Experimental Study on the Contact Freezing of Supercooled Micro-Droplets in Electrodynamic Balance

The aim of this work, was to investigate the heterogeneous ice nucleation of supercooled micro-droplets induced by contact with an ice nucleating particle (INP). The contact freezing is poorly quantified but can be potentially important for understanding precipitation mechanisms via cloud glaciation in mixed clouds. The contact freezing results are compared to results of freezing experiments in the immersion mode. The same INP is ice active at higher temperatures in the contact mode than in the immersion mode. An electrodynamic balance was used to levitate single, supercooled micro-droplets of deionized water. The droplet is exposed to a flow of mobility-selected aerosol particles. The injection of droplets and the detection of freezing events is automated. In this experiment, it is possible to calculate the collision rate separately, and the probability of freezing on a single contact. Furthermore, immersion freezing experiments are performed in the same experimental setup, and a direct comparison between immersion and contact mode is possible. As ice nucleating particles, some relevant atmospheric minerals (hematite, feldspar, illite, kaolinite), cellulose, SNOMAX®, birch pollen washing water and a mixture of illite and birch pollen washing water have been investigated. The resulting contact freezing probabilities show a temperature, particle size, and material dependency. For comparison of immersion and contact freezing results an Ice Nucleating Active Site (INAS) density has been calculated. With exclusion of SNOMAX® and birch pollen washing water, all particles have been shown to be more ice active in the contact freezing mode than in immersion mode

Synaptische Pathologie in Tau-transgenen Mausmodellen neurodegenerativer Erkrankungen

In Zeiten des demografischen Wandels erfahren Krankheiten wie die Alzheimer-Demenz, als deren größter Risikofaktor das Alter gilt, einen rasanten Anstieg der Patientenzahl. Die Erforschung der zugrundeliegenden neurodegenerativen Mechanismen und das Einbringen daraus gewonnener Erkenntnisse in die Entwicklung von Therapieansätzen oder gar Präventionsmaßnahmen sind daher von gesamtgesellschaftlicher Bedeutung - nicht zuletzt auch unter ökonomischen Gesichtspunkten, wie den gleichsam wachsenden Kosten für das Gesundheitssystem. In der vorliegenden Arbeit wurden neuropathologische Prozesse in verschiedenen transgenen Tauopathie-Mausmodellen mittels hochauflösender Mikroskopietechniken untersucht. Der Schwerpunkt lag hierbei auf der Analyse synaptischer Veränderungen im lebenden Tier, ermöglicht durch die Zwei-Photonen-Intravitalmikroskopie. Zunächst wurden in Tau P301S-Mäusen die Auswirkungen FTDP-17-mutierten humanen Tau-Proteins auf die strukturelle Plastizität neokortikaler dendritischer Spines analysiert. Dabei wurde eine im Vergleich zu Wildtyp-Mäusen verminderte Spinedichte gemessen, welche auf eine geringere Ausbildung neuer Spines zurückzuführen war. Die verbliebenen Spines zeigten morphologische Veränderungen wie ein vergrößertes Kopfvolumen - möglicher Weise zur Kompensation des Synapsenverlusts. Ergänzend wurde eine Methode zur immunhistochemischen Synapsendichtemessung an Gehirnschnitten etabliert, welche jedoch keine Effekte der Transgenexpression auf die Dichte prä- oder postsynaptischer Spezialisierungen offenbarte. Um die Rolle inflammatorischer Prozesse in Tauopathien zu analysieren, wurde die Mauslinie Tau x CXCR erzeugt. Partielle oder vollständige genetische Fraktalkinrezeptor-Deletion in diesen Mäusen erlaubte eine gezielte Modifizierung der Kommunikation zwischen Neuronen und Mikrogliazellen. Die resultierende Aktivitätserhöhung der Mikrogliazellen hatte wider Erwarten keinen signifikanten Einfluss auf die Dichte Phospho-Tau enthaltender Zellen in den untersuchten kortikalen Gehirnregionen. Zur Modellierung der Alzheimer-Demenz wurden Tau P301S-Mäuse mit der Linie APP PS1 verpaart. Die Nachkommen wiesen Alzheimer-typische histologische Läsionen wie extrazelluläre Aβ-Plaques und intrazelluläre Tau-Ablagerungen auf. Es konnte jedoch im Vergleich zur Ursprungslinie Tau P301S keine Aβ-induzierte Verstärkung der kortikalen Tau-Pathologie gemessen werden, welche die Amyloid-Kaskaden-Hypothese suggeriert. Eine intravitalmikroskopische Analyse dendritischer Spines in Tau P301S- und Tau x APP PS1-Mäusen in unterschiedlichen Krankheitsstadien sowie in Wildtyp-Wurfgeschwistern sollte die Abgrenzung Tau-bedingter von Aβ-bedingten Effekten ermöglichen. Dabei wurden Veränderungen in der strukturellen Plastizität gefunden, beispielsweise in der Spine-Neuausbildung oder in bestimmten morphologischen Fraktionen, nicht aber in der absoluten Spinedichte. Schließlich erfolgte eine elektronenmikroskopische Untersuchung neuritischer Dystrophien in einem weiteren Alzheimer-Mausmodell, der Linie 3xTg-AD. Durch immunhistochemische Markierung konnten sowohl Aβ- als auch Tau-Ansammlungen in den pathologischen Anschwellungen nachgewiesen werden. Die präsentierten Befunde zeigen u. a. die ersten intravitalmikroskopischen Langzeitstudien dendritischer Spines in Mausmodellen mit reiner Tau-Pathologie sowie damit kombinierter Aβ-Pathologie. Sie bieten grundlegende, durch Patientenuntersuchungen nicht zu gewinnende Informationen über krankhafte synaptische Veränderungen, welche als frühe Ereignisse in der Alzheimer-Demenz betrachtet werden.In times of demographic changes, a rapidly increasing number of people get affected by diseases such as Alzheimer’s disease. For this most common type of dementia, age is the main risk factor. Therefore, it is of great importance for the whole society to illuminate the underlying neurodegenerative mechanisms and to apply the gained knowledge to the development of therapeutic or even preventive procedures – not least for economic reasons, considering the simultaneously growing costs for the health care system. In the presented study, neuropathological processes in different transgenic tauopathy mouse models were investigated by means of high-resolution microscopy. The main focus was set on the analysis of synaptic changes in the living animal, enabled by two-photon in vivo imaging. At first, the effects of FTDP-17 mutated human tau-protein on the structural plasticity of neocortical dendritic spines were analysed in Tau P301S mice. In comparison to wildtype mice, the spine density was found to be reduced, which could be explained by a diminished fraction of newly formed spines. The remaining spines showed morphological changes such as an enlarged head volume, possibly compensating for the loss of synapses. Moreover, a method was established for immunohistochemical determination of synaptic densities on brain slices. However, no effect of transgene expression on the density of pre- or postsynaptic specializations could be measured. For studying the role of inflammatory processes in tauopathies, the mouse line Tau x CXCR was bred. Partial or complete deletion of the fractalkine receptor gene in these mice allowed a selective modification of the communication between neurons and microglia. Unexpectedly, the resulting increase of microglia activity did not have an influence on the density of phospho-tau bearing cells in the analysed brain regions. In order to create a model of Alzheimer’s disease, Tau P301S mice were further crossed with the line APP PS1. The offspring showed histological lesions typical for this kind of dementia, such as extracellular Aβ-plaques and intracellular tau-deposits. However, in comparison to the founder line Tau P301S, no Aβ-induced enhancement of cortical tau pathology could be measured, unlike suggested by the amyloid-cascade-hypothesis. An in vivo analysis of dendritic spines in Tau P301S and Tau x APP PS1 mice at different stages of the disease, as well as in wildtype littermates, allowed to distinguish effects caused by tau from those caused by Aβ. Thereby, changes in structural plasticity such as the emergence of new spines or the distribution of morphological fractions were detected, while the overall spine density was unaffected. Finally, neuritic dystrophies were analysed in another Alzheimer’s disease mouse model, the line 3xTg-AD, applying electron microscopy. By immunohistochemical labelling, Aβ- as well as tau-deposits could be detected inside the pathological swellings. The presented data show the first in vivo long-term study on dendritic spines in mouse models with tau-pathology only as well as in combination with Aβ-pathology. They provide new basic information about synaptic failure, which is considered to be an early event in Alzheimer’s disease and can not be obtained from patient studies likewise

Eureka-Moments in Transformers: Multi-Step Tasks Reveal Softmax Induced Optimization Problems

In this work, we study rapid, step-wise improvements of the loss in transformers when being confronted with multi-step decision tasks. We found that transformers struggle to learn the intermediate tasks, whereas CNNs have no such issue on the tasks we studied. When transformers learn the intermediate task, they do this rapidly and unexpectedly after both training and validation loss saturated for hundreds of epochs. We call these rapid improvements Eureka-moments, since the transformer appears to suddenly learn a previously incomprehensible task. Similar leaps in performance have become known as Grokking. In contrast to Grokking, for Eureka-moments, both the validation and the training loss saturate before rapidly improving. We trace the problem back to the Softmax function in the self-attention block of transformers and show ways to alleviate the problem. These fixes improve training speed. The improved models reach 95% of the baseline model in just 20% of training steps while having a much higher likelihood to learn the intermediate task, lead to higher final accuracy and are more robust to hyper-parameters

Gap Junction Dependent Cell Communication Is Modulated During Transdifferentiation of Mesenchymal Stem/Stromal Cells Towards Neuron-Like Cells

In vitro transdifferentiation of patient-derived mesenchymal stem/stromal cells (MSCs) into neurons is of special interest for treatment of neurodegenerative diseases. Although there are encouraging studies, little is known about physiological modulations during this transdifferentiation process. Here, we focus on the analysis of gap junction dependent cell-cell communication and the expression pattern of gap junction-building connexins during small molecule-induced neuronal transdifferentiation of human bone marrow-derived MSCs. During this process, the MSC markers CD73, CD90, CD105, and CD166 were downregulated while the neuronal marker Tuj1 was upregulated. Moreover, the differentiation protocol used in the present study changed the cellular morphology and physiology. The MSCs evolved from a fibroblastoid morphology towards a neuronal shape with round cell bodies and neurite-like processes. Moreover, depolarization evoked action potentials in the transdifferentiated cells. MSCs expressed mRNAs encoding Cx43 and Cx45 as well as trace levels of Cx26, Cx37- and Cx40 and allowed transfer of microinjected Lucifer yellow. The differentiation protocol increased levels of Cx26 (mRNA and protein) and decreased Cx43 (mRNA and protein) while reducing the dye transfer. Cx36 mRNA was nearly undetectable in all cells regardless of treatment. Treatment of the cells with the gap junction coupling inhibitor carbenoxolone (CBX) only modestly altered connexin mRNA levels and had little effect on neuronal differentiation. Our study indicates that the small molecule-based differentiation protocol generates immature neuron-like cells from MSCs. This might be potentially interesting for elucidating physiological modifications and mechanisms in MSCs during the initial steps of differentiation towards a neuronal lineage

Long-term in vivo imaging of fibrillar tau in the retina of P301S transgenic mice.

Tauopathies are widespread neurodegenerative disorders characterised by the intracellular accumulation of hyperphosphorylated tau. Especially in Alzheimer's disease, pathological alterations in the retina are discussed as potential biomarkers to improve early diagnosis of the disease. Using mice expressing human mutant P301S tau, we demonstrate for the first time a straightforward optical approach for the in vivo detection of fibrillar tau in the retina. Longitudinal examinations of individual animals revealed the fate of single cells containing fibrillar tau and the progression of tau pathology over several months. This technique is most suitable to monitor therapeutic interventions aimed at reducing the accumulation of fibrillar tau. In order to evaluate if this approach can be translated to human diagnosis, we tried to detect fibrillar protein aggregates in the post-mortem retinas of patients that had suffered from Alzheimer's disease or Progressive Supranuclear Palsy. Even though we could detect hyperphosphorylated tau, we did not observe any fibrillar tau or Aß aggregates. In contradiction to previous studies, our observations do not support the notion that Aβ or tau in the retina are of diagnostic value in Alzheimer's disease

High sensitivity troponin T and I reflect mitral annular plane systolic excursion being assessed by cardiac magnetic resonance imaging

Purpose: This study aims to evaluate the association between high sensitivity troponins (hsTn) and mitral annular plane systolic excursion (MAPSE) in patients undergoing cardiac magnetic resonance imaging (cMRI). Methods: Patients undergoing cMRI were prospectively enrolled. Patients with right ventricular dysfunction(< 50%) were excluded. Blood samples for measurements of hsTn and amino-terminal pro-brain natriuretic peptide (NT-proBNP) were collected at the time of cMRI. Results: 84 patients were included. Median left ventricular ejection fraction was 59% (IQR 51–64%). HsTn were correlated inversely with MAPSE within multivariable linear regression models (hsTnI: Beta − 0.19; T − 1.96; p = 0.05; hsTnT: Beta − 0.26; T − 3.26; p = 0.002). HsTn increased significantly according to decreasing stages of impaired MAPSE (p < 0.003). HsTn discriminated patients with impaired MAPSE < 11 mm (hsTnT: AUC = 0.67; p = 0.008; hsTnI: AUC = 0.64; p = 0.03) and < 8 mm (hsTnT: AUC = 0.79; p = 0.0001; hsTnI: AUC = 0.75; p = 0.001) and were still significantly associated in multivariable logistic regression models with impaired MAPSE < 11 mm (hsTnT: OR = 4.71; p = 0.002; hsTnI: OR = 4.22; p = 0.009). Conclusions: This study demonstrates that hsTn are able to reflect MAPSE being assessed by cMRI