965 resultados para Segment


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Pyramidal neurons are covered with dendritic spines, the main postsynaptic targets of excitatory (asymmetrical) synapses. However, the proximal portion of both the apical and basal dendrites is devoid of spines, suggesting a lack of excitatory inputs to this region. In the present study we used electron microscopy to analyse the proximal region of the basal dendrites of supra- and infragranular pyramidal cells to determine if this is the case. The proximal region of 80 basal dendrites sampled from the rat hindlimb representation in the primary somatosensory cortex was studied by electron microscopy A total of 317 synapses were found within this region of the dendrites, all of which were of the symmetrical type. These results suggest that glutamate receptors, although present in the cytoplasm, are not involved in synaptic junctions in the proximal portion of the dendrites. These data further support the idea that inhibitory terminals exclusively innervate the proximal region of basal dendrites.

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Previous investigations employing electropalatography (EPG) have identified articulatory timing deficits in individuals with acquired dysarthria. However, this technology is yet to be applied to the articulatory timing disturbance present in Parkinson's disease (PD). As a result, the current investigation aimed to use EPG to comprehensively examine the temporal aspects of articulation in a group of nine individuals with PD at sentence, word and segment level. This investigation followed on from a prior study (McAuliffe, Ward and Murdoch) and similarly, aimed to compare the results of the participants with PD to a group of aged (n=7) and young controls (n=8) to determine if ageing contributed to any articulatory timing deficits observed. Participants were required to read aloud the phrase I saw a ___ today'' with the EPG palate in-situ. Target words included the consonants /1/, /s/ and /t/ in initial position in both the /i/ and /a/ vowel environments. Perceptual investigation of speech rate was conducted in addition to objective measurement of sentence, word and segment duration. Segment durations included the total segment length and duration of the approach, closure/constriction and release phases of EPG consonant production. Results of the present study revealed impaired speech rate, perceptually, in the group with PD. However, this was not confirmed objectively. Electropalatographic investigation of segment durations indicated that, in general, the group with PD demonstrated segment durations consistent with the control groups. Only one significant difference was noted, with the group with PD exhibiting significantly increased duration of the release phase for /1a/ when compared to both the control groups. It is, therefore, possible that EPG failed to detect lingual movement impairment as it does not measure the complete tongue movement towards and away from the hard palate. Furthermore, the contribution of individual variation to the present findings should not be overlooked.

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Two organically modified layered silicates (with small and large diameters) were incorporated into three segmented polyurethanes with various degrees of microphase separation. Microphase separation increased with the molecular weight of the poly(hexamethylene oxide) soft segment. The molecular weight of the soft segment did not influence the amount of polyurethane intercalating the interlayer spacing. Small-angle neutron scattering and differential scanning calorimetry data indicated that the layered silicates did not affect the microphase morphology of any host polymer, regardless of the particle diameter. The stiffness enhancement on filler addition increased as the microphase separation of the polyurethane decreased, presumably because a greater number of urethane linkages were available to interact with the filler. For comparison, the small nanofiller was introduced into a polyurethane with a poly(tetramethylene oxide) soft segment, and a significant increase in the tensile strength and a sharper upturn in the stress-strain curve resulted. No such improvement occurred in the host polymers with poly(hexamethylene oxide) soft segments. It is proposed that the nanocomposite containing the more hydrophilic and mobile poly(tetramethylene oxide) soft segment is capable of greater secondary bonding between the polyurethane chains and the organosilicate surface, resulting in improved stress transfer to the filler and reduced molecular slippage. (c) 2006 Wiley Periodicals, Inc.

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PURPOSE OF REVIEW: Imaging of the crystalline lens and intraocular lens is becoming increasingly more important to optimize the refractive outcome of cataract surgery, to detect and manage complications and to ascertain advanced intraocular lens performance. This review examines recent advances in anterior segment imaging. RECENT FINDINGS: The main techniques used for imaging the anterior segment are slit-lamp biomicroscopy, ultrasound biomicroscopy, scheimpflug imaging, phakometry, optical coherence tomography and magnetic resonance imaging. They have principally been applied to the assessment of intraocular lens centration, tilt, position relative to the iris and movement with ciliary body contraction. SUMMARY: Despite the advances in anterior chamber imaging technology, there is still the need for a clinical, high-resolution, true anatomical, noninvasive technique to image behind the peripheral iris. © 2007 Lippincott Williams & Wilkins, Inc.

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We assess the accuracy of the Visante anterior segment optical coherence tomographer (AS-OCT) and present improved formulas for measurement of surface curvature and axial separation. Measurements are made in physical model eyes. Accuracy is compared for measurements of corneal thickness (d1) and anterior chamber depth (d2) using-built-in AS-OCT software versus the improved scheme. The improved scheme enables measurements of lens thickness (d 3) and surface curvature, in the form of conic sections specified by vertex radii and conic constants. These parameters are converted to surface coordinates for error analysis. The built-in AS-OCT software typically overestimates (mean±standard deviation(SD)]d1 by +62±4 μm and d2 by +4±88μm. The improved scheme reduces d1 (-0.4±4 μm) and d2 (0±49 μm) errors while also reducing d3 errors from +218±90 (uncorrected) to +14±123 μm (corrected). Surface x coordinate errors gradually increase toward the periphery. Considering the central 6-mm zone of each surface, the x coordinate errors for anterior and posterior corneal surfaces reached +3±10 and 0±23 μm, respectively, with the improved scheme. Those of the anterior and posterior lens surfaces reached +2±22 and +11±71 μm, respectively. Our improved scheme reduced AS-OCT errors and could, therefore, enhance pre- and postoperative assessments of keratorefractive or cataract surgery, including measurement of accommodating intraocular lenses. © 2007 Society of Photo-Optical Instrumentation Engineers.

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The thesis investigates the relationship between the biomechanical properties of the anterior human sclera and cornea in vivo using Schiotz tonometry (ST), rebound tonometry (RBT, iCare) and the Ocular Response Analyser (ORA, Reichert). Significant differences in properties were found to occur between scleral quadrants. Structural correlates for the differences were examined using Partial Coherent Interferometry (IOLMaster, Zeiss), Optical Coherent tomography (Visante OCT), rotating Scheimpflug photography (Pentacam, Oculus) and 3-D Magnetic Resonance Imaging (MRI). Subject groups were employed that allowed investigation of variation pertaining to ethnicity and refractive error. One hundred thirty-five young adult subjects were drawn from three ethnic groups: British-White (BW), British-South-Asian (BSA) and Hong-Kong-Chinese (HKC) comprising non-myopes and myopes. Principal observations: ST demonstrated significant regional variation in scleral resistance a) with lowest levels at quadrant superior-temporal and highest at inferior-nasal; b) with distance from the limbus, anterior locations showing greater resistance. Variations in resistance using RBT were similar to those found with ST; however the predominantly myopic HKC group had a greater overall mean resistance when compared to the BW-BSA group. OCT-derived scleral thickness measurements indicated the sclera to be thinner superiorly than inferiorly. Thickness varied with distance from the corneolimbal junction, with a decline from 1 to 2 mm followed by a successive increase from 3 to 7 mm. ORA data varied with ethnicity and refractive status; whilst axial length (AL) was associated with corneal biometrics for BW-BSA individuals it was associated with IOP in the HKC individuals. Complex interrelationships were found between ORA Additional-Waveform-Parameters and biometric data provided by the Pentacam. OCT indicated ciliary muscle thickness to be greater in myopia and more directly linked to posterior ocular volume (from MRI) than AL. Temporal surface areas (SAs, from MRI) were significantly smaller than nasal SAs in myopic eyes; globe bulbosity (from MRI) was constant across quadrants.

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The tear film, cornea and lens dictate the refractive power of the eye and the retinal image quality is principally defined by diffraction, whole eye wavefront error, scatter, and chromatic aberration. Diffraction and wave aberration are fundamentally pupil diameter dependent; however scatter can be induced by refractive surgery and in the normal ageing eye becomes an increasingly important factor defining retinal image quality. The component of visual quality most affected by the tear film, refractive surgery and multifocal contact and intraocular lenses is the wave aberration of the eye. This body of work demonstrates the effects of each of these anomalies on the visual quality of the eye. When assessing normal or borderline self-diagnosed dry eye subjects using aberrometry, combining lubricating eye drops and spray does not offer any benefit over individual products. However, subjects perceive a difference in comfort for all interventions after one hour. Total higher order aberrations increase after laser assisted sub-epithelial keratectomy performed using a solid-state laser on myopes, but this causes no significant decrease in contrast sensitivity or increase in glare disability. Mean sensitivity and reliability indices for perimetry were comparable to pre-surgery results. Multifocal contact lenses and intraocular lenses are designed to maximise vision when the patient is binocular, so any evaluation of the eyes individually is confounded by reduced individual visual acuity and visual quality. Different designs of aspheric multifocal contact lenses do not provide the same level of visual quality. Multifocal contact lenses adversely affect mean deviation values for perimetry and this should be considered when screening individuals with multifocal contact or intraocular lenses. Photographic image quality obtained through a multifocal contact or intraocular lens appears to be unchanged. Future work should evaluate the effect of these anomalies in combination; with the aim of providing the best visual quality possible and supplying normative data for screening purposes.

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DUE TO COPYRIGHT RESTRICTIONS ONLY AVAILABLE FOR CONSULTATION AT ASTON UNIVERSITY LIBRARY AND INFORMATION SERVICES WITH PRIOR ARRANGEMENT

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Purpose: To determine whether curve-fitting analysis of the ranked segment distributions of topographic optic nerve head (ONH) parameters, derived using the Heidelberg Retina Tomograph (HRT), provide a more effective statistical descriptor to differentiate the normal from the glaucomatous ONH. Methods: The sample comprised of 22 normal control subjects (mean age 66.9 years; S.D. 7.8) and 22 glaucoma patients (mean age 72.1 years; S.D. 6.9) confirmed by reproducible visual field defects on the Humphrey Field Analyser. Three 10°-images of the ONH were obtained using the HRT. The mean topography image was determined and the HRT software was used to calculate the rim volume, rim area to disc area ratio, normalised rim area to disc area ratio and retinal nerve fibre cross-sectional area for each patient at 10°-sectoral intervals. The values were ranked in descending order, and each ranked-segment curve of ordered values was fitted using the least squares method. Results: There was no difference in disc area between the groups. The group mean cup-disc area ratio was significantly lower in the normal group (0.204 ± 0.16) compared with the glaucoma group (0.533 ± 0.083) (p < 0.001). The visual field indices, mean deviation and corrected pattern S.D., were significantly greater (p < 0.001) in the glaucoma group (-9.09 dB ± 3.3 and 7.91 ± 3.4, respectively) compared with the normal group (-0.15 dB ± 0.9 and 0.95 dB ± 0.8, respectively). Univariate linear regression provided the best overall fit to the ranked segment data. The equation parameters of the regression line manually applied to the normalised rim area-disc area and the rim area-disc area ratio data, correctly classified 100% of normal subjects and glaucoma patients. In this study sample, the regression analysis of ranked segment parameters method was more effective than conventional ranked segment analysis, in which glaucoma patients were misclassified in approximately 50% of cases. Further investigation in larger samples will enable the calculation of confidence intervals for normality. These reference standards will then need to be investigated for an independent sample to fully validate the technique. Conclusions: Using a curve-fitting approach to fit ranked segment curves retains information relating to the topographic nature of neural loss. Such methodology appears to overcome some of the deficiencies of conventional ranked segment analysis, and subject to validation in larger scale studies, may potentially be of clinical utility for detecting and monitoring glaucomatous damage. © 2007 The College of Optometrists.

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The transmembrane (TM) domains in P-glycoprotein (P-gp) contain the drug binding sites and undergo conformational changes driven by nucleotide catalysis to effect translocation. However, our understanding of exactly which regions are involved in such events remains unclear. A site-directed labelling approach was used to attach thiol-reactive probes to cysteines introduced into transmembrane segment 6 (TM6) in order to perturb function and infer involvement of specific residues in drug binding and/or interdomain communication. Covalent attachment of coumarin-maleimide at residue 339C within TM6 resulted in impaired ATP hydrolysis by P-gp. The nature of the effect was to reduce the characteristic modulation of basal activity caused by transported substrates, modulators and the potent inhibitor XR9576. Photoaffinity labelling of P-gp with [(3)H]-azidopine indicated that residue 339C does not alter drug binding per se. However, covalent modification of this residue appears to prevent conformational changes that lead to drug stimulation of ATP hydrolysis.