The cell adhesion protein CAR is a negative regulator of synaptic transmission

The Coxsackievirus and adenovirus receptor (CAR) is essential for normal electrical conductance in the heart, but its role in the postnatal brain is largely unknown. Using brain specific CAR knockout mice (KO), we discovered an unexpected role of CAR in neuronal communication. This includes increased basic synaptic transmission at hippocampal Schaffer collaterals, resistance to fatigue, and enhanced long-term potentiation. Spontaneous neurotransmitter release and speed of endocytosis are increased in KOs, accompanied by increased expression of the exocytosis associated calcium sensor synaptotagmin 2. Using proximity proteomics and binding studies, we link CAR to the exocytosis machinery as it associates with syntenin and synaptobrevin/VAMP2 at the synapse. Increased synaptic function does not cause adverse effects in KO mice, as behavior and learning are unaffected. Thus, unlike the connexin-dependent suppression of atrioventricular conduction in the cardiac knockout, communication in the CAR deficient brain is improved, suggesting a role for CAR in presynaptic processes

Predominant Functional Expression of Kv1.3 by Activated Microglia of the Hippocampus after Status epilepticus

BACKGROUND:Growing evidence indicates that the functional state of microglial cells differs according to the pathological conditions that trigger their activation. In particular, activated microglial cells can express sets of Kv subunits which sustain delayed rectifying potassium currents (Kdr) and modulate differently microglia proliferation and ability to release mediators. We recently reported that hippocampal microglia is in a particular activation state after a status epilepticus (SE) and the present study aimed at identifying which of the Kv channels are functionally expressed by microglia in this model. METHODOLOGY/PRINCIPAL FINDINGS:SE was induced by systemic injection of kainate in CX3CR1(eGFP/+) mice and whole cell recordings of fluorescent microglia were performed in acute hippocampal slices prepared 48 h after SE. Microglia expressed Kdr currents which were characterized by a potential of half-maximal activation near -25 mV, prominent steady-state and cumulative inactivations. Kdr currents were almost abolished by the broad spectrum antagonist 4-Aminopyridine (1 mM). In contrast, tetraethylammonium (TEA) at a concentration of 1 mM, known to block Kv3.1, Kv1.1 and 1.2 subunits, only weakly reduced Kdr currents. However, at a concentration of 5 mM which should also affect Kv1.3 and 1.6, TEA inhibited about 30% of the Kdr conductance. Alpha-dendrotoxin, which selectively inhibits Kv1.1, 1.2 and 1.6, reduced only weakly Kdr currents, indicating that channels formed by homomeric assemblies of these subunits are not important contributors of Kdr currents. Finally, agitoxin-2 and margatoxin strongly inhibited the current. CONCLUSIONS/SIGNIFICANCE:These results indicate that Kv1.3 containing channels predominantly determined Kdr currents in activated microglia after SE

What is the role of the film viewer? The effects of narrative comprehension and viewing task on gaze control in film

Film is ubiquitous, but the processes that guide viewers' attention while viewing film narratives are poorly understood. In fact, many film theorists and practitioners disagree on whether the film stimulus (bottom-up) or the viewer (top-down) is more important in determining how we watch movies. Reading research has shown a strong connection between eye movements and comprehension, and scene perception studies have shown strong effects of viewing tasks on eye movements, but such idiosyncratic top-down control of gaze in film would be anathema to the universal control mainstream filmmakers typically aim for. Thus, in two experiments we tested whether the eye movements and comprehension relationship similarly held in a classic film example, the famous opening scene of Orson Welles' Touch of Evil (Welles & Zugsmith, Touch of Evil, 1958). Comprehension differences were compared with more volitionally controlled task-based effects on eye movements. To investigate the effects of comprehension on eye movements during film viewing, we manipulated viewers' comprehension by starting participants at different points in a film, and then tracked their eyes. Overall, the manipulation created large differences in comprehension, but only produced modest differences in eye movements. To amplify top-down effects on eye movements, a task manipulation was designed to prioritize peripheral scene features: a map task. This task manipulation created large differences in eye movements when compared to participants freely viewing the clip for comprehension. Thus, to allow for strong, volitional top-down control of eye movements in film, task manipulations need to make features that are important to narrative comprehension irrelevant to the viewing task. The evidence provided by this experimental case study suggests that filmmakers' belief in their ability to create systematic gaze behavior across viewers is confirmed, but that this does not indicate universally similar comprehension of the film narrative

Astrocyte networks and intercellular calcium propagation

International audienceAstrocytes organize in complex networks through connections by gap junction channels that are regulated by extra-and intracellular signals. Calcium signals generated in individual cells, can propagate across these networks in the form of intercellular calcium waves, mediated by diffusion of second messengers molecules such as inositol 1,4,5-trisphosphate. The mechanisms underpinning the large variety of spatiotemporal patterns of propagation of astrocytic calcium waves however remain a matter of investigation. In the last decade, awareness has grown on the morphological diversity of astrocytes as well as their connections in networks, which seem dependent on the brain area, developmental stage, and the ultra-structure of the associated neuropile. It is speculated that this diversity underpins an equal functional variety but the current experimental techniques are limited in supporting this hypothesis because they do not allow to resolve the exact connectivity of astrocyte networks in the brain. With this aim we present a general framework to model intercellular calcium wave propagation in astrocyte networks and use it to specifically investigate how different network topologies could influence shape, frequency and propagation of these waves

Funktion und Expression von Kv-Kanaelen und Neurotransmitter-Rezeptoren auf der Mikroglia [Function and expression of Kv channels and neurotransmitter receptors on microglial cells]

Mikroglia sind spezialisierte Immunzellen im Gehirn, deren Funktion hauptsaechlich darin besteht, die hochempfindlichen Neurone vor Erkrankungen zu schuetzen und deren normale Funktionen durch Sekretion neurotrophischer Stoffe zu unterstuetzen. Mikroglia tasten mit ihren beweglichen Zellauslaeufern staendig das umgebende Gewebe ab und koennen bei Veraenderungen sofort reagieren. Demnach muessen diese Zellen besonders schnelle Aktivierungsmechanismen aufweisen. Neurone erreichen schnelle Informationsweiterleitung durch Aktionspotentiale, d.h. eine Depolarisation des Membranpotentials durch das Oeffnen von Na+-Kanaelen. Moeglicherweise nutzen auch Mikroglia Ionenkanaele um sehr schnell auf Veraenderungen ihrer Umgebung reagieren zu koennen. Im Rahmen dieser Arbeit konnte gezeigt werden, dass die, durch LPS-Stimulation aktivierten spannungsgesteuerten, auswaertsrektifizierenden K+-Kanaele (voltage-gated K+ channels Kv) Kv1.5 und Kv1.3 wichtige Zellfunktionen wie Proliferation und NO-Freisetzung unterschiedlich modulieren. Um jedoch adaequat auf ein neuronales Signal reagieren zu koennen, muessen Mikroglia kontinuierlich ueber den Zustand der umliegenden Neurone informiert sein. Dazu sollten Mikroglia neuronale Signale wahrnehmen koennen. Neurone kommunizieren untereinander und auch mit Astrozyten ueber die Ausschuettung von Neurotransmittern. Deshalb war es nahe liegend zu untersuchen ob auch Mikroglia neuronale Signale in Form von Neurotransmittern wahrnehmen koennen. Im Rahmen dieser Arbeit konnten funktionelle Rezeptoren fuer Dopamin, Noradrenalin, Histamin und Serotonin auf der Mikroglia in vitro und in situ, sowohl auf amoeboiden als auch auf ramifizierten Zellen nachgewiesen werden. Die Stimulation dieser Rezeptoren bewirkt ebenfalls eine Aenderung des K+-Stromprofils, hierbei handelt es sich jedoch vermutlich um einen G-Protein gekoppelten K+ -Kanal. Demnach scheint die Aktivierung von Mikroglia massgeblich durch die Expression unterschiedlicher K+ -Kanaele beeinflusst werden. [The main functions of microglia, the immunocompetent cells in the brain, are to protect the very fragile neurons against pathological events and to support them with neurotrophic factors. Microglia continually survey their microenvironment with extremely motile processes and can immediately respond to changes. Therefore they require a rapid activation system. Neurons can respond very fast through the activation of Na+ channels and a massive depolarization of the membrane potential. Potentially microglia use similar mechanisms for a fast response. As shown in this work microglia respond to LPS activation with the induction of a voltage gated outwardly rectifying K+ current mediated by two channel proteins Kv1.5 and Kv1.3. These channels can modulate distinct immune functions such as nitric oxide release or proliferation. These channels are possibly co-expressed on microglia cells and lead to the precise immune response. For an adequate immune response the microglia need information about the state of health of the surrounding neurons. Hence they need a communication system. Neurons communicate among each other and with astrocytes via neurotransmitter release. Consequently the question arises wether microglial cells are able to sense neurotransmitters as well. I could show that microglia in vitro and in situ express functional receptors for some of the main neurotransmitters, dopamine, noradrenaline, serotonin and histamine. Ramified as well as ameboid microglia respond in the same way to dopamine, noradrenalin and histamine application, indicating that there is a common mechanism for neurotransmitter action on microglia. Receptor stimulation results again, as shown for LPS activation, in a change in the K+ current profile mediated by a G-protein coupled mechanism. According to these observations one could conclude that the activation of microglial cells is decisively influenced by the expression of K+ currents and that these curents modulate distinct functions.

Dopamine and noradrenaline control distinct functions in rodent microglial cells

Microglial cells are the immune-competent elements of the brain. They not only express receptors for chemokines and cytokines but also for neurotransmitters such as GABA [Charles et al., Mol. Cell Neurosci. 24 (2003)214], glutamate [(Noda et al., J. Neurosci. 20 (2000) 251], and adrenaline [Mori et al., Neuropharmacology 43 (2002) 1026]. Here we report the functional expression of dopamine receptors in mouse and rat microglia, in culture and brain slices. Using the patch clamp technique as the functional assay we identified D1- and D2-like dopamine receptors using subtype-specific ligands. They triggered the inhibition of the constitutive potassium inward rectifier and activated potassium outward currents in a subpopulation of microglia. Chronic dopamine receptor stimulation enhanced migratory activity and attenuated the lipopolysaccharide (LPS)-induced nitric oxide (NO) release similar as by stimulation of adrenergic receptors. While, however, noradrenaline attenuated the LPS-induced release of TNF-alpha and IL-6, dopamine was ineffective in modulating this response. We conclude that microglia express dopamine receptors which are distinct in function from adrenergic receptors