Neutrophil migration into the bovine uterine lumen following intrauterine inoculation with killed Haemophilus somnus.

Polymorphonuclear neutrophils (PMN) in bovine uterine flushings following intrauterine deposition of killed bacteria were measured and the effect of immune status on the influx of PMN into the uterine lumen during oestrus was determined. Holstein heifers were immunized with a 270-kDa outer-membrane protein (omp-270) from Haemophilus somnus. During oestrus, immunized heifers (n = 21) received an intrauterine inoculum of either a heat-killed suspension of a homologous strain of H. somnus containing omp-270 (n = 7), a heterologous strain of H. somnus lacking omp-270 (n = 7), or phosphate-buffered saline (n = 7). Five additional heifers were inseminated with extended bovine semen. Uterine contents were collected in saline lavage immediately before inoculation (t0) and at 6, 24, 48, 72, 96, and 120 h after inoculation. The semen-inoculated heifers were lavaged only at t120. All groups experienced PMN infiltration which peaked 6 h after inoculation and tended to decline thereafter. Differences were not observed between treatment groups, indicating that neither bacterial inoculation nor immune status was as important in eliciting PMN effusion as the flushing procedure itself.     

Biochemical and genetic characterization of three hamster cell mutants resistant to diphtheria toxin

We describe here three different hamster cell mutants which are resistant to diphtheria toxin and which provide models for investigating some of the functions required by the toxin inactivates elongation factor 2 (EF-2). Cell-free extracts from mutants Dtx(r)-3 was codominant. The evidence suggests that the codominant phenotype is the result of a mutation in a gene coding for EF-2. The recessive phenotype might arise by alteration of an enzyme which modifies the structure of EF-2 so that it becomes a substrate for reaction with the toxin. Another mutant, Dtx(r)-2, contained EF-2 that was sensitive to the toxin and this phenotype was recessive. Pseudomonas aeruginosa exotoxin is known to inactivate EF-2 as does diphtheria toxin and we tested the mutants for cross-resistance to pseudomonas exotoxin. Dtx(r)-1 and Dtx(r)-3 were cross-resistant while Dtx(r)-2 was not. It is known that diphtheria toxin does not penetrate to the cytoplasm of mouse cells and that these cell have a naturally occurring phenotype of diphtheria toxin resistance. We fused each of the mutants with mouse 3T3 cells and measured the resistance. We fused each of the mutants with mouse 3T3 cells and measured the resistance of the hybrid cells to diphtheria toxin. Intraspecies hybrids containing the genome of mutants Dtx(r)-1 and Dtx(r)-3 had some resistance while those formed with Dtx(r)-2 were as sensitive as hybrids derived from fusions between wild-type hamster cells and mouse 3T3 cells.     

Genotypic Diversity among Campylobacter jejuni Isolates in a Commercial Broiler Flock

Analysis of nucleic acid polymorphism in the flagellin genes of Campylobacter jejuni was used to investigate genetic diversity among Campylobacter spp. in a commercial broiler flock. Three hundred single colonies of C. jejuni were isolated from fecal samples collected weekly for 3 weeks immediately before slaughter. Both the flaA and flaB genes were amplified by PCR, and the PCR product was digested with the restriction enzyme AluI. The fragments generated were then analyzed by agarose gel electrophoresis. Among the 300 recovered isolates, five different restriction fragment length polymorphism profiles were observed. Three of these profiles were dominant during the course of the study, and the other two profiles were detected at low frequency. Analysis of genetic variation in C. jejuni over the course of an experimental infection lasting 7 weeks indicated that there was no obvious drift in the flagellin gene type. These findings demonstrate that a range of bacterial genotypes can constitute the bacterial population within a commercial poultry flock, with the most likely sources of these types being multiple environmental exposure and/or genetic drift within the population. This degree of diversity must be considered in epidemiological analyses which utilize genetic typing methods that investigate Campylobacter contamination of any food source, including poultry, to ensure that the total gene pool for C. jejuni is evaluated.     

ANTIPYRETIC ACTION OF DEXAMETHASONE ON EGTAZIC ACIDINDUCED FEVER IN RABBITS

本文用脑室灌注和Ｆｕｒａ２测定细胞内游离钙技术观察了地塞米松（ｄｅｘａｍｅｔｈａｓｏｎｅ,ＤＥＸ）对家兔乙二醇双（２氨基乙醚）四乙酸性发热效应和下丘脑细胞内游离钙浓度（［Ｃａ２＋］ｉ）的影响,借此深入探讨地塞米松解热作用的中枢机制。结果发现：脑室灌注乙二醇双（２氨基乙醚）四乙酸（０６ｎｍｏｌ）引起家兔结肠温度明显升高,静脉注射地塞米松（５ｍｇ／ｋｇ）显著抑制家兔乙二醇双（２氨基乙醚）四乙酸性发热,地塞米松（６０～１２０μｍｏｌ／Ｌ）并不影响下丘脑细胞内［Ｃａ２＋］ｉ,而事先脑室灌注抑制基因转录的放线菌素Ｄ（３ｎｍｏｌ）则完全取消了地塞米松对乙二醇双（２氨基乙醚）四乙酸性发热的解热作用。这些结果提示：地塞米松显著抑制家兔乙二醇双（２氨基乙醚）四乙酸性发热,其机制与地塞米松激活脑内某些基因的表达有关,而与下丘脑神经细胞跨膜钙离子流无关。     

Instant success for Instant Pharmacology

Instant Pharmacology (1999). Saeb-Parsy K, Assomull RG, Kahn FZ, Saeb-Parsy K, and Kelly E. John Wiley and Sons 349 pp. £19.99 pbk; ISBN 0471976393 © 1999 John Wiley & Sons, Inc.     

人眼微光下夜近视机制的研究

本文利用激光散斑屈光测试系统详细探讨了夜近视(night myopia)的产生机制。夜近视在环境亮度降低到产生暗视觉时出现,并随亮度继续降低而增大,平均值为1.35D。实验证明眼睛球差和色差不是造成夜近视的主要因素。夜近视数值在暗适应过程中呈增大的趋势。在暗视觉时,由于视野中缺少适宜的刺激,眼睛处于暗焦(dark focus)休止状态,这是造成夜近视的主要原因。     

Beyond the edges of a view: boundary extension in human scene-selective visual cortex

To allow perception of a continuous world, cortical mechanisms extrapolate missing information with highly constrained predictions about the environment just beyond the edges of a view. Here, we report functional magnetic resonance imaging evidence for extrapolation of scene layout information beyond what was physically presented, an illusion known as boundary extension. Consistent with behavioral reports, we observed boundary extension for scene-selective attenuation in the parahippocampal place area (PPA) and retrosplenial cortex (RSC), but no such extrapolation of object representations in the lateral occipital complex (LOC). These results demonstrate that scene layout representations are extrapolated beyond the confines of the perceptual input. Such extrapolation may facilitate perception of a continuous world from discontinuous views.     

瓜类枯萎病研究进展(综述)

瓜类枯萎病是由尖孢镰刀菌Fusarium oxysporum侵染引起,在全球大部分瓜类产区均有发生。该病已成为影响我国瓜类品质和产量的重要病害。本文从瓜类作物枯萎病的防治方法、致病机理和分子生物学研究等方面综述其研究现状,并对今后的研究方向进行展望。     

Rapid Induction of Ion Pulses in Tomato,Cucumber, and Maize Plants following a Foliar Application of L(+)-Adenosine

Application of picomole quantities of (+)-adenosine, a plant growth-regulating second messenger elicited by triacontanol, to tomato (Lycopersicon esculentum Mill.), maize (Zea mays L.), and cucumber (Cucumis sativa L.) foliage, increased Ca2+, Mg2+, and K+ concentrations in the exudate from the stumps of excised plants by 20 to 60% within 5 s after treatment. The change in ionic concentration of the exudate was transitory. When L(+)-adenosine and triacontanol were applied to different tomato plants at the same time, the L(+)-adenosine caused an increase in Ca2+ flux within 3 s, whereas a significant increase from triacontanol was not detectable until 5 min after application. This was expected because triacontanol elicits the formation of L(+)-adenosine. The enantiomer of L(+)-adenosine, D(-)-adenosine, had no effect on the cation concentration in tomato and inhibited the effect of L(+)-adenosine at equimolar or lower concentrations. These observations suggest that L(+)-adenosine acts by eliciting a rapidly propagated signal that increases the concentration of several ions in the apoplast. We postulate that modulations in apoplastic ion concentration, especially increases in Ca2+ concentration, constitute a mechanism by which plants regulate metabolic activity and growth in response to certain stimuli.     

beta1,6 N-acetylglucosaminyltransferase (core 2 GlcNAc-T) expression in normal rat tissues and different cell lines: evidence for complex mechanisms of regulation

The distribution of the Golgi enzyme beta1, 6-N- acetylglucosaminyltransferase (core 2 GlcNAc-T for short) has been investigated in several tissue and cell systems by combining the potentials of a polyclonal antibody and a novel, sensitive fluorescent enzyme assay. In normal rat tissues, levels of the protein were found to vary and as a general trend did not correlate with enzyme activities. Additionally, we observed tissue-specific core 2 GlcNAc-T forms of various size: 75 kDa (liver), 70 kDa (spleen), 60 kDA (heart), and 50 kDa (heart and lung). These forms might arise from differential protein modifications; alternatively, the smaller form may be a product of proteolytic cleavage, given the presence of a catalytically inactive 50 kDa species in rat serum. Chinese hamster ovary (CHO), MDAY-D2, PSA- 5E, and PYS-2 cell lines consistently displayed a 70 kDa enzyme. When induced to retrodifferentiate in the presence of butyrate + cholera toxin, CHO cells exhibited a 21-fold increase in enzyme activity, while protein levels remained constant. A similar trend was observed in the embryonal endoderm cell lines PSA-5E and PYS-2, where an approximately 100-fold difference in core 2 GlcNAc-T activity was found notwithstanding unchanged amounts of the protein and identical mRNA levels, as evidenced by RT-PCR. In contrast, levels of core 2 GlcNAc-T activity in MDAY-D2 cells correlated well with protein expression. Taken together, these observations demonstrate that core 2 GlcNAc-T expression may be subjected to multiple mechanisms of regulation and suggest that in at least some instances (i.e., PSA-5E and PYS-2 cells) expression may be regulated exclusively via posttranslational mechanism(s) of control.