EphrinB3 blocks EphB3 dependence receptor functions to prevent cell death following traumatic brain injury.

Eph receptor tyrosine kinases and their membrane-bound ligands, ephrins, have a variety of roles in the developing and adult central nervous system that require direct cell-cell interactions; including regulating axon path finding, cell proliferation, migration and synaptic plasticity. Recently, we identified a novel pro-survival role for ephrins in the adult subventricular zone, where ephrinB3 blocks Eph-mediated cell death during adult neurogenesis. Here, we examined whether EphB3 mediates cell death in the adult forebrain following traumatic brain injury and whether ephrinB3 infusion could limit this effect. We show that EphB3 co-labels with microtubule-associated protein 2-positive neurons in the adult cortex and is closely associated with ephrinB3 ligand, which is reduced following controlled cortical impact (CCI) injury. In the complete absence of EphB3 (EphB3(-/-)), we observed reduced terminal deoxynucleotidyl transferase-dUTP nick end labeling (TUNEL), and functional improvements in motor deficits after CCI injury as compared with wild-type and ephrinB3(-/-) mice. We also demonstrated that EphB3 exhibits dependence receptor characteristics as it is cleaved by caspases and induces cell death, which is not observed in the presence of ephrinB3. Following trauma, infusion of pre-clustered ephrinB3-Fc molecules (eB3-Fc) into the contralateral ventricle reduced cortical infarct volume and TUNEL staining in the cortex, dentate gyrus and CA3 hippocampus of wild-type and ephrinB3(-/-) mice, but not EphB3(-/-) mice. Similarly, application of eB3-Fc improved motor functions after CCI injury. We conclude that EphB3 mediates cell death in the adult cortex through a novel dependence receptor-mediated cell death mechanism in the injured adult cortex and is attenuated following ephrinB3 stimulation.

Characterization of partially sintered ceramic powder compacts using fluorinated gas NMR imaging.

We use nuclear magnetic resonance (NMR) imaging of C2F6 gas to characterize porosity, mean pore size, and permeability of partially sintered ceramic (Y-TZP Yttria-stabilized tetragonal-zirconia polycrystal) samples. Conventional measurements of these parameters gave porosity values from 0.18 to 0.4, mean pore sizes from 10 nm to 40 nm, and permeability from 4 nm(2) to 25 nm(2). The NMR methods are based on relaxation time measurements (T(1)) and the time dependent diffusion coefficient D(Delta). The relaxation time of C2F6 gas is longer in pores than in bulk gas and it increases as the pore sizes decrease. NMR yielded accurate porosity values after correcting for surface adsorption effects. A model for T(1) dependence on pore size that accounts for collisions between gas molecules and walls as well as surface adsorption effects is proposed. The model fits the experimental data well. Finally, the long time limit of D(Delta)/D(o), where D(o) is the bulk gas diffusion coefficient is useful for measuring tortuosity, while the short time limit was not achieved experimentally and could not be used for calculating surface-area to volume (S/V) ratios.

Constitutive magnification by the Ybb- chromosome of Drosophila melanogaster.

Ybb- is an rDNA-deficient chromosome of Drosophila that has often been used in magnification experiments to induce high-frequency reversion of bobbed (bb) chromosomes. We observed previously that Ybb- causes ring chromosome loss even when the rings are bb+, suggesting that Ybb- induces magnifying sister chromatid exchanges in bb+ rings. Here we show that the Ybb- chromosome causes low levels of bb magnification in bb+ flies. We refer to the ability of Ybb- to bypass the rDNA deficiency requirement for magnification as 'constitutive' magnification. We have magnified the ribosomal genes on the Ybb- chromosome and analysed the revertant chromosomes using genetic and molecular methods. We find that magnified Ybb- chromosomes also exhibit constitutive magnifier activity. Molecular analysis shows that both type 1 and type 2 intron+ ribosomal gene repeats are associated with magnified Ybb- chromosomes. Type 2 introns have been described previously in the rDNA of both X and Y chromosomes. However, type 1 intervening sequences are thought to be present only in X, but not Y, ribosomal genes. Some of the Ybb- type 1 insertions differ from those present in the rDNA of X chromosomes in that they contain an EcoRI site, and some may be present in tandem arrays. The constitutive magnifier activity of Ybb- may reside either in the structurally unusual ribosomal gene intervening sequences associated with the chromosome, or in the locus on YL that is required for magnification to occur.

Effects of histamine-2 receptor blockade on lidocaine kinetics.

The hypothesis that the H2-receptor blockers cimetidine and ranitidine have different effects on the disposition of lidocaine, a microsomally metabolized drug dependent on hepatic blood flow for elimination, was tested. Six normal men received lidocaine infusions (2 mg/kg over 10 minutes) and lidocaine levels were determined by HPLC. Lidocaine kinetics were studied in the untreated state (O) and in a double-blind, double-dummy design after 2 days of placebo (P), cimetidine (C, 300 mg every 6 hours by mouth), or ranitidine (R, 160 mg every 12 hours by mouth). Model-independent kinetics were estimated by the statistical moment theory. The steady-state volume of distribution was lower after cimetidine (means +/- SD: O, 156 +/- 39 L; P, 156 +/- 48 L; C, 123 +/- 20 L; and R, 174 +/- 38 L). A trend toward decreased lidocaine clearance after cimetidine was also noted (O, 1011 +/- 140 ml/min; P, 1087 +/- 227 ml/min; C, 886 +/- 214 ml/min; and R, 1143 +/- 225 ml/min). Elimination rate constants were of the same order in all four treatments. Only higher levels of alpha 1-acid glycoprotein appeared to limit the lidocaine steady-state volume of distribution. Cimetidine and ranitidine have distinctly different effects on lidocaine kinetics in normal subjects. The absence of ranitidine effects on the disposition of lidocaine, a high-extraction, high-clearance drug, suggests that H2-receptor blockade may not decrease hepatic blood flow, and that cimetidine impairs drug elimination only by inhibition of hepatic microsomal enzymes. Such interactions are not likely to occur with ranitidine.