Fear extinction relies on ventral hippocampal safety codes shaped by the amygdala.

Extinction memory retrieval is influenced by spatial contextual information that determines responding to conditioned stimuli (CS). However, it is poorly understood whether contextual representations are imbued with emotional values to support memory selection. Here, we performed activity-dependent engram tagging and in vivo single-unit electrophysiological recordings from the ventral hippocampus (vH) while optogenetically manipulating basolateral amygdala (BLA) inputs during the formation of cued fear extinction memory. During fear extinction when CS acquire safety properties, we found that CS-related activity in the vH reactivated during sleep consolidation and was strengthened upon memory retrieval. Moreover, fear extinction memory was facilitated when the extinction context exhibited precise coding of its affective zones. Last, these activity patterns along with the retrieval of the fear extinction memory were dependent on glutamatergic transmission from the BLA during extinction learning. Thus, fear extinction memory relies on the formation of contextual and stimulus safety representations in the vH instructed by the BLA

Anxiety-related activity of ventral hippocampal interneurons.

Anxiety is an aversive mood reflecting the anticipation of potential threats. The ventral hippocampus (vH) is a key brain region involved in the genesis of anxiety responses. Recent studies have shown that anxiety is mediated by the activation of vH pyramidal neurons targeting various limbic structures. Throughout the cortex, the activity of pyramidal neurons is controlled by GABA-releasing inhibitory interneurons and the GABAergic system represents an important target of anxiolytic drugs. However, how the activity of vH inhibitory interneurons is related to different anxiety behaviours has not been investigated so far. Here, we integratedin vivoelectrophysiology with behavioural phenotyping of distinct anxiety exploration behaviours in rats. We showed that pyramidal neurons and interneurons of the vH are selectively active when animals explore specific compartments of the elevated-plus-maze (EPM), an anxiety task for rodents. Moreover, rats with prior goal-related experience exhibited low-anxiety exploratory behaviour and showed a larger trajectory-related activity of vH interneurons during EPM exploration compared to high anxiety rats. Finally, in low anxiety rats, trajectory-related vH interneurons exhibited opposite activity to pyramidal neurons specifically in the open arms (i.e. more anxiogenic) of the EPM. Our results suggest that vH inhibitory micro-circuits could act as critical elements underlying different anxiety states

No Far-Infrared-Spectroscopic Gap in Clean and Dirty High-TC_C Superconductors

We report far infrared transmission measurements on single crystal samples derived from Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$. The impurity scattering rate of the samples was varied by electron-beam irradiation, 50MeV $^{16}$O$^{+6}$ ion irradiation, heat treatment in vacuum, and Y doping. Although substantial changes in the infrared spectra were produced, in no case was a feature observed that could be associated with the superconducting energy gap. These results all but rule out ``clean limit'' explanations for the absence of the spectroscopic gap in this material, and provide evidence that the superconductivity in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ is gapless.Comment: 4 pages and 3 postscript figures attached. REVTEX v3.0. Accepted for publication in Phys. Rev. Lett. IRDIRT

The spatiotemporal organisation of GABAergic interneurons during dynamic network oscillations and spatial navigation in the rodent hippocampus

Der Hippocampus ist ein Gehirnareal, das eine wichtige Rolle in der Kodierung des episodischen und des räumlichen Gedächtnisses spielt. Die genauen Interaktionen zwischen den Neuronen, die diese Kodierung ermöglichen, sind jedoch unbekannt. In der Großhirnrinde, zu der auch der Hippocampus gehört, gibt es zwei Hauptklassen von Neuronen: Exzitatorischen Pyramidenzellen und inhibitorischen GABAergen Interneurone. Die Aktivität der Pyramidenzellen korreliert mit kognitiven Prozessen wie zum Beispiel der Kodierung einer Umgebung: Pyramidenzellen im Hippocampus können zu "place cells" (Ortszellen) werden und feuern nur an einem bestimmten Ort in einer Umgebung und repräsentieren so eine kognitive Karte und ein räumliches Gedächtnis dieser Umgebung. Der Hippocampus ist ein evolutionär stark konserviertes Gehirnareal in Säugetieren und das CA1-Feld ist das Hauptausgabeareal darin. Mehr als 20 unterschiedliche GABAerge Interneurontypen wurden im CA1 Hippocampus des Nagerhirns beschrieben. Diese Interneurontypen nehmen unterschiedliche räumliche und zeitliche Bereiche ein, in denen sie die Aktivität von Pyramidenzellen während Netzwerkoszillationen modulieren. Netzwerkoszillationen reflektieren synchrone Gehirnaktivität. Zwei bedeutende Oszillationen im Hippocampus sind die Theta-Oszillationen (5-12 Hz) und die Sharp-wave-assoziierten Ripple-Oszillationen (SWR, 120-250 Hz). Theta-Oszillationen sind zum Beispiel dann vorhanden, wenn das Tier läuft, eine Gegend erkundet oder während des REM Schlafes. SWR Oszillationen treten auf während das Tier ruht oder schläft. Die Neuronenaktivität während dieser Oszillationen stehen im Zusammenhang mit der Gedächtniskonsolidierung. Der CA1 Hippocampus ist entlang seiner septotemoralen Achse in einen dorsalen, intermediären und ventralen CA1 Hippocampus organisiert (dCA1, iCA1 und vCA1). Während dCA1 hauptsächlich visuelle und räumliche Informationen verarbeitet erhalten iCA1 und vCA1 mehr nicht-räumliche Informationen, zum Bespiel über Gerüche. iCA1 und vCA1 sind direkt mit dem präfrontalen Kortex verbunden. Man vermutet, dass iCA1 unterschiedliche Informationen im Hippocampus integriert und mit dem Verhalten verbindet. Ihm kommt somit eine besondere Rolle zu. Eine besondere Dynamik entlang der septotemoralen Achse ist, dass Theta-Oszillationen von dCA1 zu vCA1 wandern. In dem ersten Projekt, das als publizierter Artikel in dieser Doktorarbeit enthalten ist, haben wir GABAerge Interneurontypen in iCA1 bestimmt und erforscht, wie sie zur zeitlichen und räumlichen Organisation der Neuronenaktivität während der wandernden Thetawelle beitragen. Weiterhin analysierten wir die Dynamik von SWR zwischen den dCA1 und iCA1 und der Aktivität von Interneuronen während dieser Ereignisse. Für dies haben wir die ix juxtazelluläre Ableitungs- und Markierungstechnik benutzt mit der wir einzelne Neurone zusammen mit der Netzwerkaktivität in dCA1 und iCA1 in anästhesierten Ratten ableiten konnten. Die Markierung der Zellen erlaubte uns die spätere Identifikation. Wir identifizierten Parvalbumin exprimierende (PV+) Korbzellen, Axo-axonische Zellen und O-LM Zellen in iCA1. Mit unserer Studie zeigen wir, dass die unterschiedliche zeitliche Organisation dieser Zelltypen eng mit den wanderenden Theta-Oszillationen verbunden ist. Das lässt vermuten, dass die gesamte neuronal Aktivität, inhibitorische wie exzitatorische, vom dCA1 zum iCA1 wandert. Sie behält jedoch ihre fundamentale Organisation während der Theta-Oszillationen und zwar mit der aufeinanderfolgender Aktivierung von Zelltypen bei: Zuerst feuern die Axo-axonischen Zellen, dann die PV+ Korbzellen und dann die O-LM Zellen zusammen mit den Pyramidenzellen. SWR-Oszillationen sind jedoch oft synchron zwischen den dCA1 und iCA1, obwohl sie auch nur lokal auftreten können. Wir haben gezeigt, wie unterschiedliche GABAerge Zelltypen mit der Pyramidenzellaktivität während dynamischer Prozesse interagieren und dadurch möglicherwiese zu wichtigen Integrationsprozessen während der Gedächtniskonsolidierung beitragen. Im zweiten, noch laufenden Projekt wollen wir den Beitrag der GABAergen Interneurontypen in CA1 Hippocampus während des Verhaltens der Tiere erforschen. Dafür benutzen wir ein virtuelles System, in dem kopffixierte Mäuse eine räumliche Aufgabe mit einem Geruchssignal in einer virtuellen Umgebung lösen müssen. Die Neuronenaktivität wird dabei entweder mit Silikonelektroden oder mit der juxtazellulären Methode in Echtzeit abgeleitet. Da es vermutet wird, dass iCA1 eine besondere integrative Rolle hat und Geruchinformation verarbeitet, versuchen wir in iCA1 abzuleiten. Bisher lassen die Ergebnisse der Silikonelektrodenmessung vermuten, dass unidentifizierte Pyramidenzellen und Interneurone den Geruch in eine räumliche Kodierung integrieren. Die Ergebnisse der juxtazellulären Experimente beinhalten eine Bistratified Zelle in iCA1 und eine Axo-axonische Zelle in iCA3. Aus den Die Ergebnisse kann geschlossen werden, dass die Aktivität dieser Zellen von der kognitiven Beanspruchung in den unterschiedlichen Bereichen der virtuellen Umgebung moduliert wird und dass die Aktivität der bistratified Zelle auch von der Verarbeitung des Geruchssignals beeinflusst wird. Diese ersten Ergebnisse könnten darauf hindeuten, dass Populationen von unterschiedlichen Interneuron-Zelltypen die kontext- und verhaltensabhängige Aktivierung von Pyramidenzellen modulieren und daher direkt auf die Kodierung kognitiver Prozesse einwirken.The hippocampus is a brain area that plays an important role in the encoding of episodic and spatial memories. But the precise interactions between neurons that give rise to this encoding are not well understood. In the cerebral cortex, to which also the hippocampus belongs, two main classes of neuron can be found: the glutamatergic pyramidal and GABAergic interneurons. The activity of pyramidal cells correlates with cognitive processes such as the encoding of an environment. Pyramidal cells in the hippocampus can become place cells, meaning they fire only in a specific location of an environment and thereby form a cognitive map and spatial memory of the environment. The hippocampus is a highly conserved brain area in mammals and the CA1 subfield represents the output area of the hippocampus. More than 20 different GABAergic interneuron types have been described in the rodent dorsal CA1 hippocampus and have been shown to occupy distinct spatiotemporal compartments modulating the activity of pyramidal cells during local field potential (LFP) network oscillations. Network oscillations reflect synchronous brain activity; in the hippocampus theta (5-12 Hz) and sharp-wave associated ripple (SWR, 120-250 Hz) oscillations are prominent. Theta oscillations are present when the animal is running, exploring an environment or during REM sleep. SWR oscillations occur during resting and sleep and neural activity during these events is related to memory consolidation processes. The CA1 hippocampus is organized along the septotemporal axis into a dorsal, intermediate and ventral CA1 (dCA1, iCA1 and vCA1, respectively). While the dCA1 processes mostly visual spatial information, the iCA1 and vCA1 receive in addition also non-spatial sensory information such as strong odour related input. The iCA1 and vCA1 also directly project to prefrontal cortex and it has been suggested that iCA1 is in a unique position to integrate information in the hippocampus and linking it to behaviour. A prominent network dynamic along the septotemporal axis is the travelling of theta oscillations from the dCA1 to the vCA1. In the first project of my thesis, included here as the published article, we investigated the GABAergic interneuron types in the iCA1 and how they are involved in the spatiotemporal organization of the travelling theta waves. We further analysed the dynamics of SWR oscialltions across dCA1 and iCA1 hippocampus and the associated activity patterns of iCA1 interneurons. We used the juxtacellular recording and labelling technique to record from single neurons together with dCA1 and iCA1 LFP in anesthetized rats. The labelling of the recorded neurons enabled the post hoc identification. We identified parvalbumin expressing (PV+) basket, axo-axonic and O-LM cells in the iCA1. In our study we showed that the distinct temporal organization of these neuron types is linked to travelling theta oscillations. vii This suggests that inhibitory and excitatory neuronal activity travels from dCA1 to iCA1, but within each location fundamental organization principles during theta oscillations are retained with sequential activation of first axo-axonic cells, then PV+ basket cells and then O-LM and pyramidal cells. In contrast, during SWR oscillations the activity of dCA1 and iCA1 is often synchronized but can also be local. We showed how different GABAergic interneurons are interacting with pyramidal cell activity during dynamic operations which might underlie important integration processes encoding memory. In the second ongoing project I aim to investigate the contribution of GABAergic interneuron types in the CA1 hippocampus during behaviour. For this I use a virtual reality system in which head-fixed mice perform an odour-cued spatial task in a virtual maze and can be recorded from at the same time with silicon probes or the juxtacellular method. Because of its suggested integrative role and stronger odour input, recordings are performed in the iCA1. Silicon probe recordings suggest that putative pyramidal cells integrate the odour stimulus into a spatial representation of the maze and different interneurons also respond specifically to the odour. With the juxtacellular experiments a bistratified cell in the iCA1 and an axo-axonic cell in the iCA3 have been recorded. The activity of these cells might be modulated by the changing cognitive load in the different parts of the virtual maze and, for the bistratified cell, also by the presence or absence of the odour processing. These results suggest that populations of different interneuron types might modulate the behaviour relevant contextual activation of pyramidal cells in space and might therefore be directly involved in the encoding of spatial memory.submitted by Thomas ForroAbweichender Titel laut Übersetzung der Verfasserin/des VerfassersZsfassung in dt. SpracheWien, Med. Univ., Diss., 2015OeBB(VLID)171642

Activity of ventral hippocampal parvalbumin interneurons during anxiety.

Anxiety plays a key role in guiding behavior in response to potential threats. Anxiety is mediated by the activation of pyramidal neurons in the ventral hippocampus (vH), whose activity is controlled by GABAergic inhibitory interneurons. However, how different vH interneurons might contribute to anxiety-related processes is unclear. Here, we investigate the role of vH parvalbumin (PV)-expressing interneurons while mice transition from safe to more anxiogenic compartments of the elevated plus maze (EPM). We find that vH PV interneurons increase their activity in anxiogenic EPM compartments concomitant with dynamic changes in inhibitory interactions between PV interneurons and pyramidal neurons. By optogenetically inhibiting PV interneurons, we induce an increase in the activity of vH pyramidal neurons and persistent anxiety. Collectively, our results suggest that vH inhibitory microcircuits may act as a trigger for enduring anxiety states

Frontiers in Cellular Neuroscience / Spike-Timing of Orbitofrontal Neurons Is Synchronized With Breathing

The orbitofrontal cortex (OFC) has been implicated in a multiplicity of complex brain functions, including representations of expected outcome properties, post-decision confidence, momentary food-reward values, complex flavors and odors. As breathing rhythm has an influence on odor processing at primary olfactory areas, we tested the hypothesis that it may also influence neuronal activity in the OFC, a prefrontal area involved also in higher order processing of odors. We recorded spike timing of orbitofrontal neurons as well as local field potentials (LFPs) in awake, head-fixed mice, together with the breathing rhythm. We observed that a large majority of orbitofrontal neurons showed robust phase-coupling to breathing during immobility and running. The phase coupling of action potentials to breathing was significantly stronger in orbitofrontal neurons compared to cells in the medial prefrontal cortex. The characteristic synchronization of orbitofrontal neurons with breathing might provide a temporal framework for multi-variable processing of olfactory, gustatory and reward-value relationships.(VLID)470102

Presentation_1_Spike-Timing of Orbitofrontal Neurons Is Synchronized With Breathing.PDF

<p>The orbitofrontal cortex (OFC) has been implicated in a multiplicity of complex brain functions, including representations of expected outcome properties, post-decision confidence, momentary food-reward values, complex flavors and odors. As breathing rhythm has an influence on odor processing at primary olfactory areas, we tested the hypothesis that it may also influence neuronal activity in the OFC, a prefrontal area involved also in higher order processing of odors. We recorded spike timing of orbitofrontal neurons as well as local field potentials (LFPs) in awake, head-fixed mice, together with the breathing rhythm. We observed that a large majority of orbitofrontal neurons showed robust phase-coupling to breathing during immobility and running. The phase coupling of action potentials to breathing was significantly stronger in orbitofrontal neurons compared to cells in the medial prefrontal cortex. The characteristic synchronization of orbitofrontal neurons with breathing might provide a temporal framework for multi-variable processing of olfactory, gustatory and reward-value relationships.</p

Anisotropic memory effects in confined colloidal diffusion

The motion of an optically trapped sphere constrained by the vicinity of a wall is investigated at times where hydrodynamic memory is significant. First, we quantify, in bulk, the influence of confinement arising from the trapping potential on the sphere's velocity autocorrelation function C(t). Next, we study the splitting of C(t) into C-parallel to(t) and C-perpendicular to(t), when the sphere is approached towards a surface. Thereby, we monitor the crossover from a slow t(-3/2) long-time tail, away from the wall, to a faster t(-5/2) decay, due to the subtle interplay between hydrodynamic backflow and wall effects. Finally, we discuss the resulting asymmetric time-dependent diffusion coefficients

Subnanometer motion of cargoes driven by thermal gradients along carbon nanotubes

An important issue in nanoelectromechanical systems is developing small electrically driven motors. We report on an artificial nanofabricated motor in which one short carbon nanotube moves relative to another coaxial nanotube. A cargo is attached to an ablated outer wall of a multiwalled carbon nanotube that can rotate and/ or translate along the inner nanotube. The motion is actuated by imposing a thermal gradient along the nanotube, which allows for subnanometer displacements, as opposed to an electromigration or random walk effect