Selective visual attention in a neurocomputational model of phase oscillators

In order to understand the dynamic property of covert selective visual attention, which is different from the proposed mechanism of the spotlight metaphor, a two-layered network of phase oscillators was developed. The first layer is related to the hippocampus and controls attention focus formation. The second layer is related to the visual cortex, and each cortical oscillator in it simulates an assembly of cells coding for a particular stimulus in the sense of feature binding. Selective visual attention is interpreted as the result of the emergent synchronization of hippocampus oscillators and a part of cortical oscillators. Numerical experiments are presented to illustrate attention focus formation and attention shifting from one set of stimuli to another. From a neurocomputational point of view, our results demonstrate that attention is an emergent property of the dynamical cell assemblies responding to the whole visual field. Received: 2 January 1998 / Accepted in revised form: 10 November 1998     

Altered outward K+ currents in Drosophila larval neurons of memory mutants rutabaga and amnesiac

K⁺ currents in cultured Drosophila larval neurons have been classified into four categories according to their inactivation time constants, relative amplitude, and response to K⁺ channel blockers 4‐AP and triethylammonium. The percentage (65%) of neurons displaying K⁺ currents which were reduced to 30% in amplitude by 5 mM cyclic adenosine monophosphate (cAMP) analog 8‐bromo‐cAMP in both Drosophila memory mutants rutabaga (rut) and amnesiac (amn) was significantly larger than that (50%) in wild type. This initial characterization provides evidence for altered K⁺ currents in both rut and amn mutants. Arachidonic acid, a specifical inhibitor of Kv4 family (shal) K⁺ channels, was found to inhibit K⁺ currents in cultured Drosophila neurons, suggesting the presence of shal channels in these neurons. © 1999 John Wiley & Sons, Inc. J Neurobiol 40: 158–170, 1999     

Distinct Acute Zones for Visual Stimuli in Different Visual Tasks in Drosophila

The fruit fly Drosophila melanogaster has a sophisticated visual system and exhibits complex visual behaviors. Visual responses, vision processing and higher cognitive processes in Drosophila have been studied extensively. However, little is known about whether the retinal location of visual stimuli can affect fruit fly performance in various visual tasks. We tested the response of wild-type Berlin flies to visual stimuli at several vertical locations. Three paradigms were used in our study: visual operant conditioning, visual object fixation and optomotor response. We observed an acute zone for visual feature memorization in the upper visual field when visual patterns were presented with a black background. However, when a white background was used, the acute zone was in the lower visual field. Similar to visual feature memorization, the best locations for visual object fixation and optomotor response to a single moving stripe were in the lower visual field with a white background and the upper visual field with a black background. The preferred location for the optomotor response to moving gratings was around the equator of the visual field. Our results suggest that different visual processing pathways are involved in different visual tasks and that there is a certain degree of overlap between the pathways for visual feature memorization, visual object fixation and optomotor response.     

Numerical simulation of fluid–structure interaction in bypassed DeBakey III aortic dissection

It was found that bypass graft alone could achieve great effects in treating aortic dissection. In order to investigate the mechanical mechanism and the haemodynamic validity of the bypassing treatment for DeBakey III aortic dissection, patient-specific models of DeBakey III aortic dissection treated with different bypassing strategies were constructed. One of the bypassing strategies is bypassing between ascending aorta and abdominal aorta, and the other is bypassing between left subclavian artery and abdominal aorta. Numerical simulations under physiological flow conditions based on fluid–structure interaction were performed using finite element method. The results show that blood flow velocity, pressure and vessel wall displacement of false lumen are all reduced after bypassing. This phenomenon indicates that bypassing is an effective surgery for the treatment of DeBakey III aortic dissection. The effectiveness to cure through lumen is better when bypassing between left subclavian artery and abdominal aorta, while the effectiveness to cure blind lumen is better when bypassing between ascending aorta and abdominal aorta.     

Finite element analysis of mechanics of neovessels with intraplaque hemorrhage in carotid atherosclerosis

Background

Intraplaque hemorrhage is a widely known factor facilitating plaque instability. Neovascularization of plaque can be regarded as a compensatory response to the blood supply in the deep intimal and medial areas of the artery. Due to the physiological function, the deformation of carotid atherosclerotic plaque would happen under the action of blood pressure and blood flow. Neovessels are subject to mechanical loading and likely undergo deformation. The rupture of neovessels may deteriorate the instability of plaque. This study focuses on the local mechanical environments around neovessels and investigates the relationship between the biomechanics and the morphological specificity of neovessels.

Methods

Stress and stretch were used to evaluate the rupture risk of the neovessels in plaque. Computational structural analysis was performed based on two human carotid plaque slice samples. Two-dimensional models containing neovessels and other components were built according to the plaque slice samples. Each component was assumed to be non-linear isotropic, piecewise homogeneous and incompressible. Different mechanical boundary conditions, i.e. static pressures, were imposed in the carotid lumen and neovessels lumen respectively. Finite element method was used to simulate the mechanical conditions in the atherosclerotic plaque.

Results

Those neovessels closer to the carotid lumen undergo larger stress and stretch. With the same distance to the carotid lumen, the longer the perimeter of neovessels is, the larger stress and the deformation of the neovessels will be. Under the same conditions, the neovessels with larger curvature suffer greater stress and stretch. Neovessels surrounded by red blood cells undergo a much larger stretch.

Conclusions

Local mechanical conditions may result in the hemorrhage of neovessels and accelerate the rupture of plaque. The mechanical environments of the neovessel are related to its shape, curvature, distance to the carotid lumen and the material properties of plaque.

     

Down-Regulation of Decapping Protein 2 Mediates Chronic Nicotine Exposure-Induced Locomotor Hyperactivity in Drosophila

Long-term tobacco use causes nicotine dependence via the regulation of a wide range of genes and is accompanied by various health problems. Studies in mammalian systems have revealed some key factors involved in the effects of nicotine, including nicotinic acetylcholine receptors (nAChRs), dopamine and other neurotransmitters. Nevertheless, the signaling pathways that link nicotine-induced molecular and behavioral modifications remain elusive. Utilizing a chronic nicotine administration paradigm, we found that adult male fruit flies exhibited locomotor hyperactivity after three consecutive days of nicotine exposure, while nicotine-naive flies did not. Strikingly, this chronic nicotine-induced locomotor hyperactivity (cNILH) was abolished in Decapping Protein 2 or 1 (Dcp2 or Dcp1) -deficient flies, while only Dcp2-deficient flies exhibited higher basal levels of locomotor activity than controls. These results indicate that Dcp2 plays a critical role in the response to chronic nicotine exposure. Moreover, the messenger RNA (mRNA) level of Dcp2 in the fly head was suppressed by chronic nicotine treatment, and up-regulation of Dcp2 expression in the nervous system blocked cNILH. These results indicate that down-regulation of Dcp2 mediates chronic nicotine-exposure-induced locomotor hyperactivity in Drosophila. The decapping proteins play a major role in mRNA degradation; however, their function in the nervous system has rarely been investigated. Our findings reveal a significant role for the mRNA decapping pathway in developing locomotor hyperactivity in response to chronic nicotine exposure and identify Dcp2 as a potential candidate for future research on nicotine dependence.     

Relationship between visual learning/memory ability and brain cAMP level in Drosophila

Using the flight simulator system, the operant conditioned visual flight orientation behavior inDrosophila was studied. It was demonstrated that the visual learning performance is associated with age; flies learn more reliably at 3–4 days than at 1–2 days of age; the cAMP level of brain is also increasing with age; the brain cAMP content of nonlearner flies of wild type is much higher than that of normal flies; the cAMP level of brain increased abnormally after being fed with caffeine, and the learning performance decred. These results imply that a moderate range of cAMP level is necessary for the visual learning and memory pmess. Abnody high or low level of cAMP causes defects of leaming and memory ability. Project supported by the National Natural Science Foundation of China rant No. 69435013) and the National Fundarnental Research Programme in China     

视觉运动图象滤波模型及其实时模拟

在充满生存竞争的动物世界,视觉的伪装与反伪装现象随处可见,视觉反伪装的原理是什么？本文对Ｒｅｉｃｈａｒｄｔ的图形－背景相对运动分辨模型加以发展,提出了视觉反伪装功能的运动图象滤波器模型。为了检验此模型,我们建立了一个生物学似真的实时运动信息加工神经网络电子装置,实现了实时、高分辨运动目标图象滤波。与Ｍｅａｄ的人工视网膜的运动目标图象检测功能相比,检测的运动目标图象的分辨率有很大提高,而噪声水平显著降低,克服了人工视网膜的一些局限性。     

Hemodynamic simulation in a novel design for femoral bypass grafts

The effectiveness of femoral bypass grafts is correlated with the geometric configuration and hemodynamics of the bypass and the arteries. As an attempt to develop a new design for femoral bypass grafts, we present a novel geometric configuration for a symmetrically implanted 2-way bypass graft. In order to investigate how the symmetric 2-way bypass grafts affect the flow patterns through the anastomosis, physiologic blood flows in 1-way and 2-way models for a fully stenosed femoral bypass were simulated with the finite element method, and the hemodynamic factors in these models were studied. The temporal and spatial distributions of flow patterns and wall shear stresses in the vicinity of distal anastomosis during the cardiac cycle were analyzed. The results computed showed that the 2-way model has more preferable hemodynamics than the 1-way model in the distribution of flow patterns and wall shear stresses, and it may improve the flow conditions and decrease the probability of restenosis. However, the limitations of the 2-way bypass model may counteract the positive effects. More detailed hemodynamic studies are necessary to fully assess the viability of the 2-way bypass graft.     

Effects of synbiotic on growth,digestibility, immune and antioxidant performance in broilers

The overuse of in-feed antibiotics has been associated with serious issues, including the developing of antibiotic-resistant pathogens and causing drug residues in poultry products. To date, many countries have restricted the use of growth-promoting antibiotics in food animals, resulting in the increased need for effective alternatives to in-feed antibiotic. Synbiotics, which are composed of probiotics and prebiotics, have been shown to act synergistically when applied simultaneously. Thus, this study investigated the effects of a synbiotic, composed of microencapsulated Lactobacillus plantarum (MLP) and fructooligosaccharide (FOS), on growth, immune and antioxidant parameters, and digestibility of calcium and phosphorus in broilers. A total of 168 newly hatched male broilers were randomly allotted to three dietary groups (n = 7): (1) a corn-soybean meal basal diet (CON); (2) basal diet + synbiotic (SYN); and (3) basal diet + aureomycin (ANT). Compared with the CON, chickens had greater average daily gain and digestibility of calcium and phosphorus in the SYN group (P < 0.05). In the SYN and ANT group, serum IgA, IgG, and IL-10 levels were higher, while the serum TNF-α, IL-2, and IL-6 levels were reduced (P < 0.05) compared to CON. Compared with CON, the level of serum malondialdehyde was lower (P < 0.05) and SOD level was higher (P < 0.05) in either SYN or ANT group. No significant differences in populations of Escherichia coli were seen in chickens among the three groups, whereas, the populations of Lactobacillus were higher (P < 0.05) in chickens in the SYN group compared with those in CON and ANT groups. Taken together, the addition of SYN, consisting of MLP and FOS, had benefits on growth, immune and antioxidant parameters, and digestibility of calcium and phosphorus, indicating its potential to serve as a substitute for antibiotics in broiler feeding.