Unconditional Positivity-Preserving and Energy Stable Schemes for a Reduced Poisson-Nernst-Planck System

The Poisson-Nernst-Planck (PNP) system is a widely accepted model for simulation of ionic channels. In this paper, we design, analyze, and numerically validate a second order unconditional positivity-preserving scheme for solving a reduced PNP system, which can well approximate the three dimensional ion channel problem. Positivity of numerical solutions is proven to hold true independent of the size of time steps and the choice of the Poisson solver. The scheme is easy to implement without resorting to any iteration method. Several numerical examples further confirm the positivity-preserving property, and demonstrate the accuracy, efficiency, and robustness of the proposed scheme, as well as the fast approach to steady states.     

Neuropathology of ALS: Spheroids

I briefly review spheroids observed in the anterior horns of the spinal cord in amyotrophic lateral sclerosis (ALS). Spheroids are argentophilic bodies more than 20 μm in diameter. Recently, some connections between the proximal axonal swellings including spheroids and the perikarya have been reported in some ALS patients with a short clinical course or mild depletion of anterior horn neurons. Most of the cell bodies directly connected with the axonal swellings appear normal, and spheroids are considered to be one of the hallmarks of the early histological changes in this disorder. Spheroids are strongly positive with anti-phosphorylated neurofilament antibody, and are also positive with calcitonin gene-related peptide and anti-peripherin antibody. Some spheroids are immunostained with anti-synaptophysin antibody and anti-ubiquitin antibody. Spheroids are not immunostained with anti-phosphorylated tau antibody, or high molecular weight microtubule associated proteins. Electron microscopically, spheroids are usually composed of densely packed accumulation of 10 nm neurofilaments with a variety of orientations, plus vesicles, dense bodies and mitochondria. When the swellings of the initial segment is relatively pronounced, the undercoating is obscured and the neurofilaments become interwoven in some parts. In the first internode of the myelinated axons, as the swellings become larger, the neurofilaments lose their parallel orientation and become intermingled. Large accumulation of neurofilaments resembling spheroids in the perikarya of large anterior horn cells suggests that spheroids could be derived not only from the axon including the proximal portion, but also from the perikarya. Structures apparently identical to axonal spheroids are observed at the light and electron microscopic levels in the proximal portion of axons of anterior horn cells in animal models intoxicated with β, β'-iminodipropionitrile (IDPN), or with aluminum, in hereditary canine spinal muscular atrophy (HCSMA). The pathogenetic mechanism is probably associated with an impairment in slow axonal transport which particularly affects the neurofilaments in IDPN and aluminum intoxication. Impairment of slow axonal transport of neurofilaments also plays an important role in the pathogenesis of ALS. The average diameter of even normalappearing initial segment is larger in ALS than in the controls. The perikarya connected with the swollen proximal axons and their dendrites almost always appear normal. These findings suggest that the slow axonal transport of neurofilaments is probably impaired in this portion of the axon at an early stage in ALS as well as animal models for human ALS. However, techniques to analyze slow axonal transport in humans still remain tobe developed. Recently, overexpression of neurofilament subunits in transgenic mice produces a condition resembling ALS. The transgenic model may offer an interesting perspective not only for testing therapeutic strategies but also for investigating in a systematic way the various genetic and environment factors controlling the onset and progression of the disease and might yield new insights on the etiology of ALS.     

猫颈部食管的交感神经支配—HRP法

用5只猫于左侧颈部食管壁内注入 HRP 溶液,通过 HRP 逆行追踪法研究颈部食管的交感神经支配,结果表明:1.长轴突型交感节前神经元直接分布到食管壁内,其标记细胞位于双侧脊髓的胸1～3节段,以胸2节段最多(占标记细胞总数的66.45％),注射侧占优势。标记细胞主要位于中间带外侧核(约占95.02%),其次为侧索、中介核、前角腹后外侧核。其细胞形态不一,以中小型细胞为主(占标记细胞总数的90.4％)。2.支配颈部食管的交感节后神经元主要位于星状神经节(约占61.99％),余者位于双侧颈前、中和2～5胸交感节内、以小细胞最多。     

Morphology of corticotectal cells in the primary visual cortex of hooded rats

In primary visual cortex of hooded rats, pyramidal cells in layer V may be classified as long, medium, or short, on the basis of the layer in which the apical dendrite terminates. The present study determines which of these types of pyramidal cells project to the superior colliculus. Two different strategies were used to label corticotectal cells with horseradish peroxidase (HRP). In the first set of experiments, a large number of corticotectal cells were labeled by retrograde transport following injection of HRP into the superior colliculus. In the second set of experiments, single unit recording was used to identify corticotectal cells physiologically by antidromic activation from the superior colliculus. These cells were then impaled and labeled by intracellular iontophoresis of HRP. The results from both techniques suggest that only long pyramidal cells send an axon to the superior colliculus. These cells are distinguished by an apical dendrite that extends into layer I. We conclude that in hooded rats corticotectal cells in primary visual cortex are the long pyramids in layer V.     

Peritoneal dialysis patient survival: a comparison between a Swedish and a Korean centre.

BACKGROUND: Dialysis patient mortality remains high, and this high mortality may be due to many factors. In peritoneal dialysis (PD) patients, old age, co-morbid diseases, malnutrition, low residual renal function (RRF) and a high peritoneal transport rate have been shown to influence survival, but the relative importance of these factors may differ between different patient populations. Besides, centre practice patterns may differ between centres and may influence patient survival. In addition, the literature suggests that dialysis patient survival may be better in Asian than in Caucasian patients. METHODS: The influence of centre and patient characteristics on patient survival was investigated in 132 Korean and 106 Swedish incident PD patients, who underwent initial biochemical measurements and assessment of adequacy of dialysis, nutritional status, RRF and peritoneal transport characteristics. RESULTS: At the start of PD, Korean patients had a higher prevalence of diabetes, peritoneal Kt/V(urea), peritoneal creatinine clearance and peritoneal fluid removal, and lower body mass index, RRF and dialysate to plasma creatinine concentration ratio (D/P Cr) compared with Swedish patients. Significantly more patients from Korea were placed on temporary haemodialysis before PD (100 out of 132) when compared with Swedish patients (21 out of 106). During the follow-up, there was a significantly higher rate of transfer to other units in Korea and a significantly higher rate of kidney transplantation in Sweden. On Kaplan-Meier analysis, overall patient survival did not differ and relative risk for death was also not different between the two centres even after adjustment for age, diabetes, cardiovascular disease, RRF and D/P Cr. On Cox proportional hazards multivariate analysis, age, diabetes, RRF and D/P Cr were found to be independent predictors of mortality in the combined cohort of patients. While age, diabetes and D/P Cr were independent predictors of mortality in Korean patients, age and RRF independently predicted mortality in Swedish patients. CONCLUSION: Although there were significant differences in centre and patient characteristics, we were unable to confirm a survival advantage for Korean over Swedish PD patients. The results of this study suggest that the reported difference in survival between Asian and Caucasian dialysis patients may have been due, in part, to differences in centre and patient characteristics rather than to race as such. The genetic influence on patient characteristics remains, however, to be elucidated.     

The use of perfluorinated emulsion for prolongation of the endurance period in lethal hypoxia

The apnea model with venovenous perfusion and blood oxygenation in a membrane oxygenator was used to study the gas transport characteristics of perfluorinated emulsion with the aim to prolong the endurance period in lethal hypoxia. The use of PFOS emulsion (40 ml/kg) as a hemodilution agent at relatively low rate of assisted perfusion (35 ml/kg×min) produced no improvement of oxygen supply during the critical period in comparison with conventional plasma substitutes. However, perfusion with oxygenated perfluorinated emulsion prolonged survival as compared with polyglucin perfusion, mainly due to the maintenance of the vitally important organs (heart and brain) and due to the improvement of microcirculation. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 124, No. 10, pp. 477–480, October, 1997     

溶剂在嵌段共聚高分子膜中的溶解与传递现象

利用石英弹簧称重法测定了308．15K时乙醇和苯在含端羟基聚丁二烯(HTPB)和端羟基聚丁二烯／丙烯腈共聚物(HTBN)的嵌段共聚聚氨酯膜中的吸收动力学曲线。结合吸收-络合吸附双模式传递模型，研究了聚氨酯膜的微相分离程度、软硬段的比例和组成以及软段分子量等因素对溶剂在膜中溶解和传递性质的影响。     

潘生丁增强氨甲蝶呤的抗肿瘤作用

外源性核苷能抵消抗代谢药对肿瘤细胞的杀伤作用;核苷转运抑制剂潘生丁则能阻断核苷的这种抵消作用,从而增强抗代谢药的细胞毒性。本研究证明,胸苷和次黄嘌呤可明显抵消氨甲蝶呤对L1210细胞的杀伤作用,潘生丁则能有效地阻断核苷的抵消作用;潘生丁和两性霉素B合用可明显增强氨甲蝶呤对小鼠S180肉瘤的抑制作用,但不增强氨甲蝶呤对动物的毒性。提示潘生丁有可能应用于肿瘤联合化疗。     

Comparative study of renal sodium transport between ouabain-hypertensive rats and ouabain-nonhypertensive rats

Objective: To compare renal sodium transport, using fractional excretions of lithium(FELi) as a marker of proximal tubule sodium reabsorption, between hypertensive and non-hypertensive ouabain-treated rats and further to elucidate the role of ouabain in pathogenesis of hypertension. Methods: Thirty male Sprague-Dawley rats weighting 180-200 g were randomly divided into normal control group and ouabain treated group. Rats were infused with 1 ml/kg·d normal saline or 27. 8μg/kg·d ouabain in-traperitoneally once a day respectively. Systolic blood pressure (SBP), heart rate and body weight were recorded weekly. Rats were sacrificed 6 weeks after treatment. Blood and 24-hour urine sample were collected to measure the serum and urinary concentration of sodium, trace lithium and creatinine. Endogenous creatinine clearance rate(Ccr), fractional excretions of sodium (FENa), fractional excretions of lithium (FELi) and fractional reabsorption of sodium in the postproximal tubules (FDRNa) were calculated. Ouabain levels of plasma and renal tissue, plasma renin activity, angiotensin I and aldosterone concentration were determined. Results: 65% of the ouabain-treated rats achieved significantly higher SBP after 4 weeks, compared with that of the saline control groups or self baseline (P<0. 01). But in the other 35% of the ouabain-treated rats, their SBP was similar with control group during the experiment (P>0. 05). The body weight, heart rate and food intake between the 3 groups were no significant differences (P> 0. 05). FELi and FDRNa were significantly lower in ouabain-hypertensive group compared with ouabain-non-hypertensive group and control group(P<0. 01 and P<0. 05). The FEu and FDRn, of ouabain-nonhyper-tensive groups were similar with control group(P>0. 05). Ccr and FENa were comparable between the 3 groups (P>0. 05). Plasma and renal tissue ouabain levels, plasma renin activity, angiotensin I and aldosterone contents in ouabain-hypertensive rats were comparable with ouabain-nonhypertensive rats. Conclusion: Increase of proximal tubule sodium reabsorption play an important role in the pathogenesis of ouabain-hypertensive rats. The change of renal sodium transport may result from regulation to renal Na+ , K + -ATPase by ouabain.