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At least 1,009 records · Page 56Linked to original sources
PubMed1994

Relationship between lateral inhibitory connections and the topography of the orientation map in cat visual cortex.

The functional and structural topography of lateral inhibitory connections was investigated in visual cortical area 18 using a combination of optical imaging and anatomical tracing techniques in the same tissue. Orientation maps were obtained by recording intrinsic signals in regions of 8.4-19 mm2. To reveal the inhibitory connections provided by large basket cells, biocytin was iontophoretically injected at identified orientation sites guided by the pattern of surface blood vessels. The axonal and dendritic fields of two retrogradely labelled large basket cells were reconstructed in layer III. Their axonal fields extended up to 1360 microns from the parent somata. In addition to single basket cells, the population of labelled basket cell axons was also studied. For this analysis anterogradely labelled basket axons running horizontally over 460-1280 microns from the core of an injection site in layer III were taken into account. The distribution of large basket cell terminals according to orientation preferences of their target regions was quantitatively assessed. Using the same spatial resolution as the orientation map, a frequency distribution of basket cell terminals dependent on orientation specificity could be derived. For individual basket cells, the results showed that, on average, 43% of the terminals provided input to sites showing similar orientation preferences (+/- 30 degrees) to those of the parent somata. About 35% of the terminals were directed to sites representing oblique-orientation [+/- (30-60) degrees], and 22% of them terminated at cross-orientation sites [+/- (60-90) degrees]. Furthermore, the possible impact of large basket cells on target cells at different distances and orientation preferences was estimated by comparing the occurrence of orientation preferences with the occurrence of basket terminals on the distance scale. It was found that a basket cell could elicit iso-orientation inhibition with a high impact between 100-400 and 800-1200 microns, strong cross-orientation inhibition at approximately 400-800 microns, and oblique-orientation inhibition between 300-500 and 700-900 microns from the parent soma. The non-isotropic topography of large basket axons suggests a complex function for this cell class, possibly including inhibition related to orientation and direction selectivity depending on the location of the target cells and possible target selectivity.

Animals↗
PubMed1995

Studies on the optic chiasm of the leopard frog. I. Selective loss of visually elicited avoidance behavior after optic chiasm hemisection.

We hemisected either the posterior or anterior portion of the optic chiasm and found that frogs were unresponsive to large looming stimuli anywhere in the visual field. Nonetheless, the animals responded to prey stimuli throughout the visual field. Responses to looming stimuli returned in 1 to 8 weeks post-surgery. After complete transection of the chiasm animals were unresponsive to both prey and large looming stimuli. Frogs responded normally to prey and looming stimuli if less than half the optic chiasm was cut or if the postoptic commissure was cut. Since responses to looming stimuli returned before cut optic fibers could regenerate, these results suggest that visual information concerning prey and large looming objects are mediated by separate optic nerve fiber systems.

Animals↗
PubMed2005

Intraoperative sentinel lymph node mapping of the lung using near-infrared fluorescent quantum dots.

BACKGROUND: The presence of lymph node metastases is an important prognostic marker with regard to non-small-cell lung cancer (NSCLC). Assessment of the sentinel lymph node (SLN) for the presence of tumor may improve staging. Our objective was to develop an optical noninvasive imaging tool that would permit intraoperative SLN mapping and provide real-time visual feedback for image-guided localization and resection. METHODS: Invisible near-infrared (NIR) light penetrates relatively deeply into tissue and background autofluorescence is low. We have developed a NIR fluorescence imaging system that simultaneously displays color video and NIR images of the surgical field. We recently engineered 15 nm nonradioactive NIR fluorescent quantum dots (QDs) as optimal lymphotrophic optical probes. The introduction of these QDs into lung tissue allows real-time visualization of draining lymphatic channels and nodes. RESULTS: In 12 Yorkshire pigs (mean weight 35 kg) we demonstrated that 200 pmol of NIR QDs injected into lobar parenchyma accurately maps lymphatic drainage and the SLN. All SLNs were strongly fluorescent and easily visualized within 5 minutes of injection. In 14 separate injections QDs localized to a mediastinal node, whereas in 2 injections QDs localized to a hilar intraparenchymal node. Histologic analysis in all cases confirmed the presence of nodal tissue. CONCLUSIONS: We report a highly sensitive rapid technique for SLN mapping of the lung. This technique permits precise real-time imaging and therefore overcomes many limitations of currently available techniques.

Animals↗
PubMed2006

Model-based analysis of excitatory lateral connections in the visual cortex.

Excitatory lateral connections within the primary visual cortex are thought to link neurons with similar receptive field properties. Here we studied whether this rule can predict the distribution of excitatory connections in relation to cortical location and orientation preference in the cat visual cortex. To this end, we obtained orientation maps of areas 17 or 18 using optical imaging and injected anatomical tracers into these regions. The distribution of labeled axonal boutons originating from large populations of excitatory neurons was then analyzed and compared with that of individual pyramidal or spiny stellate cells. We demonstrate that the connection patterns of populations of nearby neurons can be reasonably predicted by Gaussian and von Mises distributions as a function of cortical location and orientation, respectively. The connections were best described by superposition of two components: a spatially extended, orientation-specific and a local, orientation-invariant component. We then fitted the same model to the connections of single cells. The composite pattern of nine excitatory neurons (obtained from seven different animals) was consistent with the assumptions of the model. However, model fits to single cell axonal connections were often poorer and their estimated spatial and orientation tuning functions were highly variable. We conclude that the intrinsic excitatory network is biased to similar cortical locations and orientations but it is composed of neurons showing significant deviations from the population connectivity rule.

Animals↗
PubMed2002

Shadows cast by retinal blood vessels mapped in primary visual cortex.

The mammalian eye is a remarkable optical device, but its design is not perfect. The blood vessels that supply the inner retina are located in front of the photoreceptor layer, blocking access to light. Their shadows create a pattern of blindness in the field of vision that corresponds precisely to the location of the largest vessels in the eye. We show here that in squirrel monkeys, focal deprivation by blood vessels leads to rewiring of the eye's geniculocortical projections, imprinting an image of the retinal vascular tree onto the primary visual cortex. This process illustrates vividly that local imbalances in neuronal activity can influence column formation during normal development.

Animals↗
PubMed2006

Modification of the velocity distribution of H(2) molecules in a supersonic beam by intense pulsed optical gradients.

We report the acceleration and deceleration of H(2) molecules in a supersonic molecular beam by means of its interaction with an intense optical gradient from a nanosecond far-off-resonant optical pulse. The strong optical gradients are formed in the interference pattern of two intense optical pulses at 532 nm. The velocity distribution of the molecular beam, before and after the applied optical pulse, is measured by a velocity-mapped ion imaging technique. Changes in velocity up to 202 m s(-1)+/- 61 m s(-1) are observed in a molecular beam initially travelling at a mean speed of 563 m s(-1). We report the dependence of this change in velocity with the strength of the optical gradient applied.

Algorithms↗
PubMed2005

Pars plana vitrectomy for diabetic macular oedema: OCT and functional correlations.

PURPOSE: A prospective study to evaluate the macular structural and functional effects of pars plana vitrectomy (PPV) for persistent diffuse clinically significant macular oedema (CSMO). METHOD: A total of 12 patients with persistent diffuse CSMO were recruited and underwent assessment including best-corrected visual acuity, fundus fluorescein angiography, optical coherence tomography (OCT) and fine matrix mapping (FMM) at baseline and over a period of a year poststandard three-port PPV. RESULTS: The median baseline ETDRS letters score for all 12 patients was 52 (range 41-63) while at 12 months it had increased to 65 (range of 27-68), an improvement of two complete ETDRS lines (P=0.037). Similarly, there was an improvement in the perifoveal cone thresholds (P=0.02). The foveal thickening for all 12 patients ranged from a median of 183 to 751 microm (normal range 126-180 microm) and the macular volume ranged from a median of 2.13 to 6.42 mm(3) (normal <1.66 mm(3)). After surgery, both the median foveal thickness (from 334 to 280 microm) and median macular volume (from 3.24 to 2.61 mm(3)) demonstrated decreases over 12 months (P=0.01). On baseline OCT, the patients fell into two anatomically distinct groups: Group 1 (n=4) had a dome-shaped thickened macula with a partial posterior hyaloid separation and a significantly higher foveal thickness and macular volume than Group 2 (n=8) which had a diffuse low-elevation profile of the thickened macula (P=0.007). CONCLUSIONS: In this prospective study of PPV for persistent fovea-involving CSMO there was structural and functional improvement.

Aged↗
PubMed2001

Topographic-specific axon branching controlled by ephrin-As is the critical event in retinotectal map development.

The retinotectal projection is the predominant model for studying molecular mechanisms controlling development of topographic axonal connections. Our analyses of topographic mapping of retinal ganglion cell (RGC) axons in chick optic tectum indicate that a primary role for guidance molecules is to regulate topographic branching along RGC axons, a process that imposes unique requirements on the molecular control of map development. We show that topographically appropriate connections are established exclusively by branches that form along the axon shaft. Initially, RGC axons overshoot their appropriate termination zone (TZ) along the anterior-posterior (A-P) tectal axis; temporal axons overshoot the greatest distance and nasal axons the least, which correlates with the nonlinear increasing A-P gradient of ephrin-A repellents. In contrast, branches form along the shaft of RGC axons with substantial A-P topographic specificity. Topography is enhanced through the preferential arborization of appropriately positioned branches and elimination of ectopic branches. Using a membrane stripe assay and time-lapse microscopy, we show that branches form de novo along retinal axons. Temporal axons preferentially branch on their topographically appropriate anterior tectal membranes. After the addition of soluble EphA3-Fc, which blocks ephrin-A function, temporal axons branch equally on anterior and posterior tectal membranes, indicating that the level of ephrin-As in posterior tectum is sufficient to inhibit temporal axon branching and generate branching specificity in vitro. Our findings indicate that topographic branch formation and arborization along RGC axons are critical events in retinotectal mapping. Ephrin-As inhibit branching along RGC axons posterior to their correct TZ, but alone cannot account for topographic branching and must cooperate with other molecular activities to generate appropriate mapping along the A-P tectal axis.

Animals↗
PubMed1984

Deafferentation of the visual cortex: the effect on cortical cells in normal and in early monocularly deprived cats.

The optic tract was unilaterally transected and receptive field mapping and unit recordings were made for cells in the boundary of areas 17-18 in the deafferented and in the intact visual cortex of adult cats monocularly deprived during the critical developmental period. Three groups of adult animals served as controls: normal cats, early monocularly deprived (MD) cats, and optic tract transected cats. In contrast to the activity found in the intact hemisphere, the deafferented hemisphere of the experimental group was almost completely unresponsive. The ocular dominance distribution in the intact hemisphere of the experimental group (75.0% cells monocularly driven by the normal eye) was similar to that of the control MD cats (78.1%). This indicates that cutting the optic tract after the critical period does not affect the ocular dominance distribution of cortical cells induced in the intact hemisphere by early monocular deprivation. The reduction found in the proportion of visually responsive cells and the orientation and direction selective cells in the intact hemisphere of the experimental group, is mainly due to the isolation of the fellow hemisphere from its direct visual input, and the subsequent inactivation of the callosal pathway interconnecting the two visual areas.

Afferent Pathways↗
PubMed1998

Microelectrode-guided pallidotomy: technical approach and its application in medically intractable Parkinson's disease.

OBJECT: The authors describe the microelectrode recording and stimulation techniques used for localizing the caudal sensorimotor portion of the globus pallidus internus (GPi) and nearby structures (internal capsule and optic tract) in patients undergoing GPi pallidotomy. METHODS: Localization is achieved by developing a topographic map of the abovementioned structures based on the physiological characteristics of neurons in the basal ganglia and the microexcitable properties of the internal capsule and optic tract. The location of the caudal GPi can be determined by "form fitting" the physiological map on relevant planes of a stereotactic atlas. A sensorimotor map can be developed by assessing neuronal responses to passive manipulation or active movement of the limbs and orofacial structures. The internal capsule and optic tract, respectively, can be identified by the presence of stimulation-evoked movement or the patient's report of flashes or speckles of light that occur coincident with stimulation. The optic tract may also be located by identifying the neural response to flashes of light. The anatomical/physiological map is used to guide lesion placement within the sensorimotor portion of the pallidum while sparing nearby structures, for example, the external globus pallidus, nucleus basalis, optic tract, and internal capsule. The lesion location and size predicted by using physiological recording together with thin-slice high-resolution magnetic resonance imaging reconstructions of the lesion were confirmed in one patient on histological studies. CONCLUSIONS: These data provide important information concerning target identification for ablative or deep brain stimulation procedures in idiopathic Parkinson's disease and other movement disorders.

Antiparkinson Agents↗
PubMed1990

Recovery from conduction failure in optic axons spared by lesions in the rat.

A chronic preparation has been developed to determine the physiological sequelae of a lesion of optic axons, and to correlate these with the optic innervation of the superior colliculus (SC). During deep pentobarbital anesthesia: (1) Vigorous small-field (2-5 degrees) multi-unit responses were recorded from microelectrodes in the lower stratum griseum superficiale (SGS) and upper stratum opticum (SO), evoked by the motion of a 40 degrees black edge. (2) The maps of the retinal projection, obtained without immobilization of the eye, were regular in about 1/3 of cases and only slightly irregular in most of the remainder. (3) There was a rhythmic (10-20/s), retina-dependent firing of spike bursts in visually responsive SC. At a lighter level of anesthesia this bursting reduced or disappeared, and coincidentally there was a rapid enlargement of the multi-unit receptive fields (MU-RFs). It is suggested that GABA-based inhibitory mechanisms were involved in producing both the rhythmic bursting and the smaller-field MU-RFs. At either anesthetic level the movement of a 5 degrees disc produced 20-65 degrees MU-RFs. Vertical lesions which severed part of the visual pathway reduced and, if large enough, abolished responses even to a strong testing stimulus that normally produced a response from an area of visual field larger than the range of eye movement. The region of SC affected was always medial or lateral, and sites within the still-responsive area had normally small MU-RFs. Repeated mappings over the following hours to days revealed a variable recovery of response; this recovery always occurred within the silenced zone of SC nearest to the still-responsive area. Ultimately two discrete zones, responsive and silent, persisted. Mapping the SC, at 500 microns intervals, involved about 25 microelectrode penetrations. The number of sites silenced immediately postlesion was 1-24. Response returned at 1-15 of these, corresponding to 4-60% of the entire SC. Most of the recoveries occurred by 2 h postlesion, but occasionally an additional 1-3 sites recovered during the following 2-8 days. Recovered MU-RFs were small, and appropriately located within the map. Intraocular horseradish peroxidase (HRP) accumulated in severed optic axons but was transported with no obvious hindrance in spared axons alongside the lesion. Within the SC a sparse optic innervation extended beyond the responsive area, into about 0.5 mm of the region which remained silent after the recoveries were completed.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed2001

Optical recording of the neuronal activity in the brainstem-spinal cord: application of a voltage-sensitive dye.

Although there are several limitations, optical recording techniques are superior to multi-electrode mapping methods, as it is possible to record at large number of points in a small area without destroying the tissue and possible to know relative changes of membrane potentials. Optical recording techniques using voltage-sensitive dyes will be more importantly applied in the study of central respiratory control (e.g., mechanisms of respiratory rhythm generation) in the near future.

Animals↗
PubMed1997

Projection map of cytochrome b6 f complex at 8 A resolution.

The structure of the cytochrome b6 f complex has been investigated by electron microscopy and image analysis of thin three-dimensional crystals. Electron micrographs of negatively stained specimens were recorded and showed optical diffraction peaks to 10 A resolution. A projection map was calculated at 8 A resolution and showed the presence of cytochrome b6 f dimers. The extramembrane part of each monomer featured a C shape, with mean external diameter approximately of 53 A and an internal groove approximately 14 A long and approximately 9 A wide. Within each monomer, strong features were clearly resolved and tentatively attributed to some of the subunits of the cytochrome b6 f complex. The data are consistent with the Rieske iron-sulfur protein lying close to the monomer-monomer interface and the heme-bearing domain of cytochrome f far from it.

Animals↗
PubMed2002

Analysis of modes and behavior of a multiconjugate adaptive optics system.

We study the so-called three-dimensional mapping of turbulence, a method solving the cone effect (or focus anisoplanatism) by using multiple laser guide stars (LGSs). This method also permits a widening of the corrected field of view much beyond the isoplanatic field. Multiple deformable mirrors, conjugated to planes at chosen altitudes among the turbulent layers, are used to correct in real time the wave fronts measured from the LGSs. We construct an interaction matrix describing the multiconjugate adaptive optics system and analyze the eigenmodes of the system. We show that the global tilt mode is singular because it cannot be localized in altitude, so that it must be corrected only once at any altitude. Furthermore, when the tilt from the LGS cannot be measured, the singularity of the global tilt yields the delocalization of particular forms of defocus and astigmatism. This imposes the use of a single natural guide star located anywhere in the corrected field to measure these modes. We show as an example that the cone effect can be corrected with a Strehl of 0.8 with four LGSs (tilt ignored) on an 8-m telescope in the visible when a single laser star provides a Strehl of 0.1. The maximum field of view of 100 arc sec in diameter can be reconstructed with an on-axis Strehl ratio of 30%. We also show that the measurement of the height of the layers can be done with current techniques and that additional layers, not accounted for, do not significantly degrade the performance in the configuration that we model.

Journal Article↗
PubMed2006

Effect of optical property estimation accuracy on tomographic bioluminescence imaging: simulation of a combined optical-PET (OPET) system.

Inevitable discrepancies between the mouse tissue optical properties assumed by an experimenter and the actual physiological values may affect the tomographic localization of bioluminescent sources. In a previous work, the simplifying assumption of optically homogeneous tissues led to inaccurate localization of deep sources. Improved results may be obtained if a mouse anatomical map is provided by a high-resolution imaging modality and optical properties are assigned to segmented tissues. In this work, the feasibility of this approach was explored by simulating the effect of different magnitude optical property errors on the image formation process of a combined optical-PET system. Some comparisons were made with corresponding simulations using higher spatial resolution data that are typically attainable by CCD cameras. In addition, simulation results provided insights on some of the experimental conditions that could lead to poor localization of bioluminescent sources. They also provided a rough guide on how accurately tissue optical properties need to be known in order to achieve correct localization of point sources with increasing tissue depth under low background noise conditions.

Animals↗
PubMed1980

Regeneration of an abnormal ipsilateral visuotectal projection in Xenopus is delayed by the presence of optic fibres from the other eye.

Optic fibre regeneration was studied by [3H]proline autoradiography and by mapping electrophysiologically the direct visuotectal projections to the contralateral and ipsilateral tecta 12-16 weeks after sectioning the right optic nerve in Xenopus two to four weeks after metamorphosis. The experiments were carried out in three groups: (A) optic nerve section in newly metamorphosed animals with embryonic left-eye enucleation; (B) optic nerve section with simultaneous left-eye enucleation; and (C) optic nerve section with delayed left-eye enucleation 5-31 days prior to sacrifice. In all but three animals regenerated optic fibres were demonstrated morphologically both in the contralateral and ipsilateral tecta. The contralateral visuotectal projection was fully restored within the 12-16 weeks in all animals. In animals with embryonic enucleation or in those where the enucleation was carried out simultaneously with optic nerve section, a direct ipsilateral visuotectal projection was established at the same time as the restoration of the contralateral projection. In contrast, no direct ipsilateral visuotectal projection was detectable in the presence of optic fibres from the other eye in the doubly innervated tecta. However, 14-31 days after the removal of the incumbent optic fibres by left-eye enucleation a direct visuotectal projection from the right eye to the ipsilateral tectum was established, and its polarity corresponded to the normal contralateral retinotectal projection. The apparent disparity between morphological and electrophysiological findings in the doubly innervated tectum suggests that superimposed optic fibres are unable to form normal synaptic relations with tectal neurons during early regeneration, delaying the establishment of the induced direct ipsilateral visuotectal projection.

Action Potentials↗