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991.
Joseph R. Lakowicz Jzef Kuba Henryk Szmacinski Ignacy Gryczynski Peggy S. Eis Wieslaw Wiczk Michael L. Johnson 《Biopolymers》1991,31(12):1363-1378
We used time-dependent fluorescence energy transfer, time-dependent collisional quenching, and global analysis of the data resulting from these through-space and contact interactions to recover the end-to-end distance distributions and diffusion coefficients of flexible fluorescent molecules. The fluorescence decays of covalently linked tryptamine-acceptor and tryptamine-quencher pairs were measured by the frequency-domain method. These data were fit using numerical solutions of the differential equation, which predicts the time- and distance-dependent population of the excited state donors in the presence of energy transfer or collisional quenching, followed by transformation to the frequency domain for nonlinear least-squares comparison with the experimental data. We found that the energy transfer data for the donor-acceptor pair alone were adequate to recover the starting distribution and the end-to-end diffusion coefficient; however, the resolution is dramatically improved by the use of both the through-space and contact interactions. 相似文献
992.
993.
This review investigates ancient infectious diseases in the Americas dated to the
pre-colonial period and considers what these findings can tell us about the history
of the indigenous peoples of the Americas. It gives an overview, but focuses on four
microbial pathogens from this period: Helicobacter pylori,
Mycobacterium tuberculosis, Trypanosoma cruzi
and Coccidioides immitis, which cause stomach ulceration and gastric
cancer, tuberculosis, Chagas disease and valley fever, respectively. These pathogens
were selected as H. pylori can give insight into ancient human
migrations into the Americas, M. tuberculosis is associated with
population density and urban development, T. cruzi can elucidate
human living conditions and C. immitis can indicate agricultural
development. A range of methods are used to diagnose infectious disease in ancient
human remains, with DNA analysis by polymerase chain reaction one of the most
reliable, provided strict precautions are taken against cross contamination. The
review concludes with a brief summary of the changes that took place after European
exploration and colonisation. 相似文献
994.
Peggy L. Edds-Walton Solymar Rivera Matos Richard R. Fay 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2013,199(5):353-363
Previous work on auditory processing in Opsanus tau has focused on the descending octaval nucleus; however, the magnocellular octaval nucleus receives similar inputs from the otolithic endorgans. The purpose of this study was to assess whether cells in any of the three subdivisions of the magnocellular nucleus respond to auditory frequencies and encode sound source direction. Extracellular recording sites were chosen based on anatomical landmarks, and neurobiotin injections confirmed the location of auditory sites in subdivisions of the magnocellular nucleus. In general, the auditory cells in M2 and M3 responded best to frequencies at or below 100 Hz. Most auditory cells responded well to directional stimuli presented along axes in the horizontal plane. Cells in M3 (not M2) also responded to lateral line stimulation, consistent with otolithic endorgan and lateral line inputs to M3. The convergence of auditory and lateral line inputs in M3, the lack of Mauthner cells in this species, and previous evidence that the magnocellular nucleus does not contribute to ascending auditory pathways suggest to us that the large cells of M3 may play a role in rapid behavioral responses to particle motion stimuli in oyster toadfish. 相似文献
995.
Sexual advertisement in the form of acoustic display is energeticallyexpensive. Calling effort, or metabolic energy expended specificallyfor advertisement, is adjusted in some species in response tocompetition from other males or to changes in climatic conditions.The prairie mole cricket (Gryllotatpa major) is a rare insectof die south-central United States that produces its callingsong, or advertisement rail, from a specially constructed burrowin taugrass prairie soil. I found that prairie mole cricketmales do not adjust their call amplitude with competition orfemale availability, nor do they vary amplitude with soil temperatureor moisture within their established range of calling conditions.Chirp rate adjustments were made with social interactions andchanges in soil temperature, but group size did not influencecalling effort Males produced more complex calls in responseto closer calling neighbors, but prairie mole cricket malesmay selectively respond to only the nearest one to two neighbors. 相似文献
996.
Comparative analysis of the virulence control systems of Bordetella pertussis and Bordetella bronchiseptica 总被引:1,自引:0,他引:1
Guillermo Martínez de Tejada Jeff F. Miller & Peggy A. Cotter 《Molecular microbiology》1996,22(5):895-908
Bordetella pertussis and Bordetella bronchiseptica contain nearly identical BvgAS signal-transduction systems that mediate a biphasic transition between virulent (Bvg+ ) and avirulent (Bvg– ) phases. In the Bvg+ phase, the two species express a similar set of adhesins and toxins, and in both organisms the transition to the Bvg– phase occurs in response to the same environmental signals (low temperature or the presence of nicotinic acid or sulphate anion). These two species differ, however, with regard to Bvg– -phase phenotypes, host specificity, the severity and course of the diseases they cause, and also potentially in their routes of transmission. To investigate the contribution of the virulence-control system to these phenotypic differences, we constructed a chimeric B. bronchiseptica strain containing bvgAS from B. pertussis and compared it with wild-type B. bronchiseptica in vitro and in vivo . The chimeric strain was indistinguishable from the wild type in its ability to express Bvg+ - and Bvg– -phase-specific factors. However, although the chimeric strain responded to the same signals as the wild type, it differed dramatically in sensitivity to these signals; significantly more nicotinic acid or MgSO4 was required to modulate the chimeric strain compared with the wild-type strain. Despite this difference in signal sensitivity, the chimeric strain was indistinguishable from the wild type in its ability to cause respiratory-tract infections in rats, indicating that the bvgAS loci of B. pertussis and B. bronchiseptica are functionally interchangeable in vivo . By exchanging discrete fragments of bvgAS , we found that the periplasmic region of BvgS determines signal sensitivity. 相似文献
997.
Seventy-eight heterocyclic compounds, which included derivatives of furan, isoxazole, pyridine, pyrrole, and thiophene, were tested in an in vitro system for their antimicrobial activity and their strain differentiating properties against three strains of Trypanosoma cruzi (Brazil, Corpus Christi, Tulahuen) and for their effect, in tissue culture, on African Green Monkey Kidney Cells—strain Vero. Forty-eight compounds were 75–100% effective in immobilizing trypomastigote forms of the three strains tested, and 29 of these were rated nondestructive to African Green Monkey Kidney (AGMK) cells. Of these 29 compounds, 12 gave variable results ranging from complete immobilization of one strain to no apparent effect on the motility of one or two of the other strains. Nine of the compounds rated harmless to AGMK fibroblasts are proposed as a basis for constructing molecules which might be active chemotherapeutic agents against various strains of T. cruzi. 相似文献
998.
999.
1000.
Christensen Thomas A.; Harrow Ian D.; Cuzzocrea Christine; Randolph Peggy W.; Hildebrand John G. 《Chemical senses》1995,20(3):313-323
The central projections of olfactory receptor cells associatedwith two distinct types of antennal sensilla in the sphinx mothManduca sexta were revealed by anterograde staining. In bothsexes, receptor axons that arise from sexually isomorphic, type-IItrichoid sensilla (and possibly some basiconic sensilla) projectto the spheroidal glomeruli in the ipsilateral antennal lobe.Each axon terminates in one glomerulus. Axons from a limitedregion of the antenna project to glomeruli throughout the lobe,arguing against strict topographic mapping of antennal receptorcells onto the array of glomeruli. Axons of sex-pheromone-selectivereceptor cells in the male-specific type-I trichoid sensillaproject exclusively to the sexually dimorphic macroglomerularcomplex (MGC). Axons from sensilla on the dorsal surface ofthe antenna are biased toward the medial MGC and those fromventral sensilla, toward the lateral MGC. Some receptor-cellaxons branch before reaching the MGC, but their terminals arealways confined to one of the two main glomerular divisionsof the MGC, the cumulus and toroid. These findings confirm thatprimary-afferent information about pheromonal and non-pheromonalodors is segregated in the antennal lobe and suggest that thereis a functional correspondence between particular olfactoryreceptor cells and specific glomeruli. Chem. Senses 20: 313323,1995. 相似文献