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Results for “Optical mapping”

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At least 127 records · Page 7Linked to original sources
PubMed2001

Mechanism of ventricular defibrillation for near-defibrillation threshold shocks: a whole-heart optical mapping study in swine.

BACKGROUND: To study the mechanism by which shocks succeed (SDF) or fail (FDF) to defibrillate, global cardiac activation and recovery and their relationship to defibrillation outcome were investigated for shock strengths with approximately equal SDF and FDF outcomes (DFT(50)). METHODS AND RESULTS: In 6 isolated pig hearts, dual-camera video imaging was used to record optically from approximately 8000 sites on the anterior and posterior ventricular surfaces before and after 10 DFT(50) biphasic shocks. The interval between the shock and the last ventricular fibrillation activation preceding the shock (coupling interval, CI) and the time from shock onset to 90% repolarization of the immediate postshock action potential (RT(90)) were determined at all sites. Of 60 shocks, 31 were SDF. The CI (59+/-7 versus 52+/-6 ms) and RT(90) (108+/-19 versus 88+/-8 ms) were significantly longer for SDF than FDF episodes. Spatial dispersions of CI (36+/-5 versus 34+/-3 ms) and RT(90) (40+/-16 versus 40+/-8 ms) were not significantly different for SDF versus FDF episodes. The first global activation cycle appeared focally on the left ventricular apical epicardium 78+/-32 ms after the shock. CONCLUSIONS: For near-threshold shocks, defibrillation outcome correlates with the electrical state of the heart at the time of the shock and on RT. Global dispersion of RT was similar in both SDF and FDF episodes, suggesting that it is not crucial in determining defibrillation outcome after DFT(50) shocks.

Animals↗
PubMed1996

New polyacrylamide gel-based methods of sample preparation for optical microscopy: immobilization of DNA molecules for optical mapping.

New methods have been developed for rapid immobilization of biological macromolecules and other microscopic objects from aqueous solution at gel/gel, gel/solid and gel/solution interfaces using thin polyacrylamide gels covalently bound to glass surfaces. When quickly spread over a dry gel, an aqueous sample loses most of its water and low-molecular-weight solutes due to migration of these components into the gel. All optically observable objects thus become concentrated at the gel surface and may be easily located by light microscopy. Based on this, a procedure for binding DNA at a positively charged gel/solution interface was developed. A mild immobilization of the DNA molecules was obtained, allowing 'all in focus' observations of DNA digestion by restriction endonucleases with an apparent rate close to that in solution.

Acrylamides↗
PubMed2006

Optical mapping of spatiotemporal emergence of functional synaptic connections in the embryonic chick olfactory pathway.

In order to understand the functional maturation of the CNS, it is essential to first describe the functional maturation of sensory processing. We have approached this topic by following the ontogenetic patterning of neural circuit formation related to cranial and spinal sensory input using voltage-sensitive dye imaging. In previous studies, we have described the functional maturation of synapses in brainstem/midbrain neural circuits. Here, we elucidate the functional maturation of forebrain circuits by investigating neural networks related to the olfactory nerve (N. I) of chicken embryo. In the isolated N. I-olfactory bulb-forebrain preparation, application of electrical stimulation to N. I elicited excitatory postsynaptic potential (EPSP)-related slow optical signals in the olfactory bulb. The slow signal was mainly mediated by glutamate, and was easily fatigued with repetitive stimuli because of the immaturity of synapses in the embryonic CNS. Ontogenetically, the slow signal was detected from the 6-day embryonic stage, suggesting that functional synaptic connections between N. I and olfactory bulb emerge around this stage. In addition, from the 8-day embryonic stage, another response area was discriminated within the forebrain, which corresponded to the higher-ordered nucleus of the olfactory pathway. In comparison with our previous studies concerning the functional development of other cranial nerve-related sensory nuclei in the embryonic brainstem and midbrain, these results suggest that the olfactory pathway is functionally generated in the early stages of development when neural networks related to other visceral and somatic sensory inputs are also in the process of developing.

Aging↗
PubMed1995

Optical mapping of translucence changes in rat hippocampal slices during hypoxia.

We have evaluated the effects of hypoxia on changes in light transmittance (delta T/T) in rat hippocampal interface slices at 36 degrees C, using a digital imaging system. Slice translucence increased only slightly (delta T/T = 4.65% in CA1; control 2.27%) during brief hypoxia in which hypoxic spreading depression-like depolarization was not induced. If hypoxia duration was sufficient to trigger spreading depression in CA1, slice translucence increased rapidly in CA1 (delta T/T = 27.5%) and smaller, delayed changes were noted in other regions. These spreading depression-induced changes reversed slowly to control levels upon reoxygenation. Measurement of intrinsic optical signals revealed both spatial and temporal patterns of cell volume changes associated with hypoxia and spreading depression in hippocampus.

Animals↗
PubMed2001

Slow conduction in cardiac tissue: insights from optical mapping at the cellular level.

Under physiological conditions, slow conduction is essential for the function of the atrioventricular (AV) node, whereas, under pathophysiological conditions, slow conduction contributes importantly to the generation of life-threatening reentrant arrhythmias. This article addresses characteristics of slow conduction at the cellular network level during (a) a reduction of excitability, (b) a reduction of gap junctional coupling, and (c) in the setting of branching tissue structures. Microscopic impulse propagation in these settings was studied by using multiple site optical recording of transmembrane voltage in conjunction with patterned growth cultures of neonatal rat ventricular myocytes. In linear cell strands, a reduction of excitability slowed conduction by approximately 70% before block occurred. In contrast, critical reduction of gap junctional coupling induced a much higher degree of slowing (>99%) before block of conduction. Interestingly, a similar degree of conduction slowing was also observed in branching tissue structures under conditions of reduced excitability (98%). The finding of extremely slow but nevertheless safe conduction in these structures might be explained by a "pull and push" effect of the branches: by drawing electronic current from the activation wavefront, they first act as current loads which slow conduction at the branch points ("pull" effect). Then, on activation, they turn into current sources which feed current back into the system, thus supporting downstream activation and enhancing the safety of propagation ("push" effect). This "pull and push" mechanism may play a significant role in slow conduction in the AV node and in structurally discontinuous myocardium, such as the border regions of infarct scars.

Action Potentials↗
PubMed2004

Optical mapping of neural responses and their gamma-aminobutyric acid-ergic inhibitory effects in the auditory brainstem of early postnatal mice.

gamma-Aminobutyric acid (GABA)ergic neurons play important tropic and modulatory roles in the auditory pathway, especially in the early stage between postnatal Days 0 and 5. The effects of GABA and GABAa receptor antagonist were observed in this experimental study. Numerous histological and electrophysiological studies have been performed on the contribution of GABA to the auditory pathway; however, the spatio-temporal patterns of excitatory propagation and the relationships between GABA receptor and excitatory propagation have yet to be reported. Using an optical recording technique and a voltage-sensitive dye, the spatio-temporal patterns of excitatory propagation were observed in the auditory brainstem slices of early postnatal mice. A bath containing 50 microM GABA was applied, which largely inhibited the excitatory activities along the vestibulocochlear pathway. Bicuculline methiodide (BMI), a competitive antagonist against GABAa receptor, partially reversed the effects of GABA on the optical signals. Bath application of BMI alone helped to facilitate the depolarization course and its effect was apparent as an enlargement of the depolarized region from the cochlear nucleus and vestibular nucleus to some adjacent brainstem nuclei, as well as enhancing the amplitude of changes in the optical signals. The experimental results seem to suggest that GABAa receptors are widely distributed in an early postnatal auditory brainstem. GABA exhibited a greater modulating effect in the adjacent brainstem nuclei, which are involved in complex information processes, than that observed in the modulating primary auditory pathway. In the present experiment, significant GABAergic contributions to the optical recordings in the auditory brainstem were observed.

Animals↗
PubMed1983

Fiber optic mapping of the Xenopus visual system: shift in the retinotectal projection during development.

Two new techniques for assaying the retina to tectum connections in the lower vertebrate visual system are presented. These techniques allow defined regions of the retina to be stimulated, thus circumventing some of the difficulties of the more conventional retinotectal mapping techniques. Applying these techniques to the Xenopus visual system demonstrates that the retina-to-tectum projection shifts during development. The central part of the retinotectal projection moves medially and caudally about 150 microns (10% of the size of the tectum) in two weeks. The presence of such plasticity in a normal developing animal indicates that the plasticity previously observed in experimentally altered animals probably reflects a normal developmental process.

Animals↗
PubMed2003

Optical mapping technique applied to biventricular pacing: potential mechanisms of ventricular arrhythmias occurrence.

Although it has been suggested that multisite ventricular pacing alleviates heart failure by restoring ventricular electrical synchronization, the respective roles of voltage output, interventricular delay, and pacing sites in the development of ventricular arrhythmias occurrence have not been studied during biventricular pacing or LV pacing. Voltage-sensitive dye was used in eight ischemic Langerdorff-perfused guinea pig hearts to measure ventricular activation times and examine conduction patterns during multisite pacing from three RV and four LV sites. The hearts were stained with di-4-ANEPPS and mapped with a 16 x 16 photodiode array at a resolution of 625 microns per diode. Isochronal maps of RV and LV activation were plotted. Ischemia was produced by gradually halving the perfusion output over 5 minutes. Pacing the RV apex and the base of the LV anterior wall was associated with the most homogeneous and rapid activation pattern (28 +/- 9 vs 41 +/- 12 ms with the other configurations, P < 0.01), and no inducible arrhythmia. In six hearts, ventricular tachycardia could be induced when pacing from the right and left free walls with 20 ms of interventricular delay, at six times the pacing threshold output. In four hearts, simultaneous RV and LV pacing at high voltage output induced ventricular fibrillation with complex three-dimensional propagation patterns, independently of the pacing sites. During biventricular pacing with ischemia, pacing at high voltage output with a long interventricular delay is likely to induce ventricular arrhythmias, particularly when left and right pacing results in a conduction pattern orthogonal to the ventricular myocardial fibers orientation.

Animals↗
PubMed2005

Optical mapping of the atrioventricular junction.

In the normal heart, the atrioventricular node (AVN) is part of the sole pathway between the atria and ventricles, and is responsible for the appropriate atrial-ventricular delay. Under normal physiological conditions, the AVN controls appropriate frequency-dependent delay of contractions. The AVN also plays an important role in pathology: it protects ventricles during atrial tachyarrhythmia, and during sinoatrial node failure the atrioventricular (AV) junction assumes the role of pacemaker. Finally, the AV junction provides an anatomic substrate for AV nodal reentrant tachycardia, which is the most prevalent supraventricular tachycardia in humans. Using fluorescent imaging with voltage-sensitive dye and immunohistochemistry, we have investigated the structure-function relationship of the atrioventricular (AV) junction during normal conduction, reentry, and junctional rhythm. We identified the site of origin of junctional rhythm at the posterior extension of the AV node (AVN) in 78% (n=23) of the studied hearts and we found that this pacemaker is sensitive to autonomic control. For instance, when the autonomic nervous system was activated using subthreshold stimulation, a transient accelerated junctional rhythm was observed when subthreshold stimulation was terminated. A very similar phenomenon is observed clinically during slow pathway ablations treating AV nodal reentrant tachycardia (AVNRT). The autonomic control of the AV junction was investigated using immunohistochemistry, showing that the AV junction of the rabbit is very densely innervated with both cholinergic and adrenergic neurons. The posterior AV nodal extension was similar to the compact AVN as determined by morphologic and molecular investigations. In particular, both the posterior extension and the compact node express the pacemaking channel HCN4 (responsible for the IF current) and neurofilament 160. In the rabbit heart, AV junction conduction, reentrant arrhythmia, and spontaneous rhythm are governed by heterogeneity of expression of several isoforms of gap junctions and ion channels, and these properties are regulated by the autonomic nervous system. Uniform neurofilament expression suggests that AV nodal posterior extensions are an integral part of the cardiac pacemaking and conduction system.

Action Potentials↗
PubMed1997

Optical mapping of drug-induced polymorphic arrhythmias and torsade de pointes in the isolated rabbit heart.

OBJECTIVES: This study sought to 1) test the hypothesis that in the setting of bradycardia and drug-induced action potential prolongation, multiple foci of early afterdepolarizations (EADs) result in beat to beat changes in the origin and direction of the excitation wave front and are responsible for polymorphic arrhythmias; and 2) determine whether EADs may initiate nonstationary reentry, giving rise to the typical torsade de pointes (TDP) pattern. BACKGROUND: In the past, it has been difficult to associate EADs or reentry with the undulating electrocardiographic (ECG) patterns of TDP. METHODS: A voltage-sensitive dye was used for high resolution video imaging of electrical waves on the epicardial and endocardial surface of the Langendorff-perfused rabbit heart. ECG and monophasic action potentials from the right septal region were also recorded. Bradycardia was induced by ablation of the atrioventricular node. RESULTS: Perfusion of low potassium chloride Tyrode solution plus quinidine led to prolongation of the action potential and the QT interval. Eventually, EADs and triggered activity ensued, giving rise to intermittent episodes of polymorphic arrhythmia. In one experiment, triggered activity was followed by a long episode of vortex-like reentry with an ECG pattern characteristic of TDP. However, in most experiments, focal activity of varying origins and propagation patterns was observed. Triggered responses also showed varying degrees of local block. Similar results were obtained with E-4031. Burst pacing both at control conditions and in the presence of quinidine consistently led to vortex-like reentry whose ECG pattern resembled TDP. However, the cycle length of the arrhythmia with quinidine was longer than that for control ([mean +/- SEM] 194 +/- 12 vs. 132 +/- 8 ms, p < 0.03). CONCLUSIONS: Drug-induced polymorphic ventricular arrhythmias may result from beat to beat changes in wave propagation patterns initiated by EADs or EAD-induced nonstationary reentrant activity. In contrast, burst pacing-induced polymorphic tachycardia in the presence or absence of drugs is the result of nonstationary reentrant activity.

Action Potentials↗
PubMed2002

Mechanisms underlying atrioventricular nodal conduction and the reentrant circuit of atrioventricular nodal reentrant tachycardia using optical mapping.

The findings of multiple nondiscrete AV nodal pathways and asymmetric transitional zone provide a biophysical basis for understanding normal and abnormal AV node electrophysiology. Unidirectional block occurring at the transitional zone transforms the nondiscrete pathways model into a classic dual pathways physiology for AVNRT.

Action Potentials↗
PubMed2003

Near-field optical mapping of exciton wave functions in a GaAs quantum dot.

Near-field photoluminescence imaging spectroscopy of naturally occurring GaAs quantum dots (QDs) is presented. We successfully mapped out center-of -mass wave functions of an exciton confined in a GaAs QD in real space due to the enhancement of spatial resolution up to 30 nm. As a consequence, we discovered that the spatial profile of the exciton emission, which reflects the shape of a monolayer-high island, differs from that of biexciton emission, due to different distributions of the polarization field for the exciton and biexciton recombinations. This novel technique can be extensively applied to wave function engineering in the design and the fabrication of quantum devices.

Journal Article↗
PubMed2006

Imaging of cardiac movement using ratiometric and nonratiometric optical mapping: effects of ischemia and 2, 3-butaneodione monoxime.

Transmembrane voltage-sensitive fluorescent dyes are used to study electrical activity in hearts. Green and red fluorescence emissions from di-4-ANEPPS excited with 488 nm light indicate both transmembrane voltage changes and heart movement. We have previously shown that the ratio, green fluorescence divided by red fluorescence, indicates the transmembrane voltage without effects of movement. Here we examine the feasibility of measuring the movement, which is useful for the study of cardiac function, by subtracting this ratiometric signal from the red or green fluorescence signal. The results of this subtraction show tissue movement and its relative changes during cardiac ischemia and perfusion with an electromechanical uncoupling agent. By incorporating the spatial variations in fluorescence intensity from the heart, tissue movement can be qualitatively mapped to examine relative changes, however, with limited ability to quantify absolute displacement. Since these maps are obtained simultaneously with corresponding transmembrane potentials, the method allows study of spatiotemporal cardiac movement patterns and their relationship to the action potential.

Algorithms↗