Stimulation of TM3 Leydig cell proliferation via GABA(A )receptors: A new role for testicular GABA

The neurotransmitter gamma-aminobutyric acid (GABA) and subtypes of GABA receptors were recently identified in adult testes. Since adult Leydig cells possess both the GABA biosynthetic enzyme glutamate decarboxylase (GAD), as well as GABA(A )and GABA(B )receptors, it is possible that GABA may act as auto-/paracrine molecule to regulate Leydig cell function. The present study was aimed to examine effects of GABA, which may include trophic action. This assumption is based on reports pinpointing GABA as regulator of proliferation and differentiation of developing neurons via GABA(A )receptors. Assuming such a role for the developing testis, we studied whether GABA synthesis and GABA receptors are already present in the postnatal testis, where fetal Leydig cells and, to a much greater extend, cells of the adult Leydig cell lineage proliferate. Immunohistochemistry, RT-PCR, Western blotting and a radioactive enzymatic GAD assay evidenced that fetal Leydig cells of five-six days old rats possess active GAD protein, and that both fetal Leydig cells and cells of the adult Leydig cell lineage possess GABA(A )receptor subunits. TM3 cells, a proliferating mouse Leydig cell line, which we showed to possess GABA(A )receptor subunits by RT-PCR, served to study effects of GABA on proliferation. Using a colorimetric proliferation assay and Western Blotting for proliferating cell nuclear antigen (PCNA) we demonstrated that GABA or the GABA(A )agonist isoguvacine significantly increased TM3 cell number and PCNA content in TM3 cells. These effects were blocked by the GABA(A )antagonist bicuculline, implying a role for GABA(A )receptors. In conclusion, GABA increases proliferation of TM3 Leydig cells via GABA(A )receptor activation and proliferating Leydig cells in the postnatal rodent testis bear a GABAergic system. Thus testicular GABA may play an as yet unrecognized role in the development of Leydig cells during the differentiation of the testicular interstitial compartment

Evidence for a GABAergic system in rodent and human testis: Local GABA production and GABA receptors

The major neurotransmitter of the central nervous system, gamma-aminobutyric acid (GABA), exerts its actions through GABA(A), GABA(B) and GABA(C) receptors. GABA and GABA receptors are, however, also present in several non-neural tissues, including the endocrine organs pituitary, pancreas and testis. In the case of the rat testis, GABA appears to be linked to the regulation of steroid synthesis by Leydig cells via GABA(A) receptors, but neither testicular sources of GABA, nor the precise nature of testicular GABA receptors are fully known. We examined these points in rat, mouse, hamster and human testicular samples. RT-PCR followed by sequencing showed that the GABA-synthesizing enzymes glutamate decarboxylase (GAD) 65 and/or GAD67, as well as the vesicular GABA transporter vesicular inhibitory amino acid transporter (VIAAT/VGAT) are expressed. Testicular GAD in the rat was shown to be functionally active by using a GAD assay, and Western blot analysis confirmed the presence of GAD65 and GAD67. Interstitial cells, most of which are Leydig cells according to their location and morphological characteristics, showed positive immunoreaction for GAD and VIAAT/VGAT proteins. In addition, several GABA(A) receptor subunits (alpha1-3, beta1-3, gamma1-3), as well as GABAB receptor subunits R1 and R2, were detected by RT-PCR. Western blot analysis confirmed the results for GABA(A) receptor subunits beta2/3 in the rat, and immunohistochemistry identified interstitial Leydig cells to possess immunoreactive GABA(A) receptor subunits beta2/3 and alpha1. The presence of GABA(A) receptor subunit alpha1 mRNA in interstitial cells of the rat testis was further shown after laser microdissection followed by RT-PCR analysis. In summary, these results describe molecular details of the components of an intratesticular GABAergic system expressed in the endocrine compartment of rodent and human testes. While the physiological significance of this peripheral neuroendocrine system conserved throughout species remains to be elucidated, its mere presence in humans suggests the possibility that clinically used drugs might be able to interfere with testicular function. Copyright (C) 2003 S. Karger AG, Basel

Improving the light yield and timing resolution of scintillator-based detectors for positron emission tomography

Positronen-Emissions-Tomographie (PET) ist eine funktionelle medizinische Bildgebungstechnik. Die Lichtausbeute und Zeitauflösung Szintillator basierter PET Detektoren wird von diversen optischen Prozessen begrenzt. Dazu gehört die Lichtauskopplung aus Medien mit hohem Brechungsindex sowie Sensitivitätsbegrenzungen der Photodetektoren. Diese Arbeit studiert mikro- und nano-optische Ansätze um diese Einschränkungen zu überwinden mit dem Ziel das Signal-Rausch Verhältnis sowie die Bildqualität zu verbessern. Dafür wird ein Lichtkonzentrator vorgeschlagen um die Sensitivität von Silizium Photomultipliern zu erhöhen sowie dünne Schichten photonischer Kristalle um die Lichtauskopplung aus Szintillatoren zu verbessern. Die Ansätze werden mit optischen Monte Carlo Simulationen studiert, wobei die Beugungseigenschaften phot. Kristalle hierbei durch eine neuartige kombinierte Methode berücksichtigt werden. Proben der phot. Kristalle und Lichtkonzentratoren wurden mit Fertigungsprozessen der Halbleitertechnologie hergestellt und mit Hilfe eines Goniometer Aufbaus charakterisiert. Die simulierten Eigenschaften konnten hiermit sehr gut experimentell reproduziert werden. Daraufhin wurden Simulationen durchgeführt um den Einfluss beider Konzepte auf die Charakteristika eines PET Detektors zu untersuchen. Diese sagen signifikante Verbesserungen der Lichtausbeute und Zeitauflösung voraus. Darüber hinaus zeigen sie, dass sich auch die Kombination beider Ansätze positiv auf die Detektoreigenschaften auswirken. Diese Ergebnisse wurden in Lichtkonzentrator-Experimenten mit einzelnen Szintillatoren bestätigt. Da die Herstellung phot. Kristalle eine große technologische Herausforderung darstellt, wurde eine neue Fertigungstechnik namens "direct nano imprinting" entwickelt. Dessen Machbarkeit wurde auf Glasswafern demonstriert. Die Arbeit endet mit einer Diskussion der Vor- und Nachteile von Lichtkonzentratoren und phot. Kristallen und deren Implikationen für zukünftige PET Systeme.Positron emission tomography (PET) is a powerful medical imaging methodology to study functional processes. The light yield and coincident resolving time (CRT) of scintillator-based PET detectors are constrained by optical processes. These include light trapping in high refractive index media and incomplete light collection by photosensors. This work proposes the use of micro and nano optical devices to overcome these limitations with the ultimate goal to improve the signal-to-noise ratio and overall image quality of PET acquisitions. For this, a light concentrator (LC) to improve the light collection of silicon photomultipliers on the Geiger-cell level is studied. Further, two-dimensional photonic crystals (PhCs) are proposed to reduced light trapping in scintillators. The concepts are studied in detail using optical Monte Carlo simulations. To account for the diffractive properties of PhCs, a novel combined simulation approach is presented that integrates results of a Maxwell solver into a ray tracing algorithm. Samples of LCs and PhCs are fabricated with various semiconductor technologies and evaluated using a goniometer setup. A comparison between measured and simulated angular characteristics reveal very good agreement. Simulation studies of implementing LCs and PhCs into a PET detector module predict significant improvements of the light yield and CRT. Also, combining both concepts indicates no adverse effects but a rather a cumulative benefit for the detector performance. Concentrator experiments with individual scintillators confirm these simulation results. Realizing the challenges of transferring PhCs to scintillators, a novel fabrication method called direct nano imprinting is evaluated. The feasibility of this approach is demonstrated on glass wafers. The work concludes with a discussion of the benefits and drawbacks of LCs and PhCs and their implications for future PET systems

Error analysis of high-order splitting methods for nonlinear evolutionary Schrödinger equations and application to the MCTDHF equations in electron dynamics

In this work, the error behaviour of high-order exponential operator splitting methods for the time integration of nonlinear evolutionary Schrödinger equations is investigated. The theoretical analysis utilises the framework of abstract evolution equations on Banach spaces and the formal calculus of Lie derivatives. The general approach is substantiated on the basis of a convergence result for exponential operator splitting methods of (nonstiff) order p applied to the multi-configuration time-dependent Hartree–Fock (MCTDHF) equations, which are associated with a model reduction for high-dimensional linear Schrödinger equations describing free electrons that interact by Coulomb force. Provided that the analytical solution of the MCTDHF equations constituting a system of coupled linear ordinary differential equations and low-dimensional nonlinear partial differential equations satisfies suitable regularity requirements, convergence of order p − 1 in the H1 Sobolev norm and convergence of order p in the L2 norm is proven. An analogous result follows for the cubic nonlinear Schrödinger equation, which is also illustrated by a numerical experiment

Synopsis of multi-echo gradient echo strategies used for T₂^* mapping at 7.0 T.

<p><b>A).</b> Conventional multi-echo (<b>ME</b>) gradient echo for single cardiac phase myocardial T₂^* mapping. Multiple echoes are acquired after excitation to obtain a set of T₂^* weighted images. The competing constraints of inter echo time and spatial resolution inherent to the <b>ME</b> approach are addressed by the <b>B</b>) interleaved multi-shot multi-echo (<b>MS</b>) gradient echo technique. In <b>MS</b> a set of excitations is employed together with echo interleaving echoes to acquire a set of T₂^* weighted images. <b>C</b>) The multi-breath-hold multi-echo (<b>MB CINE</b>) gradient echo technique allows myocardial CINE T₂^* mapping by interleaving the echoes over several breath-holds. For benchmarking <b>D</b>) multi-echo CINE (<b>ME CINE</b>) gradient echo and <b>E</b>) multi-shot multi-echo CINE (<b>MS CINE</b>) were applied for T₂^* mapping in phantom studies. To guide the eye vertical dashed lines refer to k-space lines. Vertical solid lines refer to cardiac phases. A unipolar readout using gradient flyback was applied for all strategies.</p

B₀ distribution for global and volume selective shimming of a mid-ventricular short axis view of the heart.

<p><b>A</b>) Mid-ventricular short axis view of the heart illustrating the positioning of the volume (marked in red) used for volume selective shimming. <b>B</b>) B₀ field maps. <b>C</b>) B₀ profile along the direction of the strongest B₀ gradient which is highlighted by the dashed black line in <b>B</b>). To guide the eye the epicardial borders are marked in <b>B</b>) and <b>C</b>) by two triangles. <b>D</b>) Frequency histogram across the left ventricle. After volume selective shimming a strong susceptibility gradient at the inferior region of the heart could be reduced. The full width at half maximum is approximately 300 Hz for the globally shimmed field map and was reduced to about 80 Hz after volume selective shimming.</p

CINE T₂^* maps over the cardiac cycle.

<p>Short axis view T₂^* colour maps derived from <b>MB CINE</b> acquisitions across the cardiac cycle overlaid to conventional 2D CINE FLASH images. T₂^* values are increasing from diastole to systole, especially for endocardial layers. Macroscopic susceptibility induced T₂^* reduction effects were present at the epicardium at inferior regions.</p

B₀ distribution for global and volume selective B₀ shimming of a four chamber view of the heart.

<p><b>A</b>) Four chamber view of the heart illustrating the positioning of the volume (marked in red) used for global (left) and volume selective (right) shimming. <b>B</b>) B₀ field variation derived from global and volume selective shimming. For this subject the global shim provided a peak-to-peak field variation of about 400 Hz across the entire heart. After volume selective shimming peak-to-peak B₀ variation across the heart was reduced to approximately 80 Hz. The direction of the maximal B₀ gradient is illustrated by the dashed black line in <b>B</b>) and the corresponding profile of B₀ field distribution is plotted in <b>C</b>). To guide the eye the epicardial borders are marked in <b>B</b>) and <b>C</b>) by two triangles. The histogram of the field distribution over the left ventricle is shown in <b>D</b>). The full width at half maximum is approximately 200 Hz for the globally shimmed B₀ field map and was reduced to about 80 Hz after volume selective shimming.</p

T₂^* maps derived from single cardiac phase and dynamic CINE mapping of a four chamber and short axis view of the heart at end-diastole and end-systole.

<p>Four chamber (top) and short axis view T₂^* colour maps obtained from <b>MS</b> and <b>MB CINE</b> superimposed to anatomical 2D CINE FLASH gray scale images. For <b>MB CINE</b> a systolic and diastolic phase was chosen to match the cardiac phase with the end-systolic and end-diastolic phase derived from <b>MS</b>. T₂^* maps deduced from <b>MS</b> and <b>MB CINE</b> showed no significant differences between both methods in the segmental analysis of T₂^* values. When comparing systolic and diastolic T₂^* maps significant differences were found with p = 0.002 for MS and p = 0.01 for <b>MB CINE</b>.</p