Yoshiteru Seo

Mn‐bicine: A low affinity chelate for manganese ion enhanced MRI

The toxicity of free Mn2+ is a bottleneck for the in vivo application of manganese ion enhanced MRI. To reduce free Mn2+ concentration ([Mn2+]), a low affinity chelate reagent: N,N‐bis(2‐hydroxyethyl)glycine (bicine) was used. Considering the conditional association constant of Mn‐bicine at pH 7.4 (102.9 M−1), (i) a 100 mM Mn‐bicine solution should contain about 10 mM of free manganese ion, but (ii) free manganese will make up 3/4 of the final plasma concentration (0.5 mM) with an intravenous infusion of 100 mM Mn‐bicine. The T1 relaxivity of Mn‐bicine in a 5 mM Mn‐bicine solution was estimated as 5 mM−1 sec−1 at 24°C, 7 T in a pH range of 6.8–7.5. Mn‐bicine demonstrated a tendency for better contractility when employed with an isolated perfused frog heart, compared with MnCl2. A venous infusion of 100 mM Mn‐bicine (8.3 μmol kg−1 min−1) showed a minimal decrease and maintained a constant heart rate level and arterial pressure in rats, while rats infused with 100 mM of MnCl2 showed a significant suppression of the hemodynamic functions. Thus, Mn‐bicine appears to be a better choice for maintaining the vital conditions of experimental animals, and may improve the reproducibility of manganese ion enhanced MRI. Magn Reson Med, 2010.

Magnetic resonance imaging analysis of water flow in the mantle cavity of live Mytilus galloprovincialis

Water flow inside the shell of Mytilus galloprovincialis was measured by phase-contrast magnetic resonance imaging (MRI). In seawater without algal cells at 23°C, water approached the mussel from the posterior-ventral side, and entered through the inhalant aperture at a velocity of 40–20 mm s−1. The flow rate in the lower mantle cavity decreased to 10–20 mm s−1, the water flowed in the anterior–dorsal direction and approached the demibranches at a velocity of 5–10 mm s−1. After passing through the lamellae to the upper mantle cavity, the water stretched the interlamellar cavity, turned to the posterior–dorsal direction and accumulated in the epibranchial cavity. The water flows came together at the ventral side of the posterior adductor muscle. The velocity increased more to than 50 mm s−1 in the exhalant siphon, and exhaled out in the posterior–dorsal direction. The anterior–posterior direction of the flow was imaged every 1.92 s by the inflow effect of T1-weighted MRI. The flow seemed to be constant, and no cyclic motion of the mantles or the gills was detected. Spontaneous closure of the shells caused a quick drop of the flow in the mantle cavity. In the opening process of the shells, water flow in the interlamellar cavities increased before the opening, followed by an increase of flows in the exhalant siphon and inhalant aperture with minimum delay, reaching a plateau within 1 min of the shells opening. This provides direct evidence that the lateral cilia drive water in the mussel M. galloprovincialis.

Testing the constant-volume hypothesis by magnetic resonance imaging of Mytilus galloprovincialis heart

The constant-volume (CV) hypothesis was tested using the Mytilus galloprovincialis heart under two conditions. The volume of the ventricle, auricles and pericardium, and the flow in the heart and adjacent vessels were measured by magnetic resonance imaging. In synthetic seawater at 23°C (immersed condition), the end-diastolic volume (EDV), end-systolic volume (ESV) and stroke volume (SV) were 50%, 21% and 29% of the heart volume, respectively, and the auricle volume (VA) was maximized at end-systole. Assuming a constant volume of the heart, venous return to the auricles (IV) was constant, and out-flow from the pericardium to the kidney (IPK) was 2/3 of SV. During aerial exposure (emersed condition), EDV, ESV and SV decreased to 33%, 22% and 11%, respectively. VA was maximized at end-diastole and associated with the decrease of systolic IV to 1/2 of diastolic IV, while IPK remained at 80% of the immersed condition. Based on these results – in addition to two postulates of the CV hypothesis: (1) the total volume of the heart is always the same, and (2) ventricle contraction causes a decrease in pressure in the pericardium – we modified two postulates: (3) the low pericardial pressure maintains venous return from the anterior oblique vein to the auricle, and (4) the pressure difference between the auricle and the pericardium drives haemolymph filtration through the auricle walls. We also added a new postulate: (5) dilatation of the ventricle is associated with the haemolymph output to the kidney via the renopericardial canals.

Magnetic resonance imaging of the temporomandibular joint in the rat compared with low-powered light microscopy.

OBJECTIVE High magnetic field magnetic resonance imaging (MRI) was applied to the temporomandibular joint (TMJ) in the rat. The purpose of this study was the depiction of the internal structure of the TMJ, including the articular disc, articular cartilage, and the upper and lower joint cavities. We also proposed MRI settings and slices suitable for imaging the TMJ in the rat. METHODS Temporomandibular joints from one female and eight male Sprague Dawley rats (5-8 weeks old) and four male Wistar-Hamamatsu rats (7-8 weeks old) were used. Using scout images, the horizontal plane was defined as being parallel to the body of the basisphenoid bone underneath the base of the brain. The coronal plane was defined as a slice vertical to the horizontal plane and vertical to the longitudinal fissure of the cerebrum. The sagittal plane was defined as a slice vertical to the horizontal plane and parallel to the longitudinal fissure of the cerebrum. RESULTS T(1)-weighted MR images with a spatial resolution of 75 μm were obtained for 5 min. The temporal bone and mandibular condyle were depicted as lower signal intensity images and the articular disc was depicted as an intermediate signal intensity image. In accordance with Gd-DTPA-enhanced MR or T(2)-weighted MR images, the articular disc, articular cartilage, and the upper and lower joint cavities could be assigned clearly. CONCLUSION These MRI findings closely agreed with those observed with haematoxylin-eosin staining under light microscopy, suggesting that MRI is a useful method for analyzing the complex structure of the TMJ in the rat.

Involvement of myristoylated alanine-rich C kinase substrate phosphorylation and translocation in cholecystokinin-induced amylase release in rat pancreatic acini

Cholecystokinin (CCK) is a gastrointestinal hormone that induces exocytotic amylase release in pancreatic acinar cells. The activation of protein kinase C (PKC) is involved in the CCK-induced pancreatic amylase release. Myristoylated alanine-rich C kinase substrate (MARCKS) is a ubiquitously expressed substrate of PKC. MARCKS has been implicated in membrane trafficking in several cell types. The phosphorylation of MARCKS by PKC results in the translocation of MARCKS from the membrane to the cytosol. Here, we studied the involvement of MARCKS in the CCK-induced amylase release in rat pancreatic acini. Employing Western blotting, we detected MARCKS protein in the rat pancreatic acini. CCK induced MARCKS phosphorylation. A PKC-δ inhibitor, rottlerin, inhibited the CCK-induced MARCKS phosphorylation and amylase release. In the translocation assay, we also observed CCK-induced PKC-δ activation. An immunohistochemistry study showed that CCK induced MARCKS translocation from the membrane to the cytosol. When acini were lysed by a detergent, Triton X-100, CCK partially induced displacement of the MARCKS from the GM1a-rich detergent-resistant membrane fractions (DRMs) in which Syntaxin2 is distributed. A MARCKS-related peptide inhibited the CCK-induced amylase release. These findings suggest that MARCKS phosphorylation by PKC-δ and then MARCKS translocation from the GM1a-rich DRMs to the cytosol are involved in the CCK-induced amylase release in pancreatic acinar cells.

Changes to Muscle T 2 after Single-finger Exercise Measured with 0.2T MR Imaging

We constructed an arm holder for muscle exercise from a forearm-shaped plastic shell and magnetic resonance (MR) imaging position markers and determined the echo time (39 ms) for T₂-weighted spin-echo MR imaging from T₂values of the exercised (50 ms) and resting (32 ms) muscle at 0.2 tesla. The smallest detectable muscle was the extensor digiti minimi muscle (cross-sectional area 25 mm²). This combination could be useful to monitor finger exercise in patients undergoing physical therapy.

Mn-citrate and Mn-HIDA: intermediate-affinity chelates for manganese-enhanced MRI.

In this study we investigated two manganese chelates in order to improve the image enhancement of manganese-enhanced MRI and decrease the toxicity of free manganese ions. Since both MnCl₂ and a low-affinity chelate were associated with a slow continuous decrease of cardiac functions, we investigated intermediate-affinity chelates: manganese N-(2-hydroxyethyl)iminodiacetic acid (Mn-HIDA) and Mn-citrate. The T₁ relaxivity values for Mn-citrate (4.4 m m⁻¹ s⁻¹) and Mn-HIDA (3.3 m m⁻¹ s⁻¹) in artificial cerebrospinal fluid (CSF) were almost constant in a concentration range from 0.5 to 5 m m at 37 °C and 4.7 T. In human plasma, the relaxivity values increased when the concentrations of these Mn chelates were decreased, suggesting the presence of free Mn²⁺ bound with serum albumin. Mn-HIDA and Mn-citrate demonstrated a tendency for better contractility when employed with an isolated perfused frog heart, compared with MnCl₂. Only minimal changes were demonstrated after a venous infusion of 100 m m Mn-citrate or Mn-HIDA (8.3 µmol kg⁻¹ min⁻¹) in rats and a constant heart rate, arterial pressure and sympathetic nerve activity were maintained, even after breaking the blood-brain barrier (BBB). Mn-citrate and Mn-HIDA could not cross the intact BBB and appeared in the CSF, and then diffused into the brain parenchyma through the ependymal layer. The responses in the supraoptic nucleus induced by the hypertonic stimulation were detectable. Therefore, Mn-citrate and Mn-HIDA appear to be better choices for maintaining the vital conditions of experimental animals, and they may improve the reproducibility of manganese-enhanced MRI of the small nuclei in the hypothalamus and thalamus.

A portable infrared photoplethysmograph: heartbeat of Mytilus galloprovincialis analyzed by MRI and application to Bathymodiolus septemdierum

ABSTRACT Infrared photoplethysmogram (IR-PPG) and magnetic resonance image (MRI) of the Mytilus galloprovincialis heart were obtained simultaneously. Heart rate was varied by changing temperature, aerial exposure and hypoxia. Higher heart rates (35-20 beat min−1) were usually observed at 20°C under the aerobic condition, and typical IR-PPG represented a single peak (peak v). The upward and downward slopes of the peak v corresponded to the filling and contracting of the ventricle, respectively. A double-peak IR-PPG was observed in a wide range of heart rates (5 to 35 beats min−1) under various conditions. The initial peak v corresponded to the filling of the ventricle, and the origin of the second peak (v’) varied with the heart rate. A flat IR-PPG with a noise-level represented cardiac arrest. Although large movement of the shells and the foot caused slow waves or a baseline drift of the IR-PPG, the heart rate can be calculated from the v-v interval. Based on these results, we assembled a portable IR-PPG recording system, and measured the heartbeats of Bathymodiolus septemdierum (Mytilidae) for 24 h on a research vessel just after sampling from the deep sea, showing that IR-PPG is a noninvasive, economical, robust method that can be used in field experiments. Summary: Infrared photoplethysmogram of Mytilus heart was analyzed by magnetic resonance imaging. Portable photoplethysmographs provide a noninvasive, economical and robust method to monitor the heartbeat of mussels in field experiments.

Structure and Size-selective Permeability of the Synovial Membrane of the Temporomandibular Joint of the Mouse Measured by MR Imaging at 7T.

PURPOSE We analyzed the anatomical structure of the temporomandibular joint (TMJ) and molecular weight dependency of synovial membrane permeability in mice using 7-tesla magnetic resonance (MR) imaging. METHODS We obtained 3-dimensional (3D) T1-weighted gradient echo (3D-T1W) and 3D T2-weighted rapid acquisition with relaxation enhancement (3D-T2W RARE) MR images of the TMJ of male C57BL6 mice with voxel resolution of 65 µm. Two-dimensional (2D) T1w images were measured every 45 s before and after bolus intravenous (IV) injection of contrast reagents: gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA; 0.5 kDa); oligomer-based contrast agent (CH3-DTPA-Gd; 2.1 kDa); gadolinium-labeled polylysine (Gd-polylysine; 10 kDa); and gadolinium-labeled albumin (Gd-albumin; 74 kDa). RESULTS T1W images depicted the temporal bone and mandibular condyle as regions with lower signal intensity and the disc as a region of intermediate intensity. In the Gd-DTPA-enhanced T1W and T2W images, the articular disc could be identified as a region with lower signal intensity than that of the upper and lower joint cavities. After IV injection of Gd-DTPA or CH3-DTPA-Gd, the signal intensity of the joint cavities increased within 10 min, but this increase was not shown with Gd-polylysine and Gd-albumin. CONCLUSION The structural findings obtained by MR imaging agreed with those obtained by hematoxylin-eosin staining under light microscopy. Contrast-enhanced MR imaging suggested that smaller (<2.1 kDa) but not larger (>10 kDa) molecules can permeate the synovial membrane. Our results suggest the utility of MR imaging for analyzing the structure of the TMJ as well as permeability of the synovial membrane.

Accumulation and excretion of manganese ion in the kidney of Mytilus galloprovincialis

ABSTRACT T1-weighted magnetic resonance imaging (T1w-MRI) was employed to detect the accumulation of manganese ion (Mn2+) in urine in the kidney of the mussel Mytilus galloprovincialis, and the longitudinal relaxation rates (1/T1=R1) were measured. When the mussel was exposed to seawater containing 10 µmol l−1 Mn2+, the T1w-MRI intensity and R1 of the kidney, stomach and digestive glands were increased. Mn2+ might be taken into the hemolymph via the gastrointestinal tract, and then filtrated into the pericardium via the auricles. Although the image intensity in the pericardium was not affected by manganese, an image intensity enhancement was observed in the distal part of the renopericardial communication canals between the pericardium and the kidneys, indicating Mn2+ was concentrated in the excretion pathway. As the seawater Mn2+ concentration ([Mn2+]SW) was increased from 3 to 50 µmol l−1, R1 of the kidney (R1K) was elevated. When the mussels were immersed in 3–10 µmol l−1 [Mn2+]SW for 24 h, the Mn2+ concentration in the kidney ([Mn2+]K) showed a 15-fold increase compared with the ambient [Mn2+]SW. In the range of [Mn2+]SW from 10 to 50 µmol l−1, R1K reached a plateau level that corresponded to 200 µmol l−1 [Mn2+]K. As [Mn2+]K fell transiently, voluntary excretion of urine from the kidney was assumed. The decreases in intensity were not synchronized between the right and left kidneys, and the closure of the shells might not be essential for urinary excretion. The voluntary excretion suggested an additional explanation for the large range in metal concentratons in the kidneys of the mussel. Summary: Mytilus galloprovincialis is able to concentrate 15 times more manganese ion in the kidney compared with concentrations in ambient seawater, and has been shown to excrete urine voluntarily.