Why Buckling Stellar Bars Weaken in Disk Galaxies

Young stellar bars in disk galaxies experience a vertical buckling instability which terminates their growth and thickens them, resulting in a characteristic peanut/boxy shape when viewed edge on. Using N-body simulations of galactic disks embedded in live halos, we have analyzed the bar structure throughout this instability and found that the outer third of the bar dissolves completely while the inner part (within the vertical inner Lindblad resonance) becomes less oval. The bar acquires the frequently observed peanut/boxy-shaped isophotes. We also find that the bar buckling is responsible for a mass injection above the plane, which is subsequently trapped by specific 3-D families of periodic orbits of particular shapes explaining the observed isophotes, in line with previous work. Using a 3-D orbit analysis and surfaces of sections, we infer that the outer part of the bar is dissolved by a rapidly widening stochastic region around its corotation radius -- a process related to the bar growth. This leads to a dramatic decrease in the bar size, decrease in the overall bar strength and a mild increase in its pattern speed, but is not expected to lead to a complete bar dissolution. The buckling instability appears primarily responsible for shortening the secular diffusion timescale to a dynamical one when building the boxy isophotes. The sufficiently long timescale of described evolution, ~1 Gyr, can affect the observed bar fraction in local universe and at higher redshifts, both through reduced bar strength and the absence of dust offset lanes in the bar.Comment: 7 pages, 4 figures, ApJ Letters, in pres

Regulation of Kir4.1 expression in astrocytes and astrocytic tumors: a role for interleukin-1 beta

<p>Abstract</p> <p>Objective</p> <p>Decreased expression of inwardly rectifying potassium (Kir) channels in astrocytes and glioma cells may contribute to impaired K⁺ buffering and increased propensity for seizures. Here, we evaluated the potential effect of inflammatory molecules, such as interleukin-1β (IL-1β) on Kir4.1 mRNA and protein expression.</p> <p>Methods</p> <p>We investigated Kir4.1 (Kcnj10) and IL-1β mRNA expression in the temporal cortex in a rat model of temporal lobe epilepsy 24 h and 1 week after induction of status epilepticus (SE), using real-time PCR and western blot analysis. The U373 glioblastoma cell line and human fetal astrocytes were used to study the regulation of Kir4.1 expression in response to pro-inflammatory cytokines. Expression of Kir4.1 protein was also evaluated by means of immunohistochemistry in surgical specimens of patients with astrocytic tumors (<it>n</it> = 64), comparing the expression in tumor patients with (<it>n</it> = 38) and without epilepsy (<it>n</it> = 26).</p> <p>Results</p> <p>Twenty-four hours after onset of SE, Kir4.1 mRNA and protein were significantly down-regulated in temporal cortex of epileptic rats. This decrease in expression was followed by a return to control level at 1 week after SE. The transient downregulation of Kir4.1 corresponded to the time of prominent upregulation of IL-1β mRNA. Expression of Kir4.1 mRNA and protein in glial cells in culture was downregulated after exposure to IL-1β. Evaluation of Kir4.1 in tumor specimens showed a significantly lower Kir4.1 expression in the specimens of patients with epilepsy compared to patients without epilepsy. This paralleled the increased presence of activated microglial cells, as well as the increased expression of IL-1β and the cytoplasmic translocation of high mobility group box 1 (HMGB1).</p> <p>Conclusions</p> <p>Taken together, these findings indicate that alterations in expression of Kir4.1 occurring in epilepsy-associated lesions are possibly influenced by the local inflammatory environment and in particular by the inflammatory cytokine IL-1β.</p

Boxy/peanut/X bulges, barlenses and the thick part of galactic bars: What are they and how did they form?

Bars have a complex three-dimensional shape. In particular their inner part is vertically much thicker than the parts further out. Viewed edge-on, the thick part of the bar is what is commonly known as a boxy-, peanut- or X- bulge and viewed face-on it is referred to as a barlens. These components are due to disc and bar instabilities and are composed of disc material. I review here their formation, evolution and dynamics, using simulations, orbital structure theory and comparisons to observations.Comment: 21 pages, 7 figures, invited review to appear in "Galactic Bulges", E. Laurikainen, R. Peletier, D. Gadotti, (eds.), Springe

Three-Dimensional Bar Structure and Disc/Bulge Secular Evolution

Kn-band imaging of a sample of 30 edge-on spiral galaxies with a boxy or peanut-shaped (B/PS) bulge is discussed. Galaxies with a B/PS bulge tend to have a more complex morphology than galaxies with other bulge types, unsharp-masked images revealing structures that trace the major orbit families of three-dimensional bars. Their surface brightness profiles are also more complex, typically containing 3 or more clearly separated regions, including a shallow or flat intermediate region (Freeman Type II profiles), suggestive of bar-driven transfer of angular momentum and radial redistribution of material. The data also suggest abrupt variations of the discs' scaleheights, as expected from the vertical resonances and instabilities present in barred discs but contrary to conventional wisdom. Counter to the standard `bulge + disc' model, we thus propose that galaxies with a B/PS bulge are composed of a thin concentrated disc (a disc-like bulge) contained within a partially thick bar (the B/PS bulge), itself contained within a thin outer disc. The inner disc most likely formed through bar-driven processes while the thick bar arises from buckling instabilities. Both are strongly coupled dynamically and are formed mostly of the same (disc) material.Comment: 6 pages, including 1 figure. To appear in "Island Universes: Structure and Evolution of Disk Galaxies", ed. R. de Jong (Springer: Dordrecht

Editorial: epilepsy and neurodevelopmental diseases

The association between epilepsy and neurodevelopmental diseases is well-recognized and has gained significant attention in the field of neuroscience in recent years. One of the main reasons for this interest is the need for a better understanding of the events that lead to the development and maturation of the CNS. This is a fundamental and necessary basis for potential breakthrough strategies that could guide novel and more effective disease-modifying therapeutic approaches to neurodevelopmental syndromes that are frequently characterized by severe and drug-resistant epilepsy. The perspective of such new therapeutic strategies is very promising. At the state-of-theart, patients afflicted by these rare neurodevelopmental disorders mostly rely on “symptomatic” approaches that mitigate seizures and other major symptoms but do not target the underlying biological causes of the disease. The study of this vast field of research is extremely complex and requires a multidisciplinary approach, from neuropathological to molecular and functional studies since even “simple” triggering events (e.g., a genetic mutation) during critical periods of brain development can lead to widespread effects on brain morphological and functional features

DNA methylation-based classification of central nervous system tumours.

Accurate pathological diagnosis is crucial for optimal management of patients with cancer. For the approximately 100 known tumour types of the central nervous system, standardization of the diagnostic process has been shown to be particularly challenging-with substantial inter-observer variability in the histopathological diagnosis of many tumour types. Here we present a comprehensive approach for the DNA methylation-based classification of central nervous system tumours across all entities and age groups, and demonstrate its application in a routine diagnostic setting. We show that the availability of this method may have a substantial impact on diagnostic precision compared to standard methods, resulting in a change of diagnosis in up to 12% of prospective cases. For broader accessibility, we have designed a free online classifier tool, the use of which does not require any additional onsite data processing. Our results provide a blueprint for the generation of machine-learning-based tumour classifiers across other cancer entities, with the potential to fundamentally transform tumour pathology