Pulse-Driven Magnetoimpedance Sensor Detection of Cardiac Magnetic Activity

This study sought to establish a convenient method for detecting biomagnetic activity in the heart. Electrical activity of the heart simultaneously induces a magnetic field. Detection of this magnetic activity will enable non-contact, noninvasive evaluation to be made. We improved the sensitivity of a pulse-driven magnetoimpedance (PMI) sensor, which is used as an electric compass in mobile phones and as a motion sensor of the operation handle in computer games, toward a pico-Tesla (pT) level, and measured magnetic fields on the surface of the thoracic wall in humans. The changes in magnetic field detected by this sensor synchronized with the electric activity of the electrocardiogram (ECG). The shape of the magnetic wave was largely altered by shifting the sensor position within 20 mm in parallel and/or perpendicular to the thoracic wall. The magnetic activity was maximal in the 4th intercostals near the center of the sterna. Furthermore, averaging the magnetic activity at 15 mm in the distance between the thoracic wall and the sensor demonstrated magnetic waves mimicking the P wave and QRS complex. The present study shows the application of PMI sensor in detecting cardiac magnetic activity in several healthy subjects, and suggests future applications of this technology in medicine and biology

The Ganymede Laser Altimeter (GALA) for the Jupiter Icy Moons Explorer (JUICE): Mission, science, and instrumentation of its receiver modules

The Jupiter Icy Moons Explorer (JUICE) is a science mission led by the European Space Agency, being developed for launch in 2023. The Ganymede Laser Altimeter (GALA) is an instrument onboard JUICE, whose main scientific goals are to understand ice tectonics based on topographic data, the subsurface structure by measuring tidal response, and small-scale roughness and albedo of the surface. In addition, from the perspective of astrobiology, it is imperative to study the subsurface ocean scientifically. The development of GALA has proceeded through an international collaboration between Germany (the lead), Japan, Switzerland, and Spain. Within this framework, the Japanese team (GALA-J) is responsible for developing three receiver modules: the Backend Optics (BEO), the Focal Plane Assembly (FPA), and the Analog Electronics Module (AEM). Like the German team, GALA-J also developed software to simulate the performance of the entire GALA system (performance model). In July 2020, the Proto-Flight Models of BEO, FPA, and AEM were delivered from Japan to Germany. This paper presents an overview of JUICE/GALA and its scientific objectives and describes the instrumentation, mainly focusing on Japan’s contribution

Serotonin Augments Gut Pacemaker Activity via 5-HT3 Receptors

Serotonin (5-hydroxytryptamine: 5-HT) affects numerous functions in the gut, such as secretion, muscle contraction, and enteric nervous activity, and therefore to clarify details of 5-HT's actions leads to good therapeutic strategies for gut functional disorders. The role of interstitial cells of Cajal (ICC), as pacemaker cells, has been recognised relatively recently. We thus investigated 5-HT actions on ICC pacemaker activity. Muscle preparations with myenteric plexus were isolated from the murine ileum. Spatio-temporal measurements of intracellular Ca2+ and electric activities in ICC were performed by employing fluorescent Ca2+ imaging and microelectrode array (MEA) systems, respectively. Dihydropyridine (DHP) Ca2+ antagonists and tetrodotoxin (TTX) were applied to suppress smooth muscle and nerve activities, respectively. 5-HT significantly enhanced spontaneous Ca2+ oscillations that are considered to underlie electric pacemaker activity in ICC. LY-278584, a 5-HT3 receptor antagonist suppressed spontaneous Ca2+ activity in ICC, while 2-methylserotonin (2-Me-5-HT), a 5-HT3 receptor agonist, restored it. GR113808, a selective antagonist for 5-HT4, and O-methyl-5-HT (O-Me-5-HT), a non-selective 5-HT receptor agonist lacking affinity for 5-HT3 receptors, had little effect on ICC Ca2+ activity. In MEA measurements of ICC electric activity, 5-HT and 2-Me-5-HT caused excitatory effects. RT-PCR and immunostaining confirmed expression of 5-HT3 receptors in ICC. The results indicate that 5-HT augments ICC pacemaker activity via 5-HT3 receptors. ICC appear to be a promising target for treatment of functional motility disorders of the gut, for example, irritable bowel syndrome

Spatial Analysis of Slowly Oscillating Electric Activity in the Gut of Mice Using Low Impedance Arrayed Microelectrodes

<div><p>Smooth and elaborate gut motility is based on cellular cooperation, including smooth muscle, enteric neurons and special interstitial cells acting as pacemaker cells. Therefore, spatial characterization of electric activity in tissues containing these electric excitable cells is required for a precise understanding of gut motility. Furthermore, tools to evaluate spatial electric activity in a small area would be useful for the investigation of model animals. We thus employed a microelectrode array (MEA) system to simultaneously measure a set of 8×8 field potentials in a square area of ∼1 mm². The size of each recording electrode was 50×50 µm², however the surface area was increased by fixing platinum black particles. The impedance of microelectrode was sufficiently low to apply a high-pass filter of 0.1 Hz. Mapping of spectral power, and auto-correlation and cross-correlation parameters characterized the spatial properties of spontaneous electric activity in the ileum of wild-type (WT) and <i>W/W^v</i> mice, the latter serving as a model of impaired network of pacemaking interstitial cells. Namely, electric activities measured varied in both size and cooperativity in <i>W/W^v</i> mice, despite the small area. In the ileum of WT mice, procedures suppressing the excitability of smooth muscle and neurons altered the propagation of spontaneous electric activity, but had little change in the period of oscillations. In conclusion, MEA with low impedance electrodes enables to measure slowly oscillating electric activity, and is useful to evaluate both histological and functional changes in the spatio-temporal property of gut electric activity.</p></div

Auto-correlation analyses.

<p>Panel A shows an auto-correlation function constructed from the field potential recording at Ch28 in an ileal musculature of WT mice (the same preparation shown in Fig. 1E and Fig. 4A). Panels B and C show the distribution of the period (x-axis) and amplitude (y-axis), respectively, estimated from the adjacent peak of autocorrelation function, in the same ileal preparation shown in A. Panels D–F show auto-correlation function, period map and auto-correlation map, respectively, in the ileal musculature of <i>W/W^v</i> mice (the same preparation in Fig. 1F and Fig. 4D). The period and amplitude of autocorrelation were set to 10 in the period map, and to 0 in the autocorrelation map, respectively, in recording channels in which no peak was observed (the peak was below nought) in the frequency range of 9.4–27.0 cpm.</p

Spectral power analysis.

<p>A–B) Power spectrum transformed from field potentials at Ch 28 and pseudo-colour map constructed from the same array data used in Fig. 1E (the ileum of a WT mouse). C–D) Power spectrum and pseudo-colour map for a <i>W/W^v</i> mouse preparation. The data in Fig. 1F was used. Note the spectral peak corresponding to the oscillation frequency seen only in WT mice. E–F) Bar graphs E and F show the effect of nifedipine (1 µM) and TTX (250 nM) on the spectral power summed in all channels in WT and <i>W/W^v</i> mice, respectively. These drugs were applied to record ICC pacemaker activity by suppressing smooth muscle and enteric neurones. Asterisks represent statistical significance (<i>P</i><0.05). Note that the Y-axis is expanded in C and F.</p

Cross-correlation analyses.

<p>Panel A shows a cross-correlation function constructed from field potential recordings at Ch28 and Ch52 in an ileal musculature of WT mice (the same preparation shown in Fig. 1E). Panels B and C show the distribution of the phase-shift (x-axis) and the amplitude (y-axis), respectively, of the peak in cross-correlation functions derived from all 64Ch MEA data, in the same ileal preparation shown in A. Ch28 was used as the base channel. Panels D–F show cross-correlation function, phase-shift map and cross-correlation map, respectively, in the presence of nifedipine and TTX in the same preparation shown in A–C. Panels G–I were constructed from MEA data recorded from an ileal musculature of <i>W/W^v</i> mice (the same preparation in Fig. 5D–F).</p

8×8 MEA recording.

<p>A) Ileal musculature from mice mounted in a recording chamber with an 8×8 MEA in the centre. Extracellular field potentials were simultaneously measured at 64 channels with a high-pass filtering of 0.1 Hz. B) Alignment of MEA recording channels. C) Recording microelectrodes shown with a large magnification. D) Scheme of a recording electrode. Platinum black particles are fixed on an ITO connecting plate. Electrodes are separated with insulating polymers. E–F) Each set of 64 field potentials represent an example of simultaneous recording from ileal musculatures of WT or <i>W/W^v</i> mice in normal solution. Digital filter was not applied. Traces show field potentials of only 5 s.</p