Search

The mechanical behavior of A265 high-performance fibers was experimentally investigated at both low and high strain rates. Axial, transverse, and torsional experiments were performed to measure the five material constants on a single fiber assumed as a linear, transversely isotropic material. In order to determine the tensile response of the fiber at high rates, a modified Kolsky tensile bar, also known as a split Hopkinson tension bar (SHTB) for single-fiber tests, was used. The diameter of each fiber was measured individually using a high-resolution scanning electron microscope for accurate stress calculation. A pulse shaper technique was adopted to generate a smooth and constant-amplitude incident pulse to produce deformation in the fiber specimen at a nearly constant strain rate. The tensile strength of the fiber exhibits both rate and gage-length effects. [ABSTRACT FROM AUTHOR]

Ca(2+) signals have profound and varied effects on growth cone motility and guidance. Modulation of Ca(2+) influx and release from stores by guidance cues shapes Ca(2+) signals, which determine the activation of downstream targets. Although the precise molecular mechanisms that underlie distinct Ca(2+)-mediated effects on growth cone behaviours remain unclear, recent studies have identified important players in both the regulation and targets of Ca(2+) signals in growth cones. [ABSTRACT FROM AUTHOR]

Presents the results of a study on the use of focal laser-induced photolysis (FLIP) of caged intracellular calcium ions to turn the motile tip, the nerve growth cone. Effect of a direct, spatially restricted elevation of intracellular Ca concentration on side of the growth cone; Impact through the integration of local and global Ca signals on turning responses under different environmental conditions during guidance.

Reports on the positive turning responses of the nerve growth cone in a defined extracellular gradient of the neurotransmitter acetylcholine (ACh). Dependence of the growth response on the activation of neuronal nicotinic ACh receptors; Results of fluorescence imaging of cytosolic Ca2+ concentration.

Mild head trauma, including concussion, can lead to chronic brain dysfunction and degeneration but the underlying mechanisms remain poorly understood. Here, we developed a novel head impact system to investigate the long-term effects of mild head trauma on brain structure and function, as well as the underlying mechanisms in Drosophila melanogaster. We find that Drosophila subjected to repetitive head impacts develop long-term deficits, including impaired startle-induced climbing, progressive brain degeneration, and shortened lifespan, all of which are substantially exacerbated in female flies. Interestingly, head impacts elicit an elevation in neuronal activity and its acute suppression abrogates the detrimental effects in female flies. Together, our findings validate Drosophila as a suitable model system for investigating the long-term effects of mild head trauma, suggest an increased vulnerability to brain injury in female flies, and indicate that early altered neuronal excitability may be a key mechanism linking mild brain trauma to chronic degeneration. [ABSTRACT FROM AUTHOR]

Dendritic spines undergo actin-based growth and shrinkage during synaptic plasticity, in which the actin depolymerizing factor (ADF)/cofilin family of actin-associated proteins are important. Elevated ADF/cofilin activities often lead to reduced spine size and immature spine morphology but can also enhance synaptic potentiation in some cases. Thus, ADF/cofilin may have distinct effects on postsynaptic structure and function. We found that ADF/cofilin-mediated actin dynamics regulated AMPA receptor (AMPAR) trafficking during synaptic potentiation, which was distinct from actin's structural role in spine morphology. Specifically, elevated ADF/cofilin activity markedly enhanced surface addition of AMPARs after chemically induced long-term potentiation (LTP), whereas inhibition of ADF/cofilin abolished AMPAR addition. We found that chemically induced LTP elicited a temporal sequence of ADF/cofilin dephosphorylation and phosphorylation that underlies AMPAR trafficking and spine enlargement. These findings suggest that temporally regulated ADF/cofilin activities function in postsynaptic modifications of receptor number and spine size during synaptic plasticity. [ABSTRACT FROM AUTHOR]

Postsynaptic receptor localization is crucial for synapse development and function, but the underlying cytoskeletal mechanisms remain elusive. Using Xenopus neuromuscular junctions as a model, we found that actin depolymerizing factor (ADF)/cofilin regulated actin-dependent vesicular trafficking of acetylcholine receptors (AChRs) to the postsynaptic membrane. Active ADF/cofilin was concentrated in small puncta adjacent to AChR clusters and was spatiotemporally correlated with the formation and maintenance of surface AChR clusters. Notably, increased actin dynamics, vesicular markers and intracellular AChRs were all enriched at the sites of ADF/cofilin localization. Furthermore, a substantial amount of new AChRs was detected at these ADF/cofilin-enriched sites. Manipulation of either ADF/cofilin activity through its serine-3 phosphorylation or ADF/cofilin localization via 14-3-3 proteins markedly attenuated AChR insertion and clustering. These results suggest that spatiotemporally restricted ADF/cofilin-mediated actin dynamics regulate AChR trafficking during the development of neuromuscular synapses. [ABSTRACT FROM AUTHOR]

Axon pathfinding requires directional responses of growth cones to extracellular cues, which have been shown to involve local synthesis of protein. The identity and functions of the locally produced proteins remain, however, unclear. Here we report that Ca2+-dependent bidirectional turning of Xenopus laevis growth cones requires localized distribution and translation of β-actin messenger RNA. Both β-actin mRNA and its zipcode-binding protein, ZBP1, are localized at the growth cone and become asymmetrically distributed upon local exposure to brain-derived neurotrophic factor (BDNF). Inhibition of protein synthesis or antisense interference with β-actin mRNA-ZBP1 binding abolishes both Ca2+-mediated attraction and repulsion. In addition, attraction involves a local increase in β-actin, whereas repulsion is accompanied by a local decrease in β-actin; thus, both produce a synthesis- and ZBP1 binding-dependent β-actin asymmetry but with opposite polarities. Together with a similar asymmetry in Src activity during bidirectional responses, our findings indicate that Ca2+-dependent spatial regulation of β-actin synthesis through Src contributes to the directional motility of growth cones during guidance. [ABSTRACT FROM AUTHOR]