| 77391. |
|
|
| 77392. |
- Stagkourakis, Stefanos
(författare)
-
On innate behaviors : focus on parental behavior and aggression
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The neural substrates orchestrating a number of social behaviors, including parental behavior and aggression, are known to exist in the hypothalamus. Through the control of the pituitary gland, the hypothalamus regulates the release of a number of hormones necessary for the physiological control of bodily functions and the expression of appropriate behaviors. In recent years the neuroscience community has invested large resources in identifying, through molecular markers, subsets of neurons whose activity impacts behavioral expression. This approach, however, has several weaknesses, among which is the assumption that a neuron’s function and output adhere to generalized principles. Consequently, such investigations often fail to identify the intricate organization of neural networks, which adapt the neural code in order to tune a system’s output to the behavior it modulates. The aim of this thesis is to expand on basic neurophysiological concepts regarding the complex organization within and among neural groups. Here we addressed the principles of how a set of neurons self-tune their activity through the use of their own neurotransmitter, intra- and inter-network connectivity designs and spike rate coding of neurotransmitter release. Following this interrogation of neural network properties, we attempted to link the activity of these neural nodes to behavioral output, where we identified two distinct subsets of neurons driving parental behavior and aggression respectively. In paper I, we performed a study on the properties of autoregulation in a neural network, and identified the ionic mechanisms through which the tuberoinfundibular dopamine (TIDA) neurons control their own activity via the use of their own neurotransmitter, dopamine (DA). In paper II, we encountered an unexpected species difference in baseline activity and oscillation frequency between rat and mouse TIDA neurons. Following an in-depth investigation, we attributed this difference to the presence vs complete absence of electrical coupling in the rat and mouse TIDA cells respectively. This generated the question of how different modes of TIDA neuron activity impact DA release at their terminals, which was addressed in paper III where, using fast-scan cyclic voltammetry, we performed the first investigation coupling patterns of electrophysiological activity to DA release in the TIDA system. In paper IV we addressed the possibility that this discrepancy in TIDA neuron activity has a behavioral impact. Following a step-by-step breakdown of the lactotropic axis in the male rat and mouse, we ultimately provided a link between TIDA neuron activity and the suppression vs expression of paternal behavior in the two species. The final part of this thesis includes two studies focusing on aggressive behavior. In paper V, we performed a functional interrogation of a subset of ventral premammillary (PMv) neurons involved in intermale aggression, while in paper VI we identified that the very same neurons are activated by maternal hormones and modulate the expression of maternal aggression in lactating female mice. Overall, the work presented in this thesis provides a step forward in our understanding of neural function and on the neural substrates underlying social behavior.
|
|
| 77393. |
- Stagmo, Martin
(författare)
-
Aspects on coronary heart disease prevention in clinical practice
- 2005
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Prevention of first time disease or recurrence of coronary heart disease (CHD) is a major task for the health service. Guidelines regarding CHD prevention have been issued but studies have shown that treatment goals are inadequately met in clinical practice and there is urgent need for improved methods of implementation of guidelines. There is also a need for better risk stratification tools in order to identify asymptomatic subjects with a high risk for future CHD. This thesis has shown that: A structured, one-year, hospital-based secondary prevention programme after CHD, mainly led by specialist nurses with physician backup, could positively influence the use of lipid-lowering drugs and serum cholesterol levels several years after the end of the programme. A quality control system based on patient empowerment and education with continuous feedback to patients, nurses and physicians seemed to be welcomed by both patients and participating health care professionals. However, our system based on voluntary participation and report cards did not seem to be feasible at this time due to a high dropout rate. Reasons why targets for serum lipids were not met in the EUROASPIRE II study were that too few patients received lipid-lowering drugs, and that of those who did receive such treatment many were treated with sub-optimal doses. Ambulatory ECG with ST-analysis could add significant information on which healthy subjects with a certain accumulation of risk factors who would suffer from a major coronary event (death, AMI or revascularisation) over a 15-year time period.
|
|
| 77394. |
|
|
| 77395. |
|
|
| 77396. |
|
|
| 77397. |
|
|
| 77398. |
- Stagnell, Alexander, 1987-
(författare)
-
The Ambassador's Letter : On the Less Than Nothing of Diplomacy
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The principal aim of this dissertation is to answer the age-old question What is diplomacy? But this study approaches the question in what might, on first look, appear oblique. By employing Slavoj Žižek’s reworked notion of Ideologiekritik with respect to the history, science, and artistic explorations of diplomacy, this work begins by extracting three of its essential problems: the name, death, and representation. A presentation of the central concepts and theoretical perspectives at play in Žižek’s work is elaborated upon, focusing on his understanding of politics, ideology, and the core of the conceptual apparatus of Lacanian psychoanalysis.The overarching argument of the thesis is that diplomacy constitutes an Ideological State Apparatus, i.e. that it offers a symbolic link destined to, through ideology, repress the fundamental inconsistencies of the modern nation state, in order to secure its continuous functioning. Diplomacy is shown to constitute the name that points to the impossibility of the state to become One with itself, and the thesis aims to capture how this impossibility, and that which must be excluded from the state to keep the fantasy of fulness alive, always returns to haunt it. Empirically, this is explored by way of re-reading the history of the word diplomacy, whose modern birth coincided with the events of the French Revolution. The study seeks to retrace diplomacy through three distinct historical formations, which here are referred to as the archi-political, ultra-political, and post-political. Each of theses formations functions as a covering over of the fundamental impossibility of the state. Readings of Immanual Kant, Henry James, André Brink, Mads Brügger, and 20th century IR-theory and Diplomacy Studies are presented in order to elaborate the way in which these formations are constituted as ideological fantasies protecting the state and, for that matter, diplomacy from their abyssal ground.
|
|
| 77399. |
- Stah, Olga, 1983-
(författare)
-
Prokaryotic respiratory supercomplexes : Studies of interactions between complexes III and IV
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Respiratory processes for cellular energy conversion are carried out by the membrane-associated enzymes of the electron transfer chain (ETC). In recent years there has been emerging data showing that the members of the ETC organize into higher-level assemblies called supercomplexes (SCs) whose functional relevance is not yet fully understood. SCs composed of complexes III (cytochrome (cyt.) bc1 complex) and IV (cyt. c oxidase) are the most common. The small electron-carrier protein cyt. c shuttles electrons between complexes III and IV. In mitochondria-like ETCs cyt. c is present only in a soluble form, while in some bacteria it has additional membrane-anchored analogs or is fused to complex III forming the cyt. cc subunit, as in actinobacteria.We determined the structure of the obligate III/IV SC from actinobacterium Mycobacterium (M.) smegmatis with cryo-electron microscopy. The structure showed that the distances between the co-factors of the SC are short enough for electron transfer with the catalytically relevant rates. Complexes III and IV within the SC were intertwined. In particular, the entrance to the D-proton pathway of complex IV was shielded by a loop of the QcrB subunit of complex III, possibly influencing proton uptake characteristics. Furthermore, superoxide dismutase was shown to be an integral part of the M. smegmatis SC, which might have a functional role in the energy conservation by the SC.With the goal to unravel the structure-function relationships between complexes III and IV in the actinobacterial SCs, we investigated the charge transfer kinetics in SCs on a single-turnover time scale. Using time-resolved spectroscopic techniques we have determined the rates of electron and proton transfer upon oxidation of reduced SCs of M. smegmatis and another actinobacterium Corynebacterium glutamicum. Electron transfer from cyt. cc in complex III to the primary redox center CuA in complex IV was not rate-limiting for the SC turnover. In contrast to the canonical complex IV, certain reaction steps in SC were not pH-dependent and proton uptake kinetics through the D-pathway of complex IV was altered showing much slower kinetics. This suggests that the QcrB loop of complex III, which blocks the entrance to the D-pathway, modulates the kinetics of proton uptake in complex IV. In another study, we showed the existence of a non-obligate supercomplex in the alfa-proteobacterium Rhodobacter (R.) sphaeroides. This SC was purified and characterized biochemically. We concluded that complexes III and IV interact via the membrane-anchored version of cyt. c (MA-cyt. c), which is expressed in the bacterium in addition to the soluble variant. MA-cyt. c most likely plays a central role in forming the SC in R. sphaeroides by functionally connecting complexes III and IV.In addition to being an electron shuttle, in eukaryotes cyt. c participates in apoptosis. We investigated the consequences of anchoring the cyt. c to the membrane, similar to MA-cyt. c in R. sphaeroides, in a single-cell eukaryote Saccharomyces cerevisiae, thereby not allowing the release of cyt. c from the intermembrane space of mitochondria during the induced apoptosis.The work presented in this thesis increases our understanding of the general function-structure relationships of respiratory SCs and might have applications in potential drug development.
|
|
| 77400. |
- Stahl, Adam, 1985
(författare)
-
Momentum-space dynamics of runaway electrons in plasmas
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fast electrons in a plasma experience a friction force that decreases with increasing particle speed, and may therefore be continuously accelerated by sufficiently strong electric fields. These so-called runaway electrons may quickly reach relativistic speeds. This is problematic in tokamaks – devices aimed at producing sustainable energy through the use of thermonuclear fusion reactions – where runaway-electron beams carrying strong currents may form. If the runaway electrons deposit their kinetic energy in the plasma-facing components, these may be seriously damaged, leading to long and costly device shutdowns.Crucial to the runaway phenomenon is the behavior of the runaway electrons in two-dimensional momentum space. The interplay between electric-field acceleration, collisional momentum-space transport, and radiation reaction determines the dynamics and the growth or decay of the runaway-electron population. In this thesis, several aspects of this interplay are investigated, including avalanche multiplication rates, synchrotron radiation reaction, modifications to the critical electric field for runaway generation, rapidly changing plasma parameters, and electron slide-away. Two numerical tools for studying electron momentum-space dynamics, based on an efficient solution of the kinetic equation, are presented and used throughout the thesis. The spectrum of the synchrotron radiation emitted by the runaway electrons – a useful diagnostic for their properties – is also studied.It is found that taking the electron distribution into account properly is crucial for the interpretation of synchrotron spectra; that a commonly used numerical avalanche operator may either overestimate or underestimate the runaway-electron growth rate, depending on the scenario; that radiation reaction modifies the critical electric field, but that this modification often is small compared to other effects; that electron slide-away can occur at significantly weaker electric fields than expected; and that collisional nonlinearities may be significant for the evolution of runaway-electron populations in disruption scenarios.
|
|
