Isobaric bubble growth: a consequence of altering atmospheric gas

During certain treatments of decompression sickness following dives made with compressed air, the U.S. Navy advocates breathing helium-oxygen mixtures. However, stable nitrogen bubbles created within gelatin by decompression have been found to enlarge when the atmosphere was switched from nitrogen to helium without changing ambient pressure. This suggests that decompression sickness would be worsened by switching from nitrogen to helium in the breathing gas mixture.     

Application of an enzyme-immunoassay (EIA) for rapid screening of 5 alpha-pregnane-3,20-dione (DHP) in blood plasma of the Asian elephant, Elephas maximus.

Populations of African (Loxodonta Africana) and Asian Elephants (Elephas maximus) in zoos and safari parks are at risk due to their low reproductive success. To extend the limited knowledge of their reproductive physiology, the development of easy and practical methods for the analysis of the relevant reproductive hormones is essential to support e.g. assisted reproduction. For the measurement of 5 alpha-pregnane-3,20-dione (DHP), the predominant ovarian gestagen in both species, an enzyme-immunoassay (EIA) based on commercial reagents was applied. Advantages of this EIA are the small volume of plasma needed for evaluation (5 microliters) and the possibility of direct processing without an extraction stage. The lower limit of detection was 0.16 ng/ml, the mean recovery was 101% and the mean coefficients of variation were 7.3% (intra-assay) and 9.9% (inter-assay). In Asian elephants, DHP levels reached 15 ng/ml during the luteal phase and up to 21 ng/ml during pregnancy. Estrous cycle lengths based on the lowest DHP concentrations varied from 12 to 20 weeks (mean 15.4 +/- 2.3). In two Asian elephant cows a calf was still-borne. Thereafter, the animals reassumed ovarian activity after approximately 8 and 13 weeks, respectively. In one animal estradiol implants for hormonal contraception caused a down regulation of the ovarian function as demonstrated by an irregular pattern of DHP secretion over a period of 48 weeks. We propose the direct DHP-EIA as a suitable method for reproductive monitoring in elephants, as it can be easily established in laboratories.     

Path-Coefficient Analysis of Seed Yield Components in Euphorbia lathyris L.

The interrelationships of seed yield components in Euphorbia lathyris L. have been studied by means of path-coefficient analysis. Two of seven components, ‘Number of flowers of primary inflorescence’ and ‘Number of flowers of secondary inflorescences’ proved to be of major importance through direct effects on ‘Total number of fruits’ as indicator of seed yield. Indirect effects generally arc being canalized via the same variables. Selection for seed yield is made possible through the relation between ‘Number of secondary branches’ and ‘Number of flowers of secondary inflorescences’.     

Molecular analysis of the hotspot of recombination in the murine major histocompatibility complex

Biological and serological assays have been used to define four subregions for the I region of the major histocompatibility complex (MHC) in the order I-A, I-B, I-J, and I-E. The I-J subregion presumably encodes the I-J polypeptide of the elusive T-cell suppressor factors. Restriction enzyme site polymorphisms and DNA sequence analyses of the I region from four recombinant mouse strains were used to localize the putative I-B and I-J subregions to a 1.0-kilobase (kb) region within the E beta gene. Sequencing this region from E beta clones derived from the two mouse strains: B10.A(3R), I-Jb and B10.A(5R), I-Jk initially used to define the I-J subregion revealed that these regions are identical, hence the distinct I-Jb and I-Jk molecules cannot be encoded by this DNA. In addition, the DNA sequence data also refute the earlier mapping of the I-B subregion. Analysis of the DNA sequences of three parental and four I region recombinants reveals that the recombinant events in three of the recombinant strains occurred within a 1-kb region of DNA, supporting the proposition that a hotspot for recombination exists in the I region. The only striking feature of this hotspot is a tetramer repeat (AGGC)n that shows 80 percent homology to the minisatellite sequence which may facilitate recombination in human chromosomes.     

Hallucinogenic amphetamine selectively destroys brain serotonin nerve terminals

(+/-)-3,4-Methylenedioxyamphetamine (MDA), an amphetamine analog with hallucinogenic activity, produced selective long-lasting reductions in the level of serotonin, the number of serotonin uptake sites, and the concentration of 5-hydroxyindoleacetic acid in rat brain. Morphological studies suggested that these neurochemical deficits were due to serotonin nerve terminal degeneration. These results show that MDA has toxic activity for serotonin neurons in rats and raise the question of whether exposure to MDA and related hallucinogenic amphetamines can produce serotonin neurotoxicity in the human brain.     

Academic research. California sets up three new institutes

Three University of California campuses were chosen last week as sites for a new $900 million program designed to keep the state a world leader in research and to bolster its economy. Each of the three schools will receive $25 million a year for 4 years from the state, with companies and other sources putting up at least twice that amount.     

Molecular biology. Targeting intron insertion into DNA

In work reported on page 452, researchers have found a way to coax certain introns, bits of genetic debris that litter the DNA and interrupt the coding sequences of many genes, to hop into the exact sequences where the researchers want them. The method could enhance all sorts of genetic manipulations, from studying basic gene function to combating viral infections to delivering genes for gene therapy.