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1.
Modulation by dopamine of population spikes in area CA1 hippocampal neurons elicited by paired stimulus pulses 总被引:1,自引:0,他引:1
Extracellular recording techniques were used to study the effects of dopamine on postactivation excitability of rat area CA1 hippocampal neurons maintained in vitro. Population spikes were elicited by delivery of conditioning and test stimulus pulses to afferent fibers. The interval between the conditioning and test volley was set to separate delivery of stimuli by 10 to 80 msec. The effect of superfusion or microtopical application of dopamine (DA) on population responses to test stimulus pulses was studied. When paired stimulus volleys, separated by brief intervals (up to 40 msec), were delivered to afferent fibers, paired-pulse suppression (PPS) was indicated by the amplitude of the population spike elicited by the test volley being smaller than that elicited by the conditioning volley. When paired volleys were separated by longer intervals (40 to 80 msec), the response elicited by the test volley was larger in amplitude than that elicited by the conditioning volley, indicating paired-pulse facilitation (PPF). Following exposure to DA, the amplitude of the population response elicited by the conditioning volley was larger than the amplitude before exposure to DA. This effect was long-lasting, enduring for tens of minutes. However, when the amplitude of the conditioning population response was held constant, the PPS was decreased, indicating disinhibition. It is suggested that dopamine produces a long-lasting attenuation of an intervening inhibitory influence onto CA1 pyramidal neurons. 相似文献
2.
In-situ studies on sublittoral soft bottom macrofauna (depth: 14–16 m) employing the underwater laboratory (UWL) “Helgoland” were carried out. Sets of samples were compared for small-scale local and short-term changes in species richness, faunal abundance, numerical dominance, diversity, evenness, homogeneity, and similarity. It could be shown that minor differences in sediment quality can cause conspicuous heterogeneity within a small sampling area (diameter: ca. 100 m). Both spatfall and mortality of benthic invertebrates can change the faunal structure within a short period (two months). The degree of change varies between species and thus at stations harbouring different faunal assemblages as well. 相似文献
3.
V. R. Oberbeck C. P. Mckay T. W. Scattergood G. C. Carle J. R. Valentin 《Origins of life and evolution of the biosphere》1989,19(1):39-55
Important prebiotic organic compounds might have been transported to Earth in dust or produced in vapor clouds resulting from atmospheric explosions or impacts of comets. These compounds coalesced in the upper atmosphere with particles ejected from craters formed by impacts of large objects. Coalescence during exposure to UV radiation concentrated organic monomers and enhanced formation of oligomers. Continuing coalescence added material to the growing particles and shielded prebiotic compounds from prolonged UV radiation. These particles settled into the lower atmosphere where they were scavenged by rain. Aqueous chemistry and evaporation of raindrops containing nomomers in high temperature regions near the Earth's surface also promoted continued formation of oligomers. Finally, these oligomers were deposited in the oceans where continued prebiotic evolution led to the most primitive cell. Results of our studies suggest that prebiotic chemical evolution may be an inevitable consequence of impacting comets during the late accretion of planets anywhere in the universe if oceans remained on those planetary surfaces. 相似文献
4.
Molecular size characterization of bacterial capsular polysaccharide vaccines by high performance liquid chromatography 总被引:2,自引:0,他引:2
Bacterial capsular polysaccharides are major virulence factors and some are used as vaccinal antigens. Their molecular size is an important physicochemical criterion which correlates with immunogenicity. This article describes a new application of high performance liquid chromatography (HPLC), based on molecular sieving, for such an evaluation. This HPLC method is rapid, accurate, reproducible, requires only very low amounts of product and presents good correlation with conventional gel permeation chromatography. 相似文献
5.
H. E. Valentin A. Schönebaum A. Steinbüchel 《Applied microbiology and biotechnology》1996,46(3):261-267
A recombinant strain of Pseudomonas putida GPp104 (pHP1014::E146), which expressed the polyhydroxyalkanoic acid (PHA) synthase of Thiocapsa pfennigii exhibiting an unusual substrate specificity at a high level was incubated in two-stage batch or fed-batch accumulation experiments
with 5-hydroxyhexanoic acid (5HHx) as carbon source in the second cultivation phase, copolyesters of 3-hydroxybutyric acid
(3HB) plus 5HHx, or of 3HB, 3-hydroxyhexanoic acid (3HHx) plus 5HHx were accumulated as revealed by gas-chromatographic and
13C-NMR spectroscopic analysis. When the recombinant P. putida GPp104 was incubated with 4-hydroxyheptanoic acid (4HHp) as carbon source in the second cultivation phase, a copolyester
consisting of 3HB, 3-hydroxyvaleric acid and 3- and 4-hydroxyheptanoic acid accumulated. Providing 4-hydroxyoctanoic acid
as carbon source in the second cultivation phase led to the accumulation of a polyester that contained 1–2 mol% 4-hydroxyoctanoic
acid besides 3-hydroxyoctanoic acid, 3HHx, 3-hydroxyvaleric acid and 3HB. In addition to PHA containing these new constituents,
PHA with 4-hydroxyvaleric acid was accumulated from laevulinic acid. Eleven strains from five genera have been also analysed
for their ability to utilize different carbon sources for colony growth, which might serve as potential precursors for the
biosynthesis of PHA with unusual constituents. Although most of the carbon sources were utilized by some strains for colony
growth, accumulation experiments gave no evidence for the accumulation of new PHA by these wild-type strains.
Received: 22 April/Received revision: 23 May 1996/Accepted: 2 June 1996 相似文献
6.
7.
A cosmid gene bank of partially EcoRI-digested genomic DNA from Methylobacterium extorquens IBT no. 6 was screened for DNA fragments restoring polyhydroxyalkanoic-acid (PHA) accumulation in the PHA-negative mutant Alkaligenes eutrophus H16 PHB–4. The M. extorquens PHA-synthase structural gene phaC
Mex
was mapped on a 23-kbp EcoRI fragment by complementation studies, by hybridization experiments with heterologous DNA probes from A. eutrophus H16 encoding for phaA, phaB and phaC and by nucleic acid sequence analysis. Evidence for the presence of genes for a -ketothiolase or an acetoacetyl-coenzyme A reductase on this fragment was not obtained. The nucleotide sequence of a 3.7-kbp region was obtained. It contained the entire 1.815-kbp phaC
Mex plus approximately each 900-bp upstream and downstream of phaC
Mex. PhaC
Mex
encoded a protein of 605 amino acods with a relative molecular mass (Mr) of 66742, which exhibited 38.1% amino acid identity with the A. eutrophus PHA synthase. Determination of the N-terminal amino acid sequence of an Mr 65 000 protein, which was enriched concomitantly with the purification of PHA granules in sucrose gradients, revealed a sequence that was identical with the amino acid sequence deduced from the most probable translation start codon except for a valine, which was obviously removed post-translationally. Enzyme analysis, which was done with the native gene and a phaC
Mex
-lacZ fusion gene, gave no evidence for expression of phaC
Mex
in Escherichia coli. 相似文献
8.
Plant-parasitic nematodes cause devastating agricultural damage worldwide. Only a few synthetic nematicides can be used and their application is limited in fields. Therefore, there is a need for sustainable and environment-friendly alternatives. Nematode-trapping fungi (NTF) are natural predators of nematodes. They capture and digest them with their hyphae and are starting to being used as bio-control agents. In this study, we applied the NTF Arthrobotrys flagrans (Duddingtonia flagrans) against the wine pathogenic nematode Xiphinema index. A. flagrans reduced the number of X. index juveniles in pot cultures of Ficus carica, an alternative host plant for X. index, significantly. Sodium-alginate pellets with A. flagrans spores were produced for vineyard soil inoculation under laboratory conditions. The NTF A. conoides, A. musiformis and A. superba were enriched from several soil samples, showing their natural presence. Trap formation is an energy-consuming process and depends upon various biotic and abiotic stimuli. Here, we show that bacteria of the genus Delftia, Bacillus, Pseudomonas, Enterobacter and Serratia induced trap formation in NTF like A. conoides and A. oligospora but not in A. flagrans in the absence of nematodes. The application of NTF along with such bacteria could be a combinatorial way of efficient biocontrol in nematode-infested soil. 相似文献
9.
10.
Peter Ort Igor A. Zalunin Victor S. Gasparov Galina G. Chestukhina Valentin M. Stepanov 《Journal of Protein Chemistry》1995,14(4):241-249
Denaturation ofBacillus thuringiensis CryIIIA-endotoxin—an insecticidal protein, active againstColeoptera larvae—in concentrated guanidine hydrochloride solutions was pursued by fluorescence and circular dichroism spectroscopy and limited proteolysis. It was found that the protein consists of two fragments that differ by their stability to denaturation by guanidine hydrochloride atpH 3. The less stable fragment corresponds to the N-terminal-helical domain limited by Leu-279; the more stable one starts with Ile-280, contains about 330 amino acid residues, and corresponds to the molecule C-terminal moiety that consist of its two-structural domains forming a superdomain.Abbreviations BT
Bacillus thuringiensis
- Gdn-HCl
guanidine hydrochloride
- PAGE
electrophoresis in polyacrylamide gel
- SDS
sodium dodecylsulfate
- CD
circular dichroism 相似文献