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991.
Both the Mississippi and Missouri rivers experienced major flooding in the spring and summer of 1993, inundating much of their
floodplains for long periods, and allowing fish access to vast but previously inaccessible benthic foraging areas. In response
to the latter, we hypothesized that flathead catfish (Pylodictis olivaris) would exhibit altered post-flooding growth as compared to like-aged fish whose lives were flood-free. To test this hypothesis,
we obtained the left pectoral fin spines from hoop-netted Mississippi River flathead catfish collected in the vicinity of
Crystal City, Missouri, USA, and conducted an individual-based back-calculated growth comparison of individuals captured pre-flood
(1991) and post-flood (1996). For like-aged cohorts, our back-calculated length-at-age data clearly show that the post-flooding
growth in 1996-collected fish was superior to that of the 1991-collected fish that had experienced less exceptional flow regimes.
This outcome suggests that increased forage or/and foraging opportunities can be a consequence of flooding, and that flathead
catfish are able to capitalize on this. The natural flooding regime of big rivers may thus be an important contributor to
the growth and success of certain fish species; consequently, modifying the river’s natural hydrograph and channel morphology
may be detrimental.
Handling editor: J. A. Cambray
An erratum to this article is available at . 相似文献
992.
Lysis inhibition (LIN) of T4-infected cells was one of the foundational experimental systems for modern molecular genetics. In LIN, secondary infection of T4-infected cells results in a dramatically protracted infection cycle in which intracellular phage and endolysin accumulation can continue for hours. At the molecular level, this is due to the inhibition of the holin, T, by the antiholin, RI. RI is only 97 residues and contains an N-terminal hydrophobic domain and a C-terminal hydrophilic domain; expression of the latter domain fused to a secretory signal sequence is sufficient to impose LIN, due to its specific interaction with the periplasmic domain of the T holin. Here we show that the N-terminal sequence comprises a signal anchor release (SAR) domain, which causes the secretion of RI in a membrane-tethered form and then its subsequent release into the periplasm, without proteolytic processing. Moreover, the SAR domain confers both functional lability and DegP-mediated proteolytic instability on the released form of RI, although LIN is not affected in a degP host. These results are discussed in terms of a model for the activation of RI in the establishment of the LIN state. 相似文献
993.
Ranked set sampling (RSS) is a sampling procedure that can be considerably more efficient than simple random sampling (SRS). When the variable of interest is binary, ranking of the sample observations can be implemented using the estimated probabilities of success obtained from a logistic regression model developed for the binary variable. The main objective of this study is to use substantial data sets to investigate the application of RSS to estimation of a proportion for a population that is different from the one that provides the logistic regression. Our results indicate that precision in estimation of a population proportion is improved through the use of logistic regression to carry out the RSS ranking and, hence, the sample size required to achieve a desired precision is reduced. Further, the choice and the distribution of covariates in the logistic regression model are not overly crucial for the performance of a balanced RSS procedure. 相似文献
994.
Wu KD Zhou L Burtrum D Ludwig DL Moore MA 《Cancer immunology, immunotherapy : CII》2007,56(3):343-357
Although many multiple myeloma (MM) patients initially respond to cytotoxic therapy, most eventually relapse. Novel therapeutic
strategies employing a combination of chemotherapy with targeted biologics may significantly enhance the response of tumor
cells to treatment. We tested a fully human anti-IGF-IR antibody (A12) against MM, and showed specific inhibition of IGF-I
or serum -induced IGF-IR signaling in MM cells in vitro. The A12 as a single agent was demonstrated to exert modest to significant
inhibition of tumor growth in vivo in various subcutaneous xenograft MM models. The A12 was also evaluated in a disseminated
xenograft MM.1S NOD/SCID model as monotherapy or in combination with other drugs (bortezomib, melphalan) currently in clinical
use. The tumor burden, as determined by luciferase bioimaging, was sharply decreased, and overall survival significantly prolonged
when the therapies were combined. Immunohistochemical analysis demonstrated that the A12 treated tumors had significantly
decreased vascularization compared to control tumors. Furthermore, most MM lines constitutively secreted significant quantities
of VEGF, and this was enhanced following IGF-I treatment. Inhibition of IGF-IR by the A12 in vitro suppressed both constitutive
and IGF-I-induced secretion of VEGF, indicating that a putative anti-angiogenic mechanism associated with the A12 treatment
may contribute to its anti-tumor effect. 相似文献
995.
Whyte DG Johnson AK 《American journal of physiology. Regulatory, integrative and comparative physiology》2007,292(1):R137-R142
Mild psychological stressors provoke an acute rise in core temperature (T(C)), stimulate the hypothalamo-pituitary-adrenocortical (HPA) axis, and induce various stress-related behaviors. In the present study, we examined the effect of ablation of the anteroventral third ventricle region (AV3V) on both physiological and behavioral responses to a novel environment. T(C) was monitored in male Sprague-Dawley rats, with either sham or AV3V lesions, during a 5-h exposure to a novel environment. Trunk blood was collected, in a second group of rats, for the assessment of plasma levels of ACTH and corticosterone. Novelty-induced grooming and rearing behaviors were assessed in a third group of animals. T(C) was elevated in all animals after 30 min in the novel environment, but the rise was exaggerated in rats with AV3V lesions ( approximately 0.5 degrees C). AV3V-lesion rats maintained a higher core temperature for 2 h before it returned to the same level as the control group. Plasma levels of ACTH and corticosterone were also exaggerated in the AV3V lesion group after 30 min in a novel environment. In contrast to the physiological responses, the behavioral measures of grooming and rearing revealed no differences between the groups. The results from the current study suggest that neurons within the AV3V region exert an inhibitory influence on the HPA axis and fever developed in response to stressful psychological stimuli. They also confirm that the physiological and hormonal components of the stress response are independent of certain behavioral measures of stress. 相似文献
996.
Kanaan A Douglas RM Alper SL Boron WF Haddad GG 《American journal of physiology. Regulatory, integrative and comparative physiology》2007,293(3):R1294-R1302
Several pulmonary and neurological conditions, both in the newborn and adult, result in hypercapnia. This leads to disturbances in normal pH homeostasis. Most mammalian cells maintain tight control of intracellular pH (pH(i)) using a group of transmembrane proteins that specialize in acid-base transport. These acid-base transporters are important in adjusting pH(i) during acidosis arising from hypoventilation. We hypothesized that exposure to chronic hypercapnia induces changes in the expression of acid-base transporters. Neonatal and adult CD-1 mice were exposed to either 8% or 12% CO(2) for 2 wk. We used Western blot analysis of membrane protein fractions from heart, kidney, and various brain regions to study the response of specific acid-base transporters to CO(2). Chronic CO(2) increased the expression of the sodium hydrogen exchanger 1 (NHE1) and electroneutral sodium bicarbonate cotransporter (NBCn1) in the cerebral cortex, heart, and kidney of neonatal but not adult mice. CO(2) increased the expression of electrogenic NBC (NBCe1) in the neonatal but not the adult mouse heart and kidney. Hypercapnia decreased the expression of anion exchanger 3 (AE3) in both the neonatal and adult brain but increased AE3 expression in the neonatal heart. We conclude that: 1) chronic hypercapnia increases the expression of the acid extruders NHE1, NBCe1 and NBCn1 and decreases the expression of the acid loader AE3, possibly improving the capacity of the cell to maintain pH(i) in the face of acidosis; and 2) the heterogeneous response of tissues to hypercapnia depends on the level of CO(2) and development. 相似文献
997.
Krueger AC Madigan DL Green BE Hutchinson DK Jiang WW Kati WM Liu Y Maring CJ Masse SV McDaniel KF Middleton TR Mo H Molla A Montgomery DA Ng TI Kempf DJ 《Bioorganic & medicinal chemistry letters》2007,17(8):2289-2292
Substituted 1-hydroxy-4,4-dialkyl-3-oxo-3,4-dihydronaphthalene benzothiadiazine derivatives were investigated as inhibitors of genotype 1 HCV polymerase. Structure-activity relationship patterns for this class of compounds are discussed. It was found that the saturated alkane dialkyl units provided the most active analogs. 相似文献
998.
Pruitt JR Batt DG Wacker DA Bostrom LL Booker SK McLaughlin E Houghton GC Varnes JG Christ DD Covington M Das AM Davies P Graden D Kariv I Orlovsky Y Stowell NC Vaddi KG Wadman EA Welch PK Yeleswaram S Solomon KA Newton RC Decicco CP Carter PH Ko SS 《Bioorganic & medicinal chemistry letters》2007,17(11):2992-2997
DPC168, a benzylpiperidine-substituted aryl urea CCR3 antagonist evaluated in clinical trials, was a relatively potent inhibitor of the 2D6 isoform of cytochrome P-450 (CYP2D6). Replacement of the cyclohexyl central ring with saturated heterocycles provided potent CCR3 antagonists with improved selectivity against CYP2D6. The favorable preclinical profile of DPC168 was maintained in an acetylpiperidine derivative, BMS-570520. 相似文献
999.
Zheng QH Gao M Mock BH Wang S Hara T Nazih R Miller MA Receveur TJ Lopshire JC Groh WJ Zipes DP Hutchins GD DeGrado TR 《Bioorganic & medicinal chemistry letters》2007,17(8):2220-2224
The high-affinity choline transporter (CHT1) system is an attractive target for the development of positron emission tomography (PET) biomarkers to probe brain, cardiac, and cancer diseases. An efficient and convenient synthesis of new radiolabeled CHT1 inhibitors [(11)C]hemicholinium-3 and [(18)F]hemicholinium-3 by solid-phase extraction (SPE) technique using a cation-exchange CM Sep-Pak cartridge has been well developed. The preliminary evaluation of both tracers through biodistribution studies in 9L-glioma rats has been performed, and the uptakes in the heart and tumor were observed, while very low brain uptake was seen. 相似文献
1000.
Ferrari MC Gonzalo A Messier F Chivers DP 《Proceedings. Biological sciences / The Royal Society》2007,274(1620):1853-1859
While some prey species possess an innate recognition of their predators, others require learning to recognize their predators. The specific characteristics of the predators that prey learn and whether prey can generalize this learning to similar predatory threats have been virtually ignored. Here, we investigated whether fathead minnows that learned to chemically recognize a specific predator species as a threat has the ability to generalize their recognition to closely related predators. We found that minnows trained to recognize the odour of a lake trout as a threat (the reference predator) generalized their responses to brook trout (same genus as lake trout) and rainbow trout (same family), but did not generalize to a distantly related predatory pike or non-predatory suckers. We also found that the intensity of antipredator responses to the other species was correlated with the phylogenetic distance to the reference predator; minnows responded with a higher intensity response to brook trout than rainbow trout. This is the first study showing that prey have the ability to exhibit generalization of predator odour recognition. We discuss these results and provide a theoretical framework for future studies of generalization of predator recognition. 相似文献