Myelinating glia differentiation is regulated by extracellular matrix elasticity

The mechanical properties of living tissues have a significant impact on cell differentiation, but remain unexplored in the context of myelin formation and repair. In the PNS, the extracellular matrix (ECM) incorporates a basal lamina significantly denser than the loosely organized CNS matrix. Inhibition of non-muscle myosin II (NMII) enhances central but impairs peripheral myelination and NMII has been implicated in cellular responses to changes in the elasticity of the ECM. To directly evaluate whether mechanotransduction plays a role in glial cell differentiation, we cultured Schwann cells (SC) and oligodendrocytes (OL) on matrices of variable elastic modulus, mimicking either their native environment or conditions found in injured tissue. We found that a rigid, lesion-like matrix inhibited branching and differentiation of OL in NMII-dependent manner. By contrast, SC developed normally in both soft and stiffer matrices. Although SC differentiation was not significantly affected by changes in matrix stiffness alone, we found that expression of Krox-20 was potentiated on rigid matrices at high laminin concentration. These findings are relevant to the design of biomaterials to promote healing and regeneration in both CNS and PNS, via transplantation of glial progenitors or the implantation of tissue scaffolds

Optical properties of natural magnetite in the region from 2.5 to 50 μm

Infrared transmission measurements at 300° K from 2.5 to 50 μm have been carried out on natural magnetite (Fe3O4) from Mineville, New York. The measurements were made on magnetite powder in the form of a pellet and for two concentrations of 0.5 and 1.0 per cent. The spectrum analysis gave characteristic absorptions though broad and weak between 1100 and 200 cm-1. The absorption coefficient α, the refractive index n, the real εlunate1 and imaginary εlunate2 parts of the dielectric constant and the reflectivity R have also been calculated. © 1975

CYTOPLASMIC LOCALISATION OF AUSTRALIA ANTIGEN IN THE LIVER

Australia (Au) antigen was detected by immunofluorescence in liver specimens from 9 patients with chronic liver disease and circulating Au antigen, and from 22 Au-antigen carriers with histologically normal livers. This antigen was not found in the livers of 23 seronegative patients. Au antigen was located in the cytoplasm of hepatocytes. No nuclear fluorescence specific for Au antigen was detected. The number of fluorescent liver cells and the intensity of fluorescence were much greater in Au-antigen carriers than in patients with liver disease. No γ-globulin or β-1C was found in any the liver specimens. These results agree with the view that Au antigen may be a virus-coat material produced in excess in the cytoplasm of liver cells and suggest that its presence in the liver is unrelated to do cytopathic effects of hepatitis virus B. Most apparently healthy Au-antigen carriers may have a balanced intracellular infection which produces large amounts of Au antigen in cytoplasm of the hepatocytes but few or no infectious viruses. © 1972

Rigid-Plastic Approximations for Predicting Plastic Deformation of Cylindrical Shells Subject to Dynamic Loading

A theoretical approach was developed for predicting the plastic deformation of a cylindrical shell subject to asymmetric dynamic loads. The plastic deformation of the leading generator of the shell is found by solving for the transverse deflections of a rigid-plastic beam/string-on-foundation. The axial bending moment and tensile force in the beam/string are equivalent to the longitudinal bending moments and membrane forces of the shell, while the plastic foundation force is equivalent to the shell circumferential bending moment and membrane resistances. Closed-form solutions for the transient and final deformation profile of an impulsive loaded shell when it is in a “string” state were derived using the eigenfunction expansion method. These results were compared to DYNA 3D predictions. The analytical predictions of the transient shell and final centerline deflections were within 25% of the DYNA 3D results.United States. Office of Naval Research (Grant N000 14-94-1-1026

Rigid-Plastic Approximations for Predicting Plastic Deformation of Cylindrical Shells Subject to Dynamic Loading

A theoretical approach was developed for predicting the plastic deformation of a cylindrical shell subject to asymmetric dynamic loads. The plastic deformation of the leading generator of the shell is found by solving for the transverse deflections of a rigid-plastic beam/string-on-foundation. The axial bending moment and tensile force in the beam/string are equivalent to the longitudinal bending moments and membrane forces of the shell, while the plastic foundation force is equivalent to the shell circumferential bending moment and membrane resistances. Closed-form solutions for the transient and final deformation profile of an impulsive loaded shell when it is in a “string” state were derived using the eigenfunction expansion method. These results were compared to DYNA 3D predictions. The analytical predictions of the transient shell and final centerline deflections were within 25% of the DYNA 3D results