examined the localization of EGF, TGF alpha and their receptor (EGFR). The localization of EGF was not confirmed both mRNA and protein level through follicular development. On the other hand, the localization and expression of TGF alpha was confirmed in theca cells and EGFR in granulosa cells at antral stage.(ABSTRACT TRUNCATED AT 400 WORDS)

3-Hydroxysteroid Dehydrogenases↗
PubMed2005

Vestibular, proprioceptive, and haptic contributions to spatial orientation.

The control and perception of body orientation and motion are subserved by multiple sensory and motor mechanisms ranging from relatively simple, peripheral mechanisms to complex ones involving the highest levels of cognitive function and sensory-motor integration. Vestibular contributions to body orientation and to spatial localization of auditory and visual stimuli have long been recognized. These contributions are reviewed here along with new insights relating to sensory-motor calibration of the body gained from space flight, parabolic flight, and artificial gravity environments. Recently recognized contributions of proprioceptive and somatosensory signals to the appreciation of body orientation and configuration are described. New techniques for stabilizing posture by means of haptic touch and for studying and modeling postural mechanisms are reviewed. Path integration, place cells, and head direction cells are described along with implications for using immersive virtual environments for training geographic spatial knowledge of real environments.

Cognition↗
PubMed2002

Responses of spectrally selective cells in macaque area V2 to wavelengths and colors.

We have recorded from wavelength-selective cells in macaque monkey visual area V2, interposed between areas V1 and V4 of the color-specialized pathway, to learn whether their responses correlate with perceived colors or are determined by the wavelength composition of light reflected from their receptive fields. All the cells we recorded from were unselective for the orientation and direction of motion of the stimulus, and all were histologically identified to be in the thin cytochrome oxidase stripes. Using multi-colored "Mondrian" scenes of the appropriate spatial configuration, areas of different color were placed in the receptive field of each cell and the entire scene illuminated by three projectors, passing long-, middle-, and short-wave light, respectively, in various combinations. Our results show that wavelength-selective cells in V2 respond to an area of any color depending on whether or not it reflects a sufficient amount of light of their preferred wavelength. In addition, the responses of a third of the cells tested were also influenced by the wavelength composition of their immediate surrounds, thus signaling the result of a local spatial comparison with respect to the amount of their preferred wavelength present. The responses of all also depended on the sequence with which their receptive fields were illuminated with light of the three different wavebands: cells were activated when there was an increase (and inhibited when there was a decrease) in the amount of their preferred wavelength with respect to the other two; the temporal route taken was therefore a determining factor, and, depending on it, cells would either respond or not to a particular combination of wavelengths. We conclude that although spatiotemporal wavelength comparisons are taking place in the color-specialized subdivisions of area V2, the determination of complete color-constant behavior at the neuronal level requires further processing, in other areas.

Animals↗
PubMed1997

Localization of lipid peroxidation-derived protein epitopes in the porcine corpus luteum.

Reactive oxygen species (ROS) generated within the corpus luteum (CL) are believed to play an integral role in luteolysis. Unsaturated lipids are susceptible to peroxidation by ROS, leading to the formation of toxic aldehydes such as malondialdehyde (MDA) and 4-hydroxy-nonenal (4-HNE) that can attack cellular and extracellular proteins. Aldehyde conjugation of proteins can have diverse effects on cell function, including cross-linking of cell surface receptors, alteration of enzyme activities, and modification of lipoproteins. The objectives of the present study were to 1) determine by immunological techniques whether lipid peroxidation-derived protein epitopes (i.e., MDA- and 4-HNE-lysine) could be detected in situ during the natural life span of the CL, and 2) determine the temporal and spatial localization of these epitopes. Fresh luteal tissue was collected from young gilts at distinct phases of the estrous cycle: early (Days 4-7), mid (Days 8-12), and late (Days 14-18). Immunocytochemistry was performed on tissue sections using monoclonal antibodies against MDA-lysine and 4-HNE-lysine. Positive immunostaining was evident in porcine CL at all stages of the estrous cycle. Immunoactivity was associated primarily with the steroidogenic cells, most consistently with the large luteal cells, and was most intense in regressing tissue (i.e., late). No staining was observed in sections incubated with nonimmune mouse serum or when anti-4-HNE-lysine was preadsorbed with 4-HNE-protein preparations. Immunoblotting of protein extracts from luteal tissue revealed three major reactive bands. At least two of these bands were closely associated with extracted oxidized human low-density lipoprotein (LDL) and with 4-HNE-conjugated human apoprotein B. These results demonstrate the presence of lipid peroxidation-derived protein epitopes within the porcine CL and show that one or more of these may be an oxidized-LDL moiety. This represents the first direct in situ evidence that protein modification by lipid peroxidation products occurs during the natural luteal life span. The physiological consequences remain to be determined.

Aldehydes↗
PubMed2004

Context-independent directional cue learning by hippocampal place cells.

In a symmetrical environment possessing no other polarizing visual cues, the spatially localized firing of hippocampal place cells can be primarily orientated by a reliable distal visual stimulus, such as a white cue card. However, if such a directional cue is made unreliable by being frequently moved in full view of the rat, the rat's internal sense of direction comes, over the course of a few days, to control the orientation of place fields instead. We investigated whether this simple form of 'cue-instability' learning would transfer to a new context, in which the firing patterns of the place cells become reorganized and in which a new spatial representation is thus active. We found that after cue-instability learning, the 'remapped' place field representation in the new environment was also orientated by the internal sense of direction of the rat rather than by the cue card, showing that the cue learning generalized from one context (and hence spatial representation) to another. This contrasts with another kind of place cell learning, in which the cells can acquire the ability to discriminate two spatial locations in one context but do not transfer this discrimination to a new context. We discuss the different effects of context changes on learned place cell activity in terms of the possible architecture of the inputs to place cells.

Animals↗
PubMed2001

Immunohistochemical study on the distribution of voltage-gated K(+) channels in rat brain following transient focal ischemia.

The present study examined the spatial localizations of voltage-gated K(+) (Kv) channels in the rat brain following transient focal ischemia, using immunohistochemistry. Increased expression of Kv1.2 was obvious in the cerebral cortex, dentate gyrus, amygdala, and hypothalamic areas at 3 days following ischemic insults. There was a significant increase in Kv1.2 immunoreactivity in several cortical regions, including cingulate cortex, infralimbic cortex, dorsal peduncular cortex and piriform cortex. On the contrary, Kv1.2 immunoreactivity had not significantly increased in the hippocampal CA1-3 regions although moderate Kv1.2 immunoreactivity was found in the cell bodies and processes of some neurons. Potentially the first demonstration of spatial changes in Kv1.2 channel expression could provide important molecular basis for altered neuronal excitability after ischemic brain injury.

Amygdala↗
PubMed1997

Spatial regulation of neuronal gene expression in response to nerve growth factor.

To examine the cellular mechanisms whereby distally derived growth factors regulate nuclear responses in neurons, we have utilized compartmented cultures of sympathetic neurons to examine the regulation of two nerve growth factor (NGF)-inducible genes, tyrosine hydroxylase (TH) and p75 neurotrophin receptor (p75NTR). These studies demonstrate that NGF can signal retrogradely to mediate the induction of TH and p75NTR mRNAs. However, quantitative differences occurred as a function of the spatial localization of NGF exposure; application of NGF to cell bodies and proximal axons elicited peak levels of neuronal gene expression that were two- to threefold higher than when NGF was applied to distal axons alone. Furthermore, neurons responding maximally to NGF on distal axons were still able to respond to NGF administered to cell bodies and proximal axons. Biochemical analysis indicated that this difference in responsiveness was not due to differences in the number of TrkA/NGF receptors in the two compartments. Thus, although NGF signals retrogradely to mediate nuclear responses, the magnitude of these responses differs as a function of the spatial location of the activated NGF receptor:ligand complex. Moreover, these data suggest that neurons may be able to respond to a second cellular source of neurotrophins, even when target-derived neurotrophins are not limiting.

Animals↗
PubMed2006

Spatial clustering analysis in neuroanatomy: applications of different approaches to motor nerve fiber distribution.

Spatial organization of the nerve fibers in the peripheral nerves may be important for the studies of axonal regeneration, the degenerative nerve diseases and the construction of interfaces with peripheral nerves, such as nerve prostheses. Functional topography of motor axons related to the gastrocnemius muscle was revealed in the ventral spinal roots by retrograde tracing. Gastrocnemius muscles of adult rats were injected with the tracer Fluoro-Gold. After 3 days of survival the animals were sacrificed and their ventral roots were harvested, sectioned, and imaged on a fluorescence microscope. Maps of the traced fibers were automatically analyzed using a novel approach, local spatial clustering statistics, that tested for occurrences of clusters of motor fibers and visualized them. Thresholds indicating the presence of clustering at various scales of observation were computed based on series of Monte Carlo simulations of random spatial point patterns. Clusters were visualized by kernel interpolation. The approach was tested on simulated data and subsequently applied to the motor fiber maps in the ventral roots. Results revealed clustering of the motor fibers innervating the gastrocnemius muscle at the level of the L6 ventral spinal root. The analysis was validated using Voronoi tessellation and nearest neighbor analysis.

Animals↗
PubMed1994

Filopodia initiate choices made by sensory neuron growth cones at laminin/fibronectin borders in vitro.

Localized expression of environmental cues is thought to provide directional information to migrating neuronal growth cones by enhancing or suppressing axon outgrowth over limited regions. To investigate how such a mechanism may function in vivo, we observed growth cones of embryonic chick dorsal root ganglion neurons at a substratum border between the extracellular matrix components laminin and fibronectin in vitro using time-lapse phase-contrast and interference reflection microscopy. We found that patterns of laminin and fibronectin could locally promote or suppress the direction of growth cone migration. While migrating on either laminin or fibronectin, at least 79% of growth cones changed their rate and/or direction of outgrowth upon contact with the alternative substratum, in a manner suggesting that growth cones were selecting one substratum over the other. Complex changes in growth cone behavior were initiated by filopodial contact with the alternate substratum, suggesting that filopodia were providing intracellular signals to the growth cone. Using interference reflection microscopy, we have found that selection of a substratum is independent of the degree of close contact to the substratum. We conclude that spatially localized ECM components can direct axon outgrowth by mechanisms based on intracellular signaling through growth cone filopodia.

Animals↗
PubMed1997

Localized sampling of cytoplasm from Xenopus oocytes for capillary electrophoresis.

Continued progress in cellular physiology requires new measurement strategies which can be applied to solitary cells. Since many cellular signaling pathways act on time scales of a few seconds, there is a critical need for single-cell techniques with subsecond time resolution. Capillary electrophoresis shows great promise as a tool for the analysis of individual cells. In the present work, we describe a technique to load a capillary with picoliter to nanoliter volumes of cytoplasm and initiate electrophoresis in less than 500 ms. When cytoplasm was sampled from a Xenopus laevis oocyte previously loaded with fluorescein, calcium green, or a mixture of the two fluorophores, their fluorescent peaks were readily identifiable on the electropherogram. Since the volume of cytoplasm (< or = 30 nL) loaded into the capillary was much smaller than the 1 microL oocyte volume, spatially localized biochemical measurements were also possible. To demonstrate the utility of this new technique, the activity of the enzyme beta-galactosidase was measured in small regions of the Xenopus oocyte. Subcellular, subsecond sampling of oocyte cytoplasm will enable biochemical measurements with the resolution required to understand many cellular signal transduction pathways.

Animals↗