Regulation of Brain and Cerebrospinal Fluid Calcium by Brain Barrier Membranes Following Vitamin D-Related Chronic Hypo- and Hypercalcemia in Rats

Male Fischer-344 rats, 21 days old, were fed diets containing 0 (LOD), 2,200 (CONT), or 440,000 (HID) international units of vitamin D3 per kilogram for 12 weeks. [Ca] was measured in plasma, CSF, brain, and choroid plexus. In addition, 45Ca and 36Cl transfer coefficients (KCa and KCl) for uptake from blood into CSF and brain were determined. Although plasma ionized [Ca]s in LOD and HID rats were 50% and 136%, respectively, of values in CONT animals, CSF and brain [Ca]s ranged from only 85% to 110% of respective CONT values. Choroid plexus [Ca] was increased by 37% after HID diet, but was decreased only 10% after LOD. KCa values at CSF, parietal cortex, and pons-medulla were negatively correlated with plasma ionized [Ca], whereas KCl values at CSF and brain were not different between the diet groups. The findings demonstrate that central nervous system [Ca] is maintained during chronic hypo- or hypercalcemia by saturable transport of Ca at brain barrier membranes. This transport does not seem to involve modulation by 1,25-dihydroxyvitamin D3.     

Depletion of Brain Glutathione in Preweanling Mice by L-Buthionine Sulfoximine

Previous studies indicated that DL-buthionine sulfoximine (DL-BSO), an agent that inhibits the biosynthesis of GSH in liver and other peripheral organs, fails to suppress levels of GSH in the CNS. In the current study, preweanling mice responded to repeated injections of L-BSO with marked declines (79.6-86.5%) of GSH content in brain and spinal cord. In adult mice, the same treatment schedule produced only modest declines (17.8-29.2%) of GSH content in brain and a 55.9% decline in spinal cord. Pretreatment of preweanling mice with L-BSO represents a tool for studying the role of GSH in the CNS.     

A statistical analysis for the mouse lymphoma cell forward mutation assay

This paper illustrates the usefulness of solvent control trials and presents a statistical analysis for mouse L5178Y lymphoma data. Examination of solvent control trials establishes that the natural logarithm of mutant frequency is approximately normally distributed and that both the mean and variance of mutant frequency vary by trial. There is little evidence of downturns at higher doses in the dose-response curves studied; therefore, a trend test is proposed for the detection of an increasing dose-response curve. A Monte Carlo investigation confirms that the proposed trend test is better able to detect an increasing dose-response than 4 alternate methods of analysis.     

Respiration and soluble sugar metabolism in sugar pine embryos

Embroys excised from dormant seeds of sugar pine ( Pinus lambertiana Dougl.) incubated at 25°C (non-dormancy-breaking) or stratified at 5°C (dormancy-breaking) were analyzed to determine temperature effects on the relative activities of respiration and fermentative metabolism, the levels of soluble sugers and the activities of the hydrolytic enzymes, invertase and sucrose synthase, as related to the release of dormancy and germinatio. At 25°C, despite a sharp drop in embryo oxygen uptake after 48 h, a simultaneous decline in acetaldehyde and ethanol concentrations indicated that there was not a shift to fermentative metabolism. The concentrations of soluble sugars showed no treatment effects. Embryo invertase (EC 3.2.1.26) activity changed only slightly at either temperature, while stratification was accompanied by a 4-fold increase in sucrose synthase (EC 2.4.1.13) activity (cleavage direction). Upon transfer of stratified seeds to 25°C, embryo sucrose synthase activity rapidly increased almost 10-fold, with the increase beginning prior to germination, while mvertase activity increased 20-fold, concomitant with germination.     

Direct demonstration of actin filament annealing in vitro

Direct electron microscopic examination confirms that short actin filaments rapidly anneal end-to-end in vitro, leading over time to an increase in filament length at steady state. During annealing of mixtures of native unlabeled filaments and glutaraldehyde-fixed filaments labeled with myosin subfragment-1, the structural polarity within heteropolymers is conserved absolutely. Annealing does not appear to require either ATP hydrolysis or the presence of exogenous actin monomers, suggesting that joining occurs through the direct association of filament ends. During recovery from sonication the initial rate of annealing is consistent with a second-order reaction involving the collision of two filament ends with an apparent annealing rate constant of 10(7) M-1s-1. This rapid phase lasts less than 10 s and is followed by a slow phase lasting minutes to hours. Annealing is calculated to contribute minimally to filament elongation during the initial stages of self-assembly. However, the rapid rate of annealing of sonicated fixed filaments observed in vitro suggests that it may be an efficient mechanism for repairing breaks in filaments and that annealing together with polymer-severing mechanisms may contribute significantly to the dynamics and function of actin filaments in vivo.     

The objective structured interview for medical student selection

An objective structured interview is an integral part of the process of selecting and admitting applicants to study medicine at this university. During the nine years (to the end of 1986) that the interview has been used 1600 candidates were interviewed out of roughly 13 000 applicants, and from these, 584 students were admitted to the course. Analysis of the interview data was carried out based on two aspects of student progress: graduation with honours and failure to complete the course of study.The interview as a whole, and especially some of the subscales, appears to identify students who may fail to complete the course: it may also help to predict which students are likely to graduate with honours.