Metabotropic glutamate receptors are involved in long-term potentiation in isolated slices of rat medial frontal cortex

The prelimbic region of medial frontal cortex in the rat receives a direct input from the hippocampus and this functional connection is essential for aspects of spatial memory. Activity-dependent changes in the effectiveness of synaptic transmission in the medial frontal cortex, namely long-term potentiation (LTP) and long-term depression (LTD) can persist for tens of minutes or hours and may be the basis of learning and memory storage. Glutamatergic activation of ionotropic receptors is required to induce both LTP and LTD. We now present evidence of the involvement of metabotropic glutamate receptors in LTP in isolated slices of frontal cortex. Repetitive bursts of stimulation at theta frequencies (TBS) were applied to layer II, and monosynaptic EPSPs were monitored in layer V neurons of the prelimbic area. TBS was found to be more effective at inducing LTP than tetanic stimulation at 100 Hz and produced LTP that lasted >30 min in 8 out of 14 neurons. Tetanic stimulation at 100 Hz in the presence of the N-methyl--aspartate (NMDA)-antagonist 2-amino-5-phosphonopentanoate (AP5) was reported to be a reliable method of inducing LTD in prelimbic cortex (). However we found that this protocol did not facilitate the induction of LTD. The role of metabotropic glutamate receptors (mGluR) in LTP was assessed by using the selective, broad-spectrum antagonist (R, S)-alpha-methyl-4- carboxyphenylglycine (MCPG). This drug significantly reduced the incidence of LTP after TBS to only 1 of 14 neurons (P < 0.02, chi2 test). The pooled responses to TBS in MCPG showed significantly reduced potentiation [(P < 0.02, analysis of variance (ANOVA)]. The broad-spectrum mGluR agonist (1S, 3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) and the selective group I agonist S-3 hydroxyphenylglycine(S-3HPG) both produced membrane depolarization, an increase in number of spikes evoked by depolarizing current pulses, and a reduction in the afterhyperpolarization. Similar effects were produced by these agonists even when synaptic transmission was blocked by use of the gamma-aminobutyric acid-B (GABAB) receptor agonist, 200 microM baclofen, which suggests that group I mGluRs are present on layer V neurons. We conclude that mGluRs participate in the production of LTP in prelimbic cortex, and that this excitatory effect could be mediated by the postsynaptic group I mGluRs.     

Common migraine ("migraine without aura"): localization of the initial pain of attack

The importance of maximal versus submaximal exercise testing and the significance of heart failure on the prognostic value of exercise-provoked ST-segment depression > or = 0.1 mV was studied in 143 patients recovering from acute myocardial infarction. Patients were exercise tested prior to discharge and follow up lasted for up to 18 months (mean 17 months). End-point was first major event (i.e. first non-fatal reinfarction or death). A symptom-limited exercise test was superior to a heart-rate-limited test in detecting ST-segment depressions (27% vs. 20%: P < 0.5), and patients with ST-segment depression at lower heart rates did not have an increased risk of subsequent events compared with patients with ST-segment depression at higher heart rates (14% vs. 27%; NS). Heart failure surpassed ST-segment depression as a risk predictor (34% vs. 18%). Based on a meta-analysis including 13 studies (1987 patients) exercise-provoked ST-segment depression possessed an increased risk of subsequent major events (P < 0.0001; risk ratio = 1.90; 95% confidence limits 1.43,2.51). Thus, ST-segment depression provoked by a symptom-limited test selects patients with an increased risk of subsequent major events. In patients with a history of heart failure exercise-provoked ST-segment depression is of limited value.     

肝癌碘油栓塞后肝区平片所见碘油沉积量与疗效关系

本文分析了90例肝癌肝动脉灌注化疗碘油栓塞后,肝区平片所见碘油沉积量和疗效的关系。碘油沉积分为多,中,少三组,从ATP下降,肿瘤缩小率及一年生存率三方面比较。结果沉积多的与中等组三项都有显著差别;沉积中等的与少的组差别不明显。说明碘油沉积要达到一定的量后,疗效才会显著提高。同时分析了影响碘油沉积的几个因素。     

Effect of dual-scale microstructure on the toughness of laminar zirconia composites

Numerical study by the finite element method (FEM) is performed to investigate the effect of dual-scale microstructure on the toughness of laminar zirconia composite. The computation is based on the micromechanics constitutive model of polycrystal transformation plasticity developed by Sun et al. [10] where both transformation induced shear and softening effects during autocatalytic transformation are taken into account. The numerical simulation presented in this paper successfully reproduced the experimentally observed two effects of the dual-scale microstructure on the toughness of laminar zirconia composite, i.e., the truncation of the elongated transformation frontal zone that forms in single phase Ce-ZrO₂ and the propagation of the transformation zone along the layers normal to the crack plane. Quantitative analysis on the role of microstructure in transformation toughening of laminar zirconia composite is first carried out in the present work which will provide a starting point for the microstructural design of this novel advanced composite in the future.Presented at the Far East Fracture Group (FEFG) International Symposium on Fracture and Strength of Solids. 4–7 July 1994 in Xi'an, China.     

多灰度级显示器上的曲线绘制

光栅扫描显示器的屏幕是由位置固定的，离散的象素点所组成的，因而在其上生成的曲线只能是实际曲线的某种近似表示，并不是很美观的，例如有曲线的阶梯效应及曲线亮度不均度等问题，该文说明利用多灰度光栅显露器可以在一定程度上解决这些问题，并且用给出的主些算法绘制曲线时，可以较好地解决上述问题，这些算法在动画制作中也可有典型的应用。     

Predation of livestock ticks by chickens as a tick-control method in a resource-poor urban environment

The increasing prevalence of streptococci as causes of potentially fatal nosocomial bacteremia requires that antimicrobial agents used for empiric therapy in hospitalized patients include both pneumococci and viridans group streptococci as well as beta-hemolytic streptococci in their activity profile. In this study, the in vitro activity of cefepime, a new fourth-generation cephalosporin, was compared with other cephalosporins versus 197 nosocomial blood stream isolates of streptococci (20 Streptococcus pneumoniae, 104 viridans group, and 73 beta-hemolytic) isolated from patients at more than 30 medial centers from 1995 to 1997. Additional agents tested included penicillin, erythromycin, and vancomycin. Overall, cefepime inhibited 83% of the isolates at concentrations < or = 0.5 microgram/mL and 100% at < or = 8 micrograms/mL. By comparison, ceftazidime inhibited 35 and 88% of isolates at the same concentrations. Cefepime was approximately eightfold more potent than ceftazidime against S. pneumoniae, viridans group streptococci, and beta-hemolytic streptococci. Among the 42 isolates with penicillin MICs > 0.12 microgram/mL, 100% were inhibited by cefepime and only 48% by ceftazidime at < or = 8 micrograms/mL. The rank order of activity for all six agents against the 197 isolates was vancomycin > ceftriaxone > cefepime > penicillin > erythromycin > ceftazidime. Based on the results of the present study, cefepime and ceftriaxone were the superior cephalosporins in potency and spectrum for empiric coverage of patients at risk for streptococcal blood stream infections.     

Prenatal diagnosis: update addresses technological advances

This is the second in a series of articles provided to the readers of PENNSYLVANIA MEDICINE as an update from researchers and clinicians in this cutting-edge medical field. The series is partially sponsored through a grant from the Pennsylvania Department of Health to the University of Pittsburgh Department of Human Genetics.     

钻速模式动态辨识方法研究

目的：钻进过程是一个复杂的工艺过程，影响钻速的因素错综复杂。为钻井参数优化和实时控制，提出钻速动态模型。方法：对影响钻速的因素进行分析，用系统辨识方法建立钻速模式。结果：利用该方法建立了华北油田岔河集地区的钻速模型，取得满意结果。结论：此动态钻速模式能更准确、科学地描述钻进过程，并在钻井参数最优化、钻井过程的闭环控制等方面具有广阔的应用前景。     

冶金炉渣氮化物容量研究的进展

本文总结了近年冶金炉渣氮酸盐容量的研究方法，氮在炉渣中存在形态与炉渣氧分压的关系，炉渣氮化物容量与温度及炉渣成分的关系，并给出设计钢液脱氮渣系的基本原则。     

单轴-平面W型复合锶铁氧体的制备及其吸波特性研究

用草酸盐共沉淀和微量掺杂法研制六角晶系W型Ni,Zn,Co,Al多元复合锶铁氧体，通过调节Ni2W同Co2W的摩尔比例，可使该种铁氧体易磁化方向从C单轴型向垂于C轴的平面型转化，控制置换锶铁氧体中部分Fe3 的微量掺杂Al3 ，可以调整4πMs值，提高磁晶各向异性场，测试分析了5种不同含Co量的W型复合锶铁氧体粉料涂层的吸波特性，发现其自然共振吸收峰随Co含量增加向低频方向偏移，最高吸收峰可达32．8dB，是适用于电子隐形技术的高品位的微波吸收剂。