This critical review argues that several methods for the estimation and prediction of numbers‐at‐age, fishing mortality coefficients F, and recruitment for a stock of fish are too hard to explain to ...customers (the fishing industry, managers, etc.) and do not pay enough attention to weaknesses in the supporting data, assumptions and theory. The review is linked to North Sea demersal stocks. First, weaknesses in the various types of data used in North Sea assessments are summarized, i.e. total landings, discards, commercial and research vessel abundance indices, age‐length keys and natural mortality (M). A list of features that an ideal assessment should have is put forward as a basis for comparing different methods. The importance of independence and weighting when combining different types of data in an assessment is stressed. Assessment methods considered are Virtual Population Analysis, ad hoc tuning, extended survivors analysis (XSA), year‐class curves, catch‐at‐age modelling, and state‐space models fitted by Kalman filter or Bayesian methods. Year‐class curves (not to be confused with ‘catch‐curves’) are the favoured method because of their applicability to data sets separately, their visual appeal, simple statistical basis, minimal assumptions, the availability of confidence limits, and the ease with which estimates can be combined from different data sets after separate analyses. They do not estimate absolute stock numbers or F but neither do other methods unless M is accurately known, as is seldom true.
Muscle fibres isolated from adult Schistosoma mansoni contracted in a dose-dependent manner when exposed to elevated K+ with a maximum response obtained with 25 mM K+. These contractions were ...dependent on extracellular Ca2+ since Co2+ (5 mM) or nicardipine (1 microM) blocked the high K+ contractions. Serotonin (300 nM or higher) was required for maintenance of high K+ contractions. With concentrations of serotonin less than 300 nM the response was dose dependent. 5-Methoxytryptamine or alpha-methylserotonin at 1 microM as well as 10 microM tryptamine were able to substitute for serotonin, but 1 microM 5-carboxyamidotryptamine was ineffective. The order of potency for antagonists (10 microM) was: methiothepin > metergoline > Ly-278,584 = ketanserin. This pattern of responsiveness does not fit well with any known mammalian serotonin receptor subtype. Since forskolin, an adenylate cyclase activator, is able to mimic the action of serotonin and H89, a protein kinase inhibitor, is able to block the effect of serotonin, the effect of serotonin on contractility of the muscle may be via a cAMP-dependent pathway.
Molluscan FMRFamide and two recently discovered platyhelminth FMRFamide-related peptides (FaRPs), GNFFRFamide from the cestode Moniezia expansa and RYIRFamide from the terrestrial turbellarian ...Artioposthia triangulata, cause dose-dependent contractions of individual muscle fibres from Schistosoma mansoni in vitro. The most potent FaRP tested was the turbellarian peptide RYIRFamide, which produced a concentration-dependent effect between 10(-9) and 10(-7) M. FMRFamide and GNFFRFamide were less potent, inducing contractions between 10(-8)-10(-6) M and 10(-7)-10(-5) M respectively. The contractile effect of each of these peptides was blocked by the presence of 1 microM FMR-D-Famide. FMRF free acid did not elicit contraction of the muscle fibres. The FaRP-induced contractions did not occur if the Ca2+ was omitted and 0.5 microM EGTA was added to the extracellular medium. The FaRP-induced contractions were not blocked by the Ca2+ channel blockers nicardipine, verapamil or diltiazem, although high K+-induced contractions of these fibres were blocked by nicardipine. These data indicate the presence of FaRP receptors on schistosome muscle fibres and demonstrate their ability to mediate muscle contraction. The action of these endogenous flatworm peptides on schistosome muscle is the first demonstration of a direct excitatory effect of any putative neurotransmitter on the muscle of a flatworm, and establishes a role for FaRPs in neuromuscular transmission in trematodes. In addition, it provides the first evidence that the peptidergic nervous system is a rational target for chemotherapeutic attack in parasitic platyhelmiths.
With similar chemistry, Mn and Fe interact in their many essential roles in plants but the magnitude and mechanisms involved of these interactions are poorly understood. Leaves of soybean (a ...Mn-sensitive species) developed a mild chlorosis and small dark spots and distorted trifoliate leaves with 30 μM Mn and 0.6 μM Fe in nutrient solution (pH 5.6; 3 mM ionic strength). At 0.6 μM Fe, lower alternate leaves of sunflower (a Mn-tolerant species) were chlorotic at 30 μM Mn and had a pale chlorosis and necrosis at 400 μM Mn. A concentration of 30 and 300 μM Fe in solution alleviated these typical symptoms of Mn toxicity and decreased the concentration of Mn from >3000 to ca. 800 mg kg-1 dry mass (DM) in all leaf tissues. As expected, increased Fe supply increased Fe in leaves from <100 up to 1350 mg Fe kg-1 DM. In situ synchrotron-based X-ray fluorescence microscopy showed that increased Fe supply caused an overall decrease in Mn in the leaf tissue but had little effect on the pattern of its distribution. Similarly, X-ray absorption spectroscopy identified only slight effects of Fe supply on Mn speciation in leaf tissues. Thus, the results of this study indicate that increased Fe supply ameliorated Mn toxicity in soybean and sunflower largely through decreased Mn uptake and translocation to leaf tissues rather than through changes in Mn distribution or speciation within the leaves.
The trematode and cestode flatworms include numerous parasitic forms of major medical and economic importance. A better knowledge of the neuromuscular physiology of these animals could lead to ...development of new control measures against these parasites. Since these animals are near the stem from which all other animals have evolved, better knowledge of these animals could also yield valuable information about the early evolution of nerve and muscle systems in the animal kingdom. This review focuses on what is known about the characteristics of the somatic muscle in these animals. The anatomy of the muscles is described along with a review of current information about their electrophysiology, including descriptions of the ion channels present. Also included is a summary of recently acquired data concerning the nature of serotonin, peptide, acetylcholine and glutamate receptors on the membranes of the muscles.
We have constructed a double clad neodymium doped fiber laser operating on the three-level
F
→
I
transition. The laser has produced 11.5 W at 925 nm with 55% slope efficiency when pumped at 808 nm, ...comparable to the best previous results for a double-clad fiber configuration on this transition. Higher power pumping with both 808 nm and 880 nm sources resulted in an output of 27 W, albeit at lower slope efficiency. In both cases, output power was limited by available pump, indicating the potential for further power scaling. To suppress the stronger four-level
F
→
I
transition we developed a waveguide that provides spectral filtering distributed along the length of the fiber, based on an all-solid micro-structured optical fiber design, with resonant inclusions creating a leakage path to the cladding. The waveguide supports large mode areas and provides strong suppression at selectable wavelength bands, thus easing the restrictions on core and cladding sizes that limited power scaling of previous approaches.
DAY, T. A., A. G. MAULE, C. SHAW AND R. A. PAX.
Structure-activity relationships of FMRFamide-related peptides contracting Schistosoma mansoni muscle.
PEPTIDES 18(7) 917–921, 1997.—This study reports ...the potent myoactivity of flatworm FMRFamide-related peptides (FaRPs) on isolated muscle fibers of the human blood fluke, Schistosoma mansoni. The turbellarian peptides YIRFamide (EC50 4 ηM), GYIRFamide (EC50 1 ηM), and RYIRFamide (EC50 7 ηM), all induced muscle contraction more potently than the cestode FaRP GNFFRFamide (EC50 500 ηM). Using a series of synthetic analogs of the flatworm peptides YIRFamide, GYIRFamide and RYIRFamide, the structure-activity relationships of the muscle FaRP receptor were examined. With a few exceptions, each residue in YIRFamide is important in the maintenance of its myoactivity. Alanine scans resulted in peptides that were inactive (Ala1, Ala2, Ala3 and Ala4 YIRFamide; Ala4 and Ala5 RYIRFamide) or had much reduced potencies (Ala1, Ala2 and Ala3 RYIRFamide). Substitution of the N-terminal (Tyr1) residue of YIRFamide with the non-aromatic residues Thr or Arg produced analogs with greatly reduced potency. Replacement of the N-terminal Tyr with aromatic amino acids resulted in myoactive peptides (FIRFamide, EC50 100 ηM; WIRFamide, EC50 0.5 ηM). The activity of YIRFamide analogs which possessed a Leu2, Phe2 or Met2 residue (EC50’s 10, 1 and 3 ηM, respectively) instead of Ile2 was not significantly altered, whereas, YVRFamide had a greatly reduced (EC50 200 ηM) activity. Replacement of the Phe4 with a Tyr4 (YIRYamide) also greatly lowered potency. Truncated analogs were either inactive (FRFamide, YRFamide, HRFamide, RFamide, Famide) or had very low potency (IRFamide and MRFamide), with the exception of nLRFamide (EC50 20 ηM). YIRF free acid was inactive. In summary, these data show the general structural requirements of this schistosome muscle FaRP receptor to be similar, but not identical, to those of previously characterized molluscan FaRP receptors.
Cholinergic compounds inhibit FMRFamide-induced contractions in dispersed muscle fibres isolated from adult Schistosoma mansoni. Acetylcholine (ACh) was the most effective cholinergic agonist tested ...with an EC50 < 100 nM. Less effective were propionylcholine and arecoline with EC50 < 1 microM and butyrylcholine and carbachol with EC50 < 10 microM. Choline, muscarine, pilocarpine, nicotine, DMPP (1,1-dimethylphenylpiperazine) and levamisole were all ineffective. Amongst tested antagonists, d-tubocurarine (100 microM), mecamylamine (1 mM), scopolamine (1 mM) and quinuclidinyl benzilate (10 microM) were all ineffective. Bicuculline, picrotoxin and strychnine were also ineffective. However alpha-bungarotoxin, at 100 nM, was able to block the inhibitory ACh effect. From these data it appears that the cholinergic receptor on the schistosome muscle fibres may be of the nicotinic type, but that its pharmacology is different from that of nicotinic receptors of vertebrates as well as of nematodes or a variety of other invertebrates.
Three morphologically distinct types of muscle fibres isolated from the platyhelminth Schistosoma mansoni have been studied with whole cell current- and voltage-clamp techniques. Fibres showed a ...marked time-dependent decrease in membrane resistance in response to depolarizing current injections. Voltage-clamp experiments revealed the presence of two distinct voltage-gated outward currents. The most prominent current is a slowly activating, slowly and incompletely inactivating potassium current similar to delayed rectifier currents which have been described in a variety of cell types from a variety of organisms. Also present is a faster activating, quickly and completely inactivating potassium current that shares functional characteristics with 'A'-currents. All three of the cell types studied possess a delayed rectifier current, but only two of the three types have 'A'-currents. Though depolarization with high K+ leads to contraction of the dispersed fibres, no voltage-gated inward currents could be detected by whole cell voltage-clamp under any of our conditions.
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