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71.
The capacity for short-term adaptation is a well-established property of the horizontal (H) and vertical (V) components of saccades. It allows these directional components, which clearly serve the goal of foveation, to maintain their precision even under changing circumstances. Torsional (T) saccade components, on the other hand, which deal with the orientation of the target on the fovea, have hardly been investigated in adaptation experiments. They appear to be severely restricted by Listing's law during fixations and saccades. The main purpose of Listing's law is far from obvious but could be visual or oculomotor. Better knowledge of the adaptive capacity of the saccadic system in the torsional direction could throw new light on the functional significance of this interesting neural strategy. To study short-term plasticity in the torsional components of saccades, binocular 3D-eye positions were measured, using magnetic search foils. Five normal human subjects were instructed to make uni-directional refixation saccades, while they viewed a large visual scene. To induce a change in the torsional component, the complete stimulus was rapidly rotated during these saccades. We thoroughly investigated the torsional responses of the saccadic system, to see if any short-term adaptive response in torsional direction was induced, in which case the notion of a visual purpose for Listing's law would be strengthened. In none of our experiments, however, did we find any clear adaptive response in torsional direction. To further investigate the reliability of this result and to ascertain that our experimental conditions allowed classical gain adaptation, we also did experiments designed to achieve a combination of torsional adaptation and classic gain shortening in one of the directional components. While gain adaptation was very obvious, none of the experiments provided evidence for a short-term effect in torsion. We conclude that our experiments do not support a purely visual basis for Listing's law. 相似文献
72.
Martin Ungerer Michael Böhm Robert H. G. Schwinger Erland Erdmann 《Naunyn-Schmiedeberg's archives of pharmacology》1990,341(6):577-585
Summary The effects of the new inotropic agents saterinone, sulmazole, UD-CG 212.C1 and milrinone at A1 adenosine receptors and m-cholinoceptors were evaluated in human myocardium from patients with heart failure. At A1 adenosine receptors, all compounds inhibited 3H-DPCPX-binding to ventricular membrane preparations at micromolar concentrations. As judged from the Ki-values, the rank order of potency was saterinone > sulmazole > UD-CG 212.C1 > milrinone. The new inotropic agents also displaced the binding of 3H-QNB at m-cholinoceptors. Except for saterinone, the concentration ranges of mean Ki-values were considerably higher at m-cholinoceptors than at A1 adenosine receptors. The rank order of potency was saterinone > sulmazole > UD-CG 212.Cl > milrinone. Competition of the A1 adenosine receptor agonist R-PIA to 3H-DPCPX-binding showed a biphasic curve with a shallow slope (Hill coefficient nH = 0.63) and revealed two affinity states of the A1 adenosine receptor. In the presence of guanine nucleotides [Gpp(NH)p], the competition curve showed one low affinity class of binding sites and was shifted to the right. In contrast, the competition curves of the new inotropic agents were characterized by a monophasic, steeper slope (mean Hill coefficient nH = 0.98). Guanine nucleotides had no effect. Similar results were obtained with saterinone and carbachol at m-cholinoceptors. Competition with carbachol revealed three affinity states of the m-cholinoceptor, the superhigh affinity binding was reversed by Gpp(NH)p. Competition with saterinone revealed one class of binding sites which was not influenced by Gpp(NH)p. Accordingly, in isolated, electrically driven human atrial trabeculae, the negative inotropic effect of adenosine was antagonized concentration-dependently by saterinone, sulmazole and UD-CG 212.Cl. Similarly the negative inotropic effect of carbachol was antagonized concentration-dependently by saterinone. It is concluded that the new inotropic agents bind to A1 adenosine receptors and that their interaction is of antagonist nature. This mechanism might contribute to their capacity to enhance force of contraction by stimulation of cAMP-formation in addition to phosphodiesterase inhibition. The effects of saterinone may be partially due to antagonism at m-cholinoceptors. This is presumably not the case with the other inotropic agents studied given their low affinity for this receptor.Send offprint requests to M. Böhm at the above addressSupported by the Deutsche Forschungsgemeinschaft 相似文献
73.
M. K. Watson L. S. Jakobson 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1997,117(2):273-280
In the present study, a kinematic analysis was made of unconstrained, natural prehension movements directed toward an object
approaching the observer on a conveyor belt at one of three constant velocities, from one of three different directions (head-on
or along the fronto-parallel plane coming either from the subject′s left or right). Subjects were required to grasp the object
when it reached a target located 20 cm directly in front of the hand′s start position. The kinematic analysis revealed that
both the transport and grasp components of the movement changed in response to the experimental manipulations, but did so
in a manner that guaranteed that, for objects approaching from a given direction, hand closure would begin at a constant time
prior to object contact (regardless of the object’s approach speed). The kinematic analysis also revealed, however, that the
onset of hand closure began earlier with objects approaching from the right than from other directions – an effect which would
not be predicted if time to contact was the key variable controlling the onset of hand closure. These results, then, lend
only partial support to the theory that temporal coordination between the transport and grasp components of prehension is
ensured through their common dependence on time to contact information.
Received: 20 September 1996 / Accepted: 16 June 1997 相似文献
74.
人乳头瘤病毒(HPV)的16,18,31,33型等与宫颈癌的发病有关,其中HPV16与宫颈癌关系密切。为进一步研究HPV16的致癌性,我们用克隆的HPV16 DNA(2μg/10~5细胞)转染体外培养的人胚肺细胞,并进行了细胞存活时间、血清依赖性、着壁依赖性、间接免疫酶检测、HPV16 DNA、同源序列检测、染色体核型等生物学的研究。结果表明,转染细胞存活时间延长、在软琼脂培养基中形成集落、HPV16特异抗原得以表达、HPV16 DNA的同源序列存在于细胞中。表明本实验用HPV16DNA转染的人胚肺细胞具备转化细胞的某些特征,HPV16有使人胚肺细胞转化的作用。 相似文献
75.
In the attempt to gain a broader understanding of the causal relationships behind work-related symptoms of pain in the human
shoulder, monitoring of arm position is crucial. Different methods have been used with varying accuracy. A video-based stereometry
system, using infra-red light and reflecting markers for motion analysis, has been introduced for measurements in the fields
of ergonomics, biomechanics and sports medicine. The purpose of this study is to investigate the sources of error in using
this system for posture registration of the upper limb. Measurements are performed on a calibration fixture, on a mechanical
model of the upper limb and on a subject with an exoskeleton. Particular, attention is given to inconsistencies and relative
errors due to the finite geometrical precision with which the markers are positioned in the calibration fixture and on the
studied objects, the limited capability to align the objects relative to the coordinate system of the calibration fixture
and the errors connected to angular measurements using protractors etc. It is concluded that the system makes a valuable addition
to existing instruments for non-contact posture measurement, and produces position data with an adequate accuracy in normal
handling. 相似文献
76.
目的:探讨雌激素,胎盘生乳素,钙在妊高征发病中的作用及其相互关系,方法:采用放射免疫法及离心分析钙试剂,测定了42例妊高征患者血清雌二醇,胎盘生乳素,钙,磷及尿钙,磷的含量,34例同期门诊正常孕妇作为对照组,结果:轻度妊高征患者血清雌二醇明显增加(P〈0.05)。重度妊高征患者血清胎盘生乳素显著减少(P〈0.05),轻,中,重度妊高征患者血钙,尿钙含量显著降低(P〈0.05,P〈0.01,P〈0. 相似文献
77.
收集正常的及良性前列腺增生症(BPH)的前列腺组织,用细胞培养、同位素掺入法分别测定各例标本的组织液对Swiss3T3细胞增殖的影响。结果表明,BPH组织液促细胞增殖效应为正常前列腺的5倍。正常前列腺组织用硫酸铵分级沉淀、肝素亲和层析、NaCl浓度梯度洗脱(收集1.3~1.7mol部分),分离纯化人前列腺生长因子(hPGF)。经SDS-PAGE鉴定达电泳纯,分子量约为17000,纯化约800倍。所得的hPGF对Swiss3T3细胞的增殖刺激作用呈现浓度依赖性,BPH组织hPGF活性显著高于正常前列腺 相似文献
78.
Population toxicokinetics of tetrachloroethylene 总被引:1,自引:0,他引:1
F. Y. Bois A. Gelman J. Jiang D. R. Maszle L. Zeise G. Alexeef 《Archives of toxicology》1996,70(6):347-355
In assessing the distribution and metabolism of toxic compounds in the body, measurements are not always feasible for ethical
or technical reasons. Computer modeling offers a reasonable alternative, but the variability and complexity of biological
systems pose unique challenges in model building and adjustment. Recent tools from population pharmacokinetics, Bayesian statistical
inference, and physiological modeling can be brought together to solve these problems. As an example, we modeled the distribution
and metabolism of tetrachloroethylene (PERC) in humans. We derive statistical distributions for the parameters of a physiological
model of PERC, on the basis of data from Monster et al. (1979). The model adequately fits both prior physiological information
and experimental data. An estimate of the relationship between PERC exposure and fraction metabolized is obtained. Our median
population estimate for the fraction of inhaled tetrachloroethylene that is metabolized, at exposure levels exceeding current
occupational standards, is 1.5% [95% confidence interval (0.52%, 4.1%)]. At levels approaching ambient inhalation exposure
(0.001 ppm), the median estimate of the fraction metabolized is much higher, at 36% [95% confidence interval (15%, 58%)].
This disproportionality should be taken into account when deriving safe exposure limits for tetrachloroethylene and deserves
to be verified by further experiments.
Received: 20 April 1995/Accepted: 24 August 1995 相似文献
79.
Nobutaka Eiraku Shinji Ijichi Shinji Yashiki Mitsuhiro Osame Shunro Sonoda 《Journal of neuroimmunology》1992,37(3):223-228
The in vitro proliferation of peripheral blood lymphocytes (PBLs) without any mitogenic stimulation is one of the hallmarks of human T lymphotropic virus type I (HTLV-I) infection. Recent evidence suggests a difference in the degree of the phenomenon between HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and asymptomatic HTLV-I carriers (AC). In this article, we demonstrated several alterations in the features of the in vitro transformed lymphocytes between patients with HAM/TSP (n = 16) and AC (n = 8). The percentages of total CD8+ and CD8+CD28+ cells were significantly increased in the in vitro proliferating T lymphocytes derived from the patients with HAM/TSP when compared to those from AC. HAM/TSP was segregated from AC by the high degree of the proliferation of CD8+CD28+ cells. The expression of HTLV-I-specific antigens on the cultured PBLs was detected only in the subjects which showed low CD8+CD28+/CD4+ ratio of the in vitro proliferating lymphocytes. These findings suggest that this phenomenon distinguishes HAM/TSP from AC, not only in quantity but also in quality. 相似文献
80.
图娅 《北京中医药大学学报》1997,(5)
21世纪中医学的发展,面临着理顺民族性表述方式与国际性科学内涵关系的问题,因此必须辩证地把握结构与机能、实证科学手段与人文精神、过程与结果之间的谐调统一,这样既符合中医学术体系特征,又能与当代生命科学研究保持一致。 相似文献