猫脑干上涎核节前神经元电活动的观察

在麻醉的32只猫记录了电刺激颌下腺神经支引起的上涎核平均场电位和单位放电。逆行电刺激颌下腺神经支引起的上涎核平均场电位分布在同侧脑干背面闩部头端5.5—8mm处,与过去的组织学结果大致符合。用微电极在上涎核记录了68个对刺激颌下腺神经支有反应的单位,其中33个单位作了碰撞试验。有9个单位符合逆向反应标准,它们是真正的颌下腺节前神经元,逆行反应的潜伏期为14.4±2.5ms,其轴突传导速度为2.9±0.1m/s。其他不符合逆向反应标准的单位,对刺激颌下腺神经支仍能发生反应,估计多为中间神经元。在一部分单位观察了电刺激舌神经或味觉刺激舌引起的反应。根据这些观察对上涎核内存在复杂神经元回路的可能性作了讨论。     

Purification and characterization of particulate guanylate cyclase from sea urchin spermatozoa

The particulate form of guanylate cyclase from sea urchin spermatozoa was purified to apparent homogeneity by chromatography on GTP-Sepharose and DEAE-Sepharose and by preparative gel electrophoresis. The sedimentation coefficient (S20,w) was 6.8 and the Stokes radius was 5.1 nm, from which a native molecular weight of 157,000 was calculated. A single protein or periodic acid-Schiff staining band of 135,000 Da was observed after Na dodecyl SO4 gel electrophoresis. Antibody was produced to guanylate cyclase and was shown by electrophoretic transfer experiments (Western blot) to interact with only the Mr = 135,000 band in cases where all of the detergent-extracted protein from spermatozoa was added to the Na dodecyl SO4 gels. Although guanylate cyclase was normally bound to concanavalin A-Sepharose, after endoglycosidase H treatment it failed to bind. Treatment of the enzyme with endoglycosidase H did not alter guanylate cyclase activity, but the apparent size of the enzyme decreased to 72,000 Da on Na dodecyl SO4 gels. An analysis of carbohydrate composition indicated that the oligosaccharides contained N-acetylglucosamine, mannose, galactose, and 2-aminoerythritol in molar ratios (1:3:0.75:2); after endoglycosidase H treatment the enzyme contained essentially no carbohydrate. Major amino acids in the enzyme were aspartic (Asn) and glutamic (Gln) which accounted for approximately 25 mol % of the enzyme amino acid composition. The purified enzyme displayed linear kinetics on double reciprocal plots and had a KMnGTP = 133 microM, KM2+ = 138 microM, KiMnGTP = 122 microM, KiMn2+ = 127 microM, and a V max in excess of 15 mumol of cyclic GMP formed/min/mg of protein at 30 degrees C. Sodium nitroprusside did not stimulate the enzyme in either the presence or absence of added hemeproteins. These results indicate that the particulate form of guanylate cyclase from sea urchin spermatozoa is a glycoprotein which is distinctly different than the soluble form of the enzyme found in mammalian tissues.     

A mathematical model for the burden of diabetes and its complications

Background  

The incidence and prevalence of diabetes are increasing all over the world. Complications of diabetes constitute a burden for the individuals and the whole society.     

A two-dimensional mathematical model of percutaneous drug absorption

Background  

When a drug is applied on the skin surface, the concentration of the drug accumulated in the skin and the amount of the drug eliminated into the blood vessel depend on the value of a parameter, r. The values of r depend on the amount of diffusion and the normalized skin-capillary clearence. It is defined as the ratio of the steady-state drug concentration at the skin-capillary boundary to that at the skin-surface in one-dimensional models. The present paper studies the effect of the parameter values, when the region of contact of the skin with the drug, is a line segment on the skin surface.     

Gene doctoring: a method for recombineering in laboratory and pathogenic Escherichia coli strains

Background  

Homologous recombination mediated by the λ-Red genes is a common method for making chromosomal modifications in Escherichia coli. Several protocols have been developed that differ in the mechanisms by which DNA, carrying regions homologous to the chromosome, are delivered into the cell. A common technique is to electroporate linear DNA fragments into cells. Alternatively, DNA fragments are generated in vivo by digestion of a donor plasmid with a nuclease that does not cleave the host genome. In both cases the λ-Red gene products recombine homologous regions carried on the linear DNA fragments with the chromosome. We have successfully used both techniques to generate chromosomal mutations in E. coli K-12 strains. However, we have had limited success with these λ-Red based recombination techniques in pathogenic E. coli strains, which has led us to develop an enhanced protocol for recombineering in such strains.