Characteristics of microwave evoked body movements in mice

Microwave evoked body movements were studied in mice. A resonant cavity was used to provide head and neck exposure of the mouse to pulsed and gated continuous wave (CW) 1.25 GHz microwaves. No difference in response to pulsed and gated CW stimuli of equal average power was found. The incidence of the microwave evoked body movements increased proportionally with specific absorption (dose) when the whole-body average specific absorption rate was at a constant level (7300 W/kg). Under a constant average specific absorption rate, the response incidence reached a plateau at 0.9 kJ/kg. For doses higher than 0.9 kJ/kg, response incidence was proportional to the specific absorption rate and reached a plateau at 900 W/kg. Body movements could be evoked by a single microwave pulse. The lowest whole-body specific absorption (SA) tested was 0.18 kJ/kg, and the corresponding brain SA was 0.29 kJ/kg. Bulk heating potentials of these SAs were less than 0.1 °C. For doses higher than 0.9 kJ/kg, the response incidence was also proportional to subcutaneous temperature increment and subcutaneous heating rate. The extrapolated absolute thresholds (0% incidence) were 1.21 °C temperature increment and 0.24 °C/s heating rate. Due to high subcutaneous heating rates, these microwaves must be perceived by the mouse as an intense thermal sensation but not a pain sensation because the temperature increment was well below the threshold for thermal pain. Results of the present study should be considered in promulgation of personnel protection guideline against high peak power but low average power microwaves. © 1994 Wiley-Liss, Inc.     

Fluorescence lifetime analysis of DNA intercalated ethidium bromide and quenching by free dye

The fluorescence characteristics of ethidium bromide (Eb) complexed to calf thymus DNA have been examined using fluorescence lifetime analysis for a range of DNA (effective nucleotide concentration) to Eb molar ratios. Control of both temperature and ion concentration is necessary for reproducible analyses. Eb complexed to double stranded DNA has a maximum fluorescence lifetime of 23 ns and is easily distinguishable from a fluorescence lifetime value of 1.67 ns corresponding to unbound Eb. In a solution of calf thymus DNA containing excess Eb a binding equilibrium is reached, and this corresponds to one Eb molecule for every five nucleotides. With increasing amounts of unbound Eb, the fluorescence lifetime of the DNA-Eb complex decreases with a concomitant drop in the steady state fluorescence intensity, without a change in the amount of Eb bound to DNA. It is concluded that unbound Eb, acting via a quenching mechanism, shortens the fluorescence lifetime of bound Eb and consequently decreases the overall fluorescence intensity. This means that a different approach is necessary: time-resolved fluorescence spectroscopy directly distinguishes between a decrease in fluorescence intensity due to quenching by an excess of unbound Eb from that due to a decrease in Eb binding to double-stranded DNA. These studies suggest that techniques which measure total steady state fluorescence intensity of bound Eb in order to infer relative amounts of double-stranded DNA must be interpreted with caution. For such assays to be valid it is essential that no unbound Eb be present; otherwise a variable correction factor is required to account for unbound Eb.     

Bloom Syndrome and Maternal Uniparental Disomy for Chromosome 15

Bloom syndrome (BS) is an autosomal recessive disorder characterized by increases in the frequency of sister-chromatid exchange and in the incidence of malignancy. Chromosome-transfer studies have shown the BS locus to map to chromosome 15q. This report describes a subject with features of both BS and Prader-Willi syndrome (PWS). Molecular analysis showed maternal uniparental disomy for chromosome 15. Meiotic recombination between the two disomic chromosomes 15 has resulted in heterodisomy for proximal 15q and isodisomy for distal 15q. In this individual BS is probably due to homozygosity for a gene that is telomeric to D15S95 (15q25), rather than to genetic imprinting, the mechanism responsible for the development of PWS. This report represents the first application of disomy analysis to the regional localization of a disease gene. This strategy promises to be useful in the genetic mapping of other uncommon autosomal recessive conditions.     

Natural and Electroporation-Mediated Transformation of Methanococcus voltae Protoplasts

The lack of high-efficiency transformation systems has severely impeded genetic research on methanogenic members of the kingdom Archaeobacteria. By using protoplasts of Methanococcus voltae and an integration vector, Mip1, previously shown to impart puromycin resistance, we obtained natural transformation frequencies that were about 80-fold higher (705 transformants per μg of transforming DNA) than that reported with whole cells. Electroporation-mediated transformation of M. voltae protoplasts with covalently closed circular Mip1 DNA was possible, but at lower frequencies of ca. 177 transformants per μg of vector DNA. However, a 380-fold improvement (3,417 transformants per μg of DNA) over the frequency of natural transformation with whole cells was achieved by electroporation of protoplasts with linearized DNA. This general approach, of using protoplasts, should allow the transformation of other methanogens, especially those that may be gently converted to protoplasts as a result of their tendency to lyse in hypotonic solutions.     

Influence of Plumbing Materials on Biofilm Formation and Growth of Legionella pneumophila in Potable Water Systems

A two-stage chemostat model of a plumbing system was developed, with tap water as the sole nutrient source. The model system was populated with a naturally occurring inoculum derived from an outbreak of Legionnaires' disease and containing Legionella pneumophila along with associated bacteria and protozoa. The model system was used to develop biofilms on the surfaces of a range of eight plumbing materials under controlled, reproducible conditions. The materials varied in their abilities to support biofilm development and the growth of L. pneumophila. Elastomeric surfaces had the most abundant biofilms supporting the highest numbers of L. pneumophila CFU; this was attributed to the leaching of nutrients for bacterial growth from the materials. No direct relationship existed between total biofouling and the numbers of L. pneumophila CFU.     

BIOCHEMICAL HETEROZYGOSITY AND MORPHOLOGIC VARIATION IN A COLONY OF PAPIO HAMADRYAS HAMADRYAS BABOONS

This analysis examines the association between genetic heterozygosity and individual morphologic variation in a captive population of Papio hamadryas hamadryas consisting of 403 juveniles and adults. The population structure of the colony was artificially generated and maintained and is thus rigorously defined. Subpopulations delimited by age, sex, and degree of inbreeding are also explored. Heterozygosity, as enumerated from six simple Mendelian biochemical loci, is compared with the residual morphologic variation of each individual for each of 20 quantitative traits. Use of a sequential Bonferroni technique nullifies all significant correlations. Principal-components analysis reduces the morphometrics to a single or few significant axes in each population. The first axis of the total population contains 86.07% of the variation in the sample and the absolute values of the factor scores exhibit a significant positive correlation with heterozygosity at P < 0.05. Correcting for age- and sex-related variation in the total population with a linear model subsequently demonstrates that no significant correlation between heterozygosity and morphologic variation exists. No significant relationship is found in the inbred animals or subpopulations when age and sex are controlled. Previous studies have indicated that individuals proximal to the population mean for a specific polygenic trait exhibit a higher biochemical heterozygosity than individuals distant from the mean. The results presented here, which are based on more loci than many studies and a well-defined population, do not support this relationship. Substructuring of a population by age and sex can lead to spurious correlations with univariate or multivariate techniques. Comprehensive indices of genetic variation and rigorous statistical techniques should be used in future analyses. Studies that fail to recognize these design elements should be interpreted with caution.     

Phosphorylation and Palmitoylation of the Human D2L Dopamine Receptor in Sf9 Cells

Abstract: We have expressed and biochemically characterized the human D2_long (D2_L) dopamine receptor isoform using the baculovirus/Sf9 cell system. The expressed receptor bound ligands with a pharmacological profile similar to that reported for neuronal and cloned D2_L receptors expressed in mammalian cell lines. Dopamine binding to D2_L receptor was sensitive to guanine nucleotides, indicating receptor coupling to endogenous G proteins. A D2_L receptor-specific antibody identified two major protein species at ∼44 kDa and at ∼93 kDa in immunoblots, suggesting the presence of D2_L receptor monomers and dimers. Both species were purified by immunoprecipitation from digitonin-solubilized preparation of cells expressing D2_L receptor prelabeled with ³²P_i or [³H]-palmitate. These results constitute the first direct evidence for D2_L receptor phosphorylation and palmitoylation.     

Amino Acid Residues 226–240 of τ Which Encompass the First Lys-Ser-Pro Site of τ, Are Partially Phosphorylated in Alzheimer Paired Helical Filament-τ

Abstract: A synthetic peptide corresponding to residues 226–240 (E9 peptide) of human τ, which contains an Lys-Ser-Pro motif, was used to raise a polyclonal antibody. The antibody, E9, was 10-fold less reactive with phospho-E9 peptide than with native E9 peptide. E9 antibody was used to study the extent of phosphorylation in a modified form of τ (PHF-τ) that is found in Alzheimer's disease brain and is incorporated into paired helical filaments (PHFs). E9 immunolabeled Alzheimer's disease neurofibrillary tangles and abnormal neurites in brain sections intensely, with increased immunoreactivity detected after pretreatment of sections with phosphatase. On immunoblots and ELISA, E9 reacted with PHF-τ and recombinant human τ but not with the high and middle molecular weight neurofilament proteins. Phosphatase treatment of PHF-τ improved the E9 immunoreactivity by 30–50%. Dephosphorylated high but not middle molecular weight neurofilament protein became reactive with E9. These results indicate that <50% of the PHF-T is phosphorylated in the subregion corresponding to residues 226–240 of τ and suggest that the phosphorylation of this region may not be essential for PHF formation.     

Cation transport systems in mitochondria: Na+ and K+ uniports and exchangers

It is now well established that mitochondria contain three antiporters that transport monovalent cations. A latent, allosterically regulated K⁺/H⁺ antiport appears to serve as a cation-extruding device that helps maintain mitochondrial volume homeostasis. An apparently unregulated Na⁺/H⁺ antiport keeps matrix [Na⁺] low and the Na⁺-gradient equal to the H⁺-gradient. A Na⁺/Ca²⁺ antiport provides a Ca²⁺-extruding mechanism that permits the mitochondrion to regulate matrix [Ca²⁺] by balancing Ca²⁺ efflux against influx on the Ca²⁺-uniport. All three antiports have well-defined physiological roles and their molecular properties and regulatory features are now being determined. Mitochondria also contain monovalent cation uniports, such as the recently described ATP- and glibenclamide-sensitive K⁺ channel and ruthenium red-sensitive uniports for Na⁺ and K⁺. A physiological role of such uniports has not been established and their properties are just beginning to be defined.     

Analysis of nitrogen saturation potential in Rocky Mountain tundra and forest: implications for aquatic systems

We employed grass and forest versions of the CENTURY model under a range of N deposition values (0.02–1.60 g N m^–2 y^–1) to explore the possibility that high observed lake and stream N was due to terrestrial N saturation of alpine tundra and subalpine forest in Loch Vale Watershed, Rocky Mountain National Park, Colorado. Model results suggest that N is limiting to subalpine forest productivity, but that excess leachate from alpine tundra is sufficient to account for the current observed stream N. Tundra leachate, combined with N leached from exposed rock surfaces, produce high N loads in aquatic ecosystems above treeline in the Colorado Front Range. A combination of terrestrial leaching, large N inputs from snowmelt, high watershed gradients, rapid hydrologic flushing and lake turnover times, and possibly other nutrient limitations of aquatic organisms constrain high elevation lakes and streams from assimilating even small increases in atmospheric N. CENTURY model simulations further suggest that, while increased N deposition will worsen the situation, nitrogen saturation is an ongoing phenomenon.