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PubMed1995

Effects of bradykinin on short-term variability in blood pressure and heart rate in rats: a spectral study.

Using a spectral procedure, we studied the effects of two treatment regimens of bradykinin (BK) on the blood pressure (BP) and heart rate (HR) variabilities in conscious Wistar rats. We performed a second series of experiments with hydralazine, at doses equihypotensive to those used in BK treatments, to discriminate between a specific effect of the peptide and those induced by vasodilation. We assessed the activity of the sympathetic nervous system (SNS), using the responses to atenolol and prazosin. First, at a subhypotensive treatment regimen, BK (5 micrograms/min) increased low-frequency (LF, 0.02-0.2 Hz) and mid-frequency (MF, 0.2-0.6 Hz) frequency components of BP variability and also activated the SNS. Lesser enhancements of LF and MF areas were induced by hydralazine (0.15 mg/kg). Second, high-dose treatment regimens of BK (100 micrograms/min) and hydralazine (2 mg/kg), which markedly decreased BP, did not change the areas of the LF and MF components of BP variability, whereas overactivity of the SNS was still assessed with the adrenergic blockers. On the other hand, high-dose BK induced a sixfold increase in the amplitude of the high frequency (HF, respiratory) component of BP. The effect of bradykinin on HF domain was associated with an increase in the depth of respiration in a group of anesthetized rats. Hoe 140 (60 micrograms/kg), a B-2 BK-receptor antagonist, abolished both the effects of BK on HF fluctuations in BP and the effects on breathing pattern. Our results demonstrate that BK induced different effects on LF and MF fluctuations in BP depending on the treatment regimen, whereas the SNS was activated by the two selected treatment regimens. Therefore, the MF component of BP variability should be considered only as a marker of the activity of the SNS when the BP level was not affected. Furthermore, we characterized an amplifying effect of BK on the HF domain of BP variability partly mediated by an increase in the depth of respiration.

Adrenergic beta-Antagonists↗
PubMed2004

Ultrafast dynamic control of spin and charge density oscillations in a GaAs quantum well.

We use subpicosecond laser pulses to generate and monitor in real time collective oscillations of electrons in a modulation-doped GaAs quantum well. The observed frequencies match those of intersubband spin- and charge-density excitations. Light couples to coherent density fluctuations through resonant stimulated Raman scattering. Because the spin- and charge-related modes obey different selection rules and resonant behavior, the amplitudes of the corresponding oscillations can be independently controlled by using shaped pulses of the proper polarization.

Journal Article↗
PubMed1992

Competitive Growth of Genetically Marked Malolactic-Deficient Lactobacillus plantarum in Cucumber Fermentations.

Procedures were developed for the differential enumeration of an added strain of Lactobacillus plantarum and indigenous lactic acid bacteria (LAB) during the fermentation of brined cucumbers. The added strain was an N,N-nitrosoguanidine-generated mutant that lacked the ability to produce CO(2) from malic acid (MDC). The MDC phenotype is desirable because CO(2) production from malic acid decarboxylation has been shown to contribute to bloater formation in fermented cucumbers. A basal medium containing malic acid and adjusted to pH 4.0 permitted growth of indigenous LAB (predominantly MDC), but not growth of the added MDC culture. Transformation of the MDC culture by electroporation with cloning vector pGK12 conferred chloramphenicol resistance, which permitted selective enumeration of this culture. The reversion frequency of the MDC mutation was determined by a fluctuation test to be less than 10. The level of retention of plasmid pGK12 was greater than 90% after 10 generations in cucumber juice medium at 32 degrees C. With the procedures developed, we were able to establish the ratio of MDC to MDC LAB that results in malic acid retention in fermentations of filter-sterilized cucumber juice and unsterilized whole cucumbers under specified conditions.

Journal Article↗
PubMed1969

Influence of oxygen on development of nitrate respiration in Bacillus stearothermophilus.

A denitrifying mutant of Bacillus stearothermophilus NCA 2184, strain 2184-D, was used to explore the development of nitrate respiration in relation to oxygen respiration. Aerobically grown wild-type cultures could acquire the ability to use nitrate as a result of selection of nitrate-respiring mutants by the presence of nitrate and a reduced oxygen tension. Fluctuation analysis has revealed that the frequency of occurrence of the nitrate-respiring mutant is about 7.5 x 10(-8) per bacterium per generation. Nitrate reductase and nitrite reductase appeared to be induced sequentially in strain 2184-D by the addition of nitrate. The formation of both of these enzymes was repressed by oxygen so that cells grown aerobically with nitrate possessed a low basal level of nitrate reducatase and exhibited no denitrification. The rate of synthesis of nitrate reductase increased quickly after addition of nitrate and removal of oxygen. It then declined to a lower steady-state level. Cells grown anaerobically with nitrate retained approximately 30 to 40% of the respiratory activity of aerobically grown cells. Aeration of anaerobically grown cells in the presence of amino acids increased the respiratory activity to normal aerobic levels. This aeration promoted rapid degradation of the existing nitrate reductase with or without the added amino acids.

Bacillus↗
PubMedDate not supplied

A model for planning optimal follow-up for outpatients on warfarin anticoagulation. Warfarin Optimal Outpatient Follow-up Study Group.

Patients taking warfarin for long-term anticoagulation require frequent clinic visits to monitor the prothrombin time ratio (PTR), a measure of blood clotting. A dynamic stochastic model using nonlinear optimization was developed to select follow-up visit intervals that minimize the overall costs of patient care. Assuming that fluctuations in a patient's PTR behave as a random diffusion process, future PTR fluctuations are unknown, except as revealed by past PTRs. To determine the incidence and costs of complications in relation to PTR, the authors reviewed the charts of 216 patients who had 719 patient-years of follow-up with 695 trivial, significant, life-threatening, or fatal complications. They modeled the relationship between costs of complications and deviation of the PTR from the therapeutic target as a fourth-order convex polynomial. The model is used to compute the interval to the next follow-up visit to minimize accumulated potential costs. Variables in the optimization are the cost of a monitoring visit and the expected costs of complications. The latter are derived from the current PTR, the variability of the patient's past PTR values, the number of past PTRs available, and the target PTR for the patient. No attempt is made to predict the level of the next PTR or suggest adjustments in the warfarin dose. Shorter follow-up is recommended for patients who have histories of large fluctuations in past PTRs and for patients with few prior PTR determinations. As visits accumulate, the patient's degree of variability can be estimated more accurately and visit intervals adjusted accordingly. The scheduling method balances costs to the health care system of monitoring each patient against the expected costs of complications. This approach has the potential to reduce the number of monitoring visits necessary for safe management of anticoagulated patients with stable PTRs and to improve control among unstable patients.

Aged↗
PubMed2006

Prediction of paroxysmal atrial fibrillation using nonlinear analysis of the R-R interval dynamics before the spontaneous onset of atrial fibrillation.

BACKGROUND: New methods based on nonlinear theory have been developed to give more insight into complex heart rate (HR) dynamics. This study was designed to test the hypothesis that altered HR dynamics, as analyzed with complexity and fractal measures, may precede the spontaneous onset of paroxysmal atrial fibrillation (PAF). Secondly, the difference in the temporal change of these measurements between the different types of atrial fibrillation (AF) was assessed. METHODS AND RESULTS: From 105 Holter tapes in which PAF was recorded, 44 PAF (>or=5 min) episodes in 33 patients (22 men, 58 +/- 12 years), preceded by sinus rhythm for more than 1 h, were selected and submitted to time-and frequency-domain HR variability analyses, along with detrended fluctuation analysis, approximate entropy (ApEn) and sample entropy (SampEn). The 60 min before the onset of AF were divided into 6 10-min periods and studied using repeated measures ANOVA. PAF episodes were divided into 3 subgroups: an increased HF component and decreased L/H ratio (vagal type, n=20); increased L/H ratio and decreased HF component (sympathetic type, n=14); and non-related type (n=10). None of the time- or frequency-domain parameters showed any significant change before AF in any type of AF. The alpha(1) showed a tendency to decrease before the onset of AF and the change in alpha(1) was divergent according to the AF type. The ApEn decreased before the onset of AF (1.005+/-0.046, 60-50 min before AF to 0.894+/-0.052, 10-0 min before AF; p=0.032). The SampEn also decreased progressively before the start of AF (1.165 +/- 0.085, 60-50 min before AF to 0.887 +/- 0.077, 10-0 min before AF, p=0.003). The decrease in both the ApEn and SampEn was irrespective of the AF type. CONCLUSIONS: A reduction in the ApEn and SampEn, which reflects the nonlinear complexity of HR variability, is a hallmark of altered HR dynamics preceding the spontaneous onset of AF.

Atrial Fibrillation↗
PubMed1999

Masking and parametric effects of high-frequency light-dark cycles.

Light seems to be the only zeitgeber signal that reaches the pacemaker via specific pathways. For all nonphotic entraining agents, there might be a common mechanism that operates by feedback processes via "arousal." When entrained, the circadian system keeps a distinct phase relationship to the zeitgeber. This is achieved by daily corrections of frequency and/or phase. The phase response curves (PRCs) obtained with brief light- or dark-pulses are satisfactory in explaining such non-parametric entrainment. However, many organisms are exposed daily to one major step-up and one step-down in light intensity; hence, attention should be payed to the usefulness of step-PRCs. Zeitgebers not only entrain circadian rhythms by controlling the phase and period of the pacemaker, but also mask the overt rhythm. Many experimental data demonstrate a dependence on phase of the masking effects. It is due to this dependence on phase that organisms that become arrhythmic in constant conditions can show freerunning rhythms under the influence of permanent high-frequency light-dark (LD) cycles (the "demasking" effect). Under natural conditions, most animals are exposed to continuously fluctuating light intensities. As demonstrated by experiments with high-frequency LD cycles, either self-selected or externally controlled, the circadian system integrates over the intensities experienced, and changes its frequency accordingly. It seems likely that non-parametric entrainment plays a predominant role, but contributions of parametric effects are probably underrated.

Animals↗
PubMed1999

Evolutionary significance of isopreneemission from mosses.

Isoprene emission has been documented and characterized from species in all major groups of vascular plants. We report in our survey that isoprene emission is much more common in mosses and ferns than later divergent land plants but is absent in liverworts and hornworts. The light and temperature responses of isoprene emission from Sphagnum capillifolium (Ehrh.) Hedw. are similar to those of other land plants. Isoprene increases thermotolerance of S. capillifolium to the same extent seen in higher plants as measured by chlorophyll fluorescence. Sphagnum species in a northern Wisconsin bog experienced large temperature fluctuations similar to those reported in tree canopies. Since isoprene has been shown to help plants cope with large, rapid temperature fluctuations, we hypothesize the thermal and correlated dessication stress experienced by early land plants provided the selective pressure for the evolution of light-dependent isoprene emission in the ancestors of modern mosses. As plants radiated into different habitats, this capacity was lost multiple times in favor of other thermal protective mechanisms.

Journal Article↗
PubMed2000

The quality of experience in adolescents' daily lives: developmental perspectives.

The authors analyzed the pattern of experience fluctuation in adolescents' daily activities. Italian high school students (N = 120; 16-20 years of age) were tested with the experience sampling method, a technique based on on-line sampling of daily life and experience. A total of 4,794 forms were gathered and analyzed by means of a model for the study of experience fluctuations. Among daily activities, studying at home, doing classwork, watching television, and having structured leisure were selected as the focus of analysis on the basis of their frequency and meaning in the adolescents' lives. Results showed that (a) daily activities have unique experiential profiles, (b) engagement may be used as an index of long-term commitment to a given activity, (c) studying at home and doing classwork share this basic component and can foster behavioral development, (d) structured leisure can play an edifying role at the short-term level for a socially integrated transition to adulthood, and (e) watching television is associated with lack of goals and engagement and is a source of apathy. The results (a) shed light on the role of daily life experience in shaping individual development and (b) provide suggestions for educational and psychosocial intervention in adolescence.

Activities of Daily Living↗
PubMed2002

[Evaluation on degradation of Karst forest community and human disturbance].

Fire, reclamation, herd, and cut led to degradation of Karst forest in Guizhou Province. Five indexes as height, dominance, percentage of asexual individual, biomass, and percentage of shade-tolerant for evaluating community degradation were selected. Degraded communities were divided into six degraded grades (A-F). Community structure and function fluctuated normally in climax (A) under nature force or light human disturbance. While effect of disturbance was preponderated over the range of community fluctuation, climax community degraded evidently, and degraded degree of communities increased gradually. Degraded grades of communities were consistent to succession stages of degraded community. In degraded process, the key factor was decrease of biomass and shade-tolerant species. Degraded communities due to fire, herd, and reclamation were distributed in grades C-F, and degraded community due to cut was in grades B-C. Amount of asexual individual was influenced by disturbance type, and the amount in degraded communities due to fire and cut was more than that due to reclamation and herd. Degraded degree of different disturbed community was in order of cut community < cleared community < herded community < fired community.

Humans↗
PubMed1992

Individual transforming events in long-term cell culture of NIH 3T3 cells as products of epigenetic induction.

The NIH 3T3 line of mouse fibroblasts undergoes "spontaneous" transformation in culture, exhibited in the development of foci of transformed cells overgrowing the confluent monolayer. Evidence is provided here to support the proposition that the spontaneous generation of individual transformed variants is a product of epigenetic induction by various types of growth inhibition. Novel transformed variants generally arise after prolonged confluence and cessation of net growth, with these new types of foci appearing during a second round of confluence, although not in the first round. Few or no transformed variants exist in the cultures prior to growth constraint. The susceptibility of NIH 3T3 cells to induction of transformation is itself shown to be subject to epigenetic influence, with capacity for transformation reflecting passage histories. Cell sublines maintained in long-term subconfluent passage that allows unimpeded growth become more refractory with time to spontaneous transformation, while sublines passaged in more growth-restricting conditions maintain their sensitivity. The differing capacities of the sublines are reflected in the degree of growth inhibition required to induce individual events of spontaneous transformation, and in the frequency at which such new variants arise. Thus growth inhibition not only induces individual transforming events, but even increases cell susceptibility to further induction of transformation. These phenomena are consistent with the progressive state selection model of heritable change, which postulates a self-regulating selection of better adapted states from among those made available to a biological system during heterogeneous fluctuations in its total pattern of chemical equilibria.

3T3 Cells↗
PubMedDate not supplied

Structure of valinomycin by molecular dynamics studies.

Valinomycin is an important ionophore which exhibits a high conformational flexibility. The study of various conformations adopted by this molecule together with the study of flexibility in a given conformation can throw light on the ion transport by the ionophore across the membrane. Molecular dynamics (MD) studies are ideal to characterize the flexibility in different parts of the molecule and can also give an idea of various conformations adopted by the molecule at a given temperature. Hence MD studies at 100K have been carried out on the minimized crystal structure of the molecule to scan the possible conformations in the neighbourhood of the well known 'bracelet' like structure of uncomplexed Valinomycin, Properties, like the flexibility, average values, r.m.s. fluctuations of the various intramolecular hydrogen bonds are discussed. Energy minimization has been carried out on selected MD simulated points to analyze the characteristics of the unique conformation adopted by this molecule at this temperature.

Hydrogen Bonding↗
PubMed1989

Studies of nerve-muscle interactions in Xenopus cell culture: analysis of early synaptic currents.

We have studied the spontaneous and nerve-evoked synaptic currents during the initial period of nerve-muscle contact in Xenopus cell cultures. The precise timing of the contact was achieved by physically manipulating embryonic muscle cells into contact with co-cultured spinal neurons. Previous studies have shown that physical contact of the muscle membrane induces pulsatile release of acetylcholine (ACh) from the growth cone of these neurons, resulting in spontaneous synaptic currents (SSCs) in the muscle cell within seconds following the contact. In the present work, we first showed that these SSCs at the manipulated nerve-muscle contacts are similar to those observed at naturally occurring synapses. We then examined the possible cellular mechanisms responsible for the marked variation in SSC amplitude and showed that it most likely results from differences in either the amount of ACh contained in each release event or the extent of close membrane apposition near the release sites. During the first 20 min following the nerve-muscle contact, there was an increase in the frequency and mean amplitude of the SSCs. During a similar period, the evoked synaptic currents (ESCs), which were induced by suprathreshold electrical stimulation of the neuronal soma, also showed an increase in the mean amplitude and a reduction in the delay of onset following the stimulus. These postcontact changes in the efficacy of synaptic transmission may be related to an increase in the total area of close membrane apposition between the nerve and muscle cells. This was suggested by the finding that neurite-muscle adhesion increases over a similar postcontact period. The transition from low- to high-efficacy transmission during the early phase of contact may reflect the process of selective adhesion between the cells, and thus signify the formation of specific synapse. Analysis of the fluctuation in the ESC amplitude at the early nerve-muscle contact suggests that evoked release of ACh occurs as multiples of a quantal unit. However, this unit is apparently related to only a small subpopulation of SSCs of relatively high amplitudes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMedDate not supplied

Impact of scorpion Heterometrus fulvipes venom on cholinesterase rhythmicity in the tropical mouse Mus booduga.

Rhythmicities of acetylcholine (ACh) and acetylcholinesterase (AChE) were studied in the mouse, Mus booduga (Gray), following intramuscular injection of scorpion, Heterometrus fulvipes (C. Koch) venom. Envenomation inhibited the activity levels of ACh and AChE in all the tissues selected for experimentation. Control animals exhibited diel rhythmicity in ACh and AChE while envenomated animals showed fluctuation in the Phase (delta phi), amplitude (A), Acrophase (phi) and the extreme activity hours (X and X1).

Acetylcholine↗
PubMed1976

Mitochondrial genetics. XI. Mutations at the mitochondrial locus omega affecting the recombination of mitochondrial genes in Saccharomyces cerevisiae.

1. A series of CS revertants has been selected from various strains (both omega+ and omega-) carrying a CR mitochondrial mutation at the RIB1 locus. The properties of mitochondrial recombination exhibited by these CS revertants in various crosses, have been examined systematically. The omega allele of the CS revertants has been defined in crosses with omega+ and omega- tester strains using two criteria: the polarity of recombination and a new criterium called relative output coefficient. We found that mutations of omega appear frequently associated with the mutations at the RIB1 locus selected from omega- strains but not with those selected from omega+ strains. A new allelic form of omega (omega n) which had not been found amongst wild type yeast strains is characterised. Similarly omega n mutation was found frequently associated with CR mutants at the RIB1 locus selected from omega- CS strains but not with those selected from omega+ CS strains. The omega n mutants, and the omega+ and omega- strains, explain the groups of polarity previously observed by Coen et al. (1970). 2. Main features of mitochondrial crosses with omega n strains (omega+ x omega n, omega- x omega n and omega n x omega n) are analysed. Recombination is possible between the different mitochondrial genetic markers. No high polarity of recombination is observed and the frequency of recombinants are similar to those found in homosexual crosses (omega+ x omega+ and omega- x omega-). A striking property, observed for the first time, exists in crosses between zota+ omega n CS strains and some zota- CREO mutants: the zota- CREO are unable to integrate by recombination their CR allele into the zota+ mit-DNA of omega n CS strains while being capable of integrating it into omega+ CS or omega- CS genomes. 3. It is proposed that the omega locus is the site of initiation of non reciprocal recombination events, the omega+/omega- pairing specifically initiates the non-reciprocal act while omega+/omega n or omega-/omega n pairings do not. 4. The molecular nature of the omega n mutation and its bearing on the structure of the omega locus are discussed. It is suggested that omega n mutations correspond to macrolesions (probably deletions) of a segment of the mit-DNA covering the omega and RIB1 loci. If omega n is a partial deletions of the omega- sequence the omega+ could be an additionnal deletion of the omega n sequence. 5. The occurrence of spontaneous CR and ER mitochondrial mutations has been analysed by the Luria and Delbrück fluctuation test in omega- and omega n isonuclear strains. Results of these tests indicate that an intracellular selection of resistant copies preexisting the action of the anttibiotic occurs.

Alleles↗
PubMed1995

Apomorphine for motor fluctuations and freezing in Parkinson's disease.

OBJECTIVE: To review the pharmacokinetics and use of apomorphine in patients with Parkinson's disease; to report a case of beneficial outcome with apomorphine in a patient with Parkinson's disease with severe levodopa "on-off" fluctuations and freezing; and to outline the types of patients or situations where apomorphine may be useful. DATA SOURCES: Case reports, review articles, and relevant clinical studies identified by a MEDLINE search of the English-language literature published between 1975 and October 1994. STUDY SELECTION: Because all but 2 reports were of open-label design with small sample sizes, all studies identified were evaluated. DATA EXTRACTION: The following data were extracted from each study: apomorphine treatment duration, dosing, onset, duration, and adverse effects. The following efficacy variables were extracted: percent decrease in off periods, improvement in parkinsonian symptoms, and percent decrease in levodopa dosage. DATA SYNTHESIS: Efficacy of apomorphine following subcutaneous, rectal, sublingual, and intranasal dosage forms are evaluated. We also describe the use of apomorphine in a patient with Parkinson's disease who experienced on-off fluctuations and freezing. Based on these reports, recommendations for patient selection, product selection, and apomorphine dosing guidelines are presented. CONCLUSIONS: Apomorphine decreases off time, freezing, and levodopa requirements in patients with Parkinson's disease. It can be administered via a number of different nonoral routes; however, subcutaneous apomorphine is the most extensively studied. Rectal, sublingual, and intranasal routes also have been shown to provide benefit in motor fluctuations, but differ from the subcutaneous route in onset of action, duration of effect, and adverse effect profile.

Administration, Intranasal↗
PubMed1997

Antidepressant withdrawal reactions.

Antidepressants can cause a variety of withdrawal reactions, starting within a few days to a few weeks of ceasing the drug and persisting for days to weeks. Both tricyclic antidepressants and selective serotonin reuptake inhibitors cause similar syndromes, most commonly characterized by gastrointestinal or somatic distress, sleep disturbances, mood fluctuations and movement disorders. Most symptoms related to tricyclic antidepressant withdrawal are believed to be caused by rebound excess of cholinergic activity after prolonged anticholinergic effect on cholinergic receptors. (This situation is analogous to the adrenergic rebound that occurs after beta-blocker withdrawal.) Treatment involves restarting the antidepressant and tapering it more slowly. Alternatively, tricyclic antidepressant withdrawal symptoms often respond to anticholinergics, such as atropine or benztropine mesylate. Three case reports of antidepressant withdrawal are presented, including one featuring akathisia (motor restlessness) related to withdrawal of venlafaxine.

Adult↗
PubMed1995

Demonstrable cardiac reinnervation after human heart transplantation by carotid baroreflex modulation of RR interval.

BACKGROUND: After heart transplantation, respiration-synchronous fluctuations (0.18 to 0.35 Hz, high frequency [HF]) in RR interval may result from atrial stretch caused by changes in venous return, but slower fluctuations (0.03 to 0.15 Hz, low frequency [LF]) not due to respiration suggest reinnervation. In normal subjects, sinusoidal neck suction selectively stimulates carotid baroreceptors and causes reflex oscillations of RR interval. METHODS AND RESULTS: To evaluate the presence of reinnervation, we measured the power of RR-LF and RR-HF in 26 heart transplant recipients and 16 control subjects before and during sinusoidal neck suction at 0.1 Hz and 0.20 Hz (similar to but distinct from that of controlled respiration, 0.25 Hz) and before and during administration of atropine or beta-blocker (esmolol hydrochloride) by spectral analysis. All transplant recipients showed small respiratory HF fluctuations. Nonrespiratory LF fluctuations were present in 13 of 26 transplant recipients and increased with months since transplantation (r = .53, P < .01). HF neck suction induced a 0.20-Hz component in all 16 control subjects and none of the 26 transplant subjects. LF neck suction increased RR-LF (from 0.73 +/- 0.20 to 1.30 +/- 0.26 ln ms2, P < .001), similar to but less than in control subjects (from 6.12 +/- 0.21 to 8.27 +/- 0.21 ln ms2, P < .001). Atropine reduced all fluctuations in control subjects and blocked the HF increase caused by 0.20-Hz neck suction but not the LF increase during 0.10-Hz stimulation. Neck suction-induced changes in LF fluctuations persisted after administration of atropine in transplant recipients but were attenuated by esmolol hydrochloride, suggesting sympathetic rather than vagal reinnervation. CONCLUSIONS: The presence of baroreceptor-induced RR oscillations is evidence of functional, although incomplete, autonomic reinnervation.

Adrenergic beta-Antagonists↗