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253.
Noradrenaline (NA) metabolism in the neocortex and hippocampus was examined in rats at 1, 24, and 48 h following 15 min of reversible forebrain ischemia. As assessed by the ratio of accumulated 3,4-dihydroxyphenylalanine (DOPA) to the tissue NA level after inhibition of DOPA decarboxylase, the NA turnover rates were markedly increased (120-148% above the control) at 1 h postischemia in both the neocortex and hippocampal formation (CA1 and CA3 plus dentate gyrus). The DOPA:NA ratio went back to control levels after longer postischemic survival times. The ratio between levels of the deaminated NA metabolite, 3,4-dihydroxyphenylethyleneglycol (DOPEG), and NA, which gives another measure of NA turnover rate, showed similar changes. In the neocortex and the CA3 plus dentate gyrus, the DOPEG:NA ratio was markedly increased (89-118%) 1 h after the ischemia, but this change had disappeared at 24 and 48 h. Thus, both the DOPA accumulation experiments and the NA and DOPEG measurements indicate that following transient forebrain ischemia, there is an increased NA turnover in the hippocampus and cortex only in the early recirculation period and not after longer postischemic survival times. The degree of neuronal necrosis in the CA1 region was examined light microscopically on celestine blue-acid fuchsin-stained sections at 24, 48, and 96 h following the ischemic insult. The neuronal damage in CA1 was sparse after 24 h of recovery, had increased markedly after 48 h, and was very pronounced at 96 h.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
254.
Stephen C. Stearns Marcel Kaiser Tadeusz J. Kawecki 《Journal of evolutionary biology》1995,8(5):539-557
Canalization describes the process by which phenotypic variation is reduced by developmental mechanisms. A trait can be canalized against environmental or genetic perturbations. Stabilizing selelction should favor improved canalization, and the degree of a trait's canalization should be positively correlated with its impact on fitness. Here we report, for Drosophila melanogaster, measurements of environmental canalization for five fitness components. We compare them with measurements of genetic canalization, and we discuss the impact of inbreeding on both. In three experiments we measured the variation of fitness components within lines nested within temperature, treatment, and experiment. Lines differed in the position of a P element insert or in genetic background. Within lines flies were genetically nearly identical. We designated trait variation within lines as environmental canalization. The canalization of the traits increased with their impact on fitness, and the pattern was similar to that found for the canalization of fitness components against genetic differences, measured as the variation among lines nested within temperature, treatment, and experiment. This suggests that developmental mechanisms buffer the phenotype against both genetic and environmental disturbance. The results also suggest, less strongly, that inbreeding weakens canalization. 相似文献
255.
Stephen C. Stearns Tadeusz J. Kawecki 《Evolution; international journal of organic evolution》1994,48(5):1438-1450
Canalization is an abstract term that describes unknown developmental mechanisms that reduce phenotypic variation. A trait can be canalized against environmental perturbations (e.g., changes in temperature or nutrient quality), or genetic perturbations (e.g., mutations or recombination); this paper is about genetic canalization. Stabilizing selection should improve the canalization of traits, and the degree of canalization should be positively correlated with the traits' impact on fitness. Experiments testing this idea should measure the canalization of a series of traits whose impact on fitness is known or can be inferred, exclude differences among traits in the number of loci and alleles segregating as an explanation for the pattern of variability found, and distinguish between canalization against genetic and environmental variation. These conditions were met by three experiments within which the variation of fitness components among Drosophila melanogaster lines was measured and among which the genetic contribution to the variation among lines was clearly different. The canalization of the traits increased with their impact on fitness and did not depend on the degree of genetic differences among lines. That the flies used had been transformed by a P-element insert suggests that canalization was also effective against novel genetic variation. The results reported here cannot be explained by the classical hypothesis of reduction in the number of loci segregating for traits with greater impact on fitness and confirm that traits with greater impact on fitness are more strongly canalized. This pattern of canalization reveals an underappreciated role for development in microevolution. There is differential genetic canalization of fitness components in D. melanogaster. 相似文献
256.
The effect of algae on the production of musty-smelling compounds by actinomycetes was studied. Streptomyces spp., causing intensive musty odor, were isolated from hypertrophic Lake Kasumigaura and cultured in association with algae from the same lake. Isolate E and I effectively utilized the cyanobacteria, Microcystis aeruginosa and Anabaena spiroides, and the diatom, Synedra acus, as a carbon source and produced a musty-smelling 2-methylisoborneol in the shaken sediment cultures. High populations of algae and actinomycetes, and aerobic condition in the sediment seem responsible for the occurrence of musty odor in Lake Kasumigaura. 相似文献
257.
Tadeusz Janas Agnieszka Janiak-Osajca Teresa Janas 《Journal of biological physics》1993,19(4):295-308
The study presents an application of the theory of homeomorphic transformations of topological manifolds and the operation of the connected sum of manifolds for topological analysis of membrane transformations during the fusion process between cellular and subcellular compartments. The biological cell and the subcellular structures in the form of vesicles are modelled by an arrangement of two concentric spheres corresponding to the inner and outer layer of the membrane bounding the vesicles. The analysis shows eight succeeding topological stages of membrane transformations during the fusion process and these stages are characterized. It is concluded that there is a vectorial translocation of lipid molecules from the outer layers of the membranes before the fusion process to the internal layer of the membrane bounding the vesicle after the fusion process and there is no lipid translocation in the reverse direction. 相似文献
258.
Casein Kinase II Activity in the Postischemic Rat Brain Increases in Brain Regions Resistant to Ischemia and Decreases in Vulnerable Areas 总被引:1,自引:1,他引:0
Abstract: Casein kinase II (CKII) is a protein kinase acting in the intracellular cascade of reactions activated by growth factor receptors, and that has a profound influence on cell proliferation and survival. In this investigation, we studied the changes in the activity and levels of CKII in the rat brain exposed to 10. 15 and 20 min of transient forebrain ischemia followed by variable periods of reperfusion. The cytosolic CKII activity decreased during reperfusion by ∼ 30 and ∼ 50% in the selectively vulnerable areas, striatum and the CA1 region of the hippocampus, respectively. In the resistant CA3 region of hippocampus and neocortex, the activity increased by ∼ 20 and ∼ 60%, respectively. The postischemic changes in CKII activity were dependent on the duration of the ischemic insult. The levels of CKII did not change after ischemia, suggesting that the enzyme is modulated by covalent modification or is interacting with an endogenous inhibitor/activator. Treatment of the cytosolic fraction from cortex of rats exposed to ischemia and 1 h of reperfusion with agarose-bound phosphatase decreased the activity of CKII to control levels, suggesting that CKII activation after ischemia involves a phosphorylation of the enzyme. The correlation between postischemic CKII activity and neuronal survival implies that preservation or activation of CKII activity may be important for neuronal survival after cerebral ischemia. 相似文献
259.
Depression of Neuronal Protein Synthesis Initiation by Protein Tyrosine Kinase Inhibitors 总被引:2,自引:1,他引:1
Abstract— Growth factors stimulate cellular protein synthesis, but the intracellular signaling mechanisms that regulate initiation of mRNA translation in neurons have not been clarified. A rate-limiting step in the initiation of protein synthesis is the formation of the ternary complex among GTP, eukaryotic initiation factor 2 (elF-2), and the initiator tRNA. Here we report that genistein, a specific tyrosine kinase inhibitor, decreases tyrosine kinase activity and the content of phosphotyrosine proteins in cultured primary cortical neurons. Genistein inhibits protein synthesis by >80% in a dose-dependent manner (10–80 μg/ml) and concurrently decreases ternary complex formation by 60%. At the doses investigated, genistein depresses tyrosine kinase activity and concomitantly stimulates PKC activity. We propose that a protein tyrosine kinase participates in the initiation of protein synthesis in neurons, by affecting the activity of elF-2 directly or through a protein kinase cascade. 相似文献
260.
The effects of nine fungicides were evaluated in vitro on the entomopathogenic fungi Beauveria bassiana, Conidiobolus coronatus, C. thromboides, Metarhizium anisopliae, Paecilomyces farinosus, P. fumosoroseus, Scopulariopsis brevicaulis and Verticillium lecanii. The susceptibility of the fungi to the fungicides varied. The dithiocarbamate derivations zineb + copper oxychloride, and mancozeb completely inhibited germination of C. coronatus, C. thromboides, B. bassiana, P. farinosus, M. anisopliae and V. lecanii. The fungicides triadimefon, copper oxychloride, metalaxyl, sulfur, sulfur + nitrothal‐isopropyl and hymexazol exhibited various effects on the fungi. Usually, fungistasis was more pronounced at 15°C than at 25°C and the inhibitory effects were in direct proportion to the dosage of active ingredient (recommended field rate, 10‐fold higher and 10‐fold lower). In a few combinations, fungi partially overcame or even recovered from the initial inhibition of growth which might have resulted from delayed germination. In other cases, inhibition of growth occurred only after a delay and its intensity increased with time. Stimulation of fungal growth when it occurred was rarely permanent. Generally, adverse effects were much greater against the entomophthoraleans C. coronatus and C. thromboides than against the Hyphomycetes. Extrapolation of the results to practice and to the field situation is difficult. Nevertheless, the data presented give an idea of possible side‐effects in nature. 相似文献