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  • 1
    ISSN: 1600-0501
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The overall accuracy of a novel surgical computer-aided navigation system for placement of endosseous implants was evaluated. Five dry cadaver mandibles were scanned using high resolution computed tomography (HRCT). The position of four interforaminal dental implants was planned on the computer screen and transferred to the cadaver mandibles using VISIT, a surgical navigation software developed at the Vienna General Hospital. The specimens were HRCT-scanned again to compare the position of the implants with the preoperative plan on reformatted slices after matching of the pre- and postoperative data sets using the mutual information technique. The overall accuracy was 0.96±0.72 mm (range 0.0–3.5 mm). No perforation of the mandibular cortex or damage to the mandibular canal occurred. We conclude that computer-aided implant surgery can reach a level of accuracy where further clinical developments are feasible.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1600-0501
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: We developed a head-mounted display (HMD) with integrated computer-generated stereoscopic projection of target structures and integrated it into visit, a specific oral implant planning and navigation software. The HMD is equipped with two miniature computer monitors that project computer-generated graphics stereoscopically into the optical path. Its position is tracked by the navigation system's optical tracker and target structures are displayed in their true position over the operation site. In order to test this system's accuracy and spatial perception of the viewer, five interforaminal implants in three dry human mandibles were planned with visit and executed using the stereoscopic projection through the HMD. The deviation between planned and achieved position of the implants was measured on corresponding computed tomography (CT) scan images recorded post-operatively. The deviation between planned and achieved implant position at the jaw crest was 0.57 ± 0.49 mm measured from the lingual, and 0.58 ± 0.4 mm measured from the buccal cortex. At the tip of the implants the deviation was 0.77 ± 0.63 mm at the lingual and 0.79 ± 0.71 mm at the buccal cortex. The mean angular deviation between planned and executed implant position was 3.55 ± 2.07 degrees. The present in vitro experiment indicates that the concept of preoperative planning and transfer to the operative field by an HMD allows us to achieve an average precision within 1 mm (range up to 3 mm) of the implant position and within 3° deviation for the implant inclination (range up to 10°). Control during the drilling procedure is significantly improved by stereoscopic vision through the HMD resulting in a more accurate inclination of the implants.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 5 (1989), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Notes: This paper describes LEW (learning by watching), an implementation of a novel learning technique, and discusses its application to the learning of plans. LEW is a domain-independent learning system with user-limited autonomy that is designed to provide robust performance in realistic knowledge acquisition tasks in a variety of domains. It partly automates the knowledge acquisition process for different knowledge types, such as concepts, rules, and plans. The inputs to the system, which we call cues, consist of an environmental component and of pairs containing a problem and its solution. Unlike traditional forms of “learning from examples”, in which the system uses the teacher's answer to improve the result of a prior generalization of an example, LEW treats the problem-solution or question-answer instances, i. e., the cues themselves, as the basic units for generalization.
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  • 4
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The present study compares the effects of chronic administration of basic fibroblast growth factor (bFGF) and nerve growth factor (NGF) on various hippocampal cholinergic parameters in rats with partial unilateral fimbrial transections. Lesions resulted in marked reductions of several presynaptic cholinergic parameters: choline acetyltransferase (ChAT) activity (by 50%), [3H]-acetylcholine ([3H]ACh) synthesis (by 59%), basal and ve-ratridine (1 μM)-evoked [3H]ACh release (by 44 and 57%, respectively), and [3H]vesamicol binding site densities (by 35%). In addition, [3H]AF-DX 116/muscarinic M2 binding site densities were also modestly decreased (by 23%). In contrast, [3H]pirenzepine/muscarinic M1 and [3H]AF-DX 384/muscarinic M2/M4 binding site densities were not altered by the lesions, nor were they affected by any of the treatments. Intracerebroventricular administration of bFGF (10 ng, every other day, for 21 days) partially prevented the lesion-induced deficit in hippocampal ChAT activity, an effect that was not markedly different from that measured in the NGF-treated (1 μg intracerebroventricularly, every other day, for 21 days) rats. In rats treated with a combination of bFGF and NGF, ChAT activity was not different from that in rats treated with the individual factors alone. In contrast, the lesion-induced deficits in the other cholinergic parameters were not attenuated by bFGF treatment, although they were at least partially prevented by NGF administration. To determine whether higher concentrations of bFGF are necessary to affect cholinergic parameters other than hippocampal ChAT activity, rats were treated with 1 μg (every other day, 21 days) of the growth factor. In this group of rats, detrimental effects of bFGF, manifested by an increased death rate (46%), and marked reductions in body weight of the survivors, were observed. In addition, this concentration of bFGF appeared to exacerbate the lesion-induced reduction in [3H]ACh synthesis by hippocampal slices; [3H]ACh synthesis in lesioned hippocampi represented 36 and 52% of that in contralateral unlesioned hippocampi for the bFGF-treated and control groups, respectively. In conclusion, although bFGF administration attenuates the deficit in hippocampal ChAT activity induced by partial fimbrial transections, this does not appear to translate into enhanced functional capacity of the cholinergic terminals. This is clearly in contrast to NGF, which enhances not only hippocampal ChAT activity, but also other parameters indicative of increased function in the cholinergic terminals.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 57 (1991), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: K-252b is a kinase inhibitor structurally related to K-252a, which is known to abolish selectively the effects of nerve growth factor (NGF) on PC12 cells and PNS neurons. We tested whether K-252b, K-252a, and staurosporine, another related compound, are effective and selective inhibitors of NGF actions on CNS neurons. All three compounds, at appropriate concentrations, completely and selectively prevented the NGF-mediated activity increase of the cholinergic marker enzyme choline acetyltransferase in cultures of rat basal forebrain cells. The stimulatory effects of basic fibroblast growth factor and insulin on choline acetyltransferase in these cultures and on dopamine uptake in cultures of dissociated ventral mesencephalon were not affected. No signs of toxicity were observed in cultures treated with K-252b. In contrast, K-252a and staurosporine, at concentrations required to block the NGF actions on cholinergic cells, were cytotoxic and produced cell loss. In addition, K-252a, at higher concentrations and in the absence of growth factors, increased cell numbers. Our study suggests that K-252b is a selective and nontoxic inhibitor of NGF actions in the brain and may become a useful tool to study these actions in vivo.
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  • 6
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The distribution of myo-inositol, a substance that has been implicated in synaptic transmission, has been mapped within sections of the cat cochlear nucleus as well as some nearby regions. Highest values in the cochlear nucleus were found in regions of granule cells along the periphery of the anteroventral subdivision of the nucleus. Highest values overall were found in the molecular layer of the cerebellar flocculus. A fairly good correlation was found between myo-inositol levels and activities of the enzymes of acetyl-choline metabolism in the cat cochlear nucleus, supporting the possibility that myo-inositol may be involved in cholinergic synaptic transmission. No positive correlation was found between myo-inositol levels and the levels of glutamate, aspartate, glycine, or γ-aminobutyric acid (GABA). The most striking gradient of myo-inositol levels within a region was found in the auditory nerve, where different myo-inositol levels might be related to nerve fibers innervating different parts of the cochlea. The distribution of scyllo-inositol, a stereoisomer of myo-inositol, was also examined, and found to parallel closely the distribution of myo-inositol, with levels 4–5% as high.
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  • 7
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Cultures of dissociated striatal neurons from fetal rats were prepared, and were grown in the presence of neurotrophin-4/5 (NT-4/5) as well as the other known neurotrophins, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3). We found that acute administration of NT-4/5 to 7-day-old cultures stimulates the hydrolysis of phosphatidylinositol, an event involved in neurotrophin signal transduction. Growth of striatal cultures in the presence of NT-4/5 resulted in increased cell survival, as indicated by elevations in cell number, protein content, and a measure of mitochondrial enzyme activity (MTT assay). NT-4/5 increased GABA uptake and staining intensity in these cultures, as indicated by GABA immunocytochemistry, indicating a trophic action on GABAergic neurons, the predominant neuron type in the striatum. To further identify responsive cell populations we analysed for calretinin, a calcium-binding protein known to colocalize with GABA in a number of neuronal cells. In cultures prepared from rats of embryonic day 15, NT-4/5 strongly increased the number of calretinin-positive cells as well as calretinin levels, as determined by Western blot analysis. When the cultures were prepared from embryonic day 18 rats, NT-4/5 very strongly increased the morphological differentiation of calretinin-positive cells, whereas the increase in cell number was less prominent. All effects produced by NT-4/5 were mimicked by BDNF with similar potency. NT-3 was less effective than NT-4/5 and BDNF, and its effects were limited to cultures prepared from embryonic day 15 rats, suggesting a role in the regulation of cell survival at early developmental stages. NGF did not affect any of the measured parameters. Our findings identify NT-4/5 as potent neurotrophic factor for striatal neurons, able to promote their survival and differentiation.
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  • 8
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: This study examined how possible nerve growth factor (NGF)-induced behaviour changes after septal damage might be modulated by the lesion extent, the dose of NGF administered and the delay between surgery and the onset of testing. In a first experiment, young rats which received electrolytic septal lesions of high or low intensity (inducing respectively large and mild lesions) were treated with 10 or 30 μg NGF administered intrahippocampally in a single injection. They were tested 4 months postoperatively for open field ambulation, spontaneous alternation and radial maze performance. It was observed that irrespective of the severity of the lesions rats were impaired in the spontaneous alternation and radial maze tests; however, no obvious changes appeared in the open field test. While an NGF injection did not affect behavioural performances in rats with large lesions, it was capable of ameliorating behavioural deficits in the spontaneous alternation and radial maze tests of rats with mild lesions in both NGF dosage groups. It was also seen that lesions produced a general decrease in hippocampal choline acetyltransferase (ChAT) activity, which was not significantly affected by an NGF administration. There was no significant correlation between ChAT activity and behavioural performance of NGF-treated rats. In a second experiment, young rats received mild septal lesions and were treated with 10 μg NGF. These rats were tested 2 weeks postoperatively for radial maze performance. NGF rats exhibited similar behaviour to controls with regard to all of the variables measured. The present results suggest that a single NGF administration spares some abilities to use spatial information efficiently providing lesions are partial.
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  • 9
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. Endothelium-derived relaxing factor (EDRF) has been shown to influence arterial tone, but controversial results have been obtained studying veins. The present study was performed to determine the importance of EDRF for the inferior vena cava in the rabbit and whether blockade of the synthesis of EDRF with NG-nitro-l-arginine methyl ester may influence the reactivity of the inferior vena cava to noradrenaline.2. The inferior vena cava was excised in six New Zealand white rabbits and 12 rings were prepared for organ bath studies. Concentration-response curves were constructed for acetylcholine (10−9-10−4mol/L) and noradrenaline (10−9-10−4mol/L) before and following the administration of NG-nitro-l-arginine methyl ester.3. All rings showed concentration-dependent relaxation to acetylcholine (mean maximum: 57 ± 9%) following precon-traction with noradrenaline (EC50: 10−6mol/L). Following NG-nitro-l-arginine methyl ester, this dilation was significantly reduced to a mean maximum relaxation of 13 ± 6% (P〈0.01).4. Contraction of the inferior vena cava to increasing doses of noradrenaline reached a maximum of 5.8 ± 2.8 g before NG-nitro-l-arginine methyl ester (basal tension 1.0 ± 0.5 g). NG-nitro-l-arginine methyl ester did not affect basal tension, but the constrictor response to noradrenaline was enhanced significantly to a maximum of 9.1 ± 3.8 g (P〈0.01).5. Although it cannot be ascertained definitively from the present results, it is suggested that EDRF is mediating vasodilation of the inferior vena cava and that this vasoactive agent may also contributes significantly to the modulation of the reactivity to catecholamines.
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  • 10
    ISSN: 1369-1600
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Ethyl glucuronide (EtG) is a promising new biological state marker of recent alcohol consumption that detects alcohol use reliably over a definite time period. Other currently available markers lack acceptable sensitivity and specificity. Our aim is to elucidate under naturalistic conditions the time course of EtG excretion in urine following alcohol consumption and to show how this can be utilized for monitoring and prognosis in patients. There are no other existing data on this issue to date. One hundred and thirty-eight urine samples from 28 male alcohol withdrawal patients were drawn every 3-24 hours for up to 94 hours after hospitalization. Breath ethanol concentration (mean) at hospitalization was 900 mg/L. Patient age in years was 40.3 (mean). Determination of urine EtG was performed by gas chromatography/mass spectrometry (GC/MS) with deuterium-labelled EtG as an internal standard. The strongest correlations (p〈0.01) were found between EtG determinations in the different patient when breath ethanol concentrations (BEC) were 0 and 48 hours after BEC=0 (r=0.747), EtG 24 and 48 hours after BEC=0 (r=0.872), and in the time frame of detection (hours) of EtG and EtG 48 hours after BEC=0 (r=0.762). No significant correlation was found (Mann-Whitney test) between EtG concentrations in urine at different time points between the groups of patients with (a) 1 or less-2, (b) 3-4 or more previous hospitalizations, (c) a history of seizures (yes/no) or (d) an age above or below the median (40.5). EtG excretion in urine is not random, but seems rather to follow a kinetic profile. Furthermore our preliminary data indicate, that there is no significant difference for EtG concentration in urine when correlated to group variables such as age, seizures and hospitalizations.
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