Variations in the middle ear of the Mammalia

The comparative morphology of mammalian middle ear structures has been studied by examining the histological sections of the ears of 144 specimens of mammals which had been collected, with a few exceptions, in two expeditions to the Caribbean area. Fifty-four species of six orders of mammals were represented. Sixteen structural features or relationships were specifically studied and the bearing of taxonomic groupings on the variability was analysed.
A taxonometric analysis using these middle ear features indicated that Microdipodops may lie nearer to Dipodomys than to Perognathus.
A table presenting the detailed results has been deposited with the British Museum (Natural History).     

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。     

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.     

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.     

The centrosome and bipolar spindle assembly: Does one have anything to do with the other?

In vertebrate somatic cells, the centrosome functions as the major microtubule-organizing center (MTOC), which splits and separates to form the poles of the mitotic spindle. However, the role of the centriole-containing centrosome in the formation of bipolar mitotic spindles continues to be controversial. Cells normally containing centrosomes are still able to build bipolar spindles after their centrioles have been removed or ablated. In naturally occurring cellular systems that lack centrioles, such as plant cells and many oocytes, bipolar spindles form in the complete absence of canonical centrosomes. These observations have led to the notion that centrosomes play no role during mitosis. However, recent work has re-examined spindle assembly in the absence of centrosomes, both in cells that naturally lack them and those that have had them experimentally removed. The results of these studies suggest that an appreciation of microtubule network organization, both before and after nuclear envelope breakdown (NEB), is the key to understanding the mechanisms that regulate spindle assembly and the generation of bipolarity.Key words: centrosome, centriole, mitosis, spindle, cell cycle, meiosis, plant cell, microsurgery