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161.
C. M. Gómez 《Journal of biosciences》2008,33(5):743-753
The relationship between stimulus intensity and the probability of detecting the presence of the stimulus is described by
the psychometrical function. The probabilistic nature of this relationship is based on the stochastic behaviour of sensory
neural channels and sensory networks involved in perceptual processing (Kiang 1968). This study tries to establish a continuum
of variability across different levels of integration in the central nervous system. Once the opening and closing times of
ionic channels was simulated, a threshold to the collective behaviour of voltage-gated ionic channels was imposed in order
to generate the spike train of a single neuron. Afterwards, the trains of spikes of different neurons were added up, simulating
the activity of a sensory nerve. By adding the activity due to the stimulus to the spontaneous neural behaviour, the psychometric
function was simulated using a thresholding approach. The results can replicate the stochastic resonance phenomenon, but also
open up the possibility that attentional phenomena can be mediated not only by increasing neural activity (bursting or oscillatory),
but also by increasing noise at the neural level. 相似文献
162.
163.
The dependences of thin filament sliding velocity on the calcium concentration in solution (pCa 5 to 8) for rabbit cardiac myosin isoforms V1 and V3 were determined in a set of experiments using an in vitro motility assay with a reconstructed thin filament. The constructed pCa-versus-velocity curves had a sigmoid shape. It was demonstrated that the sliding velocity of regulated thin filament at the saturating calcium concentration (pCa 5) did not differ from the actin sliding velocity for each isoform. The determined values of Hill’s cooperativity coefficient for isomyosins V1 and V3 were 1.04 and 0.75, respectively. It was demonstrated that isomyosin V3 was more sensitive to calcium as compared with isomyosin V1. Using the same assay, the dependence of thin filament sliding velocity on the concentration of the actin-binding protein α-actinin (analog of a force-velocity dependence) was determined at the saturating calcium concentration for each myosin isoform (V1 and V3). The results suggest that the calcium regulation of V1 and V3 contractile activity follows different mechanisms. 相似文献
164.
The release of the inhibitory neurotransmitter GABA is generally enhanced under potentially cell-damaging conditions. The
properties and regulation of preloaded [3H]GABA release from mouse hippocampal slices were now studied in free radical-containing medium in a superfusion system. Free
radical production was induced by 0.01% of H2O2 in the medium. H2O2 markedly potentiated GABA release, which was further enhanced about 1.5-fold by K+ stimulation (50 mM). In Ca2+-free media this stimulation was not altered, indicating that the release was mostly Ca2+-independent. Moreover, omission of Na+ increased the release, suggesting that it is mediated by Na+-dependent transporters operating outwards, a conception confirmed by the enhancement with GABA homoexchange. Inhibition of
the release with the ion channel inhibitors diisothiocyanostilbene-2,2′-disulphonate and 4-acetamido-4′-isothiocyanostilbene-2,2′-disulphonate
indicates that Cl− channels also participate in the process. This release was not modified by the adenosine receptor (A1 and A2a) agonists and ionotropic glutamate receptor agonists kainate, N-methy-d-aspartate and 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate, whereas the agonists of metabotropic glutamate receptors
of group I [(S)-3,5-dihydroxyphenylglycine] and of group II [(2R,4R)-4-aminopyrrolidine-2,4-dicarboxylate] enhanced it by
receptor-mediated mechanisms, the effects being abolished by their respective antagonists. The group III agonist l(+)-2-amino-4-phosphonobutyrate reduced the evoked GABA release, but this was not affected by the antagonist. Furthermore,
the release was reduced by activation of protein kinase C by 4β-phorbol 12-myristate 13-acetate and by inhibition of tyrosine
kinase by genistein and of phoshoplipase by quinacrine. On the other hand, increasing cGMP levels with the phosphodiesterase
inhibitor zaprinast, selective for PDE5, 6 and 9, and NO production with the NO-generating compounds hydroxylamine, sodium
nitroprusside and S-nitroso-N-penicillamine enhanced the release. The regulation of GABA release induced by free radical production proved thus to be rather
complex. Under potentially cell-damaging conditions, the potentiation of GABA release may be a mechanism to counteract hyperactivity
and reduce the effects of excitatory amino acid release. On the other hand, reduction of GABA release could be harmful and
contribute to excitotoxic damage and neuronal degeneration. 相似文献
165.
A Basis for Spatial and Social Patterns in Ant Species: Dynamics and Mechanisms of Aggregation 总被引:5,自引:0,他引:5
Stéphanie Depickère Dominique Fresneau Jean-Louis Deneubourg 《Journal of Insect Behavior》2004,17(1):81-97
Aggregation is usually studied in functional terms, forgetting mechanisms. In this paper, experimental results on the ant Lasius niger, complemented by a model, allow us to understand the mechanisms responsible for aggregation and to study the influence of the population density on this phenomenon. The results show (1) a high level of aggregation and the emergence of a large cluster; (2) that aggregation results from an amplification mechanism—the greater the number of ants inside a cluster, the greater the time spent by one ant in this cluster; and (3) that population density has only a weak influence on the aggregation process. This method of analysis and these results can certainly be extended not only in social insects but also in other species, like subsocial arthropods. 相似文献
166.
The nucleotide sequence variation of hypervariable segment 1 (HVS1) was analyzed for mtDNAs of 88 phylogeographical clusters characteristic of African, West Eurasian, or East Eurasian populations. A significant difference in the distribution of mutations was revealed for the mitochondrial gene pools of the regional human populations. The HVS1 positions were identified whose instability is explained by strand displacement during mtDNA replication. Strand displacement was assumed to be a major mechanism of context-dependent mutagenesis associated with the regional differentiation of human populations. 相似文献
167.
168.
Over 4000 species of angiosperms are able to directly invade and parasitise other plants, but only very few are weedy and parasitise cultivated plants. Together with the witchweeds (Striga spp.) and dodders (Cuscuta spp.), the broomrapes (Orobanche spp.) affect important crops causing complete yield loses with severe infestations. Genetic resistance to parasitisation remains as one of the most desirable components in an integrated control strategy. However, breeding for resistance is a difficult task and many aspects of the host/parasite interaction remain unknown. In the present work, we review the cytological and cytochemical studies investigating the mechanisms of resistance involved in the process leading to an incompatible host–parasite interaction. We have attempted to identify the main gaps and problems related to such studies with parasitic plants and present an in‐depth review of histochemical techniques used to assess mechanisms of resistance against these parasitic plants. Furthermore, we discuss future research directions and novel techniques and finally, how such techniques can be applied and incorporated within a breeding programme. 相似文献
169.
We verified and generalized the catalytic features that selenocysteine (Sec) and cysteine (Cys) contribute to the reduction of methionine-R-sulfoxide using an anaerobic bacterial MsrB from Clostridium sp. OhILA as a model protein. The Sec-containing Clostridium MsrB form exhibited 100-fold higher activity than its Cys-containing form, revealing that Sec provided the catalytic advantage of higher activity. However, a resolving Cys was required for the thioredoxin (Trx)-dependent recycling process of the Sec-containing form. Thus, Trx could reduce the selenenylsulfide bond, but its Trx-dependent recycling process was much less efficient compared to that for the disulfide bond in the Cys-containing form, demonstrating an obvious catalytic disadvantage. These data agreed well with our previous data on mammalian MsrBs, and therefore suggested that the catalytic mechanisms, as well as the catalytic advantages and disadvantages provided by the Sec and Cys residues, are most likely conserved from anaerobic bacteria to mammals. Taken together, we propose that the use of Sec in MsrB may depend on a balance between the catalytic advantage of higher activity and the disadvantage of a less efficient regeneration process provided by this residue. 相似文献
170.
Shen JS Edwards NJ Hong YB Murray GJ 《Biochemical and biophysical research communications》2008,369(4):1071-1075
Intravenous enzyme replacement therapy (ERT) with purified glucocerebrosidase (GLA) leads to significant improvement of the clinical manifestations in patients with Type 1 Gaucher disease. However, the high doses required, slow response and inability to recover most of the infused enzyme in the target tissues may be attributed to losses occurring during transit en route to the lysosome. Preincubation of GLA with isofagomine (IFG), a slow-binding inhibitor, significantly increased stability of the enzyme to heat, neutral pH and denaturing agents in vitro. Preincubation of GLA with isofagomine prior to uptake by cultured cells results in increased intracellular enzyme activity accompanied by an increase in enzyme protein suggesting that reduced denaturation of GLA in the presence of isofagomine leads to a decrease in the degradation of the enzyme after internalization. Preincubation of GLA with slow-binding inhibitors before infusion may improve the effectiveness of ERT for Gaucher disease. 相似文献