Histogenesis of the unique morphology of proboscidean ivory

The chequered pattern (often called Schreger pattern), which can be seen by unaided eye on transverse profiles of several proboscidean tusks and which can be emphasized by the spreading pattern of the cracks or by mineral discoloration, is an autapomorph feature of the clade Elephantoidea. The pattern differs among proboscidean taxa; therefore, it allows the coarse differentiation of elephants, mammoths, and some other basal groups. Such identification methods could facilitate efforts concerned with protection of the remaining elephant populations through ivory trade restrictions, since the tooth dentine from extinct Mammuthusprimigenius and from extant Loxodontaafricana and Elephasmaximus are the most common raw materials of the ivory carvings. The aim of this study was to show the internal structure of proboscidean ivory and to revise the existing theories on the aforementioned pattern of the elephantoids with reflections on the events which lead to the development of this microstructure. Thin sections and natural crack surfaces with various orientations of M.primigenius, Elephasantiquus, Prodeinotherium, and Deinotherium tusk fragments were used to produce a three‐dimensional model which explains the features on all profiles. The “phase shift” model is introduced, which assumes a sinusoid undulation of the dentinal tubules in radial profiles in the case of elephantoids. The model was confirmed by photomicrographs, scanning electron microscopic images, interpretation of natural crack surfaces, and radial displacement analysis of the dentinal tubules. The latter proved that the adjacent waves are not in the same phase. Several new nondestructive distinguishing methods are described here on the basis of the correlation between some microscopic and macroscopic features related to the Schreger pattern. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.     

A simple integrative electrophysiological model of bursting GnRH neurons

In this paper a modular model of the GnRH neuron is presented. For the aim of simplicity, the currents corresponding to fast time scales and action potential generation are described by an impulsive system, while the slower currents and calcium dynamics are described by usual ordinary differential equations (ODEs). The model is able to reproduce the depolarizing afterpotentials, afterhyperpolarization, periodic bursting behavior and the corresponding calcium transients observed in the case of GnRH neurons.     

Module-based construction of plasmids for chromosomal integration of the fission yeast Schizosaccharomyces pombe

Integration of an external gene into a fission yeast chromosome is useful to investigate the effect of the gene product. An easy way to knock-in a gene construct is use of an integration plasmid, which can be targeted and inserted to a chromosome through homologous recombination. Despite the advantage of integration, construction of integration plasmids is energy- and time-consuming, because there is no systematic library of integration plasmids with various promoters, fluorescent protein tags, terminators and selection markers; therefore, researchers are often forced to make appropriate ones through multiple rounds of cloning procedures. Here, we establish materials and methods to easily construct integration plasmids. We introduce a convenient cloning system based on Golden Gate DNA shuffling, which enables the connection of multiple DNA fragments at once: any kind of promoters and terminators, the gene of interest, in combination with any fluorescent protein tag genes and any selection markers. Each of those DNA fragments, called a ‘module’, can be tandemly ligated in the order we desire in a single reaction, which yields a circular plasmid in a one-step manner. The resulting plasmids can be integrated through standard methods for transformation. Thus, these materials and methods help easy construction of knock-in strains, and this will further increase the value of fission yeast as a model organism.     

Analysis of the effect of medium and membrane conductance on the amplitude and kinetics of membrane potentials induced by externally applied electric fields.

The kinetics and amplitudes of membrane potential induced by externally applied electric field pulses are determined for a spherical lipid bilayer using a voltage-sensitive dye. Several experimental parameters were systematically varied. These included the incorporation of gramicidin into the membrane to alter its conductivity and the variation of the external electrolyte conductivity via changes in salt concentration. The ability of the solution to Laplace's equation for a spherical dielectric shell to quantitatively describe the membrane potential induced on a lipid bilayer could thus be critically evaluated. Both the amplitude and the kinetics of the induced potential were consistent with the predictions of this simple model, even at the extremes of membrane conductance or electrolyte concentration. The success of the experimental approach for this system encourages its application to more complex problems such as electroporation and the influences of external electric fields in growth and development.     

Mechanical role of expiratory muscles during breathing in upright dogs

To examine the mechanical effects of the abdominal and triangularis sterni expiratory recruitment that occurs when anesthetized dogs are tilted head up, we measured both before and after cervical vagotomy the end-expiratory length of the costal and crural diaphragmatic segments and the end-expiratory lung volume (FRC) in eight spontaneously breathing animals during postural changes from supine (0 degree) to 80 degrees head up. Tilting the animals from 0 degree to 80 degrees head up in both conditions was associated with a gradual decrease in end-expiratory costal and crural diaphragmatic length and with a progressive increase in FRC. All these changes, however, were considerably larger (P less than 0.005 or less) postvagotomy when the expiratory muscles were no longer recruited with tilting. Alterations in the elastic properties of the lung could not account for the effects of vagotomy on the postural changes. We conclude therefore that 1) by contracting during expiration, the canine expiratory muscles minimize the shortening of the diaphragm and the increase in FRC that the action of gravity would otherwise introduce, and 2) the end-expiratory diaphragmatic length and FRC in upright dogs are thus actively determined. The present data also indicate that by relaxing at end expiration, the expiratory muscles make a substantial contribution to tidal volume in upright dogs; in the 80 degrees head-up posture, this contribution would amount to approximately 60% of tidal volume.     

An indirect method for quantitation of cellular zinc content of timm-stained cerebellar samples by energy dispersive X-ray microanalysis

Summary The absolute concentration of zinc in the Purkinje cells of the rat cerebellum was determined by means of energy dispersive X-ray microanalysis (EDAX). Gelatine blocks with known zinc concentrations were stained by Timm's sulphide-silver method, and their silver concentrations were measured by EDAX. A linear correlation was found between the zinc and silver concentrations and this linear function was used as a quantitative calibration for evaluation of sulphide-silver staining, after perfusion with sodium-sulphide solution, fixation with glutaraldehyde, cryostat sectioning and staining of cerebellar samples in Timm's reagent.