bluuebunny/crossref_metadata_2025 huggingface dataset:
Nos inhibition increases bubble formation and reduces survival in sedentary but not exercised rats
Authors: Wisløff Ulrik , Richardson Russell S. , Brubakk Alf O.
Published: January 2003

Previously we have shown that chronic as well as a single bout of exercise 20 h prior to a simulated dive protects rats from severe decompression illness (DCI) and death. However, the mechanism behind this protection is still not known. The present study determines the effect of inhibiting nitric oxide synthase (NOS) on bubble formation in acutely exercised and sedentary rats exposed to hyperbaric pressure. A total of 45 adult female Sprague‐Dawley rats (270‐320 g) were randomly assigned into exercise or sedentary control groups, with and without NOS inhibition, using l‐NAME (0.05 or 1 mg ml−1) (a nonselective NOS inhibitor). Exercising rats ran intervals on a treadmill for 1.5 h, 20 h prior to the simulated dive. Intervals alternated between 8 min at 85–90 % of maximal oxygen uptake, and 2 min at 50–60 %. Rats were compressed (simulated dive) in a pressure chamber, at a rate of 200 kPa min−1 to a pressure of 700 kPa, and maintained for 45 min breathing air. At the end of the exposure period, rats were decompressed linearly to the ‘surface’ (100 kPa) at a rate of 50 kPa min−1. Immediately after reaching the surface the animals were anaesthetised and the right ventricle was insonated using ultrasound. The study demonstrated that sedentary rats weighing more than 300 g produced a large amount of bubbles, while those weighing less than 300 g produced few bubbles and most survived the protocol. Prior exercise reduced bubble formation and increased survival in rats weighing more than 300 g, confirming the results from the previous study. During NOS inhibition, the simulated dive induced significantly more bubbles in all sedentary rats weighing less than 300 g. However, this effect could be attenuated by a single bout of exercise 20 h before exposure. The present study demonstrates two previously unreported findings: that administration of l‐NAME allows substantial bubble formation and decreased survival in sedentary rats, and that a single bout of exercise protects NOS‐inhibited rats from severe bubble formation and death. This is the first report to indicate that biochemical processes are involved in bubble formation, and this information may be important in the search for preventive measures for and treatment of DCI.
Effect of androgen deficiency on mouse ventricular repolarization
Authors: Brouillette Judith , Trépanier‐Boulay Véronique , Fiset Céline
Published: January 2003

We previously demonstrated that female mouse ventricles have longer action potential durations (APDs) than males. This delayed repolarization results from a lower current density of the ultrarapid delayed rectifier K+ current (IK,ur) and a lower expression level of its underlying K+ channel (Kv1.5). To evaluate whether this sex difference could be attributable to the action of male sex hormones, we studied the effect of androgen deficiency on ventricular repolarization. We compared cardiac electrophysiological properties in castrated (orchiectomized; ORC) and control (CTL) male mice. Q‐Tc intervals as well as APDs measured at 20 %, 50 % and 90 % of repolarization were all significantly longer in ORC than in CTL. The current density of IK,ur was significantly lower in ORC than in CTL (at +50 mV, ORC: 29 ± 4 pA pF−1, n= 25; CTL: 48 ± 5 pA pF−1, n= 17; P= 0.006). In contrast, all the other K+ currents present in mouse ventricular myocytes were comparable between ORC and CTL. Moreover, results of Western blot analysis showed a lower expression level of Kv1.5 protein in ORC but no difference between the two groups for the other K+ channels studied. This study demonstrates that androgen deficiency leads to a reduction in the density of IK,ur and Kv1.5 in mouse ventricle, and consequently, to prolongation of APD and Q‐Tc interval. In conclusion, these findings strongly suggest that male sex hormones contribute to the sex difference that we previously reported in cardiac repolarization in adult mouse heart.
Muscle fractal vascular branching pattern and microvascular perfusion heterogeneity in endurance‐trained and untrained men
Authors: Kalliokoski Kari K. , Kuusela Tom A. , Laaksonen Marko S. , Knuuti Juhani , Nuutila Pirjo
Published: January 2003

Less heterogeneous skeletal muscle perfusion has recently been reported in endurance‐trained compared to untrained men at macrovascular level. The causes of this difference in perfusion heterogeneity are unknown as is whether the same difference is observed in microvasculature. We hypothesised that the difference could be caused by changes in muscle vascular branching pattern. Perfusion was measured in resting and exercising muscle in 14 endurance‐trained and seven untrained men using [15O]water and positron emission tomography. Fractal dimension (D) of perfusion distribution was calculated as a measure of fractal characteristics of muscle vascular branching pattern. Perfusion heterogeneity in microvascular units (1 mm3 samples) was estimated using the measured heterogeneity in voxels of positron emission tomography (PET) images (relative dispersion, RD =s.d./mean) and corresponding D values. D was similar between the groups (exercising muscle 1.11 ± 0.07 and 1.14 ± 0.06, resting muscle 1.12 ± 0.06 and 1.14 ± 0.03, trained and untrained, respectively). Trained men had lower perfusion (151 ± 44 vs. 218 ± 87 ml min−1 kg−1, P < 0.05) and macrovascular perfusion heterogeneity (relative dispersion 21 ± 5 vs. 25 ± 5 %, P < 0.05) in exercising muscle than untrained men. Furthermore, estimated perfusion heterogeneity in microvascular units in exercising muscle was also lower in trained men (33 ± 7 vs.48 ± 19 %, P < 0.05). These results show that fractal vascular branching pattern is similar in endurance‐trained and untrained men but perfusion is less heterogeneous at both the macro‐ and the microvascular level in endurance‐trained men. Thus, changes in fractal branching pattern do not explain the differences in perfusion heterogeneity between endurance‐trained and untrained men.
β2‐Adrenergic receptor polymorphism and nitric oxide‐dependent forearm blood flow responses to isoproterenol in humans
Authors: Garovic Vesna D. , Joyner Michael J. , Dietz Niki M. , Boerwinkle Eric , Turner Stephen T.
Published: January 2003

Polymorphisms in the gene encoding the β2‐adrenoceptor have been associated with interindividual differences in blood pressure and the diagnosis of hypertension. A common polymorphism resulting in a change from arginine to glycine at amino acid 16 (Arg16 → Gly) enhances agonist‐promoted downregulation of receptor expression in vitro. It is unknown whether genotype‐dependent differences in nitric oxide generation contribute to differences in vasodilator responses to β2‐agonists in vivo. To address this question, venous occlusion plethysmography was used to measure forearm blood flow responses to graded brachial artery infusions of the β‐agonist isoproterenol in 41 healthy normotensive Caucasian adults (mean age (±s.d.) = 29 ± 6 years), who were either Arg16 (n= 18) or Gly16 (n= 23) homozygotes. Compared to Arg16 homozygotes, Gly16 homozygotes demonstrated significantly greater blood flow responses to isoproterenol (P= 0.02). After inhibition of nitric oxide synthase by Nγ‐monomethyl‐l‐arginine, blood flow responses did not differ significantly between genotype groups (P= 0.27). Consequently, effects of the Arg16 → Gly polymorphism on forearm blood flow responses to isoproterenol appear to be dependent on differences in endothelial generation of nitric oxide. In contrast to previous reports based on systemic infusions of β2‐agonists, our findings indicate that regional blood flow responses to locally infused isoproterenol are significantly greater in Gly16 than in Arg16 homozygotes.
Theta oscillation coupled spike latencies yield computational vigour in a mammalian sensory system
Authors: Margrie Troy W. , Schaefer Andreas T.
Published: January 2003

Theoretical work carried out almost a decade ago proposed that subthreshold oscillations in membrane potential could be used to convert synaptic current strength into a code reliant on action potential (AP) latencies. Using whole‐cell recordings we present experimental evidence for the occurrence of prominent network‐driven subthreshold theta oscillations in mitral cells of the mouse olfactory bulb. Activity induced by both injected current and sensory input was accurately reflected in initial AP latency from the beginning of each oscillation cycle. In a network model we found that an AP latency code rather than AP number or instantaneous firing rate provided computational speed and high resolution, and was easily implemented. This coding strategy was also found to be invariant to the total input current as long as the relative input intensities to glomeruli remained constant. However, it was highly sensitive to changes in the ratios of the input currents and improved by lateral inhibitory mechanisms. Since the AP latency‐based coding scheme was dependent on the subthreshold oscillation we conclude that the theta rhythm serves a functional role in temporally reformatting the strengths and patterns of synaptic input in this sensory system.
Parallel decrease in ω‐conotoxin‐sensitive transmission and dopamine‐induced inhibition at the striatal synapse of developing rats
Authors: Momiyama Toshihiko
Published: January 2003

Whole‐cell patch‐clamp recordings of GABAergic IPSCs were made from cholinergic interneurones in slices of striatum from developing rats aged 21‐60 days postnatal. In addition, the Ca2+ channel subtypes involved in synaptic transmission, as well as dopamine (DA)‐induced presynaptic inhibition, were investigated pharmacologically with development by bath application of Ca2+ channel blockers and DA receptor agonists. The IPSC amplitude was reduced by ω‐conotoxin GVIA (ω‐CgTX) or ω‐agatoxin TK (ω‐Aga‐TK) across the whole age range, suggesting that multiple types of Ca2+ channels mediate transmission of the synapse. The IPSC fraction reduced by ω‐CgTX significantly decreased, whereas that reduced by ω‐Aga‐TK remained unchanged with development. DA or quinpirole, a D2‐like receptor agonist, presynaptically reduced the IPSC amplitude throughout development. The DA‐induced inhibition decreased with age in parallel with the decrease in N‐type Ca2+ channels. DA showed no further inhibition of IPSCs after the inhibitory effect of ω‐CgTX had reached steady state throughout development. These results demonstrate that there is a functional link between presynaptic N‐type Ca2+ channels and D2‐like DA receptors at inhibitory synapses in the striatum. They also demonstrate that the suppression of GABAergic transmission by D2‐like receptors is mediated by modulation of N‐type Ca2+ channels and decreases in parallel with the developmental decline in the contribution of N‐type Ca2+ channels to exocytosis.
Acute exposure to thyroid hormone increases Na+ current and intracellular Ca2+ in cat atrial myocytes
Authors: Wang Yong G. , Dedkova Elena N. , Fiening Jon P. , Ojamaa Kaie , Blatter Lothar A. , Lipsius Stephen L.
Published: January 2003

Whole‐cell recording methods and fluorescence microscopy were used to study the effects of acute exposure to thyroid hormone (T3) on cat atrial myocytes. Acute exposure (≈5 min) to 10 nm T3 significantly increased tetrodotoxin (TTX)‐sensitive inward Na+ current (INa) at voltages between −40 and +20 mV. At maximal INa activation (−40 mV) T3 increased peak INa by 32 %. T3 had no effect on the time course of INa decay, voltage dependence of activation, inactivation, or recovery from inactivation. Comparable exposures to reverse T3 (rT3) or T4 had no effect on INa. L‐type Ca2+ current was unaffected by acute exposure to T3. T3‐induced increases in INa were unaffected by 50 μm nickel, a blocker of T‐type Ca2+ current. T3 significantly increased cell shortening (+62 %) and could elicit spontaneous action potentials arising from Ca2+‐mediated after‐depolarizations. T3 (but not rT3) significantly increased baseline intracellular Ca2+, release of Ca2+ from sarcoplasmic reticulum (SR) and caffeine (10 mm)‐induced release of SR Ca2+. We conclude that acute T3 exposure increases Na+ influx via INa and thereby stimulates reverse‐mode Na+‐Ca2+ exchange to increase intracellular Ca2+ content and release. As a result, T3 increases contraction strength, and can initiate Ca2+‐mediated arrhythmic activity. Acute non‐genomic effects of T3 can contribute to the positive inotropy and sinus (atrial) tachycardia traditionally attributed to chronic, genomic effects of elevated thyroid hormone on atrial muscle.
Multidrug resistance transporters in the olfactory receptor neurons of Xenopus laevis tadpoles
Authors: Manzini Ivan , Schild Detlev
Published: January 2003

Olfactory receptor neurons (ORNs) are the only class of neurons that is directly exposed to the environment. Therefore, they need to deal with xenobiotic and potentially cytotoxic substances. Here we show for the first time that ORNs possess transporter systems that expel xenobiotics across the plasma membrane. Using calcein and calcium‐indicator dyes as xenobiotics, we demonstrate that ORNs appear to express the multidrug resistance P‐glycoprotein (MDR1) and multidrug resistance‐associated proteins (MRP). This endows ORNs with the ability to transport a large number of substrates including calcium‐indicator dyes and calcein across their plasma membranes. Conversely, blocking P‐glycoprotein and MRP increases the net uptake of these dyes.
Activation of mGlu receptors induces LTD without affecting postsynaptic sensitivity of CA1 neurons in rat hippocampal slices
Authors: Rammes Gerhard , Palmer Mary , Eder Matthias , Dodt Hans‐Ulrich , Zieglgänsberger Walter , Collingridge Graham L.
Published: January 2003

Two forms of long‐term depression (LTD) of excitatory synaptic transmission have been identified in the mammalian CNS, which are induced by the synaptic activation of N‐methyl‐d‐aspartate (NMDA) and metabotropic glutamate (mGlu) receptors, respectively. The mGlu receptor‐dependent form of LTD can be activated by application of 3,5‐dihydroxyphenylglycine (DHPG), a group I selective mGlu receptor agonist. DHPG‐induced LTD is increasingly being used to investigate the mechanisms of mGlu receptor‐dependent LTD. However, recent experiments have argued for both a pre‐ and postsynaptic locus of expression of DHPG‐induced LTD. In the present study we report that DHPG‐induced LTD is not associated with changes in the sensitivity of CA1 neurons to bath applied AMPA. Furthermore, in contrast to homosynaptic LTD, DHPG‐induced LTD is also not associated with changes in sensitivity to focally uncaged l‐glutamate. These data do not support the notion that DHPG‐induced LTD requires a modification of AMPA receptors, such as their internalisation, but are compatible with a presynaptic mechanism of expression.
GABAB receptor modulation of excitatory and inhibitory synaptic transmission onto rat CA3 hippocampal interneurons
Authors: Lei Saobo , McBain Chris J.
Published: January 2003

Hippocampal stratum radiatum inhibitory interneurons receive glutamatergic excitatory innervation via the recurrent collateral fibers of CA3 pyramidal neurons and GABAergic inhibition from other interneurons. We examined both presynaptic‐ and postsynaptic‐GABAB receptor‐mediated responses at both synapse types. Postsynaptic GABAB receptor‐mediated responses were absent in recordings from young (P16‐18) but present in recordings from older animals (⩾P30) suggesting developmental regulation. In young animals, the GABAB receptor agonist, baclofen, inhibited the amplitude of evoked EPSCs and IPSCs, an effect blocked by prior application of the selective antagonist CGP55845. Baclofen enhanced the paired‐pulse ratio and coefficient of variation of evoked EPSCs and IPSCs, consistent with a presynaptic mechanism of regulation. In addition, baclofen reduced the frequency of miniature IPSCs but not mEPSCs. However, baclofen reduced the frequency of KCl‐induced mEPSCs; an effect blocked by Cd2+, implicating presynaptic voltage‐gated Ca2+ channels as a target for baclofen modulation. In contrast, although Cd2+ prevented the KCl‐induced increase in mIPSC frequency, it failed to block baclofen's reduction of mIPSC frequency. Whereas N‐ and P/Q‐types of Ca2+ channels contributed equally to GABAB receptor‐mediated inhibition of EPSCs, more P/Q‐type Ca2+ channels were involved in GABAB receptor‐mediated inhibition of IPSCs. Finally, baclofen blocked the frequency‐dependent depression of EPSCs and IPSCs, but was less effective at blocking frequency‐dependent facilitation of EPSCs. Our results demonstrate that presynaptic GABAB receptors are expressed on the terminals of both excitatory and inhibitory synapses onto CA3 interneurons and that their activation modulates essential components of the release process underlying transmission at these two synapse types.
Metabolic and mitogenic signal transduction in human skeletal muscle after intense cycling exercise
Authors: Yu Mei , Stepto Nigel K. , Chibalin Alexander V. , Fryer Lee G. D. , Carling Dave , Krook Anna , Hawley John A. , Zierath Juleen R.
Published: January 2003

We determined whether mitogen‐activated protein kinase (MAPK) and 5′‐AMP‐activated protein kinase (AMPK) signalling cascades are activated in response to intense exercise in skeletal muscle from six highly trained cyclists (peak O2 uptake (V̇O2,peak) 5.14 ± 0.1 l min−1) and four control subjects (V̇O2,peak 3.8 ± 0.1 l min−1) matched for age and body mass. Trained subjects completed eight 5 min bouts of cycling at ≈85% of V̇O2,peak with 60 s recovery between work bouts. Control subjects performed four 5 min work bouts commencing at the same relative, but a lower absolute intensity, with a comparable rest interval. Vastus lateralis muscle biopsies were taken at rest and immediately after exercise. Extracellular regulated kinase (ERK1/2), p38 MAPK, histone H3, AMPK and acetyl CoA‐carboxylase (ACC) phosphorylation was determined by immunoblot analysis using phosphospecific antibodies. Activity of mitogen and stress‐activated kinase 1 (MSK1; a substrate of ERK1/2 and p38 MAPK) and α1 and α2 subunits of AMPK were determined by immune complex assay. ERK1/2 and p38 MAPK phosphorylation and MSK1 activity increased (P < 0.05) after exercise 2.6‐, 2.1‐ and 2.0‐fold, respectively, in control subjects and 1.5‐, 1.6‐ and 1.4‐fold, respectively, in trained subjects. Phosphorylation of histone H3, a substrate of MSK1, increased (P < 0.05) ≈1.8‐fold in both control and trained subject. AMPKα2 activity increased (P < 0.05) after exercise 4.2‐ and 2.3‐fold in control and trained subjects, respectively, whereas AMPKα1 activity was not altered. Exercise increased ACC phosphorylation (P < 0.05) 1.9‐ and 2.8‐fold in control and trained subjects. In conclusion, intense cycling exercise in subjects with a prolonged history of endurance training increases MAPK signalling to the downstream targets MSK1 and histone H3 and isoform‐specific AMPK signalling to ACC. Importantly, exercise‐induced signalling responses were greater in untrained men, even at the same relative exercise intensity, suggesting muscle from previously well‐trained individuals requires a greater stimulus to activate signal transduction via these pathways.
Experiences with the magnetism of conducting loops: Historical instruments, experimental replications, and productive confusions
Authors: Cavicchi Elizabeth
Published: January 2003

This study investigates nineteenth century laboratory work on electromagnetism through historical accounts and experimental replications. Oersted found that when a magnetic needle was placed in varying positions around a conducting wire, its orientation changed: in moving from a spot above the wire to one below, its sense inverted. This behavior was confusing and provocative. Early experimenters such as Johann Schweigger, Johann Poggendorff, and James Cumming engaged it by bending wire into loops. These loops, which increased the magnetic effect on a compass placed within, also provided evidence of their understanding and confusion. Coiling conducting wires around iron magnetized it, but when some wires coiled oppositely from others, the effect diminished. This effect confused contemporaries of Joseph Henry who made electromagnets, and amateurs later in the century who constructed multisection induction coils. I experienced these confusions myself while working with multilayer coils and induction coils that I made to replicate the historical instruments. This study shows how confusion can be a productive element in learning, by engaging learners to ask questions and invent experiments. By providing space for learners’ confusions, teachers can support the development of their students’ physical understandings.
The equivalence principle and the bending of light
Authors: Ferraro Rafael
Published: January 2003

The apparent discrepancy between the bending of light predicted by the equivalence principle and its corresponding value in general relativity is resolved by evaluating the deflection of light with respect to a direction that is parallel transported along the ray trajectory in 3-space. In this way the bending predicted by the equivalence principle is fulfilled in general relativity and other alternative metric theories of gravity.
The physics of stone skipping
Authors: Bocquet Lydéric
Published: January 2003

The motion of a stone skimming over a water surface is considered. A simplified description of the collisional process of the stone with water is proposed. The maximum number of bounces is estimated by considering both the slowing down of the stone and its angular stability. The conditions for a successful throw are discussed.
Mechanics of the surf skimmer revisited
Authors: Sugimoto Takeshi
Published: January 2003

The mechanics of the surf skimmer, fun sport at the beach, is re-examined by using fundamental fluid mechanics. Comparison of the existing theories and consideration of the effects previously neglected lead to the conclusion: Edge’s model is physically incorrect; Tuck and Dixon’s theory provides physical insights into the surf skimming; there are several trade-offs in the mechanics of the surf skimmer and these make this sport fun and challenging.
Hypaxial Motor Patterns and the Function of Epipubic Bones in Primitive Mammals
Authors: Reilly Stephen M. , White Thomas D.
Published: January 2003

Since the first description of epipubic bones in 1698, their functions and those of the associated abdominal muscles of monotremes and marsupial mammals have remained unresolved. We show that each epipubic bone is part of a kinetic linkage extending from the femur, by way of the pectineus muscle, to the epipubic bone, through the pyramidalis and rectus abdominis muscles on one side of the abdomen, and through the contralateral external and internal oblique muscles to the vertebrae and ribs of the opposite side. This muscle series is activated synchronously as the femur and contralateral forelimb are retracted during the stance phase in locomotion. The epipubic bone acts as a lever that is retracted (depressed) to stiffen the trunk between the diagonal limbs that support the body during each step. This cross-couplet kinetic linkage and the stiffening function of the epipubic bone appear to be the primitive conditions for mammals.
A Reversibly Switching Surface
Authors: Lahann Joerg , Mitragotri Samir , Tran Thanh-Nga , Kaido Hiroki , Sundaram Jagannathan , Choi Insung S. , Hoffer Saskia , Somorjai Gabor A. , Langer Robert
Published: January 2003

We report the design of surfaces that exhibit dynamic changes in interfacial properties, such as wettability, in response to an electrical potential. The change in wetting behavior was caused by surface-confined, single-layered molecules undergoing conformational transitions between a hydrophilic and a moderately hydrophobic state. Reversible conformational transitions were confirmed at a molecular level with the use of sum-frequency generation spectroscopy and at a macroscopic level with the use of contact angle measurements. This type of surface design enables amplification of molecular-level conformational transitions to macroscopic changes in surface properties without altering the chemical identity of the surface. Such reversibly switching surfaces may open previously unknown opportunities in interfacial engineering.
Cerenkov Radiation in Photonic Crystals
Authors: Luo Chiyan , Ibanescu Mihai , Johnson Steven G. , Joannopoulos J. D.
Published: January 2003

In a conventional material, the coherent Cerenkov radiation due to a moving charged particle is associated with a velocity threshold, a forward-pointing radiation cone, and a forward direction of emission. We describe different behavior for the Cerenkov radiation in a photonic crystal. In particular, this radiation is intrinsically coupled with transition radiation and is observable without any threshold. Within one particle-velocity range, we found a radiation pattern with a backward-pointing radiation cone. In another velocity range, backward-propagating Cerenkov radiation can be expected. Potential applications include velocity-sensitive particle detection and radiation generation at selectable frequencies.
Just How Pregnant Is the Universe?
Authors: Lazcano Antonio
Published: January 2003

Life Evolving
. Molecules, Mind, and Meaning. Christian de Duve. Oxford University Press, New York, 2002. 357 pp. $30. ISBN 0-19-515605-6.

Nobelist de Duve combines an accessible account of the history of life with discussions of additional topics, including biotechnology, extraterrestrial life, and intelligence.
Tagging along: association among individual Pacific herring (Clupea pallasi) revealed by tagging
Authors: Hay D E , McKinnell S M
Published: January 2003

More than 570 000 Pacific herring (Clupea pallasi) were tagged with external anchor tags during 429 tag release sessions between 1979 and 1992. Individually numbered tags were released in quantities of 10002000 at a time and recovered from commercial fisheries. Often several tags were recovered at the same time and place, and some recoveries occurred as "matches", where two or more tags from a single release session were recovered together. We tested the hypothesis that the frequency of matching tag recoveries occurred by chance through random mixing of tagged herring before their recapture during fishing operations. The alternative is nonrandom, positive association among tagged individuals that persisted through time and during migrations. We used a statistical method developed to address a similar question in steelhead trout (Oncorhynchus mykiss). In separate tests, we examined tag recovery data from migratory stocks in five major regions of the British Columbia. The results indicate nonrandom association of herring for periods of 6 months to several years and through migrations over considerable distances.
Dynamic geography of small pelagic fish populations in the California Current System on the regime time scale (19311997)
Authors: Rodríguez-Sánchez Rubén , Lluch-Belda Daniel , Villalobos Héctor , Ortega-García Sofia
Published: January 2003

Climate regime shifts in the Northeast Pacific appear to have forced population size changes associated with major geographical variations in the position of the center of distribution and bulk of biomass of Pacific sardine (Sardinops caeruleus). These findings help explain the disappearance of sardines around 60 years ago at the northern part of the California Current System and their return following the 1980s. The spatial processes described here differ from those suggesting that environmental regime shifts lead to progressive increasedecrease of stock abundance associated with homogeneous expansioncontraction of its distribution range around a fixed geographical center. Sardine population changes are seemingly related to environmental variability, whereas the spatial pattern of abundance for the northern anchovy (Engraulis mordax) appears to be inversely related to sardine population abundance. Anchovies increased where and when sardines were either absent or at a low population level. Thus, from the long-term and large-scale perspective, neither sardine nor anchovy populations conform to the simple homogeneous geographical range changes usually assumed. The sardine population changes its location within the ocean habitat in an evolving progression over a multidecadal time scale.
Biophysical modeling of larval Baltic cod (Gadus morhua) growth and survival
Authors: Hinrichsen H.-H , Möllmann C , Voss R , Köster F W , Kornilovs G
Published: January 2003

A coupled hydrodynamictrophodynamic individual-based model of drift and feeding was utilized to analyze the intra- and inter-annual variability in growth and survival of cod (Gadus morhua) larvae in the central Baltic Sea. Highly temporally and spatially resolved simulated flow fields were used to investigate the potential drift of larval cod from the centre of spawning effort in the Bornholm Basin towards their nursery areas through temporally resolved three-dimensional idealized prey fields. Stomach content analyses of larval cod from the Bornholm Basin revealed calanoid copepod nauplii and early copepodite stages to be the preferred prey organisms. The results of the model runs indicate that larval cod changed from a nonlimited to a food-limited stage because of the strong decrease in abundance of the calanoid copepod Pseudocalanus elongatus during the last two decades. The modeling study revealed retention and dispersal from the main spawning ground to be a key process influencing larval survival. When P. elongatus was available in the prey fields, high cod larval survival rates occurred in spring and early summer. In contrast, when P. elongatus was not available, hatched larvae had only high survival probabilities later in the year or if they were transported into shallower coastal regions.
The potential use of environmental information to manage squid stocks
Authors: Agnew D J , Beddington J R , Hill S L
Published: January 2003

Most commercially exploited squid species have short life cycles and stocks composed of recruits from a single cohort, the size of which is unknown prior to the fishing season. Recent studies suggest that strong environmentrecruitment relationships may exist for a number of squid stocks. Using simulation models based on Falkland Island Patagonian squid (Loligo gahi), the recruit abundance of which is predicted by sea-surface temperature, we propose a method for using predictive relationships in the management of squid populations. We compare a management strategy based on recruitment prediction with historical data from the fishery, which was managed in the absence of these predictions. Our results suggest that varying effort on the basis of an environmental correlate of recruitment can reduce the risk of not meeting conservation targets while increasing yield. Effort has to be reduced in years of low abundance but licensing additional effort in years of high abundance increases long-term average catches. Even if effort levels were not allowed to vary by more than 50% between years, a management strategy for L. gahi based on prediction would have resulted in higher average catches and a reduced probability of the stock biomass falling below a notional conservation limit.
Automated monitoring of a large-scale cod (Gadus morhua) migration in the open sea
Authors: Comeau Luc A , Campana Steven E , Castonguay Martin
Published: January 2003

The migration patterns of marine fishes are poorly known, in part owing to the technical limitations associated with tracking the movements of animals in deep water. Here we document a large-scale, directed, migration of Atlantic cod (Gadus morhua) off eastern Canada. Our approach was based on the acoustic tagging of 126 fish and the deployment of 69 subsurface receivers, stretching over a 160-km distance along the edge of the Laurentian Channel. After 1 year of automated recording, we found that 65% of the fish migrated out of coastal waters in two distinct runs during the summerautumn period. The offshore-migrating fish overwintered in deep Laurentian Channel waters, returning inshore in April. Individual migration routes and migration timing were variable, indicating that the cod did not aggregate in large schools during the seasonal migration events.
Nitrate stable isotopes: tools for determining nitrate sources among different land uses in the Mississippi River Basin
Authors: Chang Cecily C.Y , Kendall Carol , Silva Steven R , Battaglin William A , Campbell Donald H
Published: January 2003

A study was conducted to determine whether NO3 stable isotopes (δ15N and δ18O), at natural abundance levels, could discriminate among NO3 sources from sites with different land uses at the basin scale. Water samples were collected from 24 sites in the Mississippi River Basin from five land-use categories: (1) large river basins (>34 590 km2) draining multiple land uses and smaller basins in which the predominant land use was (2) urban, (3) undeveloped, (4) crops, or (5) crops and livestock. Our data suggest that riverine nitrates from different land uses have overlapping but moderately distinct isotopic signatures. δ18O data were critical in showing abrupt changes in NO3 source with discharge. The isotopic values of large rivers resembled crop sites, sites with livestock tended to have δ15N values characteristic of manure, and urban sites tended to have high δ18O values characteristic of atmospheric nitrate.
Global fish abundance estimation from regular sampling: the geostatistical transitive method
Authors: Bez Nicolas
Published: January 2003

This article deals with the estimation of fish biomass based on regular samplings. The geostatistical transitive method is a design-based spatially explicit method based on few and falsifiable assumptions concerning the sampling strategy. The falsifiability of a hypothesis corresponds to our capacity to control its adequacy to field data in practice. We first describe the basics of the method, mention the questions relative to the covariogram estimation, the units, and the projections of the coordinates, and explain how to fit the model to the experimental covariogram. We then apply the method to an ICES (International Council for the Exploration of the Sea) triennial mackerel egg survey, with regular sampling, and to a Moroccan octopus survey, with regular stratified sampling. To compare the present technique with existing methods, the number and the falsifiability of their respective hypotheses are considered in addition to the bias, the convergence, and the estimation variance. As is often the case, data are assumed to be synoptic, and we discuss two examples of spatiotemporal methods.
Changes in Pacific hake (Merluccius productus) migration patterns and juvenile growth related to the 1989 regime shift
Authors: Benson Ashleen J , McFarlane Gordon A , Allen Susan E , Dower John F
Published: January 2003

The response of Pacific hake (Merluccius productus) to recent changes in ocean conditions has been dramatic, with a larger proportion of the stock moving into Canadian waters in the 1990s. Additionally, after 1994, hake spawned in Canadian waters and a portion of the stock remained year round. The change in distribution corresponded with a change in growth of juvenile hake. These changes were examined in relation to upwelling and temperature. We also examined these changes in relation to changes in the abundance of euphausiids, which are the primary food supply. We propose that the 1989 regime shift differentially affected the availability of euphausiids in the northern and southern Coastal Upwelling Domain, with feeding conditions in the north improved relative to those in the south. This promoted faster growth of juveniles in the northern regions during the 1990s.
The best available science for the management of anadromous salmonids in the Columbia River Basin
Authors: Bisbal Gustavo A
Published: January 2003

Reference to the "best available science" is popular among administrators and scientists responsible for the management of anadromous salmonids in the Columbia River Basin. Regional recovery documents explicitly call for the consideration of the best available science during the formulation of policies, but they fail to elaborate on what this phrase means. In the absence of such clarification, the definition of what counts as science, how to recognize the best science from the rest, and a determination of how much of it is available invites a wide array of interpretations. Two possible remedies are proposed to alleviate this ambiguity. The first is to leave this phrase intact, but also to append an explicit definition of what each term means. This should establish sideboards for what is acceptable when compiling scientific information. The second remedy is to discontinue the impulsive use of the phrase best available science and select alternative language that more accurately reflects legislative intent. This refinement process will naturally result in other phrases tailored to the specific preferences and requirements of each situation. A decision to accept any of these alternatives may profoundly affect how science influences the management of anadromous salmonids in the Columbia River Basin.
Stream temperature responses to clearcut logging in British Columbia: the moderating influences of groundwater and headwater lakes
Authors: Mellina Eric , Moore R Dan , Hinch Scott G , Macdonald J Stevenson , Pearson Greg
Published: January 2003

Although the future timber supply in the northern hemisphere is expected to come from boreal and subboreal forests, little research has been conducted in these regions that examines the temperature responses of small, lake-headed streams to streamside timber harvesting. We examined the temperature patterns of two subboreal outlet streams in north-central British Columbia for 1 year before and 3 years after clearcut logging and found only modest changes (averaging 0.051.1°C) with respect to summer daily maximum and minimum temperatures, diurnal fluctuations, and stream cooling. A multistream comparative survey conducted in the same geographic region revealed that streams headed by small lakes or swamps tended to cool as they flowed downstream, and headwater streams warmed, regardless of whether or not timber harvesting took place. Stream cooling was attributed to a combination of warm outlet temperatures (promoted by the presence of the lakes) and cold groundwater inflows. A regression model revealed that summertime downstream warming or cooling in headwater and outlet streams could be predicted by upstream maximum summer temperatures and canopy cover. Lentic water bodies and groundwater inflows are important determinants of stream temperature patterns in subboreal forests and may subsequently moderate their responses to streamside harvesting.
Egg production of Baltic cod (Gadus morhua) in relation to variable sex ratio, maturity, and fecundity
Authors: Kraus Gerd , Tomkiewicz Jonna , Köster Friedrich W
Published: January 2003

Observed fluctuations in relative fecundity of Eastern Baltic cod (Gadus morhua L.) were related to food availability during the main feeding period and were used to develop a predictive model that explained 72% of the interannual variations in fecundity. Time series of sex ratios, maturity ogives, and relative fecundity were combined with mean weights-at-age and stock sizes from an analytical multispecies model to estimate the potential egg production (PEP). Relationships between PEP and independent estimates of realized daily and seasonal egg production from egg surveys were highly significant. The difference between estimates of potential and realized seasonal egg production was of a magnitude corresponding to the expected loss of eggs as a result of atresia, fertilization failure, and early egg mortality. The removal of interannual variability in sex ratio, maturity, and fecundity on estimates of PEP deteriorated the relationships in all three cases. PEP proved to be superior to spawning stock biomass as measure of the reproductive potential in a stock-recruitment relationship of Eastern Baltic cod. PEP in combination with the reproductive volume explained 61% of the variation in year-class strength at age 2.
Climate-forcing effects on trophically linked groundfish populations: implications for fisheries management
Authors: Jurado-Molina Jesús , Livingston Patricia
Published: January 2003

Commercially important groundfish populations in the Bering Sea are connected through the food web as predators and prey. In addition to having different trophic roles, the recruitment of these species varies on interdecadal time scales and may be related to climate forcing. We simulate the effects of fishing mortality on eight trophically linked species under two scenarios of climate regimes using the multispecies virtual population analysis (MSVPA) model and the multispecies forecasting model (MSFOR). Species respond differently to climate change assumptions and fishing mortality depending on their position in the food web. Results suggest that the assumptions regarding climate regime shifts on mean recruitment may produce effects comparable to the ones produced by fishing and predation interactions. Therefore, accurate models for fisheries management would require considering these factors and their potential interactions. Because responses are complex and difficult to predict, it is necessary to take a risk-averse approach in managing the species with the largest potential variation. The incorporation of climate regime shifts in fisheries management will require a better understanding of recruitment during a particular regime and a reliable way to identify regime shifts based on biological and (or) physical indices.
Mysid predation on amphipods and Daphnia in a shallow coastal lake: prey selection and effects of macrophytes
Authors: Wilhelm Frank M , Hamann Juliane , Burns Carolyn W
Published: January 2003

Interactions between mysids and invertebrates other than pelagic zooplankton have not been well studied. We tested the hypothesis that the mysid Tenagomysis chiltoni preys on the co-occurring amphipod Paracalliope fluviatilis in laboratory experiments. In prey size preference experiments with single prey species, male and female T. chiltoni consumed more small than large amphipods in the absence of the macrophyte Elodea canadensis, but were not selective when macrophytes were present. When offered small and large Daphnia, T. chiltoni males consumed more small than large Daphnia, whereas female T. chiltoni did not show any preference. When amphipods and Daphnia of similar size were presented together, male T. chiltoni strongly selected Daphnia in the presence and absence of E. canadensis, whereas female mysids did so only in the presence of macrophytes. The total number of prey consumed by each sex did not differ between macrophyte treatments. However, female T. chiltoni, which are larger than males, consumed more prey than males. These data suggest that mysids may be an important source of mortality to the amphipod P. fluviatilis. Mysids may also prey on amphipods in other aquatic systems where they co-occur.
Interannual variability of sperm reserves and fecundity of primiparous females of the snow crab (Chionoecetes opilio) in relation to sex ratio
Authors: Sainte-Marie Bernard , Sévigny Jean-Marie , Carpentier Mireille
Published: January 2003

Demographics of adults and reproductive condition of primiparous (first brood) females of the snow crab (Chionoecetes opilio) were monitored annually from 1994 to 2002 at a fished site to investigate the possibility that sperm supply limits embryo production. Abundance of primipara fluctuated 533-fold because of a recruitment pulse, and this caused a large oscillation in the sex ratio of adult males to primipara. Annual mean of stored ejaculate weight (SL) and potential fecundity index (PF, clutch weight × percent fertilized eggs) adjusted to constant primipara carapace width ranged from 31 to 130 mg by spermatheca and from 1.97 to 3.43 g by clutch, respectively. Annual mean of SL and number of stored sperm (range 3.81 × 106 to 35.00 × 106 sperm by spermatheca) decreased when sex ratio decreased, probably because of a combined reduction of sperm allocation and female promiscuity. Annual mean PF was negatively correlated with abundance of small males, which may reflect egg losses during postoviposition matings. Although sociosexual context has a large impact on reproductive condition of primipara, the possibility that sperm supply limits embryo production could not be confirmed or excluded because of the complexity of snow crab mating behavior.
Migration, speciation, and the evolution of diadromy in anguillid eels
Authors: Tsukamoto K , Aoyama J , Miller M J
Published: January 2003

Recent findings and hypotheses about the migration, spawning ecology, phylogenetic relationships, and possible mechanisms of speciation of anguillid eels are overviewed. The offshore distribution and otolith microstructure of small leptocephali suggest that the Japanese eel Anguilla japonica may spawn at seamounts west of the Mariana Islands in the western North Pacific during the new moon of each month from April to November. Some temperate eels have been found to remain in coastal areas after recruitment without a freshwater growth phase (ocean residents or "sea eels"), showing flexible patterns of migratory histories. Recent molecular phylogenetic studies suggest that the tropical eel Anguilla borneensis from the Borneo Island region is the most ancestral species. Every eel species or population has its own migration loop (migration route or life cycle) that connects their spawning area and growth habitats. Spatial and temporal shifts in these migration loops could cause separation into subpopulations, or speciation. Therefore, the large-scale migration of temperate eels probably evolved from local migrations of tropical eels as a result of long-distance dispersal of leptocephali from spawning sites in tropical waters of low latitude to temperate growth habitats at higher latitudes.
SOME OBSERVATIONS ON NONCOVARIANT GAUGES AND THE ε-TERM
Authors: JOGLEKAR SATISH D.
Published: January 2003

We consider the Lagrangian path-integrals in Minkowski space for gauges with a residual gauge-invariance. From rather elementary considerations, we demonstrate the necessity of inclusion of an ε-term (even) in the formal treatments, without which one may reach incorrect conclusions. We show, further, that the ε-term can contribute to the BRST WT-identities in a nontrivial way (even as ε → 0). We also show that the (expectation value of the) correct ε-term satisfies an algebraic condition. We show by considering (a commonly used) example of a simple local quadratic ε-term, that lead to additional constraints on Green's function that are not normally taken into account in the BRST formalism which ignores the ε-term, and that they are characteristic of the way the singularities in propagators are handled. We argue that for a subclass of these gauges, the Minkowski path-integral could not be obtained by a Wick rotation from a Euclidean path-integral.
PHOTON-NEUTRINO INTERACTIONS IN STRONG MAGNETIC FIELD
Authors: CHISTYAKOV M. V. , MIKHEEV N. V.
Published: January 2003

The two-photon two-neutrino interaction induced by magnetic field is investigated. In particular the processes [Formula: see text] and [Formula: see text] are studied in the presence of strong magnetic field. An effective Lagrangian and partial amplitudes of the processes are presented. Neutrino emissivities due to the reactions [Formula: see text] and [Formula: see text] are calculated taking into account the photon dispersion and large radiative corrections. A comparison of the results obtained with previous estimations and another inducing mechanisms of the processes under consideration is made.
SUPERSYMMETRY ON THE SURFACE S2
Authors: McKEON D. G. C.
Published: January 2003

By using symplectic Majorana spinors as Grassmann coordinates in a superspace associated with the supersymmetric extension of the isometry group on the spherical surface S2, it proves possible to formulate supersymmetric models on S2 using superspace techniques.