Implications of climate change for the reproductive capacity and survival of New World silversides (family Atherinopsidae).

The New World silversides (family Atherinopsidae) are found in marine, estuarine and inland waters of North, Central and South America, where they are ecologically important as forage fishes and sometimes economically important for commercial and recreational fisheries. This report reviews the knowledge of the reproductive attributes of temperate and subtropical atherinopsids in relation to temperature and discusses the potential effects of climate change on their reproduction and adaptive responses. Their reproductive cycles are primarily entrained by photoperiod with high temperature acting as a limiting factor. They are generally multiple spawners which release successive batches of eggs in spring, but some species can spawn also in autumn and even summer when temperatures do not increase excessively. The decoupling of temperature patterns and photoperiod with further global warming and associated asymmetric thermal fluctuations could lead to spawning at times or temperatures that are unsuitable for larval development and growth. Many members of this family show temperature-dependent sex determination (TSD), where the phenotypic sex of an individual is determined partly or wholly by the temperature experienced during gonadal sex differentiation, and high-temperature induced germ cell degeneration and decreased fertility. The predicted short-term reproductive responses of atherinopsids to climate change therefore include acceleration, shortening or overall disruption of spawning activity, and also more subtle, but nonetheless equally population-threatening, dysfunctions such as highly skewed sex ratios and partial or total loss of fertility. In the case of species with TSD, asymmetric thermal fluctuations could also cause larvae to encounter temperatures lower than normal during early development and be feminized. Such dysfunctions have been documented already in natural populations but are confined so far to landlocked, inland water habitats, perhaps because they impose more severe thermal fluctuations and limitations to migration and dispersal. The severity and recurrence of these dysfunctions with further climate change will depend both on the magnitude, speed and pattern of change and on how much (or how fast) physiological and behavioural traits can evolve to match the new conditions imposed by the climate, which is largely unknown. In this regard, compelling evidence is shown that numerous traits, including the sex determination system, are capable of rapid evolution and could mitigate the negative effects of temperature increases on population viability in atherinopsids.

Investigation of protein expression in magnetic field-treated human glioma cells.

We previously reported phenotypic changes in human breast cancer cells following low-level magnetic field (MF) exposure. Here proteomic methods were used to investigate the biochemical effect of MF exposure in SF767 human glioma cells. Protein alterations were studied after exposure to 1.2 microTesla (microT) MF [12 milliGauss (mG), 60 Hertz (Hz)] +/- epidermal growth factor (EGF). SF767 cells were exposed for 3 h to sham conditions (<0.2 microT ambient field strength) or 1.2 microT MF (+/-EGF; 10 ng/ml). Solubilized protein fractions (sham; 1.2 microT; sham + EGF; 1.2 microT + EGF) were loaded for electrophoresis by 2D-PAGE and stained using a colloidal Coomassie blue technique to resolve and characterize the proteins. Protein patterns were compared across groups via Student's t-test using PDQUEST software. Cell profiles revealed significant alterations in the spot density of a subset of treated cells. Automated spot excision and processing was performed prior to peptide mass fingerprinting proteins of interest. Fifty-seven proteins from the detectable pool were identified and/or found to differ significantly across treatment groups. The mean abundance of 10 identified proteins was altered following 1.2 microT exposure. In the presence of EGF six proteins were altered after low magnetic field treatment by increasing (4) or decreasing (2) in abundance. The results suggest that the analysis of differentially expressed proteins in SF767 cells may be useful as biomarkers for biological changes caused by exposure to magnetic fields.

Engineering and public health at CDC.

Engineering is the application of scientific and technical knowledge to solve human problems. Using imagination, judgment, and reasoning to apply science, technology, mathematics, and practical experience, engineers develop the design, production, and operation of useful objects or processes. During the 1940s, engineers dominated the ranks of CDC scientists. In fact, the first CDC director, Assistant Surgeon General Mark Hollis, was an engineer. CDC engineers were involved in malaria control through the elimination of standing water. Eventually the CDC mission expanded to include prevention and control of dengue, typhus, and other communicable diseases. The development of chlorination, water filtration, and sewage treatment were crucial to preventing waterborne illness. Beginning in the 1950s, CDC engineers began their work to improve public health while developing the fields of environmental health, industrial hygiene, and control of air pollution. Engineering disciplines represented at CDC today include biomedical, civil, chemical, electrical, industrial, mechanical, mining, and safety engineering. Most CDC engineers are located in the National Institute for Occupational Safety and Health (NIOSH) and the Agency for Toxic Substances and Disease Registry (ATSDR). Engineering research at CDC has a broad stakeholder base. With the cooperation of industry, labor, trade associations, and other stakeholders and partners, current work includes studies of air contaminants, mining, safety, physical agents, ergonomics, and environmental hazards. Engineering solutions remain a cornerstone of the traditional "hierarchy of controls" approach to reducing public health hazards.

Changes in gene and protein expression in magnetic field-treated human glioma cells.

Because few cancer studies have examined protein profiles and genetic regulation from a single carcinogen exposure, the objective of this study was to determine genetic change via microarray and to evaluate whether that change was a precursor to cellular protein changes. In separate but experimentally identical studies, human glioma SF767 cells were exposed for 3 h to 60-Hz magnetic fields (sham or 1.2 muT). Microarray results suggested that magnetic field treatment resulted in the up-regulation of 5 genes, whereas 25 genes were down-regulated. The mean abundance of 10 identified proteins was altered following 1.2 muT exposure relative to sham (3 increase, 7 decrease). These studies suggest a limited but complicated response in the glioma cells to the magnetic field treatment.

New T-lymphocytic cell lines for studying cell infectability by human immunodeficiency virus.

We identified five human T-lymphoid cell lines (PB-1, Sez-4, C19PL, HUT 102B and ATL-2) which highly express CD4 in addition to CXCR4 and CCR5. In order to evaluate if these cells are infectabile by human immunodeficiency virus (HIV) and could be employed as a model in HIV research we exposed these cell lines to X4 (T-cell tropic) and R5 (macrophage tropic) and subsequently tried to correlate their infectability with (i) level of chemokine coreceptor (CXCR4 and CCR5) expression, (ii) coreceptor functionality (calcium flux, chemotaxis and phosphorylation of MAPK p42/44 and AKT) and (iii) endogenous expression and secretion of HIV-related chemokines which compete with the virus for binding to CXCR4 (SDF-1/CXCL12) or CCR5 (MIP-1beta/CCL4, MIP-1alpha/CCL3, RANTES/CCL5, MCP-2/CCL8, MCP-3/CCL7 and MCP-4/CCL13). We demonstrated that while PB-1 cells are infectable by both X4 and R5 HIV, Sez-4, C91PL, HUT 102B and ATL-2 cells were infected by X4 HIV only. Moreover, we noticed that the susceptibility of these cells to HIV did not correspond either with the level of surface expression or with the functionality of CXCR4 or CCR5; however, it was modulated to some degree by the endogenously secreted HIV-related chemokines. Thus all five mature T-cell lines described here may provide useful new models for studying various aspects of HIV infection. In addition we demonstrate that the infectability of cells by HIV is modulated by so far unidentified intrinsic factors as well as some already known endogenously secreted chemokines. The identification of these factors may be important for developing new strategies to protect cells from HIV infection.

Evolution of intrinsic growth and energy acquisition rates. II. Trade-offs with vulnerability to predation in Menidia menidia.

The Atlantic silverside (Menidia menidia) exhibits countergradient latitudinal variation in somatic growth rate along the East Coast of North America. Larvae and juveniles from high-latitude populations display higher intrinsic rates of energy consumption and growth than genotypes from low-latitude populations. The existence of submaximal growth in some environments suggests that trade-offs must counter the oft-cited theoretical benefits of energy and growth maximization (e.g., "bigger is better,'' ''faster is better'') in the immature life stages. We hypothesized that energy and growth maximization trades off against investment in defense from predators. We conducted laboratory selection experiments to compare vulnerability to predation of silversides from: (1) fast-growing northern (Nova Scotia, NS) versus slow-growing southern (South Carolina, SC) source populations; (2) phenotypically manipulated fast-growing versus moderately-growing NS fish; and (3) recently fed versus unfed NS and SC fish. Tests involved fish drawn from common-garden environments and were conducted by subjecting mixed-treatment schools of size-matched silversides to natural, common piscine predators. NS silversides suffered significantly higher predation mortality than SC silversides. Parallel results were found in phenotypic manipulation of growth: NS silversides reared on a fast-growth trajectory (approximately 1.0 mm/day) were significantly more vulnerable to predation than those growing at a moderate rate (approximately 0.5 mm/day). Food consumption also affected vulnerability to predators: Silversides with large meals in their stomachs suffered significantly higher predation mortality than unfed silversides. Differences in predation vulnerability were likely due to swimming performance, not attractiveness to predators. Our findings demonstrate that maximization of energy intake and growth rate engenders fitness costs in the form of increased vulnerability to predation.

Evolution of intrinsic growth and energy acquisition rates. I. Trade-offs with swimming performance in Menidia menidia.

Latitudinal populations of the Atlantic silverside, Menidia menidia, show substantial genetic variation in rates of energy acquistion and allocation. Reared in common environments, silversides from northern latitudes consume more food, grow faster and more efficiently, store more energy, and produce greater quantities of eggs than their southern conspecifics. The persistence of seemingly inferior southern genotypes in the face of ostensibly superior northern genotypes suggest that there are hidden evolutionary trade-offs associated with these elevated acquisition and allocation rates. We tested the hypothesis that rapid growth and high levels of food consumption trade-off against locomotory performance in M. menidia. We compared both aerobic (prolonged and endurance) and anaerobic (burst) swimming capacities between intrinsically fast-growing fish from the north (Nova Scotia, NS) and intrinsically slow-growing fish from the south (South Carolina, SC) and between growth-manipulated phenotypes within each population. We also compared swimming speeds and endurance between fasted and recently fed fish within populations. Maximum prolonged and burst swimming speeds of NS fish were significantly lower than those of SC fish, and swimming speeds of fast-growing phenotypes were lower than those of slow-growing phenotypes within populations. Fed fish had lower burst speeds and less endurance than fasted fish from the same population. Thus, high rates of growth and the consumption of large meals clearly diminish swimming performance, which likely increases vulnerability to predation and decreases survival and relative fitness. The submaximal growth rate of southern M. menidia appears to be adaptive, resulting from balancing selection on rates of somatic growth.

Photochemical oxygen consumption, oxygen evolution and spectral changes during UVA irradiation of EMT6 spheroids.

Remarkable rates of oxygen consumption are observed via microelectrode measurements immediately upon the onset of 325 nm irradiation of multicell tumor spheroids. Consumption is irradiance dependent over the range 20-200 mW cm-2, and its magnitude is comparable to that observed previously in the same system using exogenous photosensitizers. Oscillations in the oxygen concentrations suggest that oxygen is also being evolved during irradiation. Oxygen evolution is likely the result of enzymatic dissociation of hydrogen peroxide, which is formed through UV-induced photochemistry. Irradiation of spheroids at 442 and at 514 nm produces a much more modest but detectable oxygen consumption. The dynamics of oxygen concentration changes are quite different at these wavelengths, suggesting a different photochemical mechanism. In these cases, initial oxygen depletion is followed immediately by a more gradual, monotonic increase in the oxygen concentration, consistent with irreversible photobleaching. No oscillations in the oxygen concentration are detectable. At 662 nm, no oxygen consumption was observed over the range of irradiances studied. Fluorescence spectra of cells prior to irradiation include contributions from anthranilic acid and reduced nicotinamide adenine dinucleotide (NADH). During 325 nm irradiation, anthranilic acid is rapidly and irreversibly bleached, while NADH emission undergoes only modest reduction.

Cone beam volume CT image artifacts caused by defective cells in x-ray flat panel imagers and the artifact removal using a wavelet-analysis-based algorithm.

The application of x-ray flat panel imagers (FPIs) in cone beam volume CT (CBVCT) has attracted increasing attention. However, due to a deficient semiconductor array manufacturing process, defective cells unavoidably exist in x-ray FPIs. These defective cells cause their corresponding image pixels in a projection image to behave abnormally in signal gray level, and result in severe streak and ring artifacts in a CBVCT image reconstructed from the projection images. Since a three-dimensional (3-D) back-projection is involved in CBVCT, the formation of the streak and ring artifacts is different from that in the two-dimensional (2-D) fan beam CT. In this paper, a geometric analysis of the abnormality propagation in the 3D back-projection is presented, and the morphology of the streak and ring artifacts caused by the abnormality propagation is investigated through both computer simulation and phantom studies. In order to calibrate those artifacts, a 2D wavelet-analysis-based statistical approach to correct the abnormal pixels is proposed. The approach consists of three steps: (1) the location-invariant defective cells in an x-ray FPI are recognized by applying 2-D wavelet analysis on flat-field images, and a comprehensive defective cell template is acquired; (2) based upon the template, the abnormal signal gray level of the projection image pixels corresponding to the location-invariant defective cells is replaced with the interpolation of that of their normal neighbor pixels; (3) that corresponding to the isolated location-variant defective cells are corrected using a narrow-windowed median filter. The CBVCT images of a CT low-contrast phantom are employed to evaluate this proposed approach, showing that the streak and ring artifacts can be reliably eliminated. The novelty and merit of the approach are the incorporation of the wavelet analysis whose intrinsic multi-resolution analysis and localizability make the recognition algorithm robust under variable x-ray exposure levels between 30% and 70% of the dynamic range of an x-ray FPI.

2-Methoxyethanol metabolism, embryonic distribution, and macromolecular adduct formation in the rat: the effect of radiofrequency radiation-induced hyperthermia.

Exposure of pregnant rats to the solvent 2-methoxyethanol (2ME) and radiofrequency (RF) radiation results in greater than additive fetal malformations (Nelson, B.K., Conover, D.L., Brightwell, W.S., Shaw, P.B., Werren, D.W., Edwards, R.M., Lary, J.M., 1991. Marked increase in the teratogenicity of the combined administration of the industrial solvent 2-methoxyethanol and radiofrequency radiation in rats. Teratology 43, 621-34; Nelson, B.K., Conover, D.L., Shaw, P.B., Werren, D.W., Edwards, R.M., Hoberman, A.M., 1994. Interactive developmental toxicity of radiofrequency radiation and 2-methoxyethanol in rats. Teratology 50, 275-93). The current study evaluated the metabolism of 14C-labeled 2ME and the distribution of methoxyacetic acid (MAA) in maternal and embryonic tissues of pregnant Sprague-Dawley rats either exposed to 10 MHz RF radiation or sham conditions. Additionally, adduct formation for both plasma and embryonic protein was tested as a possible biomarker for the observed 2ME/RF teratogenicity. Rats were administered [ethanol-1,2-(14)C]-2ME (150 mg/kg, 161 microCi/rat average) by gavage on gestation day 13 immediately before RF radiation sufficient to elevate body temperature to 42 degrees C for 30 min. Concurrent sham- and RF-exposed rats were sacrificed at 3, 6, 24 or 48 h for harvest of maternal blood, urine, embryos and extra-embryonic fluid. Tissues were either digested for determination of radioactivity or deproteinized with TCA and analyzed by HPLC for quantification of 2ME metabolites. Results show the presence of 2ME and seven metabolites, with the major metabolite, MAA, peaking at 6 h in the tissues tested. MAA, the proximal teratogen, was detectable in maternal serum, urine, embryo and extraembryonic fluid 48 h after dosing. Clearance of total body 14C was significantly reduced for the RF-exposed animals (P<0.05) for the 24-48 h period, but MAA values for serum, embryos and extraembryonic fluid were similar for both sham- and RF-exposed rats. Additionally, no difference was noted for 2ME metabolite profiles in urine or tissue for sham- or RF-exposed rats, thus eliminating an effect of RF radiation on MAA production as a possible explanation for the reported RF-2ME synergism. Subsequently, serum and embryo protein-bound adducts were evaluated by analysis of covalently bound radioactivity. Serum protein binding was significantly higher for sham than RF rats at 3- and 6-h - highest for sham rats at 6 h (519+/-95 microg as parent 2ME/g of protein) whereas RF serum values were highest at 24 h (266+/-79 microg/g protein). Embryonic protein binding was significantly higher for sham rats at 6 h, but binding was highest for both groups at 24 h (sham=229+/-71 microg/g, RF=185+/-48 microg/g). Formation of protein adducts after 2ME is thought to be related to levels of methoxyacetaldehyde, a reactive intermediate in the formation of MAA. These results suggest that no direct relationship exists for covalent binding in the embryo which would explain RF-2ME synergistic malformations. In comparison with urinary metabolites, the relatively slow elimination of adducted serum 2ME indicates that analysis of protein-bound concentrations could be a potential tool for long- term biomonitoring of worker exposure.

Porphyrin bleaching and PDT-induced spectral changes are irradiance dependent in ALA-sensitized normal rat skin in vivo.

Photobleaching kinetics of aminolevulinic acid-induced protoporphyrin IX (PpIX) were measured in the normal skin of rats in vivo using a technique in which fluorescence spectra were corrected for the effects of tissue optical properties in the emission spectral window through division by reflectance spectra acquired in the same geometry and wavelength interval and for changes in excitation wavelength optical properties using diffuse reflectance measured at the excitation wavelength. Loss of PpIX fluorescence was monitored during photodynamic therapy (PDT) performed using 514 nm irradiation. Bleaching in response to irradiances of 1, 5 and 100 mW cm-2 was evaluated. The results demonstrate an irradiance dependence to the rate of photobleaching vs irradiation fluence, with the lowest irradiance leading to the most efficient loss of fluorescence. The kinetics for the accumulation of the primary fluorescent photoproduct of PpIX also exhibit an irradiance dependence, with greater peak accumulation at higher irradiance. These findings are consistent with a predominantly oxygen-dependent photobleaching reaction mechanism in vivo, and they provide spectroscopic evidence that PDT delivered at low irradiance deposits greater photodynamic dose for a given irradiation fluence. We also observed an irradiance dependence to the appearance of a fluorescence emission peak near 620 nm, consistent with accumulation of uroporphyrin/coproporphyrin in response to mitochondrial damage.

Flat panel detector-based cone-beam volume CT angiography imaging: system evaluation.

Preliminary evaluation of recently developed large-area flat panel detectors (FPDs) indicates that FPDs have some potential advantages: compactness, absence of geometric distortion and veiling glare with the benefits of high resolution, high detective quantum efficiency (DQE), high frame rate and high dynamic range, small image lag (< 1%), and excellent linearity (approximately 1%). The advantages of the new FPD make it a promising candidate for cone-beam volume computed tomography (CT) angiography (CBVCTA) imaging. The purpose of this study is to characterize a prototype FPD-based imaging system for CBVCTA applications. A prototype FPD-based CBVCTA imaging system has been designed and constructed around a modified GE 8800 CT scanner. This system is evaluated for a CBVCTA imaging task in the head and neck using four phantoms and a frozen rat. The system is first characterized in terms of linearity and dynamic range of the detector. Then, the optimal selection of kVps for CBVCTA is determined and the effect of image lag and scatter on the image quality of the CBVCTA system is evaluated. Next, low-contrast resolution and high-contrast spatial resolution are measured. Finally, the example reconstruction images of a frozen rat are presented. The results indicate that the FPD-based CBVCT can achieve 2.75-lp/mm spatial resolution at 0% modulation transfer function (MTF) and provide more than enough low-contrast resolution for intravenous CBVCTA imaging in the head and neck with clinically acceptable entrance exposure level. The results also suggest that to use an FPD for large cone-angle applications, such as body angiography, further investigations are required.

Semen quality and hormone levels among radiofrequency heater operators.

Approximately 9,000,000 US workers are occupationally exposed to radiofrequency (RF) radiation; over 250,000 operate RF dielectric heaters. Our purpose was to determine whether male RF heater operators experience increased adverse reproductive effects reflected in reduced semen quality or altered hormone levels. We measured incident RF heater radiation exposures and RF-induced foot currents at four companies. For 12 male heater operators and a comparison group of 34 RF-unexposed men, we measured 33 parameters of semen quality and four serum hormones. Despite wide variation in individual exposure levels, near field strengths and induced foot currents did not exceed current standard levels and guidelines. We observed minor semen quality and hormonal differences between the groups, including a slightly higher mean follicle-stimulating hormone level for exposed operators (7.6 vs 5.8 mIU/mL). Further occupational studies of RF-exposed men may be warranted.

An evaluation of near infrared spectroscopy and cryospectrophotometry estimates of haemoglobin oxygen saturation in a rodent mammary tumour model.

Haemoglobin oxygen saturation in subcutaneous rat mammary tumours was measured using near infrared spectroscopy (NIRS) in vivo and in rapidly frozen sections from the same tumours using cryospectrophotometry, which reports oxygen saturation in individual blood vessels to depths of 4 mm from the tissue surface. Measurements were performed on tumours while animals breathed either room air or carbogen. In five of nine tumours, the average saturation calculated from cryospectrophotometric measurements agreed with that determined from NIRS to within 13%, and in four of these five tumours agreement was 5% or better. In the remaining four of nine tumours, where agreement was poor, the volume-averaged saturations estimated from NIRS were consistently higher than those calculated from cryospectrophotometry. Monte Carlo simulations demonstrated that the depth of tissue probed by NIRS was significantly greater than that sampled by cryospectrophotometry. Analysis of the frequency of severely hypoxic vessels showed that when NIRS reported a saturation of approximately 70% or higher, the fraction of tumour vessels with saturations less than 10% was limited to 0.06 or less. Sensitivity and specificity analysis suggests that NIRS and NIRS imaging may identify clinically relevant hypoxia, even when its spatial extent is below the resolution limit of the NIRS technique.

A comprehensive analysis of protein-protein interactions in Saccharomyces cerevisiae.

Two large-scale yeast two-hybrid screens were undertaken to identify protein-protein interactions between full-length open reading frames predicted from the Saccharomyces cerevisiae genome sequence. In one approach, we constructed a protein array of about 6,000 yeast transformants, with each transformant expressing one of the open reading frames as a fusion to an activation domain. This array was screened by a simple and automated procedure for 192 yeast proteins, with positive responses identified by their positions in the array. In a second approach, we pooled cells expressing one of about 6,000 activation domain fusions to generate a library. We used a high-throughput screening procedure to screen nearly all of the 6,000 predicted yeast proteins, expressed as Gal4 DNA-binding domain fusion proteins, against the library, and characterized positives by sequence analysis. These approaches resulted in the detection of 957 putative interactions involving 1,004 S. cerevisiae proteins. These data reveal interactions that place functionally unclassified proteins in a biological context, interactions between proteins involved in the same biological function, and interactions that link biological functions together into larger cellular processes. The results of these screens are shown here.

50-Hertz magnetic field and calcium transients in Jurkat cells: results of a research and public information dissemination (RAPID) program study.

An effect on intracellular calcium continues to be proposed as a biochemical pathway for the mediation of biologic effects of electrical-power-frequency magnetic fields (MF). However, reproducible results among laboratories are difficult to attain and the characteristics of magnetic field effects on intracellular free calcium ([Ca(2+)](i)) are not well understood. We attempted to repeat the studies of Lindström et al. [Intracellular Calcium Oscillations in a T-Cell Line by a Weak 50 Hz Magnetic Field. J Cell Physiol 156:395-398 (1993)] by investigating the effect of a 1.5-G 50-Hz MF on [Ca(2+)](i) in the Jurkat lymphocyte T-cell line. Changes in [Ca(2+)](i) were determined using microscopic imaging of fura-2 loaded Jurkat cells on poly-l-lysine-coated glass coverslips. The MF was generated by a single coil constructed with bifilar wire and located in the same plane as the cells. Cells were randomly exposed for 8 min to MF, sham field (SF), or no field (NF) conditions. The exposure condition remained coded until data analysis was complete. Each exposure period was preceded by an 8-min data collection to establish a baseline for [Ca(2+)](i). After each exposure condition, cells were exposed to anti-CD3 antibody that induced a rapid increase in [Ca(2+)](i) in responsive cells; this provided a positive control. [Ca(2+)](i) was analyzed for individual cells as spatially-averaged background-corrected 340/380 nm ratios, and a [Ca(2+)](i) transient was considered significant for positive deviations from baseline of 3 [multiple] an estimate of noise in the baseline. Typically, 25-50 cells/field were viewed and approximately 50% had no [Ca(2+)](i) transients in the baseline period and also responded to positive control. Only cells responding to positive control and lacking changes in [Ca(2+)](i) during the baseline period were considered qualified for assessment during the exposure period. The incidences of [Ca(2+)](i) transients during the exposure period for two experiments (40 [multiple] objective) were 16.5, 14.6, and 14.2% for MF, SF, and NF, respectively, and were not statistically significantly different. Previous studies by Lindström et al. [Intracellular Calcium Oscillations in a T-Cell Line after Exposure to Extremely-Low-Frequency Magnetic Fields with Variable Frequencies and Flux Densities. Bioelectromagnetics 16:41-47 (1995)] showed a high response rate (92%) for exposure to 1. 5-G 50-Hz MF when individual cells were preselected for investigation. We found no such effect when examining many cells simultaneously in a random and blind fashion. These results do not preclude an effect of MF on [Ca(2+)](i), but suggest that responsive cells, if they exist, were not identified using the approaches that we used in this study.

Adaptive variation in energy acquisition and allocation among latitudinal populations of the Atlantic silverside.

Understanding the evolution of growth rate requires knowledge of the physiology of growth. This study explored the physiological basis of countergradient variation (CnGV) in somatic growth across latitudinal populations of the Atlantic silverside, Menidia menidia. Energetics of northern (Nova Scotia, Canada) and southern (South Carolina, USA) genotypes were compared across resource levels, temperatures, and fish sizes to identify trade-offs to rapid growth. Offered unlimited resources, genotypes differed in both energy acquisition and allocation. Food consumption, growth, and efficiency of northern genotypes were consistently higher than in southern genotypes, across temperatures and body sizes. Feeding metabolism (specific dynamic action; SDA) was proportional to meal size, differing between genotypes to the extent that food consumption differed. Given limited resources, northern and southern genotypes displayed similar growth, efficiency, routine activity, and SDA across temperatures and fish sizes. Routine metabolism was equal at 17°C and 22°C, yet was significantly higher in northern fish at 28°C. Growth rates in M. menidia do not appear to trade off across environments or body sizes, i.e., at no temperature, ration, or size do southern fish outgrow northern conspecifics. Nor does submaximal growth result from increased costs of maintenance, tissue synthesis, or routine activity. Based on our findings, we propose that CnGV consumption and growth in M. menidia likely result from trade-offs with other energetic components, namely sustained and burst swimming.

Carbogen-induced changes in rat mammary tumour oxygenation reported by near infrared spectroscopy.

We have evaluated the ability of steady-state, radially-resolved, broad-band near infrared diffuse reflectance spectroscopy to measure carbogen-induced changes in haemoglobin oxygen saturation (SO2) and total haemoglobin concentration in a rat R3230 mammary adenocarcinoma model in vivo. Detectable shifts toward higher saturations were evident in all tumours (n = 16) immediately after the onset of carbogen breathing. The SO2 reached a new equilibrium within 1 min and remained approximately constant during 200-300 s of administration. The return to baseline saturation was more gradual when carbogen delivery was stopped. The degree to which carbogen increased SO2 was variable among tumours, with a tendency for tumours with lower initial SO2 to exhibit larger changes. Tumour haemoglobin concentrations at the time of peak enhancement were also variable. In the majority of cases, haemoglobin concentration decreased in response to carbogen, indicating that increased tumour blood volume was not responsible for the observed elevation in SO2. We observed no apparent relationship between the extent of the change in tumour haemoglobin concentration and the magnitude of the change in the saturation. Near infrared diffuse reflectance spectroscopy provides a rapid, non-invasive means of monitoring spatially averaged changes in tumour haemoglobin oxygen saturation induced by oxygen modifiers.