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At least 1,315 records · Page 73Linked to original sources
PubMed1999

Expression of the Vax family homeobox genes suggests multiple roles in eye development.

BACKGROUND: Homeobox gene products are thought to regulate target genes involved in the regional specification of tissues and organs. Several genes play roles in eye development. RESULTS: We isolated two new mouse homeobox genes, Vax1 and Vax2, expressed in retina primordium. The two genes share the same gene organization, consisting of three exons with predicted amino acid sequences identical in the homeodomain but diversified in other regions. At 9. 5 days post coitum, both Vax genes were expressed in optic vesicles. At 11.5-14.5 dpc, Vax1 became restricted to the optic stalk, while Vax2 was expressed in the ventral half of the neural retina. Mapping of Vax2 between D6Mit3 and D6Mit8 on chromosome 6 indicated a possible linkage with Emx1. CONCLUSIONS: The expression patterns of Vax genes suggest separate and specific involvement in eye development. Vax1 may contribute to differentiation of the neuroretina, pigmented epithelium and optic stalk, while Vax2 could function in the establishment of the dorso-ventral axis of the retina and the visual system. The chromosomal location of Vax2 suggests that Vax2-Emx1 and Vax1-Emx2 arose by chromosome duplication of the same ancestral gene.

Amino Acid Sequence↗
PubMed2002

A novel catheter design for laser photocoagulation of the myocardium to ablate ventricular tachycardia.

Nd:YAG laser energy has been proposed as an alternative to radiofrequency energy for ablation of ventricular tachycardia (VT) associated with coronary artery disease (CAD) in an effort to increase lesion size and success rates. However, issues of catheter design to maintain flexibility and ensure adequate tissue contact have hindered development of laser catheters. We developed and tested a prototype 8 Fr. steerable catheter with a flexible and extendible tip (designed to ensure tissue contact and efficient ventricular mapping), which projects the laser beam through a side port containing a lens-tipped optical fiber that rests against the endocardial surface. The catheter has a channel for simultaneous saline irrigation to displace the interceding blood and discharge a laser beam between two electrodes for bipolar mapping and a thermocouple for temperature monitoring. The catheter was tested on bench top using the epicardial surface of freshly slaughtered bovine hearts and in vivo using six anaesthetized closed-chest sheep. In vitro experiments demonstrated that lesion size increased linearly with applied power up to 40 watts. When compared to radio frequency, laser energy penetrated more deeply into the myocardium. In the in vivo studies, using increasing powers of up to 40 watts for application times of 60 to 120 seconds created circular or elliptical lesions with surface dimensions up to 12 mm x 12 mm and depth of 9 mm (full LV wall thickness with a mean lesion diameter of 9.9 +/- 5.2 mm and depth 5.8 +/- 3.2 mm). Most lesions, 16 total in both right and left ventricular walls were transmural or near transmural in thickness. Lesions demonstrated coagulation necrosis with smooth well-demarcated borders. No animal suffered cardiac perforation, hypotension, hemopericardium, damage to cardiac valves, or cavitation effect from any of the ablations. Runs of VT were seen during energy application at the highest laser outputs in two animals. In conclusion, this catheter design provides effective endocardial delivery of laser energy and is capable of creating transmural or nearly transmural lesions in vivo and in vitro, thereby potentially increasing the efficiency of VT ablation in CAD patients.

Animals↗
PubMedDate not supplied

Optical single-channel recording: imaging Ca2+ flux through individual ion channels with high temporal and spatial resolution.

Developments in imaging technology now enable visualization of the functioning of individual ion channels in living cells: something previously possible only by the electrophysiological patch-clamp technique. We review techniques that track channel gating via changes in intracellular [Ca2+] resulting from openings of Ca(2+)-permeable channels. Spatial and temporal resolution are optimized by monitoring Ca2+ close to the channel mouth, and we describe the use of two imaging modalities: confocal laser scan microscopy (linescan CLSM) and total internal reflection fluorescence microscopy (TIRFM). Both currently achieve a kinetic resolution of <10 ms, provide a simultaneous and independent readout from many channels, and enable their locations to be mapped with submicrometer resolution. TIRFM provides 2-D images from a very thin (approximately 100 nm) optical section, but it is restricted to channels in the plasma membrane of cells adhering close to a cover glass. In contrast, CLSM can image channels in intracellular membranes but, to achieve good temporal resolution, has been utilized only in a linescan mode with limited spatial information. We anticipate that imaging techniques will develop as a useful adjunct to patch-clamping for single-channel studies, with capabilities including simultaneous readout from multiple channels, high-resolution mapping of channel location, and mobility that is inaccessible by electrophysiological means. Optical single-channel recording is applicable to diverse voltage- and ligand-gated Ca(2+)-permeable channels and has potential for high-throughput functional analysis.

Animals↗
PubMed2006

Structural model of the OPA1 GTPase domain may explain the molecular consequences of a novel mutation in a family with autosomal dominant optic atrophy.

Autosomal dominant optic atrophy (ADOA) is the most frequent hereditary optic neuropathy. Three loci have been reported for ADOA: a major locus, harboring all identified mutations to date, maps to 3q28 (OPA1), a second locus is linked to 18q12.2-q12.3 (OPA4) and a third locus on 22q12.1-q13.1 (OPA5) has been reported recently. We describe a six-generation Iranian family in which optic atrophy runs as an autosomal dominant trait with an age of onset at 14-15years. We performed linkage analysis with markers mapping to 3q28 and 18q12.2-q12.3 and found linkage to 3q28. Subsequent sequencing of OPA1 identified a novel heterozygous missense mutation (c.1313A>G) replacing aspartic acid by glycine (p.D438G) in the GTPase domain of OPA1. Interestingly, another missense mutation at the same position (c.1313A>T, D438V) has been reported before in two unrelated German families, indicating a possible mutation hot spot. Further evidence supporting the importance of D438 is its conservation from human to acoelomata. OPA1 is believed to be the human orthologue of yeast MGM1, a dynamin-related protein required for the integrity of mitochondrial DNA. Homology modeling of the OPA1 GTPase domain revealed extensive structural similarity to the Dictyostelium dynamin A GTPase domain and showed that D438 may interact with residues of the G1 and the G4 motifs, which are crucial in coordinating GTP. Based on this analysis, we propose a mechanism which explains the gradual decline of vision in ADOA patients with OPA1 mutations at position 438.

Adolescent↗
PubMed1982

Connections of the octopus optic lobe: an HRP study.

The major visual centers of the octopus central nervous system are the paired optic lobes. Bidirectional transport of horseradish peroxidase (HRP) was used to determine connections of the optic lobe. Cells afferent to the optic lobe were identified by retrograde HRP transport in the following lobes of the central ganglia: anterior basal, median basal, dorsal basal, interbasal, subvertical, precommissural, brachial, and magnocellular. Labeled cells were also observed within the contralateral optic lobe, various optic tract lobes bilaterally, and in photoreceptors of the ipsilateral retina. Additionally, individual fibers, in part originating from cells in the posterior subvertical lobe, were labeled within the central neuropil core of various vertical lobules. Differences in results between superficial and deep optic lobe medulla injections indicate that some afferent projections from central sources may terminate on cell populations at specific depths within the lobe. Efferent optic lobe fibers into the superior frontal and lateral basal lobes were labeled by anterograde transport. Other possible optic lobe efferent projections terminated in supraesophageal lobes and the magnocellular lobe. The many inputs to the optic lobe from higher motor and associative centers in the central ganglia emphasize that the medulla region of the optic lobe is an exceptionally complex integrative area.

Animals↗
PubMedDate not supplied

Topographic map reorganization in cat area 17 after early monocular retinal lesions.

Neither discrete peripheral retinal lesions nor the normal optic disk produces obvious holes in one's percept of the world because the visual brain appears to perceptually "fill in" these blind spots. Where in the visual brain or how this filling in occurs is not well understood. A prevailing hypothesis states that topographic map of visual cortex reorganizes after retinal lesions, which "sews up" the hole in the topographic map representing the deprived area of cortex (cortical scotoma) and may lead to perceptual filling in. Since the map reorganization does not typically occur unless retinotopically matched lesions are made in both eyes, we investigated the conditions in which monocular retinal lesions can induce comparable map reorganization. We found that following monocular retinal lesions, deprived neurons in cat area 17 can acquire new receptive fields if the lesion occurred relatively early in life (8 weeks of age) and the lesioned cats experienced a substantial period of recovery (>3 years). Quantitative determination of the monocular and binocular response properties of reactivated units indicated that responses to the lesioned eye for such neurons were remarkably robust, and that the receptive-field properties for the two eyes were generally similar. Moreover, excitatory or inhibitory binocular interactions were found in the majority of experimental units when the two eyes were activated together. These results are consistent with the hypothesis that map reorganization after monocular retinal lesions require experience-dependent plasticity and may be involved in the perceptual filling in of blind spots due to retinal lesions early in life.

Animals↗
PubMed2002

Sol-gel based optical carbon dioxide sensor employing dual luminophore referencing for application in food packaging technology.

An optical sensor for the measurement of carbon dioxide in Modified Atmosphere Packaging (MAP) applications has been developed. It is based on the fluorescent pH indicator 1-hydroxypyrene-3,6,8-trisulfonate (HPTS) immobilised in a hydrophobic organically modified silica (ormosil) matrix. Cetyltrimethylammonium hydroxide was used as an internal buffer system. Fluorescence is measured in the phase domain by means of the Dual Luminophore Referencing (DLR) sensing scheme which provides many of the advantages of lifetime-based fluorometric sensors and makes it compatible with established optical oxygen sensor technology. The long-term stability of the sensor membranes has been investigated. The sensor displays 13.5 degrees phase shift between 0 and 100% CO2 with a resolution of better than 1% and a limit of detection of 0.08%. Oxygen cross-sensitivity is minimised (0.6% quenching in air) by immobilising the reference luminophore in polymer nano-beads. Cross-sensitivity towards chloride and pH was found to be negligible. Temperature effects were studied, and a linear Arrhenius correlation between ln k and 1/T was found. The sensor is stable over a period of at least seven months and its output is in excellent agreement with a standard reference method for carbon dioxide analysis.

Carbon Dioxide↗
PubMed2003

Spreading and synchronization of intrinsic signals in visual cortex of macaque monkey evoked by a localized visual stimulus.

Spatio-temporal maps of the occipital cortex of macaque monkeys were analyzed using optical imaging of intrinsic signals. The images obtained during localized visual stimulation (IS) were compared with the images obtained on presentation of a blank screen (IB). We first investigated spontaneous variations of the intrinsic signals by analyzing the 100 IBs for each of the three cortical areas. Slow periodical activation was observed in alternation over the cortical areas. Cross-correlation analysis indicated that synchronization of spontaneous activation only took place within each cortical area, but not between them. When a small, drifting grating (2 degrees x 2 degrees ) was presented on the fovea, a dark spot appeared in the optical image at the cortical representation of this retinal location. It spread bilaterally along the border between V1 and V2, continuing as a number of parallel dark bands covering a large area of the lateral surface of V1. Cross-correlation analysis showed that during visual stimulation the intrinsic signals over all of the three cortical areas were synchronized, with in-phase activation of V1 and V2 and anti-phase activation of V4 and V1/V2. The significance of these extensive synergistic and antagonistic interactions between different cortical areas is discussed.

Animals↗
PubMed2003

[Accurate establishment of the retinotopic topography of area 17 in cats by intrinsic signal optical imaging].

The retinotopic topography of area 17 in cats was measured by optical imaging based on intrinsic signals. When stimulated with two neighboring gratings oriented orthogonally each other, which were positioned respectively in the upper and lower visual fields, one piece of cortex that had the retinal projection corresponding to the area around the border of the two stimulus gratings became blurred in the resultant function orientation map, because the neurons in this site received excitatory signals from both the horizontal and the vertical gratings via indirect ways. This functional map of the same cortex was compared with that elicited only by a horizontal or vertical grating stimulation in the whole visual field. Accordingly, the accurate position of the retinotopic eccentricity of the cortex in visual field can be demarcated by calculating the cross correlation coefficient of the two functional maps. Furthermore, compared with the electrophysiological measure of receptive fields of single cortical neurons, the retinotopic eccentricities revealed by optical imaging were identical. This experiment provides a fast and relatively accurate method to calculate the retinotopic eccentricities in a large cortical area of the visual cortex.

Animals↗
PubMed2002

Relationships of local inhibitory and excitatory circuits to orientation preference maps in ferret visual cortex.

The contribution and precise role of intracortical circuits in generating orientation tuned responses in visual cortical neurons is still controversial. To address this question, the relationship between excitatory and inhibitory synaptic connections and orientation maps in ferret striate cortex was investigated by combining in vivo optical imaging and in vitro scanning laser photostimulation. Excitatory and inhibitory inputs to pyramidal cells originated preferentially from regions with similar orientation preference. Prominent cross-orientation inhibition was not observed, arguing against cross-orientation models of orientation selectivity. The tuning of inhibitory inputs was significantly broader in both layer 2/3 and layer 5/6 pyramidal neurons compared to the tuning of excitatory inputs. Local excitatory inputs were more prominent in the 0-20 degrees tuning difference range between pre- and postsynaptic cells than inhibitory inputs, whereas inhibition dominated in the 20-40 degrees tuning difference range. These differences in tuning of excitatory and inhibitory inputs onto individual cells are consistent with the predictions of recurrent models of orientation selectivity.

Animals↗
PubMedDate not supplied

Monitoring and visualization techniques for MR-guided laser ablations in an open MR system.

Our purpose was to develop temperature-sensitive MR sequences and image-processing techniques to assess their potential of monitoring interstitial laser therapy (ILT) in brain tumors (n = 3) and liver tumors (n = 7). ILT lasted 2 to 26 minutes, whereas images from T1-weighted fast-spin-echo (FSE) or spoiled gradient-recalled (SPGR) sequences were acquired within 5 to 13 seconds. Pixel subtraction and visualization of T1-weighted images or optical flow computation was done within less than 110 msec. Alternating phase-mapping of real and imaginary components of SPGR sequences was performed within 220 msec. Pixel subtraction of T1-weighted images identified thermal changes in liver and brain tumors but could not evaluate the temperature values as chemical shift-based imaging, which was, however, more affected by susceptibility effects and motion. Optical flow computation displayed the predicted course of thermal changes and revealed that the rate of heat deposition can be anisotropic, which may be related to heterogeneous tumor structure and/or vascularization.

Brain Neoplasms↗
PubMed1993

The diencephalon and optic tectum of the longnose gar, Lepisosteus osseus (L.): cytoarchitectonics and distribution of acetylcholinesterase.

The cytoarchitecture of nuclei in the diencephalon and the distribution of acetylcholinesterase (AChE) in the diencephalon and optic tectum were analyzed in the longnose gar, Lepisosteus osseus, a non-teleost actinopterygian fish. Nuclei were identified in the preoptic area, thalamus, posterior tubercle, hypothalamus, synencephalon, and pretectum which are homologous to like-named nuclei in teleosts and other non-teleost actinopterygians. Of particular note, a nucleus in the rostral diencephalon, nucleus rostrolateralis, which has previously been identified only in the osteoglossomorph Pantodon, is present in the long-nose gar. The posterior pretectal nucleus, previously identified in teleosts and in the bowfin Amia, is also present in gars. The small size of the posterior pretectal nucleus in gars supports the hypothesis that this nucleus was small plesiomorphically. The distribution of AChE in the diencephalon and optic tectum corresponds in most respects to that found in teleosts. The superficial pretectal nuclei, including the posterior pretectal nucleus, are strongly positive for AChE. In contrast, most of the nuclei within the preglomerular complex are negative for AChE. Acetylcholinesterase is present in some of the fibers in the optic tracts and in most retinorecipient nuclei, as well as in some other nuclei and tracts.

Acetylcholinesterase↗
PubMed1986

The effects of prenatal and neonatal monocular enucleation on visual topography in the uncrossed retinal pathway to the rat superior colliculus.

The visual representation in the uncrossed retinal projection to the superior colliculus (SC) was examined electrophysiologically by recording multi-unit responses in paralysed, anaesthetised adult rats (both pigmented and albino), which had been monocularly enucleated either prenatally or soon after birth. This manipulation partially stabilises an exuberant neonatal projection from the remaining eye to the ipsilateral SC. Neuronal responses were also stronger and the multi-unit receptive fields larger than in intact animals. Many of the visual fields recorded on penetrations in caudal SC were located in the peripheral ipsilateral visual hemifield, corresponding to nasal retina. Such receptive fields are not seen in normal animals and were not found in animals enucleated on day 3 or later. The topographic representation of the dorso-ventral retinal axis, lateral to medial in the SC, was normal in all experimental animals. The representation of the naso-temporal retinal axis was abnormal and more variable. In all operated animals as the recording electrode was moved caudally away from the rostral pole of the SC, the corresponding receptive fields moved gradually from up to 40 degrees in the ipsilateral visual hemifield to about 40 degrees into the contralateral hemifield (a location corresponding to the peripheral edge of the temporal retina). This is the mapping polarity found in the normal uncrossed retinal projection. In the enucleated animals, the map was expanded and frequently displayed a clustering of fields arising from far temporal retina. In animals enucleated prenatally or on the day of birth, visual responses could be recorded in more caudal SC. The corresponding receptive fields now moved nasally on the retina, generating reversals in the map. The most caudal penetrations in these early enucleates frequently gave receptive fields located in retina nasal to the optic disc, up to 90 degrees into the ipsilateral visual hemifield. These results demonstrate that a temporal relationship exists between the order and mapping polarity of the visual field in SC and the time of enucleation. Prenatal enucleation produces reversals of the mapping polarity in caudal SC while neonatal enucleation produces an expanded map but one with a mapping polarity appropriate for an uncrossed projection.

Action Potentials↗
PubMed1985

Binocular depth perception in the cat following early corpus callosum section.

The role of the corpus callosum in the mediation of binocular depth perception was examined by measuring monocular and binocular depth discrimination thresholds in cats which had undergone section of the corpus callosum shortly after birth. Three kittens had the posterior callosum sectioned at the age of eleven days. A fourth kitten underwent a sham operation and one additional animal served initially as an unoperated control. Monocular and binocular depth thresholds were measured for all kittens when they were between three and five months old. Although there was some individual variability, none of the callosum-sectioned kittens showed any deficits of binocular depth perception relative to normal animals. The initially unoperated kitten had its callosum sectioned at five months and was retested following surgery. Its performance did not change from preoperated levels. Finally, the three neonatal callosum-sectioned kittens underwent section of the optic chiasm when they were six months old, causing a complete breakdown in binocular depth discrimination. The results are interpreted to indicate that although the corpus callosum may be a sufficient pathway for the maintenance of stereopsis in cat, it is not necessary.

Animals↗
PubMed1994

Normal activity-dependent refinement in a compressed retinotectal projection in goldfish.

When the optic nerve in a goldfish is crushed, regenerating fibers can reform a normal retinotopic projection. Two processes are thought to generate this retinotopic order. One is an activity-independent process, presumed to be some form of substrate-directed growth, which generates rough retinotopy as seen in the early formed projection. The other is an activity-dependent process that generates fine retinotopy during a protracted period of refinement. This projection also displays two other behaviors. One is retinotopic plasticity, in which optic fibers can compensate for retinal or tectal ablations by expanding or compressing into the available tectal space while preserving retinotopic order. These plasticities can dramatically alter the scale of the projection. The other behavior is the formation of fixed synaptic sites in tectum. Optic fibers make a characteristic number of synaptic connections in tectum, which is not changed by increasing the number of invading optic fibers. This has been interpreted to mean that fibers compete for limited synaptic sites. How the two processes that generate order, substrate-directed growth, and activity-dependent refinement might each be affected by the expression of retinotopic plasticity and altered synaptic competition is largely unknown. In particular, it is not known how fine retinotopic order (activity-dependent refinement) might be affected by altering the scale of the projection. Would optic fibers from neighboring ganglion cells converge into the same-sized area of tectum, or would they expand or compress in proportion to the altered scale of the overall map? To explore this issue, the posterior half of tectum of goldfish was removed, and the optic nerve was crushed, thereby forcing regenerating fibers to form a compressed retinotopic projection onto the anterior half of tectum. Under these conditions, optic fibers are also forced to compete for half the normal number of synaptic sites. The effect on retinotopy was monitored at various times during regeneration by making a small spot injection of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) into nasal retina corresponding to fibers that would normally terminate in the missing posterior half of tectum. To distinguish between activity-dependent and activity-independent processes, retinal impulse activity was blocked in some animals by repeated intraocular injections of tetrodotoxin. The initial projection was found to be unaffected by impulse activity. Regardless of activity, nasal fibers failed initially to grow to the most posterior available regions, but instead were dispersed across much of the "incorrect" anterior half of tectum at 30 days.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1996

Positional determination of the naso-temporal retinal axis coincides with asymmetric expression of proteins along the anterior-posterior axis of the eye primordium.

We used two different methodologies to examine at what stage development retinal positional specificity is established and which molecules are responsible. The first goal was achieved by removing parts of the presumptive temporal primary optic vesicle at stage 11 (40 to 45 hr of incubation) and fate mapping of tissue with presumptive nasal properties that shifted into the wound during the events of wound-healing. Participation of the shifted tissue in the healing resulted in assembly of a temporal retina with mosaic-like projection properties, as examined by retrograde double staining of the retinal ganglion cells from the optic tectum. In addition to cells with normal temporal-rostral projections, clusters of ganglion cells with nasal-like projection identities appeared labelled within the temporal hemiretina. The number of clusters increased with the amount of resected tissue, and by almost complete ablation of the presumptive temporal anlage, a temporal hemiretina with predominantly nasal retinotectal specificity was created. These neuroanatomical results suggested that neuroepithelial cells had fixed nasal and temporal positional specificities at stage 11. To examine differences in the cells derived of either half of the eye cup, we performed biochemical one- and two-dimensional gel electrophoresis of the hemianlagen at stage 11. In addition, incorporation of 35S-methionin into newly synthesized peptides was investigated. Both techniques revealed the exclusive expression of one major and three less-abundant proteins within the presumptive nasal anlage. The most abundant of these proteins has a molecular weight of about 40 kDa and is clearly distinguishable both in gel electrophoresis and autoradiography. The asymmetric protein patterns had disappeared when the retina was analysed with the same methods at the more advanced embryonic days E4 and E6. The asymmetry in the expression of proteins in the retinal primordium may be the biochemical correlate of an early positional specification of the retinal neuroepithelium. The difference in the protein expression may explain that mixing the positionally specified cells of either origins results in projection mosaics.

Animals↗
PubMed2001

Magnetization transfer and diffusion tensor MR imaging of the optic radiations and calcarine cortex from patients with Leber's hereditary optic neuropathy.

Optic nerve abnormalities are easily detectable in patients with Leber's hereditary optic neuropathy (LHON), using magnetic resonance imaging (MRI). However, the presence of structural changes in the optic radiations and calcarine cortex of these patients is still an unresolved issue. In this study, we obtained magnetization transfer (MT) and diffusion tensor (DT) MRI to investigate the integrity of these structures in patients with LHON. Dual echo, MT- and DT-MRI scans of the brain were obtained from 10 men with LHON and 10 healthy sex- and age-matched controls. After image co-registration, we obtained MT ratio (MTR), average diffusivity (D) and fractional anisotropy (FA) maps. MTR, D and FA values for the white matter of the optic radiations and MTR and D values for the calcarine cortex were obtained using a region of interest (ROI) analysis. No macroscopic abnormalities were detected in any of the scans from LHON patients and controls. No statistically significant differences of MTR, D or FA values were found for any of the regions studied in LHON patients and healthy controls. Our results suggest that, in patients with LHON, the optic radiations and the calcarine cortex are spared from structural damage, both at a macroscopic and a microscopic level.

Adult↗
PubMed2003

Projected index computed tomography.

Projected index computed tomography (PICT) is a new imaging technique that provides a computed reconstruction of the index of refraction of a sample. PICT makes use of data from standard optical coherence tomography images taken from several view angles to determine a mapping of the refractive indices of the sample. A rectilinear propagation model is assumed, so the data are understood to be related to the line integral of the refractive index in the beam paths. These data thus provide a set of angular projections of the sample. The spatial distribution of the index of the object may then be reconstructed by use of standard filtered backprojection techniques. The resultant PICT images are free of the spatial distortion that is inherent in standard optical cross-sectional images and correspond well to the manufactured dimensions of specific samples.

Image Processing, Computer-Assisted↗