Szinaptikus moduláció és gamma-hidroxivajsav hatása a nucleus accumbens és a ventrális tegmentális area sejtjeire = Synaptic modulation and the effect of gamma-hydroxybutiric acid in the nucleus accumbens and in the ventral tegmental area

Kísérleteinkben kimutattuk az asztrociták részvételét a gamma-hidroxi vajsav (GHB) hatás közvetítésében, GHB adagolásra Ca2+ ion tranziensek léptek fel a nucleus accumbens (NA) asztrocitáiban. A GHB-val kiváltott Ca2+ ion koncentráció növekedést nem lehetett blokkolni a GHB receptor antagonista NCS-382-vel, vagy GABA-A és GABA-B receptor antagonistákkal. A GHB Ca2+ ion szint növekedést váltott ki funkcionális GABA-B receptort nem tartalmazó egerekben bizonyítva ezzel, hogy a GHB hatása az intracelluláris Ca2+ ion szintre GABA-B receptoroktól független hatás. Kísérleteink alapján feltételezhetjük, hogy az NA neuronjai és asztrocitái közötti kölcsönhatás vezet a szinaptikus kapcsolatok átrendeződéséhez az NA-ban és a különböző drogoktól való függőség kialakulásához. Ezért a drog-függőség megszüntetésére irányuló kezelések új célpontjai lehetnek az asztrociták. Kutatásaink során egy új típusú GHB receptor jelenlétét is kimutattuk a NA-ben, és találtunk egy újabb agyterületet a globus pallidus-t ahol a GABA-B receptoroknak egy olyan altípusa található amelyik nem aktiválható GHB-val. Az NA új típusú GHB receptora ideális célpontja lehet olyan gyógyszereknek amelyek a GHB függőség kialakulását gátolnák. | Our experiments showed the involvement of astrocytic activity in the development of gamma-hydroxybutyric (GHB) action. Application of GHB induced intracellular Ca2+ ion transients in the astrocytes of the nucleus accumbens. Intracellular Ca2+ ion transients were not blocked by the putative GHB receptor antagonist NCS-382, or GABA-A or GABA-B antagonists and were present in mice lacking functional GABA-B receptors. The involvement of astrocytes in the development of GHB-mediated effects can be characterized relatively easily, because GHB had no effect on neuronal voltage-gated or ionic currents. Our experiments suggest an astrocytic-neuronal interplay leading to the long-term modification of the neuronal circuitry of the nucleus accumbens (NA) underlying the development of the reinforcing properties of different drugs. Therefore astrocytes are possible new targets for medicines treating drug addiction or withdrawal. We have also demonstrated the presence of a new type of GHB receptor in the NA and found another area, the globus pallidus, where a GABA-B receptor subtype, insensitive to GHB does exist. The novel type of GHB receptor in the NA is an ideal target for medicines preventing the development of the reinforcing property of GHB

Mitokondriális károsodás in vitro epilepszia modellben = Mitochondrial malfunction during experimental status epilepticus

A kutatás célja az epileptikus aktivitás alatt fellépő Ca2+ ion-függő mitokondriális változások és szabad gyökképződés energiaháztartásra gyakorolt rövid-távú és krónikus hatásainak felderítése volt. A mitokondriális membránpotenciál és kálcium ion koncentráció vizsgálata kimutatta, hogy az epileptikus aktivitás, típusától függően különböző hatást gyakorol a sejt energiaháztartására. Interiktális aktivitás alatt az egyes mitokondriumok [Ca2+] és membránpotenciál fluktuációja követte a szinaptikus aktivitást, míg rohamszerű eseményekhez nagyszámú mitokondrium egyidejű, Ca2+ ion-függő depolarizációja társult. Bár ez a depolarizáció hátrányosan befolyásolja az ATP szintézist, a sejt szempontjából végzetes kimetelű mitokondriális permeabilizálódásra nem került sor. Hasonló szintű [Ca2+] növekedésnek kitett izolált mitokondriumokban szuperoxid gyök anion keletkezését lehetett regisztrálni gyors-kinetikai módszerekkel. A nitrogén monoxidról (NO) is sikerült kimutatni, hogy szintézise régió-specifikusan fokozódik az epileptikus aktivitás alatt. NO szintézis-gátló és gyökfogó molekulák segítségével jellemeztük az NO szerepét az interiktális és rohamszerű aktivitás közti átmenet szabályozásában a továbbiakban. Krónikusan epileptikus szövetben a rohamokat követő tartós mitokondriális metabolizmus változások az ingerléssel kiváltható NAD+ redukció csökkenésében nyilvánultak meg, ami az energiaháztartás szabályozhatóságának károsodására utal. | The aim of the study was to characterize the roles for the Ca2+ ion-dependent changes of mitochondrial energy metabolism and free radical formation in the cell energy homeostasis and epileptic injury. Epileptiform activity-dependent changes in the mitochondrial energy metabolism have been revealed by monitoring changes in mitochondrial membrane potential and Ca2+ ion concentration ([Ca2+]m) at single cell level. During the interictal phase, small-amplitude oscillations of mitochondrial membrane potential and [Ca2+]m occured, whereas seizure-like events resulted in large mitochondrial depolarisation due to intense Ca2+ ion cycling. Opening of the mitochondrial permeability transition pore did not contribute to this phenomenon. When isolated mitochondria has been exposed to a similar [Ca2+]m rise, rapid increase in superoxide radical formation was observed by fast-kinetic methods. The synthesis of NO has also been shown to increase during epileptiform activity in a region-specific manner. By applying NO-synthase inhibitors and NO-scavengers we have postulated a regulatory role for NO during the interictal activity-seizure transition. The relative contribution of NO-synthase subtypes to this phenomenon was characterized by using different NO-synthase inhibitors. In chronic epileptic tissue from patients and from a rat model of chronic epilepsy, the stimulus-induced rise in NAD reduction was decreased suggesting serious dysfunction of the regulation of energy metabolism

Glutamate Uptake Triggers Transporter-Mediated GABA Release from Astrocytes

Background: Glutamate (Glu) and c-aminobutyric acid (GABA) transporters play important roles in regulating neuronal activity. Glu is removed from the extracellular space dominantly by glial transporters. In contrast, GABA is mainly taken up by neurons. However, the glial GABA transporter subtypes share their localization with the Glu transporters and their expression is confined to the same subpopulation of astrocytes, raising the possibility of cooperation between Glu and GABA transport processes. Methodology/Principal Findings: Here we used diverse biological models both in vitro and in vivo to explore the interplay between these processes. We found that removal of Glu by astrocytic transporters triggers an elevation in the extracellular level of GABA. This coupling between excitatory and inhibitory signaling was found to be independent of Glu receptor-mediated depolarization, external presence of Ca2+ and glutamate decarboxylase activity. It was abolished in the presence of non-transportable blockers of glial Glu or GABA transporters, suggesting that the concerted action of these transporters underlies the process. Conclusions/Significance: Our results suggest that activation of Glu transporters results in GABA release through reversal of glial GABA transporters. This transporter-mediated interplay represents a direct link between inhibitory and excitatory neurotransmission and may function as a negative feedback combating intense excitation in pathological conditions such as epilepsy or ischemia

Distinct gamma oscillations in the distal dendritic fields of the dentate gyrus and the CA1 area of mouse hippocampus

The molecular layer of the dentate gyrus and the anatomically adjacent stratum lacunosum-moleculare of CA1 area, represent afferent areas at distinct levels of the hippocampal trisynaptic loop. Afferents to the dentate gyrus and CA1 area originate from different cell populations, including projection cells in entorhinal cortex layers two and three, respectively. To determine the organization of oscillatory activities along these terminal fields, we recorded local field potentials from multiple sites in the dentate gyrus and CA1 area of the awake mice, and localized gamma frequency (30150 Hz) oscillations in different layers by means of current source density analysis. During theta oscillations, we observed different temporal and spectral organization of gamma oscillations in the dendritic layers of the dentate gyrus and CA1 area, with a sharp transition across the hippocampal fissure. In CA1 stratum lacunosum-moleculare, transient mid-frequency gamma oscillations (CA1-gammaM; 80 Hz) occurred on theta cycle peaks, while in the dentate gyrus, fast (DG-gammaF; 110 Hz), and slow (DG-gammaS; 40 Hz) gamma oscillations preferentially occurred on troughs of theta waves. Units in dentate gyrus, in contrast to units in CA1 pyramidal layer, phase-coupled to DG-gammaF, which was largely independent from CA1 fast gamma oscillations (CA1-gammaF) of similar frequency and timing. Spike timing of units recorded in either CA1 area or dentate gyrus were modulated by CA1-gammaM. Our experiments disclosed a set of gamma oscillations that differentially regulate neuronal activity in the dentate gyrus and CA1 area, and may allow flexible segregation and integration of information across different levels of hippocampal circuitry.(VLID)355283

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