A Modified Technique of Rat Tail Suspension for Longer Periods of Observation

FALCAI MJ, LOUZADA MJQ, DE PAULA FJA, OKUBO R, VOLPON JB. A modified technique of rat tail suspension for longer periods of observation. Aviat Space Environ Med 2012; 83:1176-80. Background: Rat tail suspension is an accepted method to create experimental osteopenia. However, suspension periods longer than 3 wk may cause tail skin sloughing or rat slippage. The hypothesis was that a traction system with skeletal anchorage through one tail vertebra would prolong the suspension time without significant complications. Methods: There were 80 young adult female Wistar rats that were submitted to one of the following interventions: skeletal tail suspension (N = 20), skin tail suspension (N = 20), no intervention (N = 20), and a baseline control (N = 20). All animals were followed up either for 3 (N = 10) or 6 (N = 10) wk. Animals were assessed for clinical signs of stress and tolerance to suspension. The femur evaluation was in terms of mineral density content, mechanical resistance, and histomorphometry. Results/Discussion: All animals reached the 3-wk end point. However, for the 6-wk period, seven animals suspended by the skin traction method were discarded (70%) because of signs of stress and skin sloughing. In contrast, there was one loss in the skeletal suspension group (10%). All suspended animals developed similar osteopenia at 3 wk characterized by decreased bone mineral content, weakened bone resistance, and loss of femoral mass. At 6 wk, all suspended animals had similar osteopenic parameters, but they were not statistically different from those of the rats in the 3-wk groups. Therefore, suspension longer than 3 wk did not increase the bone deterioration in the femur.

Valence band tail states in disordered superlattices embedded in wide parabolic AlGaAs well

Optical properties of intentionally disordered multiple quantum well (QW) system embedded in a wide AlGaAs parabolic well were investigated by photoluminescence (PL) measurements as functions of the laser excitation power and the temperature. The characterization of the carriers localized in the individual wells was allowed due to the artificial disorder that caused spectral separation of the photoluminescence lines emitted by different wells. We observed that the photoluminescence peak intensity from each quantum well shifted to high energy as the excitation power was increased. This blue-shift is associated with the filling of localized states in the valence band tail. We also found that the dependence of the peak intensity on the temperature is very sensitive to the excitation power. The temperature dependence of the photoluminescence peak energy from each QW was well fitted using a model that takes into account the thermal redistribution of the localized carriers. Our results demonstrate that the band tails in the studied structures are caused by alloy potential fluctuations and the band tail states dominate the emission from the peripheral wells. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4730769]

Tail bridging vs. patchiness

The subject of this thesis are the interactions between nucleosome core particles (NCPs). NCPs are the primary storage units of DNA in eucaryotic cells. Each NCP consists of a core of eight histone proteins and a strand of DNA, which is wrapped around about two times. Each histone protein has a terminal tail passing over and between the superhelix of the wrapped DNA. Special emphasis was placed on the role of the histone tails, since experimental ndings suggest that the tails have a great in uence on the mutual attraction of the NCPs. In those experiments Mangenot et al. observe a dramatic change in the con guration of the tails, which is accompanied by evidence of mutual attraction between NCPs, when a certain salt concentration is reached. Existing models used in the theoretical approaches and in simulations focus on the description of the histone core and the wrapped DNA, but neglect the histone tails. We introduce the multi chain complex as a new simulation model. Here the histone core and the wrapping DNA are modelled via a charged sphere, while the histone tails are represented by oppositely charged chains grafted on the sphere surface. We start by investigating the parameter space describing a single NCP. The Debye-Huckel potential is used to model the electrostatic interactions and to determine the e ective charge of the NCP core. This value is subsequently used for a study of the pairinteraction of two NCPs via an extensive Molecular Dynamics study. The monomer distribution of the full chain model is investigated. The existence of tail bridges between the cores is demonstrated. Finally, by discriminating between bridging and non-bridging con gurations, we can show that the effect of tail bridging between the spheres does indeed account for the observed attraction. The full chain model can serve as a model to study the acetylation of the histone tails of the nucleosome. The reduction of the charge fraction of the tails, that corresponds to the process of acetylation, leads to a reduction or even the disappearance of the attraction. A recent MC study links this e ect to the unfolding of the chromatin ber in the case of acetylated histone tails. In this case the acetylation of the histone tails leads to the formation of heterochromatin, and one could understand how larger regions of the genetic information could be inactivated through this mechanism.

Quadratically Hyponormal Weighted Shifts with Recursive Tail

We characterize positive quadratic hyponormality of the weighted shift W-alpha(x) associated to the weight sequence alpha(x) : 1, 1, root x, (root u, root v, root w)(Lambda) with Stampfli recursive tail, and produce an interval in x with non-empty interior in the positive real line for quadratic hyponormality but not positive quadratic hyponormality for such a shift. (C) 2013 Elsevier Inc. All rights reserved.

Preparation of intact bovine tail intervertebral discs for organ culture

The intervertebral disc (IVD) is the joint of the spine connecting vertebra to vertebra. It functions to transmit loading of the spine and give flexibility to the spine. It composes of three compartments: the innermost nucleus pulposus (NP) encompassing by the annulus fibrosus (AF), and two cartilaginous endplates connecting the NP and AF to the vertebral body on both sides. Discogenic pain possibly caused by degenerative intervertebral disc disease (DDD) and disc herniations has been identified as a major problem in our modern society. To study possible mechanisms of IVD degeneration, in vitro organ culture systems with live disc cells are highly appealing. The in vitro culture of intact bovine coccygeal IVDs has advanced to a relevant model system, which allows the study of mechano-biological aspects in a well-controlled physiological and mechanical environment. Bovine tail IVDs can be obtained relatively easy in higher numbers and are very similar to the human lumbar IVDs with respect to cell density, cell population and dimensions. However, previous bovine caudal IVD harvesting techniques retaining cartilaginous endplates and bony endplates failed after 1-2 days of culture since the nutrition pathways were obviously blocked by clotted blood. IVDs are the biggest avascular organs, thus, the nutrients to the cells in the NP are solely dependent on diffusion via the capillary buds from the adjacent vertebral body. Presence of bone debris and clotted blood on the endplate surfaces can hinder nutrient diffusion into the center of the disc and compromise cell viability. Our group established a relatively quick protocol to "crack"-out the IVDs from the tail with a low risk for contamination. We are able to permeabilize the freshly-cut bony endplate surfaces by using a surgical jet lavage system, which removes the blood clots and cutting debris and very efficiently reopens the nutrition diffusion pathway to the center of the IVD. The presence of growth plates on both sides of the vertebral bone has to be avoided and to be removed prior to culture. In this video, we outline the crucial steps during preparation and demonstrate the key to a successful organ culture maintaining high cell viability for 14 days under free swelling culture. The culture time could be extended when appropriate mechanical environment can be maintained by using mechanical loading bioreactor. The technique demonstrated here can be extended to other animal species such as porcine, ovine and leporine caudal and lumbar IVD isolation.

Synthesis Of Linoleate Analogs With Longer Alkyl Termini To Test For Proposed "Tail-First" Binding In SBLO-1

Lipoxygenases are nonheme-iron proteins that catalyze the oxygenation of polyunsaturated fatty acids to give conjugated diene hydroperoxides. For example, soybean lipoxygenase-1 (SBLO-1) converts linoleate into 13-(S)-hydroperoxy-9(Z),11(E)-octadecadienoate (13(S)-HPOD). Although the crystal structure of SBLO-1 has been determined, it is still unclear how the substrate binds at the active site. This absence of knowledge makes it difficult to understand the role of the enzyme during catalysis of the reaction. We hypothesize that SBLO-1 binds linoleate ¿tail-first¿, so that the methyl terminus is within a hydrophobic pocket deep within the enzyme. It is believed that the hydrophobic residue phenylalanine-557 at this site has stabilizing interactions with the terminal methyl group on linoleate. To test this hypothesis, we have developed a synthetic pathway that will yield linoleate analogs with longer fatty acid chains by 1 and 2 more carbons at the alkyl terminus. These substrates will be analyzed through kinetic assays done in combination with wild type SBLO-1 and mutants in which we have replaced phenylalanine-557 with valine.