| 1. |
- Compte, A., et al.
(author)
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Temporally Irregular Mnemonic Persistent Activity in Prefrontal Neurons of Monkeys during a Delayed Response Task
- 2003
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In: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 90:5, s. 3441-3454
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Journal article (peer-reviewed)abstract
- An important question in neuroscience is whether and how temporal patterns and fluctuations in neuronal spike trains contribute to information processing in the cortex. We have addressed this issue in the memory-related circuits of the prefrontal cortex by analyzing spike trains from a database of 229 neurons recorded in the dorsolateral prefrontal cortex of 4 macaque monkeys during the performance of an oculomotor delayed-response task. For each task epoch, we have estimated their power spectrum together with interspike interval histograms and autocorrelograms. We find that 1) the properties of most (about 60%) neurons approximated the characteristics of a Poisson process. For about 25% of cells, with characteristics typical of interneurons, the power spectrum showed a trough at low frequencies (<20 Hz) and the autocorrelogram a dip near zero time lag. About 15% of neurons had a peak at <20 Hz in the power spectrum, associated with the burstiness of the spike train, 2) a small but significant task dependency of spike-train temporal structure: delay responses to preferred locations were characterized not only by elevated firing, but also by suppressed power at low (<20 Hz) frequencies, and 3) the variability of interspike intervals is typically higher during the mnemonic delay period than during the fixation period, regardless of the remembered cue. The high irregularity of neural persistent activity during the delay period is likely to be a characteristic signature of recurrent prefrontal network dynamics underlying working memory.
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| 2. |
- Los, Marek Jan, et al.
(author)
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Activation and caspase-mediated inhibition of PARP : A molecular switch between fibroblast necrosis and apoptosis in death receptor signaling
- 2002
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In: Molecular Biology of the Cell. - : American Society for Cell Biology. - 1059-1524 .- 1939-4586. ; 13:3, s. 978-988
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Journal article (peer-reviewed)abstract
- Death ligands not only induce apoptosis but can also trigger necrosis with distinct biochemical and morphological features. We recently showed that in L929 cells CD95 ligation induces apoptosis, whereas TNF elicits necrosis. Treatment with anti-CD95 resulted in typical apoptosis characterized by caspase activation and DNA fragmentation. These events were barely induced by TNF, although TNF triggered cell death to a similar extent as CD95. Surprisingly, whereas the caspase inhibitor zVAD prevented CD95-mediated apoptosis, it potentiated TNF-induced necrosis. Cotreatment with TNF and zVAD was characterized by ATP depletion and accelerated necrosis. To investigate the mechanisms underlying TNF-induced cell death and its potentiation by zVAD, we examined the role of poly(ADP-ribose)polymerase-1 (PARP-1). TNF but not CD95 mediated PARP activation, whereas a PARP inhibitor suppressed TNF-induced necrosis and the sensitizing effect of zVAD. In addition, fibroblasts expressing a noncleavable PARP-I mutant were more sensitive to TNF than wild-tvpe cells. Our results indicate that TNF induces PARP activation leading to ATP depletion and subsequent necrosis. In contrast, in CD95-mediated apoptosis caspases cause PARP-1 cleavage and thereby maintain ATP levels. Because ATP is required for apoptosis, we suggest that PARP-1 cleavage functions as a molecular switch between apoptotic and necrotic modes of death receptor-induced cell death.
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| 3. |
- Wang, Y D, et al.
(author)
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Determination of the stress orientation distribution function using pulsed neutron sources
- 2003
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In: Journal of applied crystallography. - 0021-8898 .- 1600-5767. ; 36:1, s. 14-22
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Journal article (peer-reviewed)abstract
- The stress orientation distribution function (SODF) was recently introduced as a mean-field representation to describe the grain- orientation dependence of intergranular stress. Pulsed neutron sources are ideally suited for the determination of the SODF since multiple reflections can be measured simultaneously with comparable precision. A method is developed for constructing the SODF from strain pole figures measured with a pulsed neutron source and demonstrated with cold-rolled interstitial-free steel. The experimental results are compared with those measured with a reactor-based constant-wavelength diffractometer. It is shown that access to a large number of reflections on a pulsed neutron source improves the precision of the experimental SODF and facilitates in situ studies of the evolution of the intergranular stress during deformation and annealing.
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| 4. |
- Xu, DW, et al.
(author)
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Downregulation of telomerase reverse transcriptase mRNA expression by wild type p53 in human tumor cells
- 2000
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In: Oncogene. - 0950-9232 .- 1476-5594. ; 19:45, s. 5123-5133
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Journal article (peer-reviewed)abstract
- The p53 tumor suppressor protein inhibits the formation of tumors through induction of cell cycle arrest and/or apoptosis, In the present study we demonstrated that p53 is also a powerful inhibitor of human telomerase reverse transcriptase (hTERT), a key component for telomerase, Activation of either exogenous temperature-sensitive (ts) p53 in BL41 Burkitt lymphoma cells or endogenous wild type (wt) p53 at a physiological level in MCF-7 breast carcinoma cells triggered a rapid downregulation of hTERT mRNA expression, independently of the induction of the p53 target gene p21, Co-transfection of an hTERT promoter construct with wt p53 but not mutant p53 in HeLa cells inhibited the hTERT promoter activity. Furthermore, the activation of the hTERT promoter in Drosophila Schneider SL2 cells was completely dependent on the ectopic expression of Sp1 and was abrogated by wt p53, Finally, wt p53 inhibited Sp1 binding to the hTERT proximal promoter by forming a p53-Sp1 complex. Since activation of telomerase, widely observed in human tumor cell lines and primary tumors, is a critical step in tumorigenesis, wt p53-triggered inhibition of hTERT/telomerase expression may reflect yet another mechanism of p53-mediated tumor suppression. Our findings provide new insights into both the biological function of p53 and the regulation of hTERT/telomerase expression.
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| 5. |
- Björneholm, O., et al.
(author)
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Doppler splitting of in-flight auger decay of dissociating oxygen molecules : The localization of delocalized core holes
- 2000
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In: Physical Review Letters. - : AMERICAN PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 84:13, s. 2826-2829
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Journal article (peer-reviewed)abstract
- By exploiting the core-excitation-induced dissociation of O-2, we find that the Auger emission exhibits a Doppler-like energy shift. We show this to be a manifestation of localization of the core hole and propose that the problem of core-hole localization versus delocalization in core-hole spectroscopies may be resolved by considering the nature of the measurement.
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| 6. |
- Durbeej, Bo, et al.
(author)
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Lignin biosynthesis and degradation − a major challenge for computational chemistry
- 2003
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In: High Performance Computing for Computational Science — VECPAR 2002. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783540008521 - 9783540365693 ; , s. 137-165
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Conference paper (peer-reviewed)abstract
- In the present chapter we review a series of computational studies related to lignin biosynthesis and degradation, with the aim to understand at a molecular level processes crucial to paper and pulp industries. Due to the complexity of the problem, a wide variety of computational approaches are employed, each with its own merits. From the theoretical studies we are able to draw conclusions regarding the behavior of lignol monomers and their corresponding dehydrogenated radicals in aqueous solution and in lipid bilayers, and reaction mechanisms, conformations and relative stabilities of lignol dimers.
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| 7. |
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| 8. |
- Wang, HG, et al.
(author)
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Interval cancers in the Norwegian Breast Cancer Screening Program : Frequency, characteristics and use of HRT
- 2001
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In: International Journal of Cancer. - 0020-7136 .- 1097-0215. ; 94:4, s. 594-598
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Journal article (peer-reviewed)abstract
- Breast cancers diagnosed between screening examinations among women who attend a breast cancer screening program are defined as interval cancers. The Norwegian Breast Cancer Screening Program started as a pilot project in 1996, and data from the first 2-year interval are available. Our study quantifies interval cancers in the pilot project and explores characteristics and factors that may be associated with interval cancer. Interval cancers in the screening population were identified through the Cancer Registry of Norway. The frequency of invasive interval cancer was calculated as cases per 10,000 screened and as observed/expected ratio. Characteristics of the interval cancers were compared to screening-detected and clinical cancers. Breast density was assessed in a blinded review of 3 categories of screening mammograms. Information on hormone replacement therapy (HRT) use was collected from a questionnaire. The frequency of invasive interval cancers was 18.2 (15.9-20.7) per 10,000 screened and the observed/expected ratio was 0.49 (0.43-0.56). The frequency in the second year of the interval was higher than reported from other programs. The median tumor size of the interval cancers was 19.5 mm and 44.0% of the patients had affected axillary lymph nodes. The interval cancer cases had higher proportions of dense breasts and reported use of HRT compared to screen normal and screening-detected cases. The reported frequency of interval cancers is similar to comparable programs. The interval cancers differed significantly from the cancers detected in the first screening round and were more similar to clinical cancers. Interval cancer was associated with dense breasts and use of HRT. Screening programs must keep these associations in focus. (C) 2001 Wiley-Liss, Inc.
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| 9. |
- Willander, Magnus, et al.
(author)
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Optical properties of InAs quantum dots
- 2002
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In: Acta Physica Polonica. A. - : Polish Academy of Sciences Warsaw. - 0587-4246 .- 1898-794X. ; 102:4-5, s. 567-576
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Journal article (peer-reviewed)abstract
- InAs quantum dots grown on GaAs substrate were investigated by optical spectroscopy. We particularly emphasized on the photoluminescence intensity, the stability of the photoluminescence intensity versus temperatures and wavelength of the InAs dot emission at various thermal treatments and different structures. We found that hydrogen can strongly passivate nonradiative centers without causing any structure degradation, and both n- and p-type modulation doping can reduce the decrease in the photoluminescence intensity when the sample temperature increases from the helium temperature to room temperature. The emission wavelength and the efficiency of the InAs quantum dots can also be manipulated by choosing proper materials of cap layer.
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| 10. |
- Zhao, QX, et al.
(author)
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Nonradiative centers in InAs dots grown on GaAs substrates for 1.3 mu m emission
- 2003
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In: Physics Letters A. - : Elsevier Science B.V., Amsterdam.. - 0375-9601 .- 1873-2429. ; 315:02-Jan, s. 150-155
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Journal article (peer-reviewed)abstract
- Nonradiative centers in InAs dots grown on GaAs substrates are investigated in this study. The emission from InAs dots close to 1.3 mum is monitored under different excitation densities and different excitation energy. The used samples were also treated by hydrogen plasma in order to suppress the nonradiative centers. The purpose of this work is to study how nonradiative centers influence the efficiency of InAs dots emission and whether the nonradiative centers can be reduced. Our results clearly illustrate that there indeed exist nonradiative centers, both at the interface between the InAs dots and surrounding layers and in the GaAs layers, which can be suppressed by H-treatments. A technique to estimate relative amount of nonradiative centers is also discussed.
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