Increased Neuronal Nitric Oxide Synthase in Alzheimer's Disease Mediates Spontaneous Calcium Signaling and Divergent Glutamatergic Calcium Responses

Nitrosative stress is a feature of Alzheimer's disease (AD). Aims: We aimed to identify the cause underpinning increased nitric oxide (NO) in neurons and the impact of NO on neuronal function in AD. Results: We analyzed neuronal nitric oxide synthase (nNOS) protein levels in postmortem tissue and induced pluripotent stem cell (iPSC)-derived neurons from Alzheimer's patients and controls by immunohistochemistry and Western blots. Furthermore, we assessed the impact of modulating nNOS function or NO levels on neuronal glutamatergic signaling using calcium imaging. We show that nNOS protein levels are increased in early and severely affected brain regions of AD postmortem tissue, but not late and mildly affected regions, or cognitively normal individuals. The increased nNOS phenotype was also present in iPSC-derived neurons from late-onset Alzheimer's disease (LOAD) patients compared with controls, along with increased levels of nitrite, a stable marker of NO. Innovation: We observed a divergent functional impact of NO that included strengthening the calcium response in control neurons, while dysregulating calcium signaling and altering the amplitude and kinetics of the calcium responses to glutamate in the AD neurons. Pharmacological scavenging of NO or inhibition of nNOS prevented aberrant spontaneous calcium signaling in AD neurons. Conclusion: Together these data identify increases in nNOS protein in AD. Functional data suggest that NO modulation of glutamatergic calcium signaling is neuroprotective under nonpathogenic conditions, with increased nNOS and NO contributing to dysregulated spontaneous calcium signaling in AD neurons.

Standardized angiographic projections allow evaluation of coronary artery side branches with quantitative flow ratio (QFR)

Quantitative flow ratio (QFR) is a novel, software-based noninvasive method for the quantitative evaluation of coronary physiology. QFR results correlate with invasive FFR measurements in the three main epicardial coronary arteries. However, QFR data for the evaluation of coronary side branches (SB) are scarce. The evaluation of QFR-performance of SB was retrospective and prospective. Eighty-seven patients with suspected chronic coronary syndrome, who received angiography using routine core lab projections, were retrospectively analyzed. On the second part 37 patients, who received angiography using recommended standardized coronary angiography projections, were prospectively analyzed. Quantitative analysis was performed for SB with a maximum lumen diameter proximal of ≥2 mm based on quantitative coronary angiography (QCA) by two certified experts with the software QAngio XA 3D 3.2. Using routine projections, QFR computation in 55 % of the SB were obtained (123 out of 224). Using standardized projections, 85 % of SB were computed by QFR (64 out of 75; p < 0.001 vs routine projections). The fluoroscopy time for recommended projections was not significantly different as opposed to routine projections (3.75 ± 2.2 vs. 4.58 ± 3.00 min, p = 2.6986). Using the standardized projections was associated with a higher amount of contrast medium (53.44 ± 24.23 vs. 87.95 ± 43.73 ml, p < 0.01), longer overall procedure time (23.23 ± 16.35 vs. 36.14 ± 17.21 min, p < 0.01) and a higher dose area product (1152.28 ± 576.70 vs. 2540.68 ± 1774.07 cGycm2, p < 0.01). Our study shows that the blood flow of the vast majority of coronary SB can be determined non-invasively by QFR in addition to the main epicardial coronary arteries when standardized projections are used.

Parameter Inference for an Astrocyte Model using Machine Learning Approaches

Astrocytes are the largest subset of glial cells and perform structural, metabolic, and regulatory functions. They are directly involved in the communication at neuronal synapses and the maintenance of brain homeostasis. Several disorders, such as Alzheimer's, epilepsy, and schizophrenia, have been associated with astrocyte dysfunction. Computational models on various spatial levels have been proposed to aid in the understanding and research of astrocytes. The difficulty of computational astrocyte models is to fastly and precisely infer parameters. Physics informed neural networks (PINNs) use the underlying physics to infer parameters and, if necessary, dynamics that can not be observed. We have applied PINNs to estimate parameters for a computational model of an astrocytic compartment. The addition of two techniques helped with the gradient pathologies of the PINNS, the dynamic weighting of various loss components and the addition of Transformers. To overcome the issue that the neural network only learned the time dependence but did not know about eventual changes of the input stimulation to the astrocyte model, we followed an adaptation of PINNs from control theory (PINCs). In the end, we were able to infer parameters from artificial, noisy data, with stable results for the computational astrocyte model.

Comparison of quantitative flow ratio (QFR) and instantaneous wave-free ratio (iFR) or resting full-cycle ratio (RFR) during daily routine in the catheterization laboratory

Background

The prognosis of patients with coronary artery disease (CAD) depends strongly on the hemodynamic relevance of the stenosis. The gold standard is the invasive evaluation of the stenosis using Fractional Flow Reserve (FFR), instantaneous wave-free ratio (iFR) or Resting Full-Cycle Ratio (RFR). The use of invasive procedures remains low due to procedural factors and costs. Quantitative Flow Ratio (QFR) is a novel, software-based method to evaluate the physiology of coronary lesions during cardiac catheterization. Computing a three-dimensional model of the vessel based on two angiographic recordings and analyzing the fluid dynamics of the contrast medium flow, the software computes the FFR. In the setting of clinical studies, it has been demonstrated that QFR is feasible and correlates well with FFR. The aim of this study is to compare feasibility and reliability of QFR with established measurements of the iFR or RFR in daily routine.

Methods

Patients with an indication for an invasive coronary angiography and a stenosis of 30 to 90% were simultaneously assessed using QFR and iFR/RFR in a routine setting. The QFR-computation was performed online by a certified expert with QAngio XA 3D 3.2. The following outcome parameters were analyzed: time to result, volume of applicated contrast medium, applicated dose area product, result of the evaluation. The results have been registered for both methods, respectively.

Results

102 coronary arteries were analyzed using QFR and iFR or RFR. QFR shows a good correlation (r=0.753, AUC=0.922) and accuracy (agreement 89.22%, sensitivity 95.83%, specificity 83.33%, PPV 83.64%, NPV 95.74%). The data show that QFR delivers significantly faster results and reduces the procedure related applicated radiation dose from in median 598.8 cGy cm2 to 306.75 cG ycm2 (p&lt;0.001). The study shows no significant difference regarding the amount of contrast medium used.

Conclusion

QFR has a good diagnostic agreement and can reduce procedure length and applicated radiation dose. Thereby QFR could increase the use of physiologically guided coronary interventions in daily routine.

Funding Acknowledgement

Type of funding sources: None.

Evaluation of coronary artery side branches (SB) with Quantitative Flow Ratio (QFR) by comparing the use of recommended angiographic projections with routine angiographic projections as Reference

Background

Contrast-flow quantitative flow ratio (QFR) is a novel, noninvasive method for the quantitative evaluation of coronary physiology using computational fluid dynamics based on 3D vessel reconstruction in angiograms. Computing this 3D-model with analyzing the dynamics of the contrast medium flow with a specialized algorithm, the software computes the virtual FFR. This new technique has shown a high accuracy in determining the functional significance of coronary stenosis of the three main epicardial coronary arteries using the gold standard FFR as reference. However, QFR data for the evaluation of coronary side branches (SB) are scarce. Therefore, the study aimed to determine the feasibility of this novel method to analyze SB and to characterize optimal viewing angles for evaluation using QFR.

Methods

A total of 87 patients, who underwent invasive coronary angiography with routine core lab projections, were enrolled in the study and were analyzed retrospectively by two certified experts with the software QAngio XA 3D 3.2. In addition, 37 patients were enrolled prospectively using coronary angiography projections recommended for the virtual QFR-Analysis. Quantitative Analysis was performed only for SB with a maximum lumen diameter (MLD) of ≥2mm. The following outcome parameters were analyzed: baseline characteristics, anatomical SB parameters such as MLD (mm) and vessel length (VL; mm) of the SB, result of the QFR-computation and procedure parameters, such as use of applicated contrast medium and fluoroscopy time.

Results

187 side branches (obtuse marginal [OM], diagonal branch [DB], intermediate artery [IA], posterolateral branch [PLB] and posterior descending artery [PDA]) were analyzed using QFR. Out of 87 patients undergoing an invasive coronary angiography with routine core lab projections with 244 SB ≥2mm, 123 SB (55%) were computable with the use of QFR. In the prospective cohort of 37 patients with recommended angiographic projections for QFR analysis of main branches, 75 SB ≥2mm were found. 64 of the 75 SB (84%) were computable with the use of QFR. The use of recommended projections led to an overall higher evaluability of SB (85% vs. 55%). The data show that the fluoroscopy time for recommended QFR projections was not significantly different as the time for routine cath lab projections (3.7±2.2 vs. 4.6±3, p=2.69). The study shows a significant increase of the amount of contrast medium used for QFR projections (55.4±24.2 vs. 87.9±43.7, p&lt;0.01).

Conclusion

To our knowledge this is the first study evaluating QFR for SB analysis. QFR is feasible for the routine assessment of side branches (SD) with MLD ≥2mm. The use of recommended projections significantly improved the quality of the QFR SB analysis apart from PDA, without increasing the fluoroscopy time during coronary angiography. Overall QFR could increase the use of physiologically guided coronary interventions, not only for the main epicardial vessels, but also for the SB.

Funding Acknowledgement

Type of funding sources: None.

Wie geht es dem akademischen Mittelbau?

Zum sogenannten Mittelbau zählen Doktoranden und Doktorandinnen, Postdocs, Nachwuchsgruppenleiter und -leiterinnen, Junior- und Tenure-Track-Professoren und -Professorinnen. Insbesondere Promovierende sowie Postdoktoranden und Postdoktorandinnen sind, noch mehr als früher, von den komplexen strukturellen und finanziellen Problematiken des Wissenschafts- und Lehrbetriebs betroffen, und das in vielerlei Hinsicht über Fächer hinweg. Der Flaschenhals auf dem Weg zur Professur oder einer anderweitig verstetigten Forschungs- oder Lehrstelle führt in der akademischen Karriere zu prekären Beschäftigungsverhältnissen. Die schwierige Vereinbarkeit von Familie und akademischer Karriere erzeugt eine zusätzliche Benachteiligung, insbesondere von Wissenschaftlerinnen. Mangelnde Qualitätssicherung sowie fehlende zuverlässige und vertrauenswürdige Prozesse erschweren die Aufdeckung und Aufarbeitung von Konflikten während der Promotionsphase und der Zeit des Postdoktorats. Der Beirat des wissenschaftlichen Nachwuchses (GI-WiN) der Gesellschaft für Informatik e. V. (GI) fordert und empfiehlt in einem Positionspapier (10.1007/s00287-020-01250-x) mehrere Maßnahmen zur Stabilisierung von Karriere- und Beschäftigungssituation des Mittelbaus. Der vorliegende Artikel fasst die Ergebnisse einer Umfrage zur Ergänzung und empirischen Untermauerung dieser Empfehlungen zusammen. Die vorliegende Umfrage wurde mit dem Anspruch erhoben, Daten aus allen Fachbereichen – nicht nur der Informatik – zu sammeln. In den Ergebnissen zeigte sich, dass diesen vielfältigen Herausforderungen begegnet werden muss, die in Nicht-MINT-Fächern und MINT-Fächern ähnlich empfunden werden. Die Schaffung von unbefristeten Stellen für die Phase nach der Promotion wurde im Rahmen der Umfrage als besonders wünschenswert angesehen. Vorgeschlagen wurde auch die Abschaffung von Lehrstühlen und die Einführung einer Departmentstruktur. Des Weiteren wurde die Trennung von Begutachtung und Betreuung vor allem bei der Promotion angeregt. Die letzten 2 Jahre im Zeichen der COVID-19-Pandemie waren für einen großen Teil der Betroffenen von fehlendem fachlichen Austausch und sowohl beruflichen als auch privaten Zusatzbelastungen geprägt. Diese Ergebnisse können über die genannten Fachbereiche hinaus eine Entscheidungsgrundlage für eine gerechtere Wissenschaftspolitik liefern und bessere Arbeits- und Karrierebedingungen für den wissenschaftlichen Nachwuchs erwirken.

Astrocytes Exhibit a Protective Role in Neuronal Firing Patterns under Chemically Induced Seizures in Neuron-Astrocyte Co-Cultures

Astrocytes and neurons respond to each other by releasing transmitters, such as γ-aminobutyric acid (GABA) and glutamate, that modulate the synaptic transmission and electrochemical behavior of both cell types. Astrocytes also maintain neuronal homeostasis by clearing neurotransmitters from the extracellular space. These astrocytic actions are altered in diseases involving malfunction of neurons, e.g., in epilepsy, Alzheimer's disease, and Parkinson's disease. Convulsant drugs such as 4-aminopyridine (4-AP) and gabazine are commonly used to study epilepsy in vitro. In this study, we aim to assess the modulatory roles of astrocytes during epileptic-like conditions and in compensating drug-elicited hyperactivity. We plated rat cortical neurons and astrocytes with different ratios on microelectrode arrays, induced seizures with 4-AP and gabazine, and recorded the evoked neuronal activity. Our results indicated that astrocytes effectively counteracted the effect of 4-AP during stimulation. Gabazine, instead, induced neuronal hyperactivity and synchronicity in all cultures. Furthermore, our results showed that the response time to the drugs increased with an increasing number of astrocytes in the co-cultures. To the best of our knowledge, our study is the first that shows the critical modulatory role of astrocytes in 4-AP and gabazine-induced discharges and highlights the importance of considering different proportions of cells in the cultures.

Prognostic value of secondary cardiac alterations in patients with moderate aortic valve stenosis

Purpose

Echocardiographic characteristics that predict the progression of moderate aortic valve stenosis (mAS) are lacking. The aim of the present study was to evaluate the prognostic value of left ventricular hypertrophy (LVH), diastolic dysfunction (DD) and pulmonary artery hypertension (PAH) in patients with mAS.

Methods

A total of 137 patients with asymptomatic mAS (age 72±10 years; females: 51 (37%); Blood Pressure: 143±21 / 78±13 mmHg) were included. Echocardiography was performed at baseline and at follow-up every six or/and twelve months. Patients with concomitant valvular defects, hypertrophic cardiomyopathy or chronic obstructive pulmonary disease were excluded. mAS was defined by current guideline criteria. Left ventricular ejection fraction (LVEF), LVH (LV mass index, males: &gt;115g/m2, females: &gt;95 g/m2), DD (E/e' &gt;14) and PAH (maximum regurgitant velocity of tricuspid valve (TRVmax) &gt;2.8m/s) were assessed.

mAS patients were divided into 4 subgroups based on the number of secondary cardiac alterations: (0) no; (1) one; (2) two; (3) three cardiac alterations. The primary endpoint was progression to severe AS with indication for treatment (effective aortic orifice area (EOA) by continuity equation &lt;1 cm2/&lt;0.6 cm2/m2) or the onset of symptoms.

Results

mAS patients showed (0) no secondary cardiac alterations in 20% (n=28), (1) one in 40% (n=55), (2) two in 26% (n=35) and (3) three in 14% (n=19). Among mAS subgroups, no significant differences were observed for age and comorbidities. Echocardiographic parameters are summarised in Tab.1. In general, mAS patients with ≥ two cardiac alterations showed significantly smaller EOA ((0): 1.32±0.19 vs. 1.29±0.19, p&gt;0.05; (1): 1.26±0.21 vs. 1.18±0.21, p&gt;0.05; (2): 1.29±0.20 vs. 1.01±0.20, p&lt;0.01; (3): 1.31±0.16 vs. 1.06±0.25, p&lt;0.01) and higher mean pressure gradients (PGmean) ((0): 19.8±6.64 vs. 21.8±6.32, p&gt;0.05; (1): 20.0±9.26 vs. 22.3±9.94, p&gt;0.05; (2): 22.7±9.32 vs. 30.5±12.61, p&lt;0.01 (3): 25.0±8.87 vs. 29.4±10.67, p&lt;0.01) between baseline and follow-up (mean follow-up 20±9 months). Further, decrease of EOA/days was significantly higher in these patients ((0) −0.003; (1) −0.006; (2) −0.016; (3) −0.028; p&lt;0.01, Fig. 1). As shown in Kaplan-Meier curve, mAS with ≥ two cardiac alterations showed rapid progression of moderate to severe AS (Fig. 2).

Conclusions

In 40% of patients with mAS ≥ two secondary cardiac alterations (LV hypertrophy, DD and PAH) were observed. The presence of ≥ two of these secondary cardiac alterations is associated with rapid progression of mAS.

Funding Acknowledgement

Type of funding sources: None. Figure 1Figure 2

Neuronal and Astrocytic Regulations in Schizophrenia: A Computational Modelling Study

According to the tripartite synapse model, astrocytes have a modulatory effect on neuronal signal transmission. More recently, astrocyte malfunction has been associated with psychiatric diseases such as schizophrenia. Several hypotheses have been proposed on the pathological mechanisms of astrocytes in schizophrenia. For example, post-mortem examinations have revealed a reduced astrocytic density in patients with schizophrenia. Another hypothesis suggests that disease symptoms are linked to an abnormality of glutamate transmission, which is also regulated by astrocytes (glutamate hypothesis of schizophrenia). Electrophysiological findings indicate a dispute over whether the disorder causes an increase or a decrease in neuronal and astrocytic activity. Moreover, there is no consensus as to which molecular pathways and network mechanisms are altered in schizophrenia. Computational models can aid the process in finding the underlying pathological malfunctions. The effect of astrocytes on the activity of neuron-astrocyte networks has been analysed with computational models. These can reproduce experimentally observed phenomena, such as astrocytic modulation of spike and burst signalling in neuron-astrocyte networks. Using an established computational neuron-astrocyte network model, we simulate experimental data of healthy and pathological networks by using different neuronal and astrocytic parameter configurations. In our simulations, the reduction of neuronal or astrocytic cell densities yields decreased glutamate levels and a statistically significant reduction in the network activity. Amplifications of the astrocytic ATP release toward postsynaptic terminals also reduced the network activity and resulted in temporarily increased glutamate levels. In contrast, reducing either the glutamate release or re-uptake in astrocytes resulted in higher network activities. Similarly, an increase in synaptic weights of excitatory or inhibitory neurons raises the excitability of individual cells and elevates the activation level of the network. To conclude, our simulations suggest that the impairment of both neurons and astrocytes disturbs the neuronal network activity in schizophrenia.

Parametric exploration of cellular swelling in a computational model of cortical spreading depression

Cortical spreading depression (CSD) is a slowly propagating wave of depolarization of brain cells, followed by temporary silenced electrical brain activity. Major structural changes during CSD are linked to neuronal and possibly glial swelling. However, basic questions still remain unanswered. In particular, there are open questions regarding whether neurons or glial cells swell more, and how the cellular swelling affects the CSD wave propagation.In this study, we computationally explore how different parameters affect the swelling of neurons and astrocytes (starshaped glial cells) during CSD and how the cell swelling alters the CSD wave spatial distribution. We apply a homogenized mathematical model that describes electrodiffusion in the intraand extracellular space, and discretize the equations using a finite element method. The simulations are run with a twocompartment (extracellular space and neurons) and a threecompartment version of the model with astrocytes added. We consider cell swelling during CSD in four scenarios: (A) incorporating aquaporin-4 channels in the astrocytic membrane, (B) increasing the neuron/astrocyte ratio to 2:1, (C) blocking and increasing the Na⁺/K⁺-ATPase rate in the astrocytic compartment, and (D) blocking the Cl^- channels in astrocytes. Our results show that increasing the water permeability in the astrocytes results in a higher astrocytic swelling and a lower neuronal swelling than in the default case. Further, elevated neuronal density increases the swelling in both neurons and astrocytes. Blocking the Na⁺/K⁺-ATPase in the astrocytes leads to an increased wave width and swelling in both compartments, which instead decreases when the pump rate is raised. Blocking the Cl^- channels in the astrocytes results in neuronal swelling, and a shrinkage in the astrocytes. Our results suggest a supporting role of astrocytes in preventing cellular swelling and CSD, as well as highlighting how dysfunctions in astrocytes might elicit CSD.

A Computational Model of Interactions Between Neuronal and Astrocytic Networks: The Role of Astrocytes in the Stability of the Neuronal Firing Rate

Recent research in neuroscience indicates the importance of tripartite synapses and gliotransmission mediated by astrocytes in neuronal system modulation. Although the astrocyte and neuronal network functions are interrelated, they are fundamentally different in their signaling patterns and, possibly, the time scales at which they operate. However, the exact nature of gliotransmission and the effect of the tripartite synapse function at the network level are currently elusive. In this paper, we propose a computational model of interactions between an astrocyte network and a neuron network, starting from tripartite synapses and spanning to a joint network level. Our model focuses on a two-dimensional setup emulating a mixed in vitro neuron-astrocyte cell culture. The model depicts astrocyte-released gliotransmitters exerting opposing effects on the neurons: increasing the release probability of the presynaptic neuron while hyperpolarizing the post-synaptic one at a longer time scale. We simulated the joint networks with various levels of astrocyte contributions and neuronal activity levels. Our results indicate that astrocytes prolong the burst duration of neurons, while restricting hyperactivity. Thus, in our model, the effect of astrocytes is homeostatic; the firing rate of the network stabilizes to an intermediate level independently of neuronal base activity. Our computational model highlights the plausible roles of astrocytes in interconnected astrocytic and neuronal networks. Our simulations support recent findings in neurons and astrocytes in vivo and in vitro suggesting that astrocytic networks provide a modulatory role in the bursting of the neuronal network.

P2701Comparison of myocardial ischemia assessed by contrast-flow quantitative flow ratio (cQFR) and by stress MRI in patients with stable coronary artery disease

Background

Contrast-flow quantitative flow ratio (cQFR) is a new technology for evaluation of coronary stenosis. cQFR allows to derive the fractional flow reserve (FFR) from coronary angiograms. Based on a three dimensional coronary model, FFR is calculated from computational fluid dynamics. Head to head comparisons with FFR showed an overall diagnostic accuracy of 85%. cQFR does not require coronary wires or hyperemia. However, the ability of cQFR to detect myocardial ischemia is unknown. Therefore, the aim of this study was to evaluate the relationship between cQFR and myocardial ischemia assessed by stress magnetic resonance imaging (stress MRI).

Methods

cQFR analysis was performed in patients selected from the hospital database who received stress MRI and coronary angiography. A relevant ischemia on stressMRI was defined as a perfusion deficit in ≥2 of 16 segments. The cQFR was based on 3-dimensional quantitative coronary angiography (3D-QCA) using the QAngio XA 3D 1.1, Medis Medical Imaging System, Leiden, The Netherlands. Two blinded investigators analysed all 3 main coronary vessels of each patient measuring diameter stenosis (DS), area stenosis (AS) and cQFR. A cQFR of ≤0.8 was considered abnormal. The primary endpoint was sensitivity and specificity of cQFR using stress MRI as a reference standard.

Results

125 vessels of 53 patients could be fully analysed by cQFR (78.6%). The sensitivity of cQFR in detecting significant epicardial stenoses of coronary vessels with documented ischemia in stress MRI was 75%, the specificity was 87%. The 3D-QCA-derived diameter stenoses and area stenoses in vessels with positive stress MRI were significantly higher than in vessels without ischemia (see Table 1).

Table 1. Means of diameter stenosis (DS) und area stenosis (AS) with interquartile range (IQR) Total (n=125) Ischemia (n=32) No Ischemia (n=93) p-value DS [%] 42.3 (28.3–53.1) 57.1 (47–68.5) 37.7 (27.6–45.1) <0.0001 AS [%] 51.8 (32.4–69.7) 68.9 (56.8–85.9) 46.5 (29.7–62.7) <0.0001

Conclusion

The analysis reveals a high correlation between relevant coronary stenosis measured by cQFR and ischemic areas detected by stress MRI. Differences between the two methods are plausible because stress MRI detects ischemia due to other reasons than epicardial stenosis. Further randomized studies are mandatory to verify the prognostic significance of the cQFR measurements.

Astrocyte lineage cells are essential for functional neuronal differentiation and synapse maturation in human iPSC-derived neural networks

Human astrocytes differ dramatically in cell morphology and gene expression from murine astrocytes. The latter are well known to be of major importance in the formation of neuronal networks by promoting synapse maturation. However, whether human astrocyte lineage cells have a similar role in network formation has not been firmly established. Here, we investigated the impact of human astrocyte lineage cells on the functional maturation of neural networks that were derived from human induced pluripotent stem cells (hiPSCs). Initial in vitro differentiation of hiPSC-derived neural progenitor cells and immature neurons (glia+ cultures) resulted in spontaneously active neural networks as indicated by synchronous neuronal Ca²⁺ transients. Depleting proliferating neural progenitors from these cultures by short-term antimitotic treatment resulted in strongly astrocyte lineage cell-depleted neuronal networks (glia- cultures). Strikingly, in contrast to glia+ cultures, glia- cultures did not exhibit spontaneous network activity. Detailed analysis of the morphological and electrophysiological properties of neurons by patch clamp recordings revealed reduced dendritic arborization in glia- cultures. In addition, a reduced action potential frequency upon current injection in pyramidal-like neurons was observed, whereas the electrical excitability of multipolar neurons was unaltered. Furthermore, we found a reduced dendritic density of PSD95-positive excitatory synapses, and more immature properties of AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) miniature excitatory postsynaptic currents (mEPSCs) in glia- cultures, suggesting that the maturation of glutamatergic synapses depends on the presence of hiPSC-derived astrocyte lineage cells. Intriguingly, addition of the astrocyte-derived synapse maturation inducer cholesterol increased the dendritic density of PSD95-positive excitatory synapses in glia- cultures.

Combined Experimental and System-Level Analyses Reveal the Complex Regulatory Network of miR-124 during Human Neurogenesis

Non-coding RNAs regulate many biological processes including neurogenesis. The brain-enriched miR-124 has been assigned as a key player of neuronal differentiation via its complex but little understood regulation of thousands of annotated targets. To systematically chart its regulatory functions, we used CRISPR/Cas9 gene editing to disrupt all six miR-124 alleles in human induced pluripotent stem cells. Upon neuronal induction, miR-124-deleted cells underwent neurogenesis and became functional neurons, albeit with altered morphology and neurotransmitter specification. Using RNA-induced-silencing-complex precipitation, we identified 98 high-confidence miR-124 targets, of which some directly led to decreased viability. By performing advanced transcription-factor-network analysis, we identified indirect miR-124 effects on apoptosis, neuronal subtype differentiation, and the regulation of previously uncharacterized zinc finger transcription factors. Our data emphasize the need for combined experimental- and system-level analyses to comprehensively disentangle and reveal miRNA functions, including their involvement in the neurogenesis of diverse neuronal cell types found in the human brain.

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miR-124 is not essential for neurogenesis from human iPSCs

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miR-124 regulation mediates neuroprotection and refines neuronal cell fates

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miRNA knockout characterization by experimental and advanced computational analyses

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Identification of 98 targets including the neuronal feature repressor ZNF787

Understanding the role of astrocytic GABA in simulated neural networks

Astrocytes actively influence the behavior of the surrounding neuronal network including changes of the synaptic plasticity and neuronal excitability. These dynamics are altered in diseases like Alzheimer's, where the release of the gliotransmitter GABA is increased by affected, so called reactive astrocytes. In this paper, we aim to simulate a neural network with altered astrocytic GABA release. Therefore, we use our developed neuron-astrocyte model, called INEXA, which includes astrocyte controlled tripartite synapses and the astrocyte-astrocyte interaction. Our results show that GABA released by astrocytes may be responsible for synchronous inhibition of postsynaptic neurons. With increased GABA inhibition, the spike and burst rate decreased while the burst duration and spikes per burst remain similar. To our knowledge, it is the first time that the effect of this gliotransmitter to the neural network was simulated.

Measures of spike train synchrony for data with multiple time scales

BACKGROUND

Measures of spike train synchrony are widely used in both experimental and computational neuroscience. Time-scale independent and parameter-free measures, such as the ISI-distance, the SPIKE-distance and SPIKE-synchronization, are preferable to time scale parametric measures, since by adapting to the local firing rate they take into account all the time scales of a given dataset.

NEW METHOD

In data containing multiple time scales (e.g. regular spiking and bursts) one is typically less interested in the smallest time scales and a more adaptive approach is needed. Here we propose the A-ISI-distance, the A-SPIKE-distance and A-SPIKE-synchronization, which generalize the original measures by considering the local relative to the global time scales. For the A-SPIKE-distance we also introduce a rate-independent extension called the RIA-SPIKE-distance, which focuses specifically on spike timing.

RESULTS

The adaptive generalizations A-ISI-distance and A-SPIKE-distance allow to disregard spike time differences that are not relevant on a more global scale. A-SPIKE-synchronization does not any longer demand an unreasonably high accuracy for spike doublets and coinciding bursts. Finally, the RIA-SPIKE-distance proves to be independent of rate ratios between spike trains.

COMPARISON WITH EXISTING METHODS

We find that compared to the original versions the A-ISI-distance and the A-SPIKE-distance yield improvements for spike trains containing different time scales without exhibiting any unwanted side effects in other examples. A-SPIKE-synchronization matches spikes more efficiently than SPIKE-synchronization.

CONCLUSIONS

With these proposals we have completed the picture, since we now provide adaptive generalized measures that are sensitive to firing rate only (A-ISI-distance), to timing only (ARI-SPIKE-distance), and to both at the same time (A-SPIKE-distance).

Network-Wide Adaptive Burst Detection Depicts Neuronal Activity with Improved Accuracy

Neuronal networks are often characterized by their spiking and bursting statistics. Previously, we introduced an adaptive burst analysis method which enhances the analysis power for neuronal networks with highly varying firing dynamics. The adaptation is based on single channels analyzing each element of a network separately. Such kind of analysis was adequate for the assessment of local behavior, where the analysis focuses on the neuronal activity in the vicinity of a single electrode. However, the assessment of the whole network may be hampered, if parts of the network are analyzed using different rules. Here, we test how using multiple channels and measurement time points affect adaptive burst detection. The main emphasis is, if network-wide adaptive burst detection can provide new insights into the assessment of network activity. Therefore, we propose a modification to the previously introduced inter-spike interval (ISI) histogram based cumulative moving average (CMA) algorithm to analyze multiple spike trains simultaneously. The network size can be freely defined, e.g., to include all the electrodes in a microelectrode array (MEA) recording. Additionally, the method can be applied on a series of measurements on the same network to pool the data for statistical analysis. Firstly, we apply both the original CMA-algorithm and our proposed network-wide CMA-algorithm on artificial spike trains to investigate how the modification changes the burst detection. Thereafter, we use the algorithms on MEA data of spontaneously active chemically manipulated in vitro rat cortical networks. Moreover, we compare the synchrony of the detected bursts introducing a new burst synchrony measure. Finally, we demonstrate how the bursting statistics can be used to classify networks by applying k-means clustering to the bursting statistics. The results show that the proposed network wide adaptive burst detection provides a method to unify the burst definition in the whole network and thus improves the assessment and classification of the neuronal activity, e.g., the effects of different pharmaceuticals. The results indicate that the novel method is adaptive enough to be usable on networks with different dynamics, and it is especially feasible when comparing the behavior of differently spiking networks, for example in developing networks.

From in silico astrocyte cell models to neuron-astrocyte network models: A review

The idea that astrocytes may be active partners in synaptic information processing has recently emerged from abundant experimental reports. Because of their spatial proximity to neurons and their bidirectional communication with them, astrocytes are now considered as an important third element of the synapse. Astrocytes integrate and process synaptic information and by doing so generate cytosolic calcium signals that are believed to reflect neuronal transmitter release. Moreover, they regulate neuronal information transmission by releasing gliotransmitters into the synaptic cleft affecting both pre- and postsynaptic receptors. Concurrent with the first experimental reports of the astrocytic impact on neural network dynamics, computational models describing astrocytic functions have been developed. In this review, we give an overview over the published computational models of astrocytic functions, from single-cell dynamics to the tripartite synapse level and network models of astrocytes and neurons.

Spectral Entropy Based Neuronal Network Synchronization Analysis Based on Microelectrode Array Measurements

Synchrony and asynchrony are essential aspects of the functioning of interconnected neuronal cells and networks. New information on neuronal synchronization can be expected to aid in understanding these systems. Synchronization provides insight in the functional connectivity and the spatial distribution of the information processing in the networks. Synchronization is generally studied with time domain analysis of neuronal events, or using direct frequency spectrum analysis, e.g., in specific frequency bands. However, these methods have their pitfalls. Thus, we have previously proposed a method to analyze temporal changes in the complexity of the frequency of signals originating from different network regions. The method is based on the correlation of time varying spectral entropies (SEs). SE assesses the regularity, or complexity, of a time series by quantifying the uniformity of the frequency spectrum distribution. It has been previously employed, e.g., in electroencephalogram analysis. Here, we revisit our correlated spectral entropy method (CorSE), providing evidence of its justification, usability, and benefits. Here, CorSE is assessed with simulations and in vitro microelectrode array (MEA) data. CorSE is first demonstrated with a specifically tailored toy simulation to illustrate how it can identify synchronized populations. To provide a form of validation, the method was tested with simulated data from integrate-and-fire model based computational neuronal networks. To demonstrate the analysis of real data, CorSE was applied on in vitro MEA data measured from rat cortical cell cultures, and the results were compared with three known event based synchronization measures. Finally, we show the usability by tracking the development of networks in dissociated mouse cortical cell cultures. The results show that temporal correlations in frequency spectrum distributions reflect the network relations of neuronal populations. In the simulated data, CorSE unraveled the synchronizations. With the real in vitro MEA data, CorSE produced biologically plausible results. Since CorSE analyses continuous data, it is not affected by possibly poor spike or other event detection quality. We conclude that CorSE can reveal neuronal network synchronization based on in vitro MEA field potential measurements. CorSE is expected to be equally applicable also in the analysis of corresponding in vivo and ex vivo data analysis.

Simulation of developing human neuronal cell networks

Background

Microelectrode array (MEA) is a widely used technique to study for example the functional properties of neuronal networks derived from human embryonic stem cells (hESC-NN). With hESC-NN, we can investigate the earliest developmental stages of neuronal network formation in the human brain.

Methods

In this paper, we propose an in silico model of maturating hESC-NNs based on a phenomenological model called INEX. We focus on simulations of the development of bursts in hESC-NNs, which are the main feature of neuronal activation patterns. The model was developed with data from developing hESC-NN recordings on MEAs which showed increase in the neuronal activity during the investigated six measurement time points in the experimental and simulated data.

Results

Our simulations suggest that the maturation process of hESC-NN, resulting in the formation of bursts, can be explained by the development of synapses. Moreover, spike and burst rate both decreased at the last measurement time point suggesting a pruning of synapses as the weak ones are removed.

Conclusions

To conclude, our model reflects the assumption that the interaction between excitatory and inhibitory neurons during the maturation of a neuronal network and the spontaneous emergence of bursts are due to increased connectivity caused by the forming of new synapses.

Differentially expressed genes in L6 rat skeletal muscle myoblasts after incubation with inflammatory cytokines

OBJECTIVE

The mechanism underlying exercise intolerance in chronic heart failure is still unclear. An increased concentration of inflammatory cytokines could be detected in the serum of patients with chronic heart failure (CHF) exhibiting a correlation with the severity of the disease. The variety of molecular alterations triggered by these cytokines in the skeletal muscle is almost unknown. The study was designed to analyze the differential gene expression in skeletal muscle myoblasts after stimulation with inflammatory cytokines.

METHODS

L6 rat skeletal muscle myoblasts were incubated for 24 h with a combination of IL-1beta/IFN-gamma and the differential gene expression profile was determined by a PCR-based subtractive hybridization method.

RESULTS

Out of 173 picked clones 141 different sequences could be identified. By comparison with Genebank, the identity of 73 genes (51.7%) could be confirmed, whereas the rest did not show a homology to any known gene. Some of the identified genes are known to be altered in patients with CHF.

CONCLUSION

In summary, the results of this study provide information about changes in gene expression after exposure of skeletal muscle cells to inflammatory cytokines. This information may yield a new gene pool, worthwhile to be analyzed in skeletal muscle of patients with chronic heart failure.