Detection of forces and displacements along the axial direction in an optical trap

We present measurements of the forces on, and displacements of, an optically trapped bead along the propagation direction of the trapping laser beam (the axial direction). In a typical experimental configuration, the bead is trapped in an aqueous solution using an oil-immersion, high-numerical-aperture objective. This refractive index mismatch complicates axial calibrations due to both a shift of the trap center along the axial direction and spherical aberrations. In this work, a known DNA template was unzipped along the axial direction and its characteristic unzipping force-extension data were used to determine 1), the location of the trap center along the axial direction; 2), the axial displacement of the bead from the trap center; and 3), the axial force exerted on the bead. These axial calibrations were obtained for trap center locations up to approximately 4 microm into the aqueous solution and with axial bead displacements up to approximately 600 nm from the trap center. In particular, the axial trap stiffness decreased substantially when the trap was located further into the aqueous solution. This approach, together with conventional lateral calibrations, results in a more versatile optical trapping instrument that is accurately calibrated in all three dimensions.     

Modular functional organisation of the axial locomotor system in salamanders

Most investigations on tetrapod locomotion have been concerned with limb movements. However, there is compelling evidence that the axial musculoskeletal system contributes to important functions during locomotion. Adult salamanders offer a remarkable opportunity to examine these functions because these amphibians use axial undulations to propel themselves in both aquatic and terrestrial environments. In this article, we review the currently available biological data on axial functions during various locomotor modes in salamanders. We also present data showing the modular organisation of the neural networks that generate axial synergies during locomotion. The functional implication of this modular organisation is discussed.     

Leaf shelter-building caterpillars harness forces generated by axial retraction of stretched and wetted silk

Leaf shelter-building caterpillars generate most of the force required to pull leaf surfaces together by stretching silk strands while spinning. Axially retractive forces produced by columns of stretched strands enabled caterpillars in our study to generate forces as great as 0.3 Newtons (i.e., a 30-g force). We found that caterpillar silk also contracts instantly when wetted, producing an additional, though smaller, axially retractive force. Contraction ratios (final length/ original length) of the wetted silk of 19 species ranged from 0.21 to 0.93 and were smallest among species that use their silk to make leaf shelters. Our study, the first to identify the specific sources of the energy harnessed by caterpillars to tie, roll, or fold leaves, indicates that silk properties and caterpillar behavior have coevolved to facilitate the leaf shelter-building process.     

Spatial localization and properties of pacemaker potentials in the canine rectoanal region

The present study investigated the spatial organization of electrical activity in the canine rectoanal region and its relationship to motility patterns. Contraction and resting membrane potential (E(m)) were measured from strips of circular muscle isolated 0.5-8 cm from the anal verge. Rapid frequency [25 cycles/min (cpm)] E(m) oscillations (MPOs, 12 mV amplitude) were present across the thickness of the internal anal sphincter (IAS; 0.5 cm) and E(m) was constant (-52 mV). Between the IAS and the proximal rectum an 18 mV gradient in E(m) developed across the muscle thickness with the submucosal edge at -70 mV and MPOs were replaced with slow waves (20 mV amplitude, 6 cpm). Slow waves were of greatest amplitude at the submucosal edge. Nifedipine (1 micro M) abolished MPOs but not slow waves. Contractile frequency changes were commensurate with the changes in pacemaker frequency. Our results suggest that changing motility patterns in the rectoanal region are associated with differences in the characteristics of pacemaker potentials as well as differences in the sites from which these potentials emanate.     

线粒体功能缺陷和神经系统疾病

线粒体呼吸链缺陷一直被认为是诱发线粒体疾病的重要因素,这有助于研究人员阐释其遗传和临床多样性。然而,线粒体的其他功能也具有重要意义,包括蛋白质运输、细胞器动力学和细胞凋亡。调控这些功能的基因缺陷不仅导致神经和精神疾病,而且还导致年龄相关的神经变性疾病。因此,引起越来越多的关注。在讨论呼吸链缺陷引起相关神经系统疾病的一些致病难题后,就线粒体动力学改变引起的相关神经系统疾病病因和常见神经变性疾病的病理生理机制作一综述。     

The blood-brain barrier in health and chronic neurodegenerative disorders

The blood-brain barrier (BBB) is a highly specialized brain endothelial structure of the fully differentiated neurovascular system. In concert with pericytes, astrocytes, and microglia, the BBB separates components of the circulating blood from neurons. Moreover, the BBB maintains the chemical composition of the neuronal "milieu," which is required for proper functioning of neuronal circuits, synaptic transmission, synaptic remodeling, angiogenesis, and neurogenesis in the adult brain. BBB breakdown, due to disruption of the tight junctions, altered transport of molecules between blood and brain and brain and blood, aberrant angiogenesis, vessel regression, brain hypoperfusion, and inflammatory responses, may initiate and/or contribute to a "vicious circle" of the disease process, resulting in progressive synaptic and neuronal dysfunction and loss in disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, and others. These findings support developments of new therapeutic approaches for chronic neurodegenerative disorders directed at the BBB and other nonneuronal cells of the neurovascular unit.     

Comparison of rectoanal mucosal swab cultures and fecal cultures for determining prevalence of Escherichia coli O157:H7 in feedlot cattle

We compared fecal samples with samples collected with rectoanal mucosa swabs (RAMS) to determine the prevalence of Escherichia coli O157 in feedlot cattle (n = 747). Escherichia coli O157 was detected in 9.5% of samples collected with RAMS and 4.7% of samples tested by fecal culture. Pulsed-field gel electrophoresis analysis of isolates suggested that the strains colonizing the rectoanal junction were the same as those from the feces. Mucosal swab sampling was more sensitive than fecal sampling for determining the prevalence of E. coli O157 in feedlot cattle.     

Comparison of functional domains in vertebrate-type ferredoxins

The vertebrate-type Cys(4)Fe(2)S(2) ferredoxins are a class of small acidic proteins that typically act as electron shuttles between NAD(P)H-dependent reductases and monoxygenases, particularly cytochromes P450. Nuclear magnetic resonance assignments and detailed analysis of nuclear Overhauser effects permit the direct comparison of the functional C-terminal domains of three vertebrate-type ferredoxins, the mammalian adrenodoxin (Adx) and the bacterial ferredoxins putidaredoxin (Pdx) and terpredoxin (Tdx). In particular, homologous hydrogen-bonding networks involving a conserved basic residue (His 49 in Pdx, His 56 in Adx, Arg 49 in Tdx) are detailed. This hydrogen bond network appears to play a role in the mechanical transmission of redox-dependent conformational and dynamic changes from the iron-sulfur binding loop to the C-terminal domain. Hydrogen/deuterium exchange measurements have been made in Adx as a function of oxidation state for comparison with previous studies of Pdx and Tdx. The results of these measurements highlight the importance of the conserved basic residue in the linkage between oxidation state and protein dynamics. Finally, a series of mutations have been made in the C-terminal domain of Pdx, including one, Y51F, that disrupts the proposed hydrogen-bonding network without perturbing steric and hydrophobic interactions in the functional domain. Although the mutant is considerably destabilized with respect to wild-type Pdx, relatively unperturbed chemical shifts for residues near the site of the mutation and NOEs between water and Phe 51 suggest that the network is reconstituted with a solvent water in place of the tyrosine hydroxyl group in this mutant.     

Integrative control of rectoanal reflex in guinea pigs through lumbar colonic nerves

The aim of the present study was to analyze the neuromodulation of rectoanal reflex activity by lumbar sympathetic nerves in guinea pigs. The mechanical activities of the rectum were recorded with a balloon connected to a pressure transducer, and those of the internal anal sphincter (IAS) were recorded with a custom-made strain gauge force transducer. Gradual and sustained rectal distension evoked the rectoanal reflex, causing cholinergic contractions of the rectum and synchronous nitrergic relaxations of the IAS. Section of the lumbar colonic nerves enhanced both rectal contractions and IAS relaxations. Section of the 13th thoracic cord abolished both rectal contractions and IAS relaxations, but section of the lumbar colonic nerves restored them. Lumbar sympathectomy and pithing sacral cords greatly diminished these rectal contractions and IAS relaxations, but the intrinsic reflex component remained. NG-nitro-L-arginine methyl ester enhanced the intrinsic reflex-mediated contraction of the rectum and abolished reflex-mediated relaxation of the IAS and converted into cholinergic contractions. The present results indicate that the extrinsic lumbar inhibitory outflow causes marked inhibition of the rectoanal reflex via the lumbar colonic nerves.     

The functional form of angular forces around transition metal ions in biomolecules.

A method for generating angular forces around sigma-bonded transition metal ions is generalized to treat pi-bonded configurations. The theoretical approach is based on an analysis of ligand-field and small-cluster Hamiltonians based on the moments of the electron state distribution. The functional forms that are obtained involve a modification of the usual expression of the binding energy as a sum of ligand-ligand interactions, which, however, requires very little increase in CPU time. The angular interactions have simple forms involving sin and cos functions, whose relative weights depend on whether the ligands are sigma- or pi-bonded. They describe the ligand-field stabilization energy to an accuracy of about 10%, and the interaction energy of covalently bonded systems to an accuracy of better than 4%. The resulting functional forms for the force field are used to model the structure of small clusters, including fragments of the copper blue protein structure. Large deviations from the typical square copper coordination are found when pi-bonded ligands are present.     

Reproductive disorders in dairy cattle. II. Interrelationships between pre-or post-service infectious and functional disorders

This retrospective study was aimed at investigating the interrelationships between the various post-partum reproductive disorders whose incidence distribution was reported in a previous paper. There were 343 calving cows, and 319 of them were inseminated at least once. Although approximately one-third of the cows suffered from metritis, its influence on subsequent pathology was only minor. No within-animal relationship could be found between post-partum cyclic anestrus and post-AI anestrus. The distribution of repeat breeding cows showed that almost half of them also had post-AI anestrus, and only 17% had no other disorders. Previous metritis accounted for only 10% of these cases. Embryonic mortality was related only to post-partum cyclic anestrus. Finally, it was found that approximately half of the cows suffered from more than one reproductive disorder with many different relations between the disorders within individuals during post partum. In conclusion, optimal efficiency of post-partum reproduction requires careful checking of all possible disorders.     

Efficacy of EEG biofeedback procedures in correcting stress-related functional disorders

A promising approach to nondrug correction of human stress-induced functional disorders based on double EEG biofeedback (EEGBF) has been substantiated and experimentally tested. According to this approach, narrow-band EEG oscillators that are characteristic of each patient and detectable in real-time are simultaneously used in two independent feedback loops: the traditional adaptive biofeedback loop and an additional resonance stimulation loop. In the latter loop, the feedback signals from individual narrow-band EEG oscillators serve for automatic modulation of the parameters of sensory stimuli and are not perceived consciously by the subject. The combined use of the active (conscious perception) and passive (automatic modulation) feedback signals from narrow-band EEG components of the patient have been demonstrated to offer the possibility of a substantial increase in the efficacy of EEGBF.