Verification of biomechanical methods employed in a comprehensive study of mild traumatic brain injury and the effectiveness of American football helmets

Concussion, or mild traumatic brain injury, occurs in many activities, mostly as a result of the head being accelerated. A comprehensive study has been conducted to understand better the mechanics of the impacts associated with concussion in American football. This study involves a sequence of techniques to analyse and reconstruct many different head impact scenarios. It is important to understand the validity and accuracy of these techniques in order to be able to use the results of the study to improve helmets and helmet standards. Two major categories of potential errors have been investigated. The first category concerns error sources specific to the use of crash test dummy instrumentation (accelerometers) and associated data processing techniques. These are relied upon to establish both linear and angular head acceleration responses. The second category concerns the use of broadcast video data and crash test dummy head-neck-torso systems. These are used to replicate the complex head impact scenarios of whole body collisions that occur on the football field between two living human beings. All acceleration measurement and processing techniques were based on well-established practices and standards. These proved to be reliable and reproducible. Potential errors in the linear accelerations due to electrical or mechanical noise did not exceed 2% for the three different noise sources investigated. Potential errors in the angular accelerations due to noise could be as high as 6.7%, due to error accumulation of multiple linear acceleration measurements. The potential error in the relative impact velocity between colliding heads could be as high as 11%, and was found to be the largest error source in the sequence of techniques to reconstruct the game impacts. Full-scale experiments with complete crash test dummies in staged head impacts showed maximum errors of 17% for resultant linear accelerations and 25% for resultant angular accelerations.     

Developmental expression and assembly of connexins into homomeric and heteromeric gap junction hemichannels in the mouse mammary gland

During the development of the mammary gland, duct-lining epithelial cells progress through a program of expansive proliferation, followed by a terminal differentiation that allows for the biosynthesis and secretion of milk during lactation. The role of gap junction proteins, connexins, in the development and function of this secretory epithelium was investigated. Connexins, Cx26 and Cx32, were differentially expressed throughout pregnancy and lactation in alveolar cells. Cx26 poly-(A)(+) RNA and protein levels increased from early pregnancy, whereas Cx32 was detectable only during lactation. At this time, immunolocalization of connexins by confocal microscopy and immunogold labeling of high-pressure frozen freeze-substituted tissue showed that both connexins colocalized to the same junctional plaque. Analysis of gap junction hemichannels (connexons) isolated from lactating mammary gland plasma membranes by a rate-density centrifugation procedure, followed by immunoprecipitation and by size-exclusion chromatography, showed that Cx26 and Cx32 were organized as homomeric and heteromeric connexons. Structural diversity in the assembly of gap junction hemichannels demonstrated between pregnant and lactating mammary gland may account for differences in ionic and molecular signaling that may physiologically influence the onset and/or maintenance of the secretory phenotype of alveolar epithelial cells.     

Oligomeric structure of bAE3 protein

The "brain" form of the anion exchanger protein 3 (bAE3) has been purified to homogeneity from the rabbit kidney by differential centrifugation and immunoaffinity chromatography. A single protein band of approximately 165 kDa was detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. Monomers, dimers (a major component), and a higher oligomeric form (apparently tetramers) were found after oxidative cross-linking of purified bAE3. The largest form of bAE3 was separated from dimers and monomers by sucrose gradient centrifugation and was studied by transmission electron microscopy to confirm a tetrameric structure. Two main types of bAE3 images were detected, round (approximately 11-14 nm) and square-shaped (approximately 12 x 12 nm). Image analysis revealed fourfold rotational symmetry of both the round and square-shaped images, indicating that bAE3 consists of multiples of 4 subunits. We conclude that bAE3 in Triton X-100 solution is predominantly a mixture of dimers and tetramers with a smaller amount of monomers.     

Synaptic thermoprotection in a desert-dwelling Drosophila species

Synaptic transmission is a critical mechanism for transferring information from the nervous system to the body. Environmental stress, such as extreme temperature, can disrupt synaptic transmission and result in death. Previous work on larval Drosophila has shown that prior heat-shock exposure protects synaptic transmission against failure during subsequent thermal stress. This induced thermoprotection has been ascribed to an up-regulation of the inducible heat-shock protein, Hsp70. However, the mechanisms mediating natural thermoprotection in the wild are unknown. We compared synaptic thermosensitivity between D. melanogaster and a desert species, D. arizonae. Synaptic thermosensitivity and the functional limits of the related locomotor behavior differed significantly between closely related, albeit ecologically distinct species. Locomotory behavior of wandering third instar D. arizonae larvae was less thermosensitive and the upper temperature limit of locomotory function exceeded that of D. melanogaster by 6 degrees C. Behavioral results corresponded with significantly lower synaptic thermosensitivity at the neuromuscular junction in D. arizonae. Prior heat-shock protected only D. melanogaster by increasing relative excitatory junctional potential (EJP) duration, the time required for EJP failure at 40 degrees C, and the incidence of EJP recovery following heat-induced failure. Hsp70 induction profiles following heat-shock demonstrate up-regulation of inducible Hsp70 in D. melanogaster but not in D. arizonae. However, expression of Hsp70 under control conditions is greater in D. arizonae. These results suggest that the mechanisms of natural thermoprotection involve an increase in baseline Hsp70 expression.     

Identification of novel HLA-A2-restricted human immunodeficiency virus type 1-specific cytotoxic T-lymphocyte epitopes predicted by the HLA-A2 supertype peptide-binding motif

Virus-specific cytotoxic T-lymphocyte (CTL) responses are critical in the control of human immunodeficiency virus type 1 (HIV-1) infection and will play an important part in therapeutic and prophylactic HIV-1 vaccines. The identification of virus-specific epitopes that are efficiently recognized by CTL is the first step in the development of future vaccines. Here we describe the immunological characterization of a number of novel HIV-1-specific, HLA-A2-restricted CTL epitopes that share a high degree of conservation within HIV-1 and a strong binding to different alleles of the HLA-A2 superfamily. These novel epitopes include the first reported CTL epitope in the Vpr protein. Two of the novel epitopes were immunodominant among the HLA-A2-restricted CTL responses of individuals with acute and chronic HIV-1 infection. The novel CTL epitopes identified here should be included in future vaccines designed to induce HIV-1-specific CTL responses restricted by the HLA-A2 superfamily and will be important to assess in immunogenicity studies in infected persons and in uninfected recipients of candidate HIV-1 vaccines.     

Phase transformations in a model mesenchymal tissue

Connective tissues, the most abundant tissue type of the mature mammalian body, consist of cells suspended in complex microenvironments known as extracellular matrices (ECMs). In the immature connective tissues (mesenchymes) encountered in developmental biology and tissue engineering applications, the ECMs contain varying amounts of randomly arranged fibers, and the physical state of the ECM changes as the fibers secreted by the cells undergo fibril and fiber assembly and organize into networks. In vitro composites consisting of assembling solutions of type I collagen, containing suspended polystyrene latex beads ( approximately 6 microm in diameter) with collagen-binding surface properties, provide a simplified model for certain physical aspects of developing mesenchymes. In particular, assembly-dependent topological (i.e., connectivity) transitions within the ECM could change a tissue from one in which cell-sized particles (e.g., latex beads or cells) are mechanically unlinked to one in which the particles are part of a mechanical continuum. Any particle-induced alterations in fiber organization would imply that cells could similarly establish physically distinct microdomains within tissues. Here we show that the presence of beads above a critical number density accelerates the sol-gel transition that takes place during the assembly of collagen into a globally interconnected network of fibers. The presence of this suprathreshold number of beads also dramatically changes the viscoelastic properties of the collagen matrix, but only when the initial concentration of soluble collagen is itself above a critical value. Our studies provide a starting point for the analysis of phase transformations of more complex biomaterials including developing and healing tissues as well as tissue substitutes containing living cells.     

Nicotine's oxidative and antioxidant properties in CNS

Nicotine has been reported to be therapeutic in some patients with certain neurodegenerative diseases and to have neuroprotective effects in the central nervous system. However, nicotine administration may result in oxidative stress by inducing the generation of reactive oxygen species in the periphery and central nervous system. There is also evidence suggesting that nicotine may have antioxidant properties in the central nervous system. The antioxidant properties of nicotine may be intracellular through the activation of the nicotinic receptors or extracellular by acting as a radical scavenger in that it binds to iron. The possibility that nicotine might be used to treat some symptoms of certain neurodegenerative diseases underlies the necessity to determine whether nicotine has pro-oxidant, antioxidant or properties of both. This review discusses the studies that have addressed this issue, the behavioral effects of nicotine, and the possible mechanisms of action that result from nicotine administration or nicotinic receptor activation.     

A completely foreign receptor can mediate an interferon-gamma-like response

A tripartite receptor comprising the external region of the erythropoietin (Epo) receptor, the transmembrane and JAK-binding domains of the gp130 subunit of the interleukin-6 (IL-6) receptor, and a seven amino acid STAT1 recruitment motif (Y440) from the interferon (IFN)-gamma receptor, efficiently mediates an IFN-gamma-like response. An analogous completely foreign chimeric receptor in which the Y440 motif is replaced with the Y905 motif from gp130 also mediates an IFN-gamma-like response, but less efficiently. The IFNGR1 signal-transducing subunit of the IFN-gamma receptor is tyrosine phosphorylated through the chimeric receptors and the endogenous IL-6 and OSM receptors. Cross phosphorylation of IFNGR1 is not, however, required for the IFN-gamma-like response through the chimeric receptors, nor does it mediate an IFN-gamma-like response to IL-6 or OSM. The data argue strongly for modular JAK/STAT signalling and against any rigid structural organization for the "pathways" involved. They emphasize the likely high degree of overlap between the signals generated from disparate JAK-receptor complexes and show that relatively minor changes in such complexes can profoundly affect the response.