Ultrastructural observations on the hypothalamic arcuate nuclei of aged rats in the fasting/refeeding model

The arcuate nucleus of the hypothalamus (ARH) is involved in the control of energy homeostasis. This is the first study on the ultrastructural response of ARH neurons in aged rats after short-term fasting and subsequent refeeding. Male Wistar rats (24 weeks old) were fasted for 48 or 96 hours and were then refed for 24 hours. The controls were normally fed. The rats received water ad libitum. In both groups of fasting animals, we observed a rearrangement of the arcuate rough endoplasmic reticulum (RER) and Golgi complexes to form membranous whorls. Moreover, refeeding for 24 hours did not reverse this process. The RER was frequently found to be well organized into lamellar bodies composed of several cisternae. The membranous whorls were composed of concentric layers of endoplasmic reticulum and Golgi complexes. In addition, multiform lipofuscin granules were observed in close relationship with Golgi complexes and membranous whorls. Lipofuscin granules within the neurons of the arcuate nucleus are assumed to be a morphological manifestation of oxidative stress phenomena, which are presumably implicated in the formation of membranous whorls in both fasting and fasting/refed animals. This observation correlates with a significant increase in 8-isoprostane serum levels in the fasting and fasting/refed animals as compared to the fed control rats

The effect of fasting on the ultrastructure of the hypothalamic arcuate nucleus in young rats

In the present study, we described ultrastructural changes occurring in the neurons of the hypothalamic arcuate nucleus after food deprivation. Young male Wistar rats (5 months old, n = 12) were divided into three groups. The animals in Group I were used as control (normally fed), and the rats in Groups II and III were fasted for 48 hours and 96 hours, respectively. In both treated groups, fasting caused rearrangement of the rough endoplasmic reticulum forming lamellar bodies and membranous whorls. The lamellar bodies were rather short in the controls, whereas in the fasting animals they became longer and were sometimes participating in the formation of membranous whorls composed of the concentric layers of the smooth endoplasmic reticulum. The whorls were often placed in the vicinity of a very well developed Golgi complex. Some Golgi complexes displayed an early stage of whorl formation. Moreover, an increased serum level of 8-isoprostanes, being a reliable marker of total oxidative stress in the body, was observed in both fasting groups of rats as compared to the control

Nonlocal resistance and its fluctuations in microstructures of band-inverted HgTe/(Hg,Cd)Te quantum wells

We investigate experimentally transport in gated microsctructures containing a band-inverted HgTe/Hg_{0.3}Cd_{0.7}Te quantum well. Measurements of nonlocal resistances using many contacts prove that in the depletion regime the current is carried by the edge channels, as expected for a two-dimensional topological insulator. However, high and non-quantized values of channel resistances show that the topological protection length (i.e. the distance on which the carriers in helical edge channels propagate without backscattering) is much shorter than the channel length, which is ~100 micrometers. The weak temperature dependence of the resistance and the presence of temperature dependent reproducible quasi-periodic resistance fluctuations can be qualitatively explained by the presence of charge puddles in the well, to which the electrons from the edge channels are tunnel-coupled.Comment: 8 pages, 4 figures, published versio

Field Effect Transistors for Terahertz Detection: Physics and First Imaging Applications

Resonant frequencies of the two-dimensional plasma in FETs increase with the reduction of the channel dimensions and can reach the THz range for sub-micron gate lengths. Nonlinear properties of the electron plasma in the transistor channel can be used for the detection and mixing of THz frequencies. At cryogenic temperatures resonant and gate voltage tunable detection related to plasma waves resonances, is observed. At room temperature, when plasma oscillations are overdamped, the FET can operate as an efficient broadband THz detector. We present the main theoretical and experimental results on THz detection by FETs in the context of their possible application for THz imaging.Comment: 22 pages, 12 figures, review pape

Interferometric probes of many-body localization

We propose a method for detecting many-body localization (MBL) in disordered spin systems. The method involves pulsed, coherent spin manipulations that probe the dephasing of a given spin due to its entanglement with a set of distant spins. It allows one to distinguish the MBL phase from a non-interacting localized phase and a delocalized phase. In particular, we show that for a properly chosen pulse sequence the MBL phase exhibits a characteristic power-law decay reflecting its slow growth of entanglement. We find that this power-law decay is robust with respect to thermal and disorder averaging, provide numerical simulations supporting our results, and discuss possible experimental realizations in solid-state and cold atom systems.Comment: 5 pages, 4 figure

Characterization of Mott-insulating and superfluid phases in the one-dimensional Bose--Hubbard model

We use strong-coupling perturbation theory, the variational cluster approach (VCA), and the dynamical density-matrix renormalization group (DDMRG) method to investigate static and dynamical properties of the one-dimensional Bose--Hubbard model in both the Mott-insulating and superfluid phases. From the von Neumann entanglement entropy we determine the central charge and the transition points for the first two Mott lobes. Our DMRG results for the ground-state energy, momentum distribution function, boson correlation function decay, Mott gap, and single particle-spectral function are reproduced very well by the strong-coupling expansion to fifth order, and by VCA with clusters up to 12 sites as long as the ratio between the hopping amplitude and on-site repulsion, t/U, is smaller than 0.15 and 0.25, respectively. In addition, in the superfluid phase VCA captures well the ground-state energy and the sound velocity of the linear phonon modes. This comparison provides an authoritative estimate for the range of applicability of these methods. In strong-coupling theory for the Mott phase, the dynamical structure factor is obtained from the solution of an effective single-particle problem with an attractive potential. The resulting resonances show up as double-peak structure close to the Brillouin zone boundary. These high-energy features also appear in the superfluid phase which is characterized by a pronounced phonon mode at small momenta and energies, as predicted by Bogoliubov and field theory. In one dimension, there are no traces of an amplitude mode in the dynamical single-particle and two-particle correlation functions.Comment: 15 pages, 12 figure

Temperature-induced topological phase transition in HgTe quantum wells

We report a direct observation of temperature-induced topological phase transition between trivial and topological insulator in HgTe quantum well. By using a gated Hall bar device, we measure and represent Landau levels in fan charts at different temperatures and we follow the temperature evolution of a peculiar pair of "zero-mode" Landau levels, which split from the edge of electron-like and hole-like subbands. Their crossing at critical magnetic field $B_c$ is a characteristic of inverted band structure in the quantum well. By measuring the temperature dependence of $B_c$, we directly extract the critical temperature $T_c$, at which the bulk band-gap vanishes and the topological phase transition occurs. Above this critical temperature, the opening of a trivial gap is clearly observed.Comment: 5 pages + Supplemental Materials; Phys. Rev. Lett. (accepted

Ultrastructural response of arcuate nucleus neurons to fasting in aged rats

The arcuate nucleus of the hypothalamus (ARH) is involved in the control of energy homeostasis. Leptin - an adipocyte derived hormone - is known to act on the hypothalamic nuclei and thus to control body weight by food intake reduction. Oxidative stress is believed to be implicated in leptin signalling. However, its relevance for leptin-induced signal transduction within ARH remains unclear. The goal of the study was to investigate the effect of fasting on morphological alterations of the neuronal endoplasmic reticulum/Golgi network as well as on the expression of leptin receptors in the arcuate nucleus of aged rats. Male Wistar rats, aged 24 months, were fasted for 96 hours. The control animals were fed ad libitum. Membranous whorls in the ARH neurons were visualized using the electron microscopy technique. Leptin receptors in the membranes of ARH neurons were determined immunohistochemically (IHC), and soluble leptin receptors in the plasma as well as plasma isoprostanes were quantified immunochemically (ELISA). An intense formation of membranous whorls was observed, directly associated with the cisternae of the rough endoplasmic reticulum, as well as lamellar bodies. Interestingly, the whorls were often localized near a well-developed Golgi complex. Moreover, some Golgi complexes displayed an early stage of whorl formation. Groups of residual lipofuscin granules were found in the immediate proximity of the whorls. An increased immunoreactivity with neuronal leptin receptors suggests that hypersensitive neurons may still effectively respond to the fasting serum levels of leptin, mediating ultrastructural transformation of ARH neurons during short-term fasting. Having observed a significant accumulation of lipofuscin granules and a marked increase of total 8-isoprostane serum level in the fasting rats, we hypothesize that signal transduction within the neurons of ARH is dependent on oxidative stress phenomena