Pyramidal neurons in the superficial layers of rat retrosplenial cortex exhibit a late-spiking firing property

The rodent granular retrosplenial cortex (GRS) is reciprocally connected with the hippocampus. It is part of several networks implicated in spatial learning and memory, and is known to contain head-direction cells. There are, however, few specifics concerning the mechanisms and microcircuitry underlying its involvement in spatial and mnemonic functions. In this report, we set out to characterize intrinsic properties of a distinctive population of small pyramidal neurons in layer 2 of rat GRS. These neurons, as well as those in adjoining layer 3, were found to exhibit a late-spiking (LS) firing property. We established by multiple criteria that the LS property is a consequence of delayed rectifier and A-type potassium channels. These were identified as Kv1.1, Kv1.4 and Kv4.3 by Genechip analysis, in situ hybridization, single-cell reverse transcriptase-polymerase chain reaction, and pharmacological blockade. The LS property might facilitate comparison or integration of synaptic inputs during an interval delay, consistent with the proposed role of the GRS in memory-related processes.RIKEN Brain Science Institut

Neurotrophin-3 Is Involved in the Formation of Apical Dendritic Bundles in Cortical Layer 2 of the Rat

Apical dendritic bundles from pyramidal neurons are a prominent feature of cortical neuropil but with significant area specializations. Here, we investigate mechanisms of bundle formation, focusing on layer (L) 2 bundles in rat granular retrosplenial cortex (GRS), a limbic area implicated in spatial memory. By using microarrays, we first searched for genes highly and specifically expressed in GRS L2 at postnatal day (P) 3 versus GRS L2 at P12 (respectively, before and after bundle formation), versus GRS L5 (at P3), and versus L2 in barrel field cortex (BF) (at P3). Several genes, including neurotrophin-3 (NT-3), were identified as transiently and specifically expressed in GRS L2. Three of these were cloned and confirmed by in situ hybridization. To test that NT-3–mediated events are causally involved in bundle formation, we used in utero electroporation to overexpress NT-3 in other cortical areas. This produced prominent bundles of dendrites originating from L2 neurons in BF, where L2 bundles are normally absent. Intracellular biocytin fills, after physiological recording in vitro, revealed increased dendritic branching in L1 of BF. The controlled ectopic induction of dendritic bundles identifies a new role for NT-3 and a new in vivo model for investigating dendritic bundles and their formation

Die visuelle Darstellung von Migranten – Wandel und Kontinuitäten im deutschen Mediendiskurs

Ausgehend von dem Konzept der Mediatisierung im Hinblick auf eine Verknüpfung von medialem und politischem Diskurs wird in dieser Arbeit untersucht, inwiefern sich die visuelle Rahmung von Migranten im Nachrichtenmagazin Der Spiegel im Sommer 2015 im Vergleich zu den 1990er Jahren, in denen integrationspolitische Bemühungen noch weitgehend vernachlässigt wurden, gewandelt hat. Mittels einer Verbindung von ikonografisch-ikonologischer Bildinterpretation und visueller Framing-Analyse werden verschiedene Frames innerhalb der beiden Untersuchungszeiträume identifiziert. Im Zeitraum zu Beginn der 1990er Jahre dominieren demnach der Belastungs- und Überforderungs-Frame, der Bedrohungs-Frame, der Verzweiflungsund Hilfsbedürftigkeits-Frame sowie der Kriminalitäts- und Missbrauchs-Frame in der visuellen Migrations-Berichterstattung des Spiegel. Während der Belastungs- und Überforderungs-Frame sowie der Verzweiflungs- und Hilfsbedürftigkeits-Frame auch in der Berichterstattung 2015 zu finden sind, entfallen der Bedrohungs- sowie der Kriminalitäts- und Missbrauchs-Frame und werden durch den Solidaritäts- und Willkommens-Frame, den Gemeinschafts- und Integrations-Frame sowie den Arbeits- und (ökonomischen) Nutzen-Frame ersetzt. Dies bestätigt die forschungsleitende Annahme, die visuelle Berichterstattung über Migranten sei im Vergleich zu den 1990er Jahren und im Zuge gesellschaftspolitischer Veränderungen integrationsorientierter sowie differenzierter geworden

Detection of p75 mRNA in developing marsupial CNS by cross- hybridization with rat oligonucleotide probes

We analyzed the distribution of mRNAs encoding the low-affinity neurotrophin receptor (p75) in the CNS of adult and neonatal opossum (Monodelphis demestica) by in situ hybridization with oligodeoxynucleotide probes complementary to cloned rat sequences. During the first 2 postnatal weeks high levels of p75 message were present in the mantle zone throughout the neural tube, in basal forebrain neurons, in motoneurons, and in cerebellar cell layers. Transcript expression decreased with age. In adult CNS only a few cells in the basal forebrain expressed high levels of p75 mRNA. Nerve growth factor upregulated p75 mRNA signals in dorsal root ganglia of cultured 7 day old whole-CNS preparations. Our results indicate the usefulness of rat p75 oligodexynucleotide probes to identify homologous species of transcripts in the CNS of a non-eutherian mammal.Supported by Swiss National Research Fund (3100-42.028.94).Peer reviewe

Chronic Loss of CA2 Transmission Leads to Hippocampal Hyperexcitability

International audienceHippocampal CA2 pyramidal cells project into both the neighboring CA1 and CA3 subfields, leaving them well positioned to influence network physiology and information processing for memory and space. While recent work has suggested unique roles for CA2, including encoding position during immobility and generating ripple oscillations, an interventional examination of the integrative functions of these connections has yet to be reported. Here we demonstrate that CA2 recruits feedforward inhibition in CA3 and that chronic genetically engineered shutdown of CA2-pyramidal-cell synaptic transmission consequently results in increased excitability of the recurrent CA3 network. In behaving mice, this led to spatially triggered episodes of network-wide hyperexcitability during exploration accompanied by the emergence of high-frequency discharges during rest. These findings reveal CA2 as a regulator of network processing in hippocampus and suggest that CA2-mediated inhibition in CA3 plays a key role in establishing the dynamic excitatory and inhibitory balance required for proper network function

Dissipation Lifetime of Catalysis as a Dynamical System

Catalysis is a critical mechanism to direct chemical reactions in biology and chemistry. However, quantitatively predicting their properties such as activity or stability is difficult, due to the lack of an equation which can be applied to various reaction mechanisms. Here, we report an equation which estimates the lifetime of a catalyst by analyzing their mechanism from a dynamical systems perspective. Furthermore, as proof of concept, we show its consistency with experiments by performing the oxygen evolution reaction on manganese oxide. The equation successfully rationalizes the time until the activity decreases to 10 % of the initial value with an expected error of 20 %, providing the first quantitative model to predict the lifetime of a chemical system

A hypothalamic novelty signal modulates hippocampal memory

International audienceThe ability to recognize information that is incongruous with previous experience is critical for survival. Novelty signals have therefore evolved in the mammalian brain to enhance attention, perception and memory1,2. Although the importance of regions such as the ventral tegmental area3,4 and locus coeruleus5 in broadly signalling novelty is well-established, these diffuse monoaminergic transmitters have yet to be shown to convey specific information on the type of stimuli that drive them. Whether distinct types of novelty, such as contextual and social novelty, are differently processed and routed in the brain is unknown. Here we identify the supramammillary nucleus (SuM) as a novelty hub in the hypothalamus6. The SuM region is unique in that it not only responds broadly to novel stimuli, but also segregates and selectively routes different types of information to discrete cortical targets-the dentate gyrus and CA2 fields of the hippocampus-for the modulation of mnemonic processing. Using a new transgenic mouse line, SuM-Cre, we found that SuM neurons that project to the dentate gyrus are activated by contextual novelty, whereas the SuM-CA2 circuit is preferentially activated by novel social encounters. Circuit-based manipulation showed that divergent novelty channelling in these projections modifies hippocampal contextual or social memory. This content-specific routing of novelty signals represents a previously unknown mechanism that enables the hypothalamus to flexibly modulate select components of cognition