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Spontaneous Oscillations (spontaneous + oscillation)

Distribution by Scientific Domains
Life Sciences75%

Selected Abstracts

Spontaneous oscillation and mechanically induced calcium waves in chondrocytes

CELL BIOCHEMISTRY AND FUNCTION, Issue 2 2006
Taisuke Kono
Abstract The characteristics of spontaneous calcium (Ca2+) oscillation and mechanically induced Ca2+ waves in articular chondrocytes were studied. In some, but not all, chondrocytes in sliced cartilage and primary cultures, we observed spontaneous oscillation of intracellular Ca2+ that never spread to adjacent cells. In contrast, a mechanical stimulus to a single cell by touching with a glass rod induced an increase of intracellular Ca2+ that spread to neighboring cells in a wave-like manner, even though there was no physical contact between the cells. This indicated the release of some paracrine factor from the mechanically stimulated cells. Application of ultrasonic vibration also induced an oscillation of intracellular Ca2+. The application of a uridine 5,-triphosphate (UTP), UTP, induced a transient increase in intracellular Ca2+ and the release of adenosine 5,-triphosphate (ATP) in cultured chondrocytes. A P2 receptor antagonist (suramin) and blockers of Cl, channels, niflumic acid and 4,4,-diisothiocyanostilbene-2,2,-disulfonic acid (DIDS), reduced the UTP-induced ATP release. The results indicated that Cl, channels were involved in the extracellular release of ATP following mechanical or P2Y receptor stimulation. Thus, ATP stimulation of P2Y receptors elicits an increase in intracellular Ca2+, triggering further release of ATP from adjacent cells, thereby expanding the Ca2+ wave in chondrocytes. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Dynamic changes in the direction of the theta rhythmic drive between supramammillary nucleus and the septohippocampal system

HIPPOCAMPUS, Issue 6 2006
Bernat Kocsis
Abstract Neurons in the supramammillary nucleus (SUM) of urethane-anesthetized rats fire rhythmically in synchrony with hippocampal theta rhythm. As these neurons project to the septum and hippocampus, it is generally assumed that their role is to mediate ascending activation, leading to the hippocampal theta rhythm. However, the connections between SUM and the septohippocampal system are reciprocal; there is strong evidence that theta remains in the hippocampus after SUM lesions and in the SUM after lesioning the medial septum. The present study examines the dynamics of coupling between rhythmic discharge in the SUM and hippocampal field potential oscillations, using the directionality information carried by the two signals. Using directed transfer function analysis, we demonstrate that during sensory-elicited theta rhythm and also during short episodes of theta acceleration of spontaneous oscillations, the spike train of a subpopulation of SUM neurons contains information predicting future variations in rhythmic field potentials in the hippocampus. In contrast, during slow spontaneous theta rhythm, it is the SUM spike signal that can be predicted from the preceding segment of the electrical signal recorded in the hippocampus. These findings indicate that, in the anesthetized rat, SUM neurons effectively drive theta oscillations in the hippocampus during epochs of sensory-elicited theta rhythm and short episodes of theta acceleration, whereas spontaneous slow theta in the SUM is controlled by descending input from the septohippocampal system. Thus, in certain states, rhythmically firing SUM neurons function to accelerate the septal theta oscillator, and in others, they are entrained by a superordinate oscillatory network. © 2006 Wiley-Liss Inc. [source]

Baroreflex Sensitivity: Measurement and Clinical Implications

ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 2 2008
Maria Teresa La Rovere M.D.
Alterations of the baroreceptor-heart rate reflex (baroreflex sensitivity, BRS) contribute to the reciprocal reduction of parasympathetic activity and increase of sympathetic activity that accompany the development and progression of cardiovascular diseases. Therefore, the measurement of the baroreflex is a source of valuable information in the clinical management of cardiac disease patients, particularly in risk stratification. This article briefly recalls the pathophysiological background of baroreflex control, and reviews the most relevant methods that have been developed so far for the measurement of BRS. They include three "classic" methods: (i) the use of vasoactive drugs, particularly the ,-adrenoreceptor agonist phenylephrine, (ii) the Valsalva maneuver, which produces a natural challenge for the baroreceptors by voluntarily increasing intrathoracic and abdominal pressure through straining, and (iii) the neck chamber technique, which allows a selective activation/deactivation of carotid baroreceptors by application of a negative/positive pressure to the neck region. Two more recent methods based on the analysis of spontaneous oscillations of systolic arterial pressure and RR interval are also reviewed: (i) the sequence method, which analyzes the relationship between increasing/decreasing ramps of blood pressure and related increasing/decreasing changes in RR interval through linear regression, and (ii) spectral methods, which assess the relationship (in terms of gain) between specific oscillatory components of the two signals. The limitations of the coherence criterion for the computation of spectral BRS are discussed, and recent proposals for overcoming them are presented. Most relevant clinical applications of BRS measurement are finally reviewed with particular reference to patients with myocardial infarction and heart failure. [source]