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241.
Maxim K. Elias 《Pal?ontologische Zeitschrift》1962,36(1):29-37
The type specimen ofGonioloboceras goniolobum (Meek), rediscovered by Spath in the British Museum, is the foundation for a more accurate comparative study of this and other species ofGonioloboceras.Gonioloboceras described asG. goniolobum byElias in 1938 is differentiated asGonioloboceras schmidti, new species. Suture sets (new term) for several growth stages inG. goniolobum (Meek),G. welleriSmith,G. schmidtiElias, G.eliasiMiller &Owen, andG. asiaticumLibrovitch are assembled and used for differentiation of the species.The Kazakhstan goniatite faunule containingG. asiaticum is considered of very late Pennsylvanian age. 相似文献
242.
R. Schoysman B. Lejeune E. Van Roosendaal L. Segal P. Vanderzwalmen M. Nijs B. Vandamme G. Bertin 《Andrologie》1996,6(4):432-439
The authors report their experience with the use of spermatids in TESE programs where mature spermatozoa could not be isolated from testicular biopsies. The details of the indications for spermatid insemination, the technicity of the procedure and the results are exposed. 相似文献
243.
Verónica Alvarez Maubecin Viviana N. Sanchez Marcelo D. Rosato Siri Bruce D. Cherksey Mutzuyuki Sugimori Rodolfo Llinás Osvaldo D. Uchitel 《Journal of neurochemistry》1995,64(6):2544-2551
Abstract: The voltage-dependent calcium channels present in mammalian and chicken brain synaptosomes were characterized pharmacologically using specific blockers of L-type channels (1,4-dihydropyridines), N-type channels (ω-conotoxin GVIA), and P-type channels [funnel web toxin (FTX) and ω-agatoxin IVA]. K+-induced Ca2+ uptake by chicken synaptosomes was blocked by ω-conotoxin GVIA (IC50 = 250 nM). This toxin at 5 µM did not block Ca2+ entry into rat frontal cortex synaptosomes. FTX and ω-agatoxin IVA blocked Ca2+ uptake by rat synaptosomes (IC50 = 0.17 µl/ml and 40 nM, respectively). Likewise, in chicken synaptosomes, FTX and ω-agatoxin IVA affected Ca2+ uptake. FTX (3 µl/ml) exerted a maximal inhibition of 40% with an IC50 similar to the one obtained in rat preparations, whereas with ω-agatoxin IVA saturation was not reached even at 5 µM. In chicken preparations, the combined effect of saturating concentrations of FTX (1 µl/ml) and different concentrations of ω-conotoxin GVIA showed no additive effects. However, the effect of saturating concentrations of FTX and ω-conotoxin GVIA was never greater than the one observed with ω-conotoxin GVIA. We also found that 60% of the Ca2+ uptake by rat and chicken synaptosomes was inhibited by ω-conotoxin MVIID (1 µM), a toxin that has a high index of discrimination against N-type channels. Conversely, nitrendipine (10 µM) had no significant effect on Ca2+ uptake in either the rat or the chicken. In conclusion, Ca2+ uptake by rat synaptosomes is potently inhibited by different P-type Ca2+ channel blockers, thus indicating that P-type channels are predominant in this preparation. In contrast, Ca2+ uptake by chicken synaptosomes is sensitive to ω-conotoxin GVIA, FTX, ω-agatoxin IVA, and ω-conotoxin MVIID. This suggests that a channel subtype with a mixed pharmacology is present in chicken synaptosomes. 相似文献
244.
245.
Neurotrophic Effects of l-DOPA in Postnatal Midbrain Dopamine Neuron/Cortical Astrocyte Cocultures 总被引:4,自引:1,他引:3
Abstract: l -DOPA is toxic to catecholamine neurons in culture, but the toxicity is reduced by exposure to astrocytes. We tested the effect of l -DOPA on dopamine neurons using postnatal ventral midbrain neuron/cortical astrocyte cocultures in serum-free, glia-conditioned medium. l -DOPA (50 µ M ) protected against dopamine neuronal cell death and increased the number and branching of dopamine processes. In contrast to embryonically derived glia-free cultures, where l -DOPA is toxic, postnatal midbrain cultures did not show toxicity at 200 µ M l -DOPA. The stereoisomer d -DOPA (50–400 µ M ) was not neurotrophic. The aromatic amino acid decarboxylase inhibitor carbidopa (25 µ M ) did not block the neurotrophic effect. These data suggest that the neurotrophic effect of l -DOPA is stereospecific but independent of the production of dopamine. However, l -DOPA increased the level of glutathione. Inhibition of glutathione peroxidase by l -buthionine sulfoximine (3 µ M for 24 h) blocked the neurotrophic action of L-DOPA. N -Acetyl- l -cysteine (250 µ M for 48 h), which promotes glutathione synthesis, had a neurotrophic effect similar to that of l -DOPA. These data suggest that the neurotrophic effect of l -DOPA may be mediated, at least in part, by elevation of glutathione content. 相似文献
246.
247.
A. Jagannadha Rao N. Mathialagan S. G. Kotagi N. R. Moudgal 《Journal of biosciences》1984,6(2):97-106
The regulation of secretion of chorionic gonadotropin in primates has been studied using bothin vivo andin vitro models.In vivo studies using the pregnant bonnet monkey revealed that at the doses tested, the administration of progesterone or estradiol 17Β in combination or alone did not result in any appreciable change in the duration or magnitude of serum chorionic gonadotropin levels. However, administration of lutropin-releasing hormone by intravenous route resulted in significant increase in chorionic gonadotropin levels within 30–60 min and the extent of stimulation seemed to depend on the state of pregnancy. Forin vitro studies, explants or cells prepared from first trimester human placenta has been used. The functional integrity of these cells has been established by demonstrating the binding of [125I]-labelled human chorionic gonadotropin antibody to the cells as well as the synthesis of [3H]-labelled human chorionic gonadotropin.In vitro studies using the cells revealed that addition of lutropin-releasing hormone caused a significant increase in chorionic gonadotropin and estradiol 17Β secreted into the medium. Thus bothin vivo andin vitro results suggest that lutropin-releasing hormone could be one of the factors involved in regulation of chorionic gonadotropin secretion in primates. 相似文献
248.
Two-dimensional (2-D) gel analysis of replication intermediates in the Chinese hamster dihydrofolate reductase domain has suggested that nascent chains can initiate at any of a large number of sites scattered throughout a ~50 kb “initiation locus” (although the level of initiation detected at any given site within this region was relatively low). This result contrasts markedly with data from anin vitro strand switching assay suggesting that >80% of initiations occur within a single 500 bp fragment lying within the initiation locus. In an effort to reconcile these two disparate views of the initiation reaction, we have questioned the validity of our 2-D gel data in several ways. We show here that: 1) the number of replication bubbles detected in the DHFR locus in the early S period is markedly increased when the cells are released from a synchronizing agent that inhibits initiationper se, rather than from aphidicolin, which is a chain elongation inhibitor; 2) initiation in the DHFR domain occurs only during the first 90 min of the S period, as would be expected of an early-firing origin; 3) a pulse of3H-thymidine moves through the structures observed on 2-D gels with the kinetics expected ofbonafide replication intermediates; and 4) preparations of replication intermediates that are subsequently analyzed on 2-D gels appear, by electron microscopy, to represent the typical theta structures and single-forked molecules expected of bidirectional origins of replication; no unusual structures (e.g., microbubbles) were seen. 相似文献
249.
Paula N. Friedman Edith H. Wang Karen Meerovitch Nahum Sonenberg Carol Prives 《Chromosoma》1992,102(1):S60-S66
We have characterized the effects of p53 on several biochemical activities of simian virus 40 (SV40) large tumor (T) antigen. While p53 induced a strong inhibition of the T antigen DNA helicase activity, surprisingly, its RNA helicase activity was stimulated. This supports the liklihood that the DNA and RNA helicase activities of T antigen reflect discrete functions. p53 did not significantly affect the ATP-dependent conversion of T antigen monomers to hexamers. However, the ability of these hexamers to assemble on a DNA fragment containing the viral origin was impaired by p53. Thus, these results suggest that p53 inhibits the function but not the formation of T antigen multimers. This conclusion was further supported by the observation that the addition of a purified p53:T antigen complex was as inhihitory as free p53 to the DNA helicase activity of free T antigen. Thus our data indicates that the targets of p53 inhibition are the functional units of T antigen, namely the hexamers. 相似文献
250.
Lahja Uitto Jussi Halleeen Päivi Remes Tapio Kesti Juhani E. Syväoja 《Chromosoma》1992,102(1):S142-S146
The 3′→5′ exonuclease activity of highly purified large form of human DNA polymerase epsilon was studied. The activity removes mononucleotides from the 3′ end of an oligonucleotide with a non-processive mechanism and leaves 5′-terminal trinucleotide non-hydrolyzed. This is the case both with single-stranded oligonucleotides and with oligonucleotides annealed to complementary regions of M13DNA. However, the reaction rates with single-stranded oligonucleotides are at least ten-fold when compared to those with completely base-paired oligonucleotides. Conceivably, mismatched 3′ end of an oligonucleotide annealed to M13DNA is rapidly removed and the hydrolysis is slown down when double-stranded region is reached. The preferential removal of a non-complementary 3′ end and the non-processive mechanism are consistent with anticipated proofreading function. In addition to the 3′→5′ exonuclease activity, an 5′→3′ exonuclease activity is often present even in relatively highly purified DNA polymerase epsilon preparates suggesting that such an activity may be an essential com-ponent for the action of this enzymein vivo. Contrary to the 3′→5′ exonuclease activity, the 5′→3′ exonuclease is separable from the polymerase activity. 相似文献