The functional role of GABA and glycine in monaural and binaural processing in the inferior colliculus of horseshoe bats

The functional role of GABA and glycine in monaural and binaural signal analysis was studied in single unit recordings from the central nucleus of the inferior colliculus (IC) of horseshoe bats (Rhinolophus rouxi) employing microiontophoresis of the putative neurotransmitters and their antagonists bicuculline and strychnine. Most neurons were inhibited by GABA (98%; N= 107) and glycine (92%; N = 118). Both neurotransmitters appear involved in several functional contexts, but to different degrees. Bicuculline-induced increases of discharge activity (99% of cells; N= 191) were accompanied by changes of temporal response patterns in 35 % of neurons distributed throughout the IC. Strychnine enhanced activity in only 53% of neurons (N= 147); cells exhibiting response pattern changes were rare (9%) and confined to greater recording depths. In individual cells, the effects of both antagonists could markedly differ, suggesting a differential supply by GABAergic and glycinergic networks. Bicuculline changed the shape of the excitatory tuning curve by antagonizing lateral inhibition at neighboring frequencies and/or inhibition at high stimulation levels. Such effects were rarely observed with strychnine. Binaural response properties of single units were influenced either by antagonization of inhibition mediated by ipsilateral stimulation (bicuculline) or by changing the strength of the main excitatory input (bicuculline and strychnine)

The Development of a Single Frequency Place in the Mammalian Cochlea: The Cochlear Resonance in the Mustached Bat Pteronotus parnellii

Cochlear microphonic potentials (CMs) were recorded from the sharply tuned, strongly resonant auditory foveae of 1- to 5-week-old mustached bats that were anesthetized with Rompun and Ketavet. The fovea processes Doppler-shifted echo responses of the constant-frequency component of echolocation calls. During development, the frequency and tuning sharpness of the cochlear resonance increases, and CM ringing persists for longer after the tone. CM is relatively insensitive at tone onset and grows linearly with increased stimulus level. During the tone, the CM is more sensitive and grows compressively with increased stimulus level and phase leads onset CM by 90° for frequencies below the resonance. CM during the ringing is also sensitive and compressive and phase leads onset CM by 180° below the resonance and lags it by 180° above the resonance. Throughout postnatal development, CMs measured during the tone and in the ringing increase both in sensitivity and compression. The cochlear resonance appears to be attributable to interaction between two oscillators. The more broadly tuned oscillator dominates the onset response, and the narrowly tuned oscillator dominates the ringing. Early in development, mechanical coupling between the oscillators results in a relatively broadly tuned system with several frequency modes in the CM at tone onset and in the CM ringing. Beating occurs between the resonance and the stimulus response during the tone and between two components of the narrowly tuned oscillator at tone offset. At maturity, the CM has three modes for frequencies within 10 kHz of the resonance at tone onset and a single, sharply tuned mode in the ringing

Synchronization of a Nonlinear Oscillator: Processing the Cf Component of the Echo-Response Signal in the Cochlea of the Mustached Bat

Cochlear microphonic potential (CM) was recorded from the CF2 region and the sparsely innervated zone (the mustached bat's cochlea fovea) that is specialized for analyzing the Doppler-shifted echoes of the first-harmonic (~61 kHz) of the constant-frequency component of the echolocation call. Temporal analysis of the CM, which is tuned sharply to the 61 kHz cochlear resonance, revealed that at the resonance frequency, and within 1 msec of tone onset, CM is broadly tuned with linear magnitude level functions. CM measured during the ongoing tone and in the ringing after tone offset is 50 dB more sensitive, is sharply tuned, has compressive level functions, and the phase leads onset CM by 90°: an indication that cochlear responses are amplified during maximum basilar membrane velocity. For high-level tones above the resonance frequency, CM appears at tone onset and after tone offset. Measurements indicate that the two oscillators responsible for the cochlear resonance, presumably the basilar and tectorial membranes, move together in phase during the ongoing tone, thereby minimizing net shear between them and hair cell excitation. For tones within 2 kHz of the cochlear resonance the frequency of CM measured within 2 msec of tone onset is not that of the stimulus but is proportional to it. For tones just below the cochlear resonance region CM frequency is a constant amount below that of the stimulus depending on CM measurement delay from tone onset. The frequency responses of the CM recorded from the cochlear fovea can be accounted for through synchronization between the nonlinear oscillators responsible for the cochlear resonance and the stimulus tone

Bildungsradio Ö1 und WDR 5 - informelle Lernprozesse im öffentlich-rechtlichen Hörfunk

In dieser Arbeit über informelles Lernens im Radio war es das Ziel herauszufinden, wo die Stärken und Schwächen in der Vermittlung und Rezeption von Wissensinhalten im Radio liegen. Ein wichtiger Teil dieser Arbeit ist die Abgrenzung des Begriffs “informelles Lernen” und das Feld des informellen Lernens in der Freizeit und an Hand des Radios abzuhandeln. Eine wichtige theoretische Aufarbeitung dieser Arbeit ist mit dem Begriff der Qualität im Zusammenhang mit informellem Lernen aus pädagogischer und journalistischer Sicht verbunden. Ebenso wurden die Mediennutzung des Bildungsradios und der Einfluss des Internet auf das Bildungsradio untersucht. Vor diesem theoretischem Hintergrund wurden die Radiosender Ö1 und WDR 5 zur empirischen Untersuchung herangezogen. Mittels qualitativer Interviews wurden vier Hörer und ein Experte für jeden Sender befragt. Die Ergebnisse wurden anschließend ausgewertet und mit theoretischen Erkenntnissen verglichen. Die Ergebnisse zeigen, dass die Hörer die Angebote des Ö1 und WDR 5 als Anlass sehen sich weiterzubilden und neue Dinge zu lernen. Informelles Lernen kann durch Inhalte aus dem Radio stattfinden und durch die Produktion qualitativ hochwertiger, zielgruppenspezifischer Angebote durch den Sender forciert werden.The goal of this thesis is to identify the paedagogical strengths and weaknesses of informal learning via broadcast radio.  A key theoretical discussion in this work revolves around clarifying the term “informal learning” and the related concepts of quality, both in the pedagoical and journalistic sense. This discussion, which forms the theoretical basis of the work, is complemented by an empirical study of two radio stations: Ö1 (Austrian) and WDR 5 (German). From each of these radio stations, four listeners and two experts were interviewed. The results were evaluated and discussed in the context of the theoretical background. The results show that the listeners perceive the programming of Ö1 and WDR 5 as creating an incentive for self-education. The findings indicate that  informal learning can take place through the radio if the production is of high quality

Simulations of Nonthermal Electron Transport in Multidimensional Flows: Application to Radio Galaxies

We have developed an economical, effective numerical scheme for cosmic-ray transport suitable for treatment of electrons up to a few hundreds of GeV in multidimensional simulations of radio galaxies. The method follows the electron population in sufficient detail to allow computation of synthetic radio and X-ray observations of the simulated sources, including spectral properties (see the companion paper by Tregillis et al. 1999). The cosmic-ray particle simulations can follow the effects of shock acceleration, second-order Fermi acceleration as well as radiative and adiabatic energy losses. We have applied this scheme to 2-D and 3-D MHD simulations of jet-driven flows and have begun to explore links between dynamics and the properties of high energy electron populations in radio lobes. The key initial discovery is the great importance to the high energy particle population of the very unsteady and inhomogeneous flows, especially near the end of the jet. Because of this, in particular, our simulations show that a large fraction of the particle population flowing from the jet into the cocoon never passes through strong shocks. The shock strengths encountered are not simply predicted by 1-D models, and are quite varied. Consequently, the emergent electron spectra are highly heterogeneous. Rates of synchrotron aging in "hot-spots" seem similarly to be very uneven, enhancing complexity in the spectral properties of electrons as they emerge into the lobes and making more difficult the task of comparing dynamical and radiative ages.Comment: 7 pages, 1 figure; to appear in Life Cycles of Radio Galaxies, ed. J. Biretta et al., New Astronomy Review

Imunomodulační a diferenciační vlastnosti MSC v myším modelu poškozené rohovky a sítnice

Kmenové buňky obecně představují potenciál pro léčbu řady onemocnění a poruch, které jsou v dnešní době léčitelné pouze obtížně nebo s řadou vedlejších účinků. Mezi dnes velmi zkoumané kmenové buňky patří námi použité mezenchymální kmenové buňky (MSCs, mesenchymal stem cells). MSCs mají značný imunomodulační a regenerační potenciál pro terapii degenerativních poruch a závažných poškození různých částí oka nebo i dalších orgánů. Stejně tak by jejich aplikace mohla sloužit jako podpůrná léčba při transplantacích rohovky a jiných zánětlivých stavech oka. Při studiu těchto imunomodulačních vlastnosti MSCs jsme se zaměřili především na jejich schopnost diferenciace v buňky různých tkání (v našem případě rohovkového epitelu a sítnice), produkci imunomodulačních molekul v zánětlivém prostředí, schopnosti migrace do místa poškození a jejich lokální protizánětlivé, regenerační a antiapoptotické působení. Terapeutické účinky MSCs jsme testovali na myším modelu poškození povrchu oka, modelu degenerace sítnice a mechanismus tohoto účinku jsme testovali v in vitro modelech s explantáty těchto tkání. Při léčbě závažných poškození rohovky je již používána terapie pomocí limbálních kmenových buněk. Tato léčba je však vhodná pouze pro určité malé procento pacientů, u kterého je potřeba tyto kmenové buňky získat ze...Stem cells, in general, represent the potential for treating many diseases and disorders that are currently difficult to treat or the therapy has many side effects. One of the stem cells widely investigated these days are mesenchymal stem cells (MSCs). MSCs have the considerable immunomodulatory and regenerative potential for treating degenerative disorders and severe damage to various parts of the eye or other organs. Likewise, their application could serve as supportive therapy in corneal transplantation and other eye inflammatory conditions. In this study of immunomodulatory properties of MSCs, we have focused mainly on their ability to differentiate into cells of different tissue types (in our case, corneal epithelium and retina), their production of immunomodulatory molecules in the inflammatory environment, their ability to migrate to the site of the injury, and their local anti-inflammatory, regenerative, and anti-apoptotic effects. In addition, we tested the therapeutic effects of MSCs in a mouse model of ocular surface injury and a model of retinal degeneration. Finally, we investigated the mechanism of this effect in in vitro models with explants of these tissues. Limbal stem cells (LSCs) are already used to treat severe corneal damage as limbal stem cell deficiency. However, this...Katedra buněčné biologieDepartment of Cell BiologyPřírodovědecká fakultaFaculty of Scienc

Low-frequency sound affects active micromechanics in the human inner ear

Noise-induced hearing loss is one of the most common auditory pathologies, resulting from overstimulation of the human cochlea, an exquisitely sensitive micromechanical device. At very low frequencies (less than 250 Hz), however, the sensitivity of human hearing, and therefore the perceived loudness is poor. The perceived loudness is mediated by the inner hair cells of the cochlea which are driven very inadequately at low frequencies. To assess the impact of low-frequency (LF) sound, we exploited a by-product of the active amplification of sound outer hair cells (OHCs) perform, so-called spontaneous otoacoustic emissions. These are faint sounds produced by the inner ear that can be used to detect changes of cochlear physiology. We show that a short exposure to perceptually unobtrusive, LF sounds significantly affects OHCs: a 90 s, 80 dB(A) LF sound induced slow, concordant and positively correlated frequency and level oscillations of spontaneous otoacoustic emissions that lasted for about 2 min after LF sound offset. LF sounds, contrary to their unobtrusive perception, strongly stimulate the human cochlea and affect amplification processes in the most sensitive and important frequency range of human hearing

Characterization of a Structural Intermediate of Flavivirus Membrane Fusion

Viral membrane fusion proceeds through a sequence of steps that are driven by triggered conformational changes of viral envelope glycoproteins, so-called fusion proteins. Although high-resolution structural snapshots of viral fusion proteins in their prefusion and postfusion conformations are available, it has been difficult to define intermediate structures of the fusion pathway because of their transient nature. Flaviviruses possess a class II viral fusion protein (E) mediating fusion at acidic pH that is converted from a dimer to a trimer with a hairpin-like structure during the fusion process. Here we show for tick-borne encephalitis virus that exposure of virions to alkaline instead of acidic pH traps the particles in an intermediate conformation in which the E dimers dissociate and interact with target membranes via the fusion peptide without proceeding to the merger of the membranes. Further treatment to low pH, however, leads to fusion, suggesting that these monomers correspond to an as-yet-elusive intermediate required to convert the prefusion dimer into the postfusion trimer. Thus, the use of nonphysiological conditions allows a dissection of the flavivirus fusion process and the identification of two separate steps, in which membrane insertion of multiple copies of E monomers precedes the formation of hairpin-like trimers. This sequence of events provides important new insights for understanding the dynamic process of viral membrane fusion

Three-dimensional magnetohydrodynamic simulations of the evolution of magnetic fields in Fanaroff-Riley class II radio sources

Radio observations of Fanaroff-Riley class II sources often show correlations between the synchrotron emission and the linear-polarimetric distributions. Magnetic position vectors seem to align with the projected emission of both the radio jets and the sources' edges. Using statistics we study such relation as well as its unknown time evolution via synthetic polarisation maps of model FR II sources formed in 3D-MHD numerical simulations of bipolar, hypersonic and weakly magnetised jets. The magnetic field is initially random with a Kolmogorov power spectrum, everywhere. We investigate the structure and evolution of magnetic fields in the sources as a function of the power of jets and the observational viewing angle. Our synthetic polarisation maps agree with observations, showing B-field vectors which are predominantly aligned with the jet axis, and show that magnetic fields inside sources are shaped by the jets' backflow. Polarimetry is found to correlate with time, the viewing angle and the jet-to-ambient density contrast. The magnetic structure inside thin elongated sources is more uniform than inside more spherical ones. We see jets increase the magnetic energy in cocoons in proportion to the jet velocity and the cocoon width. Filaments in the synthetic emission maps suggest turbulence develops in evolved sources.Comment: Accepted for publication in the MNRAS. 21 pages, 11 figure

Diffusion Monte Carlo calculations for the ground states of atoms and ions in neutron star magnetic fields

The diffusion quantum Monte Carlo method is extended to solve the old theoretical physics problem of many-electron atoms and ions in intense magnetic fields. The feature of our approach is the use of adiabatic approximation wave functions augmented by a Jastrow factor as guiding functions to initialize the quantum Monte Carlo prodecure. We calcula te the ground state energies of atoms and ions with nuclear charges from Z= 2, 3, 4, ..., 26 for magnetic field strengths relevant for neutron stars.Comment: 6 pages, 1 figure, proceedings of the "9th International Conference on Path Integrals - New Trends and Perspectives", Max-Planck-Institut fur Physik komplexer Systeme, Dresden, Germany, September 23 - 28, 2007, to be published as a book by World Scientific, Singapore (2008