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Sustained Oscillations (sustained + oscillation)

Distribution by Scientific Domains

Life Sciences	60%

Selected Abstracts

Nonlinear Dynamics of Regulation of Bacterial trpOperon: Model Analysis of Integrated Effects of Repression, Feedback Inhibition, and Attenuation

BIOTECHNOLOGY PROGRESS, Issue 4 2002
Zhi-Long Xiu
The trpoperon encodes the five genes for the enzymes required to convert chorismate to tryptophan, and its switching on and off is controlled by both feedback repression and attenuation in response to different levels of tryptophan in the cell. Repression of the operon occurs when tryptophan concentration is high, and attenuation fine-tunes the transcription level at a lower cellular concentration of tryptophan. An extended mathematical model is established in this study to describe the switching on and off of the trpoperon by considering the integrated effects of repression and attenuation. The influences of cell growth rate on the biosynthesis of tryptophan, stability and dynamic behavior of the trpoperon are investigated. Sustained oscillations of tryptophan levels are predicted from the regulated turning on and off of the trpoperon. It is interesting to note that during such oscillations the regulation of transcription displays a kind of "on" and "off" state in terms of gene expression, indicating the existence of a genetic circuit or switch in the regulation of the trpoperon. Time lags between transcription and translation are also predicted and may explain the occurrence of such oscillation phenomenon. [source]

Persistent rhythmic oscillations induced by nicotine on neonatal rat hypoglossal motoneurons in vitro

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2006
Nerijus Lamanauskas
Abstract Patch-clamp recording from hypoglossal motoneurons in neonatal Wistar rat brainstem slices was used to investigate the electrophysiological effects of bath-applied nicotine (10 µm). While nicotine consistently evoked membrane depolarization (or inward current under voltage clamp), it also induced electrical oscillations (3,13 Hz; lasting for , 8.5 min) on 40% of motoneurons. Oscillations required activation of nicotinic receptors sensitive to dihydro-,-erythroidine (0.5 µm) or methyllycaconitine (5 nm), and were accompanied by enhanced frequency of spontaneous glutamatergic events. The slight voltage dependence of oscillations and their block by the gap junction blocker, carbenoxolone, suggest they originate from electrically coupled neurons. Network nicotinic receptors desensitized more slowly than motoneuron ones, demonstrating that network receptors remained active longer to support heightened release of the endogenous glutamate necessary for enhancing the network excitability. The ionotropic glutamate receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and the group I metabotropic receptor antagonist, (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA), suppressed oscillations, while the NMDA receptor antagonist, d -amino-phosphonovaleriate (APV), produced minimal depression. Nicotine-evoked oscillations constrained spike firing at low rates, although motoneurons could still generate high-frequency trains of action potentials with unchanged gain for input depolarization. This is the first demonstration that persistent activation of nicotinic receptors could cause release of endogenous glutamate to evoke sustained oscillations in the theta frequency range. As this phenomenon likely represented a powerful process to coordinate motor output to tongue muscles, our results outline neuronal nicotinic acetylcholine receptors (nAChRs) as a novel target for pharmacological enhancement of motoneuron output in motor dysfunction. [source]

Optimal observability of sustained stochastic competitive inhibition oscillations at organellar volumes

FEBS JOURNAL, Issue 1 2006
Kevin L. Davis
When molecules are present in small numbers, such as is frequently the case in cells, the usual assumptions leading to differential rate equations are invalid and it is necessary to use a stochastic description which takes into account the randomness of reactive encounters in solution. We display a very simple biochemical model, ordinary competitive inhibition with substrate inflow, which is only capable of damped oscillations in the deterministic mass-action rate equation limit, but which displays sustained oscillations in stochastic simulations. We define an observability parameter, which is essentially just the ratio of the amplitude of the oscillations to the mean value of the concentration. A maximum in the observability is seen as the volume is varied, a phenomenon we name system-size observability resonance by analogy with other types of stochastic resonance. For the parameters of this study, the maximum in the observability occurs at volumes similar to those of bacterial cells or of eukaryotic organelles. [source]

Population, Unemployment and Economic Growth Cycles: A Further Explanatory Perspective

METROECONOMICA, Issue 2-3 2003
Luciano Fanati
In this paper we investigate the dynamic interaction between economic growth, unemployment, income distribution and population growth. The reference framework combines rational behaviour of agents with endogenous fertility and unemployment, while profits are the determinant of the accumulation of firms. In particular the supply of labour is determined by the micro-founded fertility choices of individuals. We first demonstrate, consistently with the empirical evidence, the existence of a positive income growth trend with sustained oscillations, therefore providing an alternative explanation of the relation between growth and cycle. Moreover interesting results are given on the relation between unemployment and growth. So far the literature has traditionally shown a negative relation between unemployment and growth (with the exception of the positive relation arising in a Schumpeter ,creative' disruption context). In contrast, we find a twofold effect of unemployment (via its effects on population) on economic growth: this can be both positive or negative depending on the relative level of the cost of childrearing of employed and unemployed persons, and on the level of unemployment benefits. This allows us to argue that an increase in unemployment benefit,as has occurred in recent years in many countries such as France and Spain,could lead to wide demo-economic fluctuations and to a positive effect of unemployment on economic growth. [source]

Cell Population Modeling and Parameter Estimation for Continuous Cultures of Saccharomyces cerevisiae

BIOTECHNOLOGY PROGRESS, Issue 5 2002
Prashant Mhaskar
Saccharomyces cerevisiae is known to exhibit sustained oscillations in chemostats operated under aerobic and glucose-limited growth conditions. The oscillations are reflected both in intracellular and extracellular measurements. Our recent work has shown that unstructured cell population balance models are capable of generating sustained oscillations over an experimentally meaningful range of dilution rates. A disadvantage of such unstructured models is that they lack variables that can be compared directly to easily measured extracellular variables. Thus far, most of our work in model development has been aimed at achieving qualitative agreement with experimental data. In this paper, a segregated model with a simple structured description of the extracellular environment is developed and evaluated. The model accounts for the three most important metabolic pathways involved in cell growth with glucose substrate. As compared to completely unstructured models, the major advantage of the proposed model is that predictions of extracellular variables can be compared directly to experimental data. Consequently, the model structure is well suited for the application of estimation techniques aimed at determining unknown model parameters from available extracellular measurements. A steady-state parameter selection method developed in our group is extended to oscillatory dynamics to determine the parameters that can be estimated most reliably. The chosen parameters are estimated by solving a nonlinear programming problem formulated to minimize the difference between predictions and measurements of the extracellular variables. The efficiency of the parameter estimation scheme is demonstrated using simulated and experimental data. [source]