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PubMed2006

Frequency of RNA-RNA interaction in a model of the RNA World.

The RNA World model for prebiotic evolution posits the selection of catalytic/template RNAs from random populations. The mechanisms by which these random populations could be generated de novo are unclear. Non-enzymatic and RNA-catalyzed nucleic acid polymerizations are poorly processive, which means that the resulting short-chain RNA population could contain only limited diversity. Nonreciprocal recombination of smaller RNAs provides an alternative mechanism for the assembly of larger species with concomitantly greater structural diversity; however, the frequency of any specific recombination event in a random RNA population is limited by the low probability of an encounter between any two given molecules. This low probability could be overcome if the molecules capable of productive recombination were redundant, with many nonhomologous but functionally equivalent RNAs being present in a random population. Here we report fluctuation experiments to estimate the redundancy of the set of RNAs in a population of random sequences that are capable of non-Watson-Crick interaction with another RNA. Parallel SELEX experiments showed that at least one in 10(6) random 20-mers binds to the P5.1 stem-loop of Bacillus subtilis RNase P RNA with affinities equal to that of its naturally occurring partner. This high frequency predicts that a single RNA in an RNA World would encounter multiple interacting RNAs within its lifetime, supporting recombination as a plausible mechanism for prebiotic RNA evolution. The large number of equivalent species implies that the selection of any single interacting species in the RNA World would be a contingent event, i.e., one resulting from historical accident.

Bacillus subtilis↗

PubMed1997

Spatially filtering functional magnetic resonance imaging data.

When constructing MR images from acquired spatial frequency data, it can be beneficial to apply a low-pass filter to remove high frequency noise from the resulting images. This amounts to attenuating high spatial frequency fluctuations that can affect detected MR signal. A study is presented of spatially filtering MR data and possible ramifications on detecting regionally specific activation signal. It is shown that absolute activation levels are strongly dependent on the parameters of the filter used in image construction and that significance of an activation signal can be enhanced through appropriate filter selection. A comparison is made between spatially filtering MR image data and applying a Gaussian convolution kernel to statistical parametric maps.

Magnetic Resonance Imaging↗

PubMed1983

Free amino acid concentrations in blood cells of two brothers with gyrate atrophy of the choroid and retina with hyperornithinaemia.

In this study we selected blood cells as accessible tissues and measured the free amino acid concentrations in erythrocytes, lymphocytes, and granulocytes of two patients with gyrate atrophy with hyperornithinaemia. We found that ornithine concentrations were elevated in blood cells, to different degrees depending on the type of cell, and that aspartic acid concentrations were low in erythrocytes. We also investigated the fluctuation of free amino acid concentrations in blood cells up to 24 h after the oral administration of ornithine. The ornithine concentration in the blood cells of the patients reached a peak 2 h after the oral administration, and remained high for at least 4 h, although after 2 h the concentration curves differed in the three types of cells.

Adult↗

PubMed2004

Four-year monitoring of parasite communities in gobiid fishes of the south-western BalticII. Infracommunity.

The parasite infracommunity of five goby species (Pomatoschistus minutus, P. pictus, P.microps, Gobiusculus flavescens, Gobius niger) from the south-western Baltic was investigated during spring, summer and autumn of the years 1997-2000. The mean parasite species number in single hosts was high, ranging between 1.1 (P. minutus), 2.1 (P. pictus) to even 3.3 (P. microps). Gobius niger is the only host which lives longer than a year and is infested by almost identical parasites for longer times, i.e. the parasite species composition has greater homogeneity. Most intensity of infestation values peaked in summer and were lowest in autumn; only a few exceptions were found in spring or autumn. Only the Digenea Podocotyle atomon and Cryptocotyle concavum were abundant enough to show a clear seasonal fluctuation in Pomatoschistus minutus, P. pictus and Gobiusculus flavescens. Aphalloides timmi and Apatemon gracilis (Digenea) also attained high intensities in P. microps. These four parasite species and, additionally, Cryptocotyle lingua (Digenea), and Hysterothylacium sp. (Nematoda) can be strongly accumulated from either prey or free-swimming larvae and, thus, decisively influence the structure of the infracommunities. Due to selection by filter mechanisms, rare parasites settle rather by chance after competition with other species. The number of parasite species usually increased significantly with host growth. As many as four parasite species were found at the same time in the intestinal tract microhabitat of Gobius niger and P. minutus; at most three parasite species were present on the skin and fins or in the body cavity. The level of infection is due to the respective life history patterns and the kinds of prey, which harbour different parasites as intermediate hosts. Additionally, it depends on the time of appearance of goby offspring in the course of the year.

Animals↗

PubMed1992

Ion channel formation by duramycin.

The formation of ion channels by the nonadecapeptide antibiotic duramycin was examined using black lipid membranes and using the patch-clamp technique. In black lipid membranes made from glyceryl monooleate or a phosphatidylcholine/phosphatidylethanolamine mixture, duramycin induced complex fluctuations in membrane conductance, some step-like and some which were incapable of being resolved into discrete conductance states. Both conductance and largest step size increased with time. A similar time-dependent increase in conductance was seen in patch-clamp experiments with HCA-7 Colony 29 human colonic epithelial cell. The channels displayed weak anion selectivity and the smaller channels formed in patches from epithelial cells showed weak inward-rectification. Channel formation by duramycin was achieved at lower concentrations when the black lipid membrane was made with phospholipid rather than with glyceryl monooleate. Lower concentrations were effective in generating conductances in epithelial cells than in bilayers. It is concluded that duramycin forms ion channels in both artificial and biological membranes. Accumulation of duramycin and coalescence of initially small channels into larger ones is considered to be responsible for the recorded behaviour and to final disruption of membranes.

Anti-Bacterial Agents↗

PubMed2004

Treatment in myotonia and periodic paralysis.

The myotonic disorders, including the myotonic dystrophies (myotonic dystrophy type 1, DM1; myotonic dystrophy type 2, DM2/PROMM/PDM), the muscle channelopathies or non-dystrophic myotonias (chloride, sodium, calcium and potassium channelopathies) are all characterized by myotonia and muscle weakness despite different pathophysiology involved in these disorders. Myotonia may affect the eye, facial and jaw muscles as well as the hands and legs. It may be painful and disabling. Muscle weakness may be episodical as in the paralytic attacks of the sodium and calcium channelopathies or culminate in permanent muscle weakness as in the calcium channelopathies and some sodium channelopathies associated to specific point mutations. The severity of myotonia may fluctuate in the myotonic dystrophies, but weakness is usually fixed, affecting neck flexors, facial and jaw muscles as well as proximal and distal muscles of the limbs. Despite the recent progress in molecular genetics the precise mechanisms responsible for myotonia and weakness are not fully understood and there is no standardized treatment strategy. We present a review of selected treatment trials in the myotonic disorders and the muscle channelopathies, and discuss our experience in the treatment of myotonia and muscle weakness, with reference to the limits and advantages of treatment trials in this field.

Biopsy↗

PubMed2000

CAP components and EEG synchronization in the first 3 sleep cycles.

OBJECTIVE: There is consolidated evidence that stage changes in sleep are closely related to spontaneous EEG fluctuations centered on the 20-40 periodicity of the cyclic alternating pattern (CAP). The present investigation aimed at assessing the involvement of the different components of CAP in the process of build-up, maintenance and demolition of deep non-REM (NREM) sleep. METHODS: CAP parameters were quantified in the first 3 sleep cycles (SC1, SC2, SC3), selected from polysomnographic recordings of 25 healthy sound sleepers belonging to an extensive age range (10-49 years). Only ideal SCs were selected, i.e. the ones uninterrupted by intervening wakefulness and in which all stages were represented and linked in a regular succession of a descending branch, a trough and an ascending branch. RESULTS: Among the first 3 SCs, a total amount of 45 (SC1, 16; SC2, 13; SC3, 16) met the inclusion requirements. SCI contained the highest amount of slow wave sleep (43.7 min) and the lowest values of CAP rate (31.6%). The number of phase A1 subtypes remained unmodified across the 3 SCs (SC1, 48; SC2, 48; SC3, 48), whereas both subtypes A2 (SC1, 9; SC2, 14; SC3, 14) and A3 (SC1, 2; SC2, 8; SC3, 10) increased significantly (P<0.028 and P<0.0001, respectively). The A1 subtypes composed more than 90% of all the A phases collected in the descending branches and in the troughs, while the A2 and A3 subtypes were the major representatives (64.3%) of the A phases occurring in the ascending branches. CONCLUSIONS: Within the dynamic organization of sleep, the non-random distribution of CAP sequences, with their succession of slow (subtypes A1) and rapid (subtypes A2 and A3) EEG shifts, seem to be responsible for sculpturing EEG synchrony under the driving and alternating forces of NREM and REM sleep.

Adolescent↗

PubMed2006

Dosimetry limitations and a dose correction methodology for step-and-shoot IMRT.

For the step-and-shoot intensity-modulated radiation therapy (IMRT) technique, the combination of high dose rate, multiple beam segments and low dose per segment can lead to significant differences between the planned dose and the dose delivered to the patient. In this technique, a dose delivery inaccuracy known as the 'overshoot' effect is caused by the dose servo control system. This typically occurs in the first and last beam segments and causes an over- and underdose, respectively. Some dose positional error in the segment sequence is also possible there. Commercial ionization chambers (RK-type) and radiographic Kodak films were used for the measurements. The reported results were obtained using the Pinnacle(3)-V6.2 treatment planning system and a Varian Clinac 21 EX linear accelerator equipped with a 120-leaf Millennium MLC. The dose inaccuracy measurements were based on the comparison of the dose and profiles for reference fields and fields irradiated with the step-and-shoot technique. For our linear accelerators, an 'overshoot' effect ranging from 0.1 to 0.6 MU was found, corresponding to a dose rate from 100 to 600 MU min(-1), respectively. For segments with off-axis distances from 0 to 5.5 cm with >3.5 MU per segment and all dose rates, a MLC leaf-position error of <1 mm was measured. For segments with an off-axis distance of 9.5 cm, a positional error >2 mm was measured for 600 MU min(-1) and 1 MU per segment. The purpose of this study was to find a correction method for segmental dose errors caused by the 'overshoot' effect when small monitor unit and high dose rate are used. To better represent the fluctuation of the segment doses in the beam, a dose ratio between reference and step-and-shoot irradiated fields was defined. A method for the correction of segment dose inaccuracies and a quality assurance programme for the 'overshoot' effect were developed. The ordering of the biggest segment shape in the segment sequence was studied for ten randomly selected prostate patients planned for IMRT. The results of this work can be used to improve the agreement between the planned and delivered doses for IMRT.

Film Dosimetry↗

PubMed1993

Detection, typing, and subtyping of enteric adenoviruses 40 and 41 from fecal samples and observation of changing incidences of infections with these types and subtypes.

Monoclonal antibody (MAb) preparations specific for the enteric adenoviruses of subgenus F (AdF) were generated and evaluated as typing reagents in virus neutralization tests and enzyme-linked immunosorbent assays (ELISAs). A panel of 11 genome types of adenovirus 40 (Ad40), 24 genome types of Ad41, and 47 adenovirus prototype strains was used to determine the specificities of the MAbs in the two assays. In this way two MAbs, MAb 40-1 (anti-Ad40) and MAb 41-1 (anti-Ad41) were selected. These two MAbs showed strict type specificity in both assays. A third MAb reacted in an ELISA with all 47 human adenovirus types. With two other MAbs, three antigenic subtypes of Ad41 could be distinguished by their reactivities in virus neutralization tests and ELISAs. On the basis of the five selected MAbs, a sensitive ELISA system was developed for the direct detection and simultaneous typing and subtyping of Ad40 and Ad41 present in stool specimens. The five MAbs were also used to study the epidemiology of infections with Ad40 and Ad41 in The Netherlands in the period 1981 through 1989. It was shown that there were no significant fluctuations in the annual incidence of the cluster of enteric adenoviruses as a whole. This cluster should therefore be considered to belong to the "endemic" rather than the "epidemic" adenoviruses. The relative incidence of Ad40 infections compared with that of Ad41 infections changed considerably during the period studied; the proportion of Ad41 infections rose from about 30% in 1981 to about 95% in 1986, after which it stabilized at 90 to 95%. The proportion of one of the subtypes of Ad41 (Ad41 subtype M3) increased from about 40 to 80% in the same period.

Adenovirus Infections, Human↗

PubMed2006

A protein dynamics study of photosystem II: the effects of protein conformation on reaction center function.

Molecular dynamics simulations have been performed to study photosystem II structure and function. Structural information obtained from simulations was combined with ab initio computations of chromophore excited states. In contrast to calculations based on the x-ray structure, the molecular-dynamics-based calculations accurately predicted the experimental absorbance spectrum. In addition, our calculations correctly assigned the energy levels of reaction-center (RC) chromophores, as well as the lowest-energy antenna chlorophyll. The primary and secondary quinone electron acceptors, Q(A) and Q(B), exhibited independent changes in position over the duration of the simulation. Q(B) fluctuated between two binding sites similar to the proximal and distal sites previously observed in light- and dark-adapted RC from purple bacteria. Kinetic models were used to characterize the relative influence of chromophore geometry, site energies, and electron transport rates on RC efficiency. The fluctuating energy levels of antenna chromophores had a larger impact on quantum yield than did their relative positions. Variations in electron transport rates had the most significant effect and were sufficient to explain the experimentally observed multi-component decay of excitation in photosystem II. The implications of our results are discussed in the context of competing evolutionary selection pressures for RC structure and function.

Computer Simulation↗

PubMed1994

Quality control of extemporaneously prepared microdose captopril capsules: weight variation versus content uniformity.

Microdose (1 mg) captopril therapy is commonly used for the initial dose titration in patients with congestive heart failure. Since this dosage form is not commercially available, it has to be extemporaneously compounded. Quality control of each batch is commonly evaluated using the weight variation technique described in the USP. Despite careful titration with microdose, captopril capsules variability in patient's response has been observed. In order to explain this fluctuation, the actual content of extemporaneously compounded microdose captopril capsules was evaluated using a high pressure liquid chromatographic assay. Microdose captopril capsules were prepared by triturating 25 mg tablets with lactose in a mortar using standard geometric dilution technique and a Sharpe-Dohme hand-operated capsule filling machine. Forty-eight microdose captopril capsules were randomly selected from the compounded batch and were individually assayed for captopril amount. The mean +/- standard deviation (SD) amount of captopril in each capsule was 1.27 g +/- 0.31 mg with a range of 0.84 g to 1.96 mg. The coefficient of variation was 24.5%. Ten captopril capsules were randomly selected from the compounded batch and were individually weighed. The capsules had a mean weight +/- SD of 198.3 g +/- 21.2 mg and a coefficient of variation of 7.3%. Even though the extemporaneously prepared microdose captopril capsules were within acceptable limits for weight variation described in the USP, the actual dose administered to the patients could vary by as much as 24.5%.

Capsules↗

PubMedDate not supplied

[Mortality in young adults: international comparisons].

In searching for an epidemiological indicator which might reflect the impact of the widespread use of various drugs among California youth in the late 1960s, the customary sources of health statistics were found to be unsatisfactory due to the lack of consensus on diagnosis of drug related problems. Examination of mortality of young adults (persons aged 15-24, YAM) showed marked and paradoxical rises when drug use was rising. Males and Blacks had higher rates than females and Whites; motor vehicle accidents were the largest single overall cause. But the rise, both in California and the US was proportionally greater among women and motor vehicle accidents did not contribute to the rise. Examination of rates during mid-1970s for various countries showed that for countries with per capita income less than about $3,000 per year, YAM due to diseases was very closely correlated with per capita income. Above that external cause, YAM and particularly that due to motor vehicle accidents, increased with per capita income. The increase was steeper in some countries than in others. The difference in these two groups of countries was correlated with fraction of national income spent on education and with ethnic homogeneity. In the US fluctuations in YAM paralleled admissions for heroin use. As part of the Epidemiological Revolution, young adult mortality complements infant mortality, since it is closely related to social health, employment opportunities and appropriateness of education. Further, it is important for the potential development of a country, region, or community. This report examines YAM data for mid-1980s from selected countries and notes major changes during the past decade, most countries having shown striking decreases. In some countries high rates of suicide, homicide and death due to civil disorders provide an incentive for further improvement. In other countries, the high rates for death attributed to motor vehicle crashes compels attention. Involvement of young persons themselves in plans for improvement of their opportunities seems an essential strategy, for which the educational strategies suggested by Freire seem to be appropriate.

Adolescent↗

PubMed2005

Housekeeping gene selection for real-time RT-PCR normalization in potato during biotic and abiotic stress.

Plant stress studies are more and more based on gene expression. The analysis of gene expression requires sensitive, precise, and reproducible measurements for specific mRNA sequences. Real-time RT-PCR is at present the most sensitive method for the detection of low abundance mRNA. To avoid bias, real-time RT-PCR is referred to one or several internal control genes, which should not fluctuate during treatments. Here, the non-regulation of seven housekeeping genes (beta-tubulin, cyclophilin, actin, elongation factor 1-alpha (ef1alpha), 18S rRNA, adenine phosphoribosyl transferase (aprt), and cytoplasmic ribosomal protein L2) during biotic (late blight) and abiotic stresses (cold and salt stress) was tested on potato plants using geNorm software. Results from the three experimental conditions indicated that ef1alpha was the most stable among the seven tested. The expression of the other housekeeping genes tested varied upon stress. In parallel, a study of the variability of expression of hsp20.2, shown to be implicated in late blight stress, was realized. The relative quantification of the hsp20.2 gene varied according to the internal control and the number of internal controls used, thus highlighting the importance of the choice of internal controls in such experiments.

Cold Temperature↗

PubMed1984

Influence of actinomycin-D on the diurnal rhythm of cytoplasmic RNA in the neurocytes of selected nuclei of mouse hypothalamus.

The influence of a single dose of actinomycin-D (1 mg/kg body weight) on the diurnal rhythm of cytoplasmic RNA was studied in neurocytes of the supraoptic nucleus (SON), paraventricular nucleus (PVN), and arcuate nucleus (AN) by microspectrophotometer. Cosinor analysis of the obtained results revealed a disturbed diurnal rhythm of cytoplasmic RNA in the animals treated with actinomycin-D. The mean diurnal RNA content in the SON, PVN, and AN neurocytes decreased, the amplitude of diurnal fluctuation was reduced and the acrophase was shifted to earlier hours.

Animals↗

PubMed2003

Neuroactive steroids reduce neuronal excitability by selectively enhancing tonic inhibition mediated by delta subunit-containing GABAA receptors.

Neuroactive steroids are potent modulators of gamma-aminobutyric acid type A receptors (GABAARs), and their behavioral effects are generally viewed in terms of altered inhibitory synaptic transmission. Here we report that, at concentrations known to occur in vivo, neuroactive steroids specifically enhance a tonic inhibitory conductance in central neurons that is mediated by extrasynaptic delta subunit-containing GABAARs. The neurosteroid-induced augmentation of this tonic conductance decreases neuronal excitability. Fluctuations in the circulating concentrations of endogenous neuroactive steroids have been implicated in the genesis of premenstrual syndrome, postpartum depression, and other anxiety disorders. Recognition that delta subunit-containing GABAARs responsible for a tonic conductance are a preferential target for neuroactive steroids may lead to novel pharmacological approaches for the treatment of these common conditions.

Animals↗

PubMed1988

Incorporation in lipid bilayers of a large conductance cationic channel from mitochondrial membranes.

Membranes from subcellular fractions of adrenal medulla were incorporated in phospholipid bilayers formed at the tip of microelectrodes. Current fluctuations recorded in the presence of a transmembrane potential revealed the existence of a voltage-dependent channel of large conductance. This channel is characterized by fast kinetics and four conductance levels separated by jumps of 100, 220 and 220 pS in 150 mM NaCl. It is permeant to Na+,K+, tetraethylammonium, Cl- and acetate and has some cation selectivity. Exposure to trypsin or pronase abolished the voltage-dependence. Upon subcellular fractionation, the activity was found to be associated with mitochondria. A similar activity was observed in mitochondrial fractions from other organs. By its kinetics, its selectivity and its potential-dependence, this channel differs from the voltage-dependent anion channel of outer mitochondrial membranes.

Adrenal Medulla↗

PubMed1978

l/f noise in black lipid membranes induced by ionic channels formed by chemically dimerized gramicidin A.

The noise behavior of lipid bilayer membranes, doped with a chemically dimerized gramicidin A, was investigated. In contrast to normal gramicidin A, which generates a Lorentzian type power spectrum due to the formation and disappearance of conducting dimers, the current power spectrum density Sm(f) obtained with this gramicidin A derivative showed over several orders of magnitude a clear l/f behavior. The intensity of this l/f component was analyzed as a function of the membrane-applied voltage, membrane resistance, electrolyte concentration, and composition. The relationship between the mean-square fluctuation in current and the membrane current mean value was found to follow Hooge's equation, i.e., deltaI2 = alphaI2m/Nf where N is the number of channels and alpha is a constant equal to 1.0 X 10(-2). It is suggested that a l/f type noise was observed because the chemically dimerized form of gramicidin A produces long lasting cation selective channels.

Gramicidin↗

PubMed1994

Functional influence of the central noradrenergic system on the skin conductance activity in rats.

Pharmacological studies on neuroleptics and amphetamine strongly suggest that some dysfunction of the central catecholamine system may play a key role in the pathogenesis of schizophrenia. Our previous studies have demonstrated that intraventricular administration of 6-hydroxydopamine, a selective neurotoxin of the catecholamine neuron, can reproduce schizophrenia-like abnormalities in the skin conductance activity. In the present experiments, effects of pharmacological modulation of the central noradrenergic activity were studied in rats. Stimulation of the central noradrenergic activity by yohimbine (0.6 mg/kg, i.m.) slowed down the habituation of the skin conductance response (SCR) and increase the spontaneous fluctuation of the skin conductance (SF), while inhibition of the activity by clonidine (0.06 mg/kg, i.m.) accelerated or obliterated the SCR and decreased the SF frequency. If the functional significance of the central noradrenergic system lies in vigilance control, the present results are consistent with classical theory in psychophysiology: the habituation rate of SCR and the frequency of SF are correlated well with each other and both indices reflect arousal level. The disorder of the system should produce not only these psychophysiological abnormalities but also psychological disturbances; i.e., overarousal and underarousal syndromes. Therefore, the dysfunction of the noradrenergic system might constitute an essential aspect of schizophrenic disorder.

Acoustic Stimulation↗