Ventricular Lumen Research Articles

Accelerated high‐frame‐rate mouse heart cine‐MRI using compressed sensing reconstruction

We introduce a new protocol to obtain very high-frame-rate cinematographic (Cine) MRI movies of the beating mouse heart within a reasonable measurement time. The method is based on a self-gated accelerated fast low-angle shot (FLASH) acquisition and compressed sensing reconstruction. Key to our approach is that we exploit the stochastic nature of the retrospective triggering acquisition scheme to produce an undersampled and random k-t space filling that allows for compressed sensing reconstruction and acceleration. As a standard, a self-gated FLASH sequence with a total acquisition time of 10 min was used to produce single-slice Cine movies of seven mouse hearts with 90 frames per cardiac cycle. Two times (2×) and three times (3×) k-t space undersampled Cine movies were produced from 2.5- and 1.5-min data acquisitions, respectively. The accelerated 90-frame Cine movies of mouse hearts were successfully reconstructed with a compressed sensing algorithm. The movies had high image quality and the undersampling artifacts were effectively removed. Left ventricular functional parameters, i.e. end-systolic and end-diastolic lumen surface areas and early-to-late filling rate ratio as a parameter to evaluate diastolic function, derived from the standard and accelerated Cine movies, were nearly identical.

Left-Right Locomotor Circuitry Depends on RhoA-Driven Organization of the Neuroepithelium in the Developing Spinal Cord

RhoA is a key regulator of cytoskeletal dynamics with a variety of effects on cellular processes. Loss of RhoA in neural progenitor cells disrupts adherens junctions and causes disorganization of the neuroepithelium in the developing nervous system. However, it remains essentially unknown how the loss of RhoA physiologically affects neural circuit formation. Here we show that proper neuroepithelial organization maintained by RhoA GTPase in both the ventral and dorsal spinal cord is critical for left-right locomotor behavior. We examined the roles of RhoA in the ventral and dorsal spinal cord by deleting the gene in neural progenitors using Olig2-Cre and Wnt1-Cre mice, respectively. RhoA-deleted neural progenitors in both mutants exhibit defects in the formation of apical adherens junctions and disorganization of the neuroepithelium. Consequently, the ventricular zone and lumen of the dysplastic region are lost, causing the left and right sides of the gray matter to be directly connected. Furthermore, the dysplastic region lacks ephrinB3 expression at the midline that is required for preventing EphA4-expressing corticospinal neurons and spinal interneurons from crossing the midline. As a result, aberrant neuronal projections are observed in that region. Finally, both RhoA mutants develop a rabbit-like hopping gait. These results demonstrate that RhoA functions to maintain neuroepithelial structures in the developing spinal cord and that proper organization of the neuroepithelium is required for appropriate left-right motor behavior.

Macrocyclic contrast agents for magnetic resonance imaging of chronic myocardial infarction: intraindividual comparison of gadobutrol and gadoterate meglumine

To compare 0.15 mmol/kg gadobutrol for late gadolinium enhancement (LGE) imaging of chronic myocardial infarction with a relaxivity-adjusted dose of gadoterate meglumine (Gd-DOTA). Seventeen patients with suspected chronic myocardial infarction underwent LGE imaging at 1.5 T, acquiring an inversion-recovery-prepared gradient echo sequence 15 min after contrast agent administration. Each patient underwent LGE imaging twice, once after administration of 0.15 mmol/kg gadobutrol (r1 = 5.2 l mmol(-1) s(-1)) and after 0.22 mmol/kg Gd-DOTA (r1 = 3.6 l mmol(-1) s(-1)). Two readers independently determined infarct size and contrast-to-noise ratios of infarcted myocardium to remote myocardium (CNR(remote)) and to the left ventricular lumen (CNR(lumen)). LGE was present in 14 patients. Infarct sizes determined after administration of gadobutrol [23.4 ml; 95 % CI (14.4; 32.5)] and Gd-DOTA [22.1 ml; 95 % CI (13.0; 31.1)] were not statistically different (P = 0.22). The CNR(remote) of LGE in infarcted myocardium on gadobutrol- and Gd-DOTA-enhanced images was 44.1 [95 % CI (31.0; 57.1)] and 45.2 [95 % CI (32.2; 58.3)], respectively (P = 0.73). CNR(lumen) was significantly higher on gadobutrol-enhanced LGE images [12.7; 95 % CI (2.5; 23.0) versus 6.8; 95 % CI (-3.5; 17.0); P = 0.02]. At relaxivity-adjusted doses, gadobutrol and Gd-DOTA yielded similar infarct sizes with superior contrast between infarcted myocardium and left ventricular lumen on gadobutrol-enhanced images.

Primary Leiomyosarcoma in the Heart of a Guinea Pig

Leiomyosarcoma was diagnosed in the heart of a 3-year-old female guinea pig. Neoplastic tissue was located in the ventricular septum extending into the right ventricular lumen, but was not obvious grossly. Microscopically, the mass was nodular and infiltrative and was composed of streams and bundles of spindle cells. Immunohistochemically, the neoplastic cells expressed vimentin and α-smooth muscle actin. There was no cross striation of the muscle cells. This is the first report of cardiac leiomyosarcoma in a guinea pig.

Gadobutrol for Magnetic Resonance Imaging of Chronic Myocardial Infarction

To compare 0.15 mmol/kg gadobutrol with 0.20 mmol/kg gadopentetate dimeglumine with regard to late gadolinium enhancement (LGE) of infarcted myocardium at magnetic resonance (MR) imaging. Twenty patients with history of chronic myocardial infarction underwent 2 cardiac MR examinations at 1.5 Tesla. For the evaluation of myocardial infarction, late gadolinium enhancement (LGE) imaging was performed with an inversion recovery-prepared gradient-echo sequence 15 minutes after administration of either gadobutrol (r1 = 5.2 mmol(-1)s(-1)) or gadopentetate dimeglumine (r1 = 4.1 mmol(-1)s(-1)). The dose of the contrast agents was adjusted based on the relaxivity of both contrast agents. Hence, gadobutrol and gadopentetate dimeglumine were administered at 0.15 mmol/kg and 0.20 mmol/kg, respectively. Contrast-to-noise ratios (CNR) between infarcted myocardium and remote myocardium (CNR remote) and between infarcted myocardium and left ventricular lumen (CNR lumen) were assessed by 2 independent readers. Additionally, infarct size was assessed semiautomatically by using a threshold of 5 standard deviations above the mean signal intensity of remote myocardium. Subendocardial or transmural LGE was present in 16 of 20 (80%) patients. The optimal inversion time for LGE imaging did not differ significantly between gadobutrol and gadopentetate dimeglumine (275 ± 21 milliseconds [range, 240-320 milliseconds] and 282 ± 23 milliseconds [range, 240-330 milliseconds], respectively; P = 0.32). The CNR remote after administration of gadobutrol (40.0 ± 4.6; 95% confidence interval [CI]: 30.3; 49.7) and gadopentetate dimeglumine (40.6 ± 4.6; 95% CI: 30.9; 50.3) did not show significant differences (P = 0.90), whereas gadobutrol yielded a significantly higher CNR lumen (6.2 ± 3.6; 95% CI: -1.5; 13.9) compared with gadopentetate dimeglumine (0.8 ± 3.6; 95% CI: -6.9; 8.5). Infarct size after administration of gadobutrol (23.7 ± 4.7 mL; 95% CI: 13.6; 33.7) and gadopentetate dimeglumine (23.7 ± 4.7 mL;95% CI: 13.7; 33.8) was not statistically different (P = 0.94). There was an excellent correlation between gadobutrol- and gadopentetate dimeglumine-enhanced assessment of infarct size (Spearman r = 0.99 and r = 0.97 for reader 1 and 2, respectively). This pilot study shows that 0.15 mmol/kg gadobutrol is an effective contrast agent for LGE imaging with better delineation of infarcted myocardium from left ventricular lumen than 0.20 mmol/kg gadopentetate dimeglumine.

Over 2-year disease-free survival after multimodality therapy of a primary cardiac lymphoma

This comment deals with our study regarding the innovative, sequential therapy of a primary cardiac lymphoma. Primary cardiac T-cell lymphoma is defined as a non-Hodgkin lymphoma (NHL) involving only the heart and/or the pericardium, or as an NHL with the main bulk of the tumor located on the heart. It is an extremely rare disease with a typical heterogeneous clinical manifestation and 100% mortality if left untreated. Herein we describe a clinical follow-up of 26 months in a young female patient with eventful heart failure due to the uncommon diagnosis of a primary cardiac T-cell lymphoma. The patient underwent emergent veno-arterial extracorporeal membrane oxygenation (ECMO) implantation with the suspicion of a fulminant viral myocarditis. When rapidly complete contractile cardiac arrest and an almost complete obliteration of the ventricular lumen occurred within 1 day of emergency cardiectomy, implantation of a custom-made biventricular assist device (BVAD) was done and 12 days later successful heart transplantation was performed. In addition, she underwent chemotherapy (CHOP regime) and reduced immunosuppression, always maintained in the subtherapeutic range. The first myocardial biopsy, 2 weeks after transplantation, the patient showed single tumor cells within the graft, but all consecutive biopsies confirmed complete resolution of T-cell infiltration. Six months after transplantation endomyocardial biopsies revealed mild rejection, which was successfully treated with bolus steroids. At 1 year, heart catheterization showed no transplant vasculopathy and a normal ejection fraction of 65%. Severe facial actinomycotic infection occurred on a single occasion, which was treated successfully with surgery, antibiotics and antimycotics. Most recently, more than 2 years later, routine staging, including clinical examination, computed tomography (CT) scans, ultrasound evaluation and endomyocardial biopsy, indicated no evidence of tumor recurrence. The last endomyocardial biopsy showed no rejection (A0, ISHLT 0R). Except for persistently impaired renal function, without the

Dynamic late gadolinium enhancement simply quantified using myocardium to lumen signal ratio: Normal range of ratio and diffuse abnormal enhancement of cardiac amyloidosis

To detect abnormal myocardial tissue in patients with diffuse myocardial disease, we propose a simple technique of late gadolinium enhancement (LGE) using routine myocardial imaging modalities. We retrospectively reviewed LGE images from 51 patients with normal myocardium and 10 patients with pathologically proven cardiac amyloidosis (CA). We obtained sequential LGE images from patients at 2, 5, 10, and 20 minutes after injection of Gd-DTPA (0.15 mmol/kg) with a fixed inversion time of 300 msec. We evaluated the signal intensity ratio of the myocardium to the left ventricular lumen (M/L) in one long and two short axial sections within 463 and 120 segments of normal myocardium and CA, respectively. Visually unenhanced and enhanced regions of myocardium were evaluated in each segment of patients with CA. Among normal myocardium, M/L (means ± standard deviation; SD) was stable with time (2, 5, 10, and 20 min: 0.34 ± 0.03, 0.31 ± 0.05, 0.34 ± 0.07, and 0.42 ± 0.11, respectively). The calculated M/L of unenhanced (0.60 ± 0.20, 0.68 ± 0.19, 0.76 ± 0.20, and 1.09 ± 0.25, respectively) and enhanced myocardium (0.77 ± 0.27, 0.99 ± 0.29, 1.20 ± 0.40, and 1.45 ± 0.54, respectively) in patients with CA was significantly greater than that seen for the normal myocardium at each time and increased over time. In patients with CA, diffuse myocardial abnormalities can be demonstrated using M/L, and this technique may be useful for the characterization of other myocardial diseases.

Cardiac Magnetic Resonance of Left Ventricular Trabeculation

Historically, left ventricular noncompaction (LVNC) was considered to be a rare form of cardiomyopathy; however, during the past decade, there has been a significant increase in reports of patients with LVNC. Using either echocardiography or cardiac magnetic resonance (CMR) imaging, LVNC is relatively straightforward to diagnose in individuals expressing a typical phenotype. However, the diagnosis may be challenging to make in those individuals who express more subtle phenotypes of LVNC. CMR imaging offers a more detailed examination of myocardial structure and composition compared with other imaging modalities, such as echocardiography. With more common use of CMR, there has been increased appreciation of the degree of trabeculation of the LV. The ventricle comprises 2 myocardial layers: the compact myocardium and the trabecular myocardium. During cardiac development, after heart looping, the myocardium becomes deeply trabeculated through a clonal outgrowth of embryonic cardiomyocytes.1 After the coronary arteries form and provide a ready supply of oxygen and nutrients, the LV undergoes compaction accompanied by resolution of the deep trabeculae. Persistence of the LV trabeculae in the postnatal myocardium may be associated with cardiomyopathy, and LVNC is classified as a cardiomyopathy.2,3 Article see p 139 There is a lack of consensus surrounding LVNC diagnostic criteria. The imaging criteria for LVNC differ depending on whether echocardiography or CMR is used. Both imaging modalities use the ratio of the thickness of the trabeculated layer to the thickness of the compacted layer (T/C). However, a commonly used diagnostic criterion for echocardiography requires the T/C to be >2.0 at end systole,4 whereas the diagnostic criterion for CMR is T/C …

Occlusion of surgical opening of the ventricular system with fibrinogen-coated collagen fleece: a case collection study

BackgroundImplantation of 1,3-bis (2-chloroethyl)-1-nitrosourea (BCNU) wafer for malignant glioma is not recommended in the case of surgical opening of the ventricular system during microsurgical tumor resection because the wafer material may dislocate from the resection cavity into the ventricular system and cause obstructive hydrocephalus. TachoSil is an adhesive collagen fleece used in different surgical disciplines that provides an air- and liquid-tight seal closing communications between the ventricular system and the resection cavity after tumor removal.MethodsOcclusion of ventricular defects with TachoSil after microsurgical glioma resection was performed in two patients with newly diagnosed and seven patients with recurrent malignant glioma prior to BCNU wafer implantation into the resection cavity. Early postoperative cranial computed tomography (CCT)/MRI and follow-up MRI at 3 months’ intervals were performed with a median follow-up of 10.4 months.ResultsThe collagen fleece was identified as a linear structure hypodense/hypointense to white matter on postoperative CT/MRI separating the resection cavity from the ventricular lumen in all cases. In no case did early CCT/MRI or follow-up MRI reveal wafer material within the ventricular system. In no case did signs of obstructive hydrocephalus occur.ConclusionSealing of the ventricular system using a fibrinogen-coated collagen fleece effectively separates the resection cavity from the ventricular system and allows implantation of BCNU wafers into the resection cavity. No morphological evidence for wafer material dislocation into the ventricular system or obstruction of CSF pathways was found in nine patients who received 41 follow-up MRI over 10.4 months of follow-up.

Dependence of cardiac trabeculation on neuregulin signaling and blood flow in zebrafish

Maturation of the developing heart requires the structural elaboration of the embryonic ventricle through the process of trabeculation. Trabeculae form as the ventricular myocardium protrudes into the lumen of the chamber, thereby increasing muscle mass and altering functional output. Little is understood about the cellular basis for trabeculation and its genetic regulation. Here, we establish the utility of the zebrafish embryo for the analysis of the mechanisms driving trabeculation. In zebrafish, we can follow trabeculation in four dimensions and define morphologically discrete stages for the initiation, propagation, and network elaboration that form the ventricular trabeculae. We find that Neuregulin/ErbB signaling is required for the initial protrusion of the myocardium into the ventricular lumen. Additionally, we demonstrate that optimal blood flow through the ventricle is important for the advancement of trabeculation. Thus, our results indicate that the zebrafish provides a valuable model for investigating possible causes of congenital defects in trabeculation.

Effects of gadolinium contrast agent on aortic blood flow and myocardial strain measurements by phase-contrast cardiovascular magnetic resonance.

BackgroundQuantitative blood flow and aspects of regional myocardial function such as myocardial displacement and strain can be measured using phase-contrast cardiovascular magnetic resonance (PC-CMR). Since a gadolinium-based contrast agent is often used to measure myocardial infarct size, we sought to determine whether the contrast agent affects measurements of aortic flow and myocardial displacement and strain. Phase-contrast data pre and post contrast agent was acquired during free breathing using 1.5T PC-CMR.ResultsFor aortic flow and regional myocardial function 12 and 17 patients were analysed, respectively. The difference pre and post contrast agent was 0.03 ± 0.16 l/min for cardiac output, and 0.1 ± 0.5 mm for myocardial displacement. Linear regression for myocardial displacement (MD) after and before contrast agent (CA) showed MDpostCA = 0.95MDpreCA+0.05 (r = 0.95, p < 0.001). For regional myocardial function, the contrast-to-noise ratios for left ventricular myocardial wall versus left ventricular lumen were pre and post contrast agent administration 7.4 ± 3.3 and 4.4 ± 8.9, respectively (p < 0.001). The contrast-to-noise ratios for left ventricular myocardial wall versus surrounding tissue were pre and post contrast agent administration -16.9 ± 22 and -0.2 ± 6.3, respectively (p < 0.0001).ConclusionsQuantitative measurements of aortic flow yield equal results both in the absence and presence of gadolinium contrast agent. The total examination time may thereby be reduced when assessing both viability and quantitative flow using PC-CMR, by assessing aortic flow post contrast agent administration. Phase-contrast information for myocardial displacement is also assessable both in the absence and presence of contrast agent. However, delineation of the myocardium may be difficult or impossible post contrast agent due to the lower image contrast. Acquisition of myocardial displacement should therefore be performed pre contrast agent using current PC-CMR sequences.

Claudin‐5a in developing zebrafish brain barriers: another brick in the wall

Claudins serve essential roles in regulating paracellular permeability properties within occluding junctions. Recent studies have begun to elucidate developmental roles of claudins within immature tissues. This work has uncovered an involvement of several claudins in determining tight junction properties that have an effect on embryonic morphogenesis and physiology. During zebrafish brain morphogenesis, Claudin-5a determines the paracellular permeability of tight junctions within a transient neuroepithelial-ventricular barrier that maintains the hydrostatic fluid pressure required for brain ventricular lumen expansion. However, the roles of Claudins in development may well extend beyond being mere junctional components. Several post-translational modifications of Claudins have been characterized that indicate a direct regulation by developmental signals. This review focuses on the involvement of Claudin-5a in cerebral barrier formation in the zebrafish embryo and includes some speculations about possible modes of regulation.

Cortical Neural Precursors Inhibit Their Own Differentiation via N-Cadherin Maintenance of β-Catenin Signaling

Little is known about the architecture of cellular microenvironments that support stem and precursor cells during tissue development. Although adult stem cell niches are organized by specialized supporting cells, in the developing cerebral cortex, neural stem/precursor cells reside in a neurogenic niche lacking distinct supporting cells. Here, we find that neural precursors themselves comprise the niche and regulate their own development. Precursor-precursor contact regulates beta-catenin signaling and cell fate. In vivo knockdown of N-cadherin reduces beta-catenin signaling, migration from the niche, and neuronal differentiation in vivo. N-cadherin engagement activates beta-catenin signaling via Akt, suggesting a mechanism through which cells in tissues can regulate their development. These results suggest that neural precursor cell interactions can generate a self-supportive niche to regulate their own number.

Epithelial relaxation mediated by the myosin phosphatase regulator Mypt1 is required for brain ventricle lumen expansion and hindbrain morphogenesis

We demonstrate that in the zebrafish hindbrain, cell shape, rhombomere morphogenesis and, unexpectedly, brain ventricle lumen expansion depend on the contractile state of the neuroepithelium. The hindbrain neural tube opens in a specific sequence, with initial separation along the midline at rhombomere boundaries, subsequent openings within rhombomeres and eventual coalescence of openings into the hindbrain ventricle lumen. A mutation in the myosin phosphatase regulator mypt1 results in a small ventricle due to impaired stretching of the surrounding neuroepithelium. Although initial hindbrain opening remains normal, mypt1 mutant rhombomeres do not undergo normal morphological progression. Three-dimensional reconstruction demonstrates cell shapes within rhombomeres and at rhombomere boundaries are abnormal in mypt1 mutants. Wild-type cell shape requires that surrounding cells are also wild type, whereas mutant cell shape is autonomously regulated. Supporting the requirement for regulation of myosin function during hindbrain morphogenesis, wild-type embryos show dynamic levels of phosphorylated myosin regulatory light chain (pMRLC). By contrast, mutants show continuously high pMRLC levels, with concentration of pMRLC and myosin II at the apical side of the epithelium, and myosin II and actin concentration at rhombomere boundaries. Brain ventricle lumen expansion, rhombomere morphology and cell shape are rescued by inhibition of myosin II function, indicating that each defect is a consequence of overactive myosin. We suggest that the epithelium must ;relax', via activity of myosin phosphatase, to allow for normal hindbrain morphogenesis and expansion of the brain ventricular lumen. Epithelial relaxation might be a widespread strategy to facilitate tube inflation in many organs.

Enhanced postmyocardial infarction fibrosis via stimulation of the transforming growth factor-β-Smad2 signaling pathway: role of transient receptor potential vanilloid type 1 channels

To test the hypothesis that the transient receptor potential vanilloid type 1 (TRPV1) channels modulate postmyocardial infarction (MI) fibrosis and matrix formation via the transforming growth factor-beta-Smad signaling pathway to conserve cardiac function and geometrical regeneration. Several lines of evidence indicate that activation of TRPV1 expressed in afferent nerve fibers innervating the heart may preserve cardiac function after MI. However, the underlying mechanisms of TRPV1-mediated protection are largely unknown. TRPV1-null mutant (TRPV1) and wild-type mice were subjected to left anterior descending coronary ligation or sham operation. Seven days after MI, TRPV1 mice showed an increased infarct size and mortality rate (P < 0.001) when compared with wild-type mice. Enzyme-linked immunosorbent assay analysis showed that transforming growth factor-beta1, vascular endothelial growth factor, and matrix metalloproteinase-2 expression were upregulated to a greater extent in TRPV1 than in wild-type mice after MI (P < 0.001). Western blot showed that Smad2 expression was enhanced in TRPV1 compared with wild-type mice after MI (P < 0.001). Quantitative immunohistochemistry analysis showed that myofibroblast infiltration, capillary density, and collagen content were greater in TRPV1 compared with wild-type mice after MI (P < 0.001), and that the left ventricular lumen was enlarged and the wall thinner in TRPV1 compared with wild-type mice after MI (P < 0.001). Echocardiographic examination showed end-systolic and end-diastolic diameters were increased and the ejection fraction reduced in TRPV1 compared with wild-type mice after MI (P < 0.001). Thus, ablation of TRPV1 markedly enhances post-MI fibrosis and impairs myocardial contractile performance, leading to increased propensity of functional heart failure and mortality possibly via stimulation of the transforming growth factor-beta-Smad2 signaling pathway. These data indicate that TRPV1 plays a protective role in MI healing and regeneration.

Endothelinergic cells in the subependymal region of mice

Endothelin (ET) is a small peptide that activates astrocyte proliferation, regulates proliferation and migration of embryonic neural precursor cells and stimulates glioblastoma growth. We found that in mouse brain, ET and its receptor B (ETRB) were highly expressed in the subependymal zone (SEZ), an adult neurogenic niche. Cells with ET immunoreactivity (ET + cells) selectively appeared along the lateral and dorsal walls of the lateral ventricle. They also appeared in the cingular region of the corpus callosum. Subependymal ET + cells also displayed prominin (PRO), glial fibrillary acidic protein (GFAP) and ETRB immunoreactivities. ET + processes traversed the ependymal epithelium and approached the ventricular lumen. Ependymal cells only showed ETRB-ir. A small but consistent number of ET + cells displayed proliferation markers: 5-bromo-2′-deoxyuridine (BrdU) incorporation, and minichromosome maintenance protein 2 (Mcm2). Cortical injury and G-CSF increased subependymal endothelinergic cells and their proliferation markers. Our findings suggest that ET and ETRB might be associated with regulation of adult neural stem cells and their migration through neurogenic and gliogenic pathways.

Ectopic Thyroid in the Aortic Valve of a Han Wistar Rat

Histological examination of the heart of a clinically normal, 10-week-old female Han Wistar rat revealed a 600 x 400-mum mass of ectopic thyroid tissue within the subendothelial connective tissue of the aortic valve. The mass protruded into the left ventricular lumen and was composed of single layers of cuboidal to low-columnar epithelium organized into follicles often containing colloid. Parafollicular cells were not evident. To the authors' knowledge, this is the first report of intracardiac ectopic thyroid gland in the rat and the first report of ectopic thyroid within a heart valve in a mammal.

Establishment of a neuroepithelial barrier by Claudin5a is essential for zebrafish brain ventricular lumen expansion

Lumen expansion driven by hydrostatic pressure occurs during many morphogenetic processes. Although it is well established that members of the Claudin family of transmembrane tight junction proteins determine paracellular tightness within epithelial/endothelial barrier systems, functional evidence for their role in the morphogenesis of lumenized organs has been scarce. Here, we identify Claudin5a as a core component of an early cerebral-ventricular barrier system that is required for ventricular lumen expansion in the zebrafish embryonic brain before the establishment of the embryonic blood-brain barrier. Loss of Claudin5a or expression of a tight junction-opening Claudin5a mutant reduces brain ventricular volume expansion without disrupting the polarized organization of the neuroepithelium. Perfusion experiments with the electron-dense small molecule lanthanum nitrate reveal that paracellular tightness of the cerebral-ventricular barrier decreases upon loss of Claudin5a. Genetic analyses show that the apical neuroepithelial localization of Claudin5a depends on epithelial cell polarity and provide evidence for concerted activities between Claudin5a and Na(+),K(+)-ATPase during luminal expansion of brain ventricles. These data establish an essential role of a barrier-forming Claudin in ventricular lumen expansion, thereby contributing to brain morphogenesis.

Functional Role of Mitochondrial Ryanodine Receptor Type 1 in the Heart

We recently demonstrated the existence of type 1 ryanodine receptors (RyR1) in the mitochondria of cardiac muscle cells (Beutner et al, 2001, 2005, Altschafl et al, 2007). However, the functional significance of mitochondrial type 1 ryanodine receptors (mitoRyR1), especially in the whole heart preparations, remains unclear. We determined the cardiac phenotype of knock-in mice harboring an RyR1 mutation (RyR1Y522S) that promotes RyR1 Ca2+ leak and results in malignant hyperthermia and central cores in humans. In Langendorff perfused hearts, isoproterenol (10-50 nM) infusion induced a significantly (p 8). We studied the morphology of cardiac mitochondria using electron microscopy. Cardiac mitochondria in RyR1Y522S/WT mice (3-18 months old) exhibit a lower density of cristae, a higher incidence of mitochondrial clustering and misalignment with sarcomeres, and a dissociation of mitochondria from myofilaments, as routinely observed in controls (n>5). Finally, we examined the heart structure of homozygous RyR1Y522S/Y522S embryos, which die prior to birth. Compared to RyR1Y522S/WT and wild-type littermates, RyR1Y522S/Y522S embryos developed normally until approximately embryonic day (E) 14.5, after which their hearts exhibit significant myocyte disarray, lack ventricular lumen and display evidence of heart failure. These results are consistent with the hypothesis that mitoRyR1 plays an important role in the proper development and regulation of cardiac structure and function.

In vivo imaging of the cyclic changes in cross‐sectional shape of the ventricular segment of pulsating embryonic chick hearts at stages 14 to 17: A contribution to the understanding of the ontogenesis of cardiac pumping function

The cardiac cycle-related deformations of tubular embryonic hearts were traditionally described as concentric narrowing and widening of a tube of circular cross-section. Using optical coherence tomography (OCT), we have recently shown that, during the cardiac cycle, only the myocardial tube undergoes concentric narrowing and widening while the endocardial tube undergoes eccentric narrowing and widening, having an elliptic cross-section at end-diastole and a slit-shaped cross-section at end-systole. Due to technical limitations, these analyses were confined to early stages of ventricular development (chick embryos, stages 10-13). Using a modified OCT-system, we now document, for the first time, the cyclic changes in cross-sectional shape of beating embryonic ventricles at stages 14 to 17. We show that during these stages (1) a large area of diminished cardiac jelly appears at the outer curvature of the ventricular region associated with formation of endocardial pouches; (2) the ventricular endocardial lumen acquires a bell-shaped cross-section at end-diastole and becomes compressed like a fireplace bellows during systole; (3) the contracting portions of the embryonic ventricles display stretching along its baso-apical axis at end-systole. The functional significance of our data is discussed with respect to early cardiac pumping function.