Glutamatergic alterations in the cortex of genetic absence epilepsy rats

<p>Abstract</p> <p>Background</p> <p>In absence epilepsy, the neuronal hyper-excitation and hyper-synchronization, which induce spike and wave discharges in a cortico-thalamic loop are suspected to be due to an imbalance between GABA and glutamate (GLU) neurotransmission. In order to elucidate the role played by GLU in disease outcome, we measured cortical and thalamic extracellular levels of GLU and GABA. We used an <it>in vivo </it>quantitative microdialysis approach (no-net-flux method) in an animal model of absence epilepsy (GAERS). In addition, by infusing labelled glutamate through the microdialysis probe, we studied <it>in vivo </it>glutamate uptake in the cortex and thalamus in GAERS and non-epileptic control (NEC) rats. Expression of the vesicular glutamate transporters VGLUT1 and VGLUT2 and a synaptic component, synaptophysin, was also measured.</p> <p>Results</p> <p>Although extracellular concentrations of GABA and GLU in the cortex and thalamus were not significantly different between GAERS and NEC rats, cortical GLU uptake was significantly decreased in unrestrained awake GAERS. Expression of VGLUT2 and synaptophysin was increased in the cortex of GAERS compared to NEC rats, but no changes were observed in the thalamus.</p> <p>Conclusion</p> <p>The specific decrease in GLU uptake in the cortex of GAERS linked to synaptic changes suggests impairment of the glutamatergic terminal network. These data support the idea that a change in glutamatergic neurotransmission in the cortex could contribute to hyperexcitability in absence epilepsy.</p

Monitoring Molecules in Neurosciences ; Un congrès international sponsorisé par l'AFSTAL

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INTERETS ET LIMITES DE LA MICRODIALYSE INTRACEREBRALE COUPLEE A L'ELECTROPHORESE CAPILLAIRE POUR L'ETUDE DES ACIDES AMINES EXCITATEURS CEREBRAUX

DANS LE SYSTEME NERVEUX CENTRAL, LE GLUTAMATE (GLU) ET L'ASPARTATE (ASP) SONT A LA FOIS DES NEUROTRANSMETTEURS (ACIDES AMINES EXCITATEURS, AAE) ET DES COMPOSES IMPLIQUES DANS LE METABOLISME GENERAL. AINSI, LE GLU ET L'ASP EXTRACELLULAIRES PEUVENT CORRESPONDRE A UNE LIBERATION SYNAPTIQUE D'AAE OU AU METABOLISME GENERAL. COMME LA CINETIQUE DE LA NEUROTRANSMISSION EST PLUS RAPIDE QUE CELLE DES PROCESSUS METABOLIQUES, LES MESURES DES CONCENTRATIONS EXTRACELLULAIRES DE GLU ET D'ASP DEVRAIENT REFLETER LES VARIATIONS EN AAE SI ELLES SONT EFFECTUEES A UNE FREQUENCE ELEVEE. CECI PEUT ETRE REALISE PAR MICRODIALYSE INTRA-CEREBRALE COUPLEE A L'ELECTROPHORESE CAPILLAIRE AVEC DETECTION DE FLUORESCENCE INDUITE PAR LASER (CE-LIFD). CE TRAVAIL, EFFECTUE IN VIVO DANS LE STRIATUM DE RAT, A ETE DE DETERMINER : A) SI UNE APPROCHE COMBINANT MICRODIALYSE ET CE-LIFD PERMET, EN REVELANT DES MECANISMES RAPIDES, DE SUIVRE LES VARIATIONS EN AAE EXTRACELLULAIRES, ET, B) SI CE MEILLEUR SUIVI DES AAE FAIT APPARAITRE DES DIFFERENCES DANS LES FLUCTUATIONS DE GLU ET D'ASP, APPUYANT L'HYPOTHESE D'UNE REGULATION DIFFERENTIELLE DES DEUX AAE. NOUS AVONS D'ABORD MONTRE QUE, DANS LES CONDITIONS BASALES, CHEZ LE RAT ANESTHESIE, LE GLU ET L'ASP EXTRACELLULAIRES NE REFLETENT PAS UNE LIBERATION D'AAE ET SUIVENT UN RYTHME CIRCANNUEL. DE PLUS, LE GLU ET L'ASP SONT INFLUENCES DIFFEREMMENT PAR LES CANAUX SODIQUES VOLTAGE-DEPENDANTS ET LE CA 2 + EXTRACELLULAIRE. L'ADMINISTRATION LOCALE DE N-METHYL-D-ASPARTATE, ENTRAINE DES VARIATIONS RAPIDES DES CONCENTRATIONS DE GLU ET D'ASP, QUI RESULTENT EN PARTIE D'UNE MISE EN JEU D'AAE. UNE REGULATION DIFFERENTIELLE DU GLU ET DE L'ASP PAR LES RECEPTEURS NMDA A ETE MISE EN EVIDENCE. ENFIN, NOUS AVONS RECHERCHE, CHEZ LE RAT VIGILE ET LIBRE DE SE MOUVOIR, SI LES AAE STRIATAUX SONT MIS EN JEU AU COURS DE STRESS. LA CONCENTRATION EN ASP ET EN GLU EST INCHANGEE AU COURS D'UN STRESS DE CONTENTION, D'EXPOSITION A L'ETHER OU D'UNE HYPOXIE HYPOXIQUE MODEREE. CES RESULTATS ILLUSTRENT LE FAIT QUE, MALGRE LA HAUTE RESOLUTION TEMPORELLE APPORTE PAR LE COUPLAGE A LA CE-LIFD, L'ETUDE SPECIFIQUE DES AAE PAR MICRODIALYSE RESTE DELICATE DANS UN PARADIGME PHYSIOLOGIQUE, PRINCIPALEMENT A CAUSE DES MULTIPLES FONCTIONS DANS LESQUELLES LE GLU ET L'ASP SONT IMPLIQUES ET DU CLOISONNEMENT ENTRE LES COMPARTIMENTS INTRA- ET EXTRA-SYNAPTIQUES.LYON1-BU.Sciences (692662101) / SudocSudocFranceF

Advances and Pitfalls in the Capillary Electrophoresis Analysis of Aggregates of Beta Amyloid Peptides

Alzheimer’s disease is characterized by the accumulation of brain amyloid plaques composed of aggregates of amyloid β (Aβ) peptides. The present paper describes a novel and easy-to-run capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) method for the specific analysis of fibrillar forms of Aβ aggregates obtained after in vitro incubation of Aβ 1-40 monomer. For that purpose, an affinity CE-LIF approach in which the ligand thioflavine T was added to the running buffer has been used, leading to the separation and detection of various fibrillar aggregates which migrated as spikes. The procedure has been optimized to get spikes only corresponding to Aβ aggregates, through the careful elimination of interfering factors and the electrophoretic validation of the link between spikes and particulate material. This method exhibited semi-quantification capabilities, led to the separation of Aβ fibrillar aggregates of different sizes and showed that highly concentrated solutions of Aβ peptides led to the formation of aggregates of larger size than lower-concentrated solution did. Advances brought by this method as well as future development needed to overcome its present limitations are discussed

Synthèse de fluorocyclodextrines et étude de ces systèmes à l'auto-organisation en vue d'applications biomédicales

Le travail réalisé consiste en la synthèse de nouvelles cyclodextrines modifiées par des chaînes perfluoro-alkyles. La première partie de ce mémoire est consacrée à la synthèse de ces macrocycles : les cyclodextrines sont fonctionnalisées en face primaire par des chaînes fluorées de longueurs variables et dont la jonction entre la chaîne et la cyclodextrine peut être modifiée. L'introduction contrôlée du nombre de chaînes (1,2 ou 7) a aussi été étudiée. Dans une deuxième partie, les propriétés physico-chimiques de ces cyclodextrines amphiphiles ont été étudiées. Certaines, solubles dans l'eau, ont montré une organisation particulière d'auto inclusion, phénomène démontré par diverses méthodes (fluorescence, UV-vis., RMN du 19F et du 1H). D'autres plus hydrophobes ont montré leur capacité à s'auto-organiser à l'interface air-eau (isothermes de Langmuir) et dans l'eau sous forme de nanosphères. Ces objets peuvent encapsuler un principe actif de nature hydrophile : la caféine avec des taux pouvant être supérieur à 50%. La libération contrôlée de cette molécule a montré l'intérêt de ces nouvelles cyclodextrines fluoroalkylées en tant que transporteur de principes actifs.LYON1-BU.Sciences (692662101) / SudocSudocFranceF

Differential involvement of amygdala and cortical NMDA receptors activation upon encoding in odor fear memory

International audienceAlthough the basolateral amygdala (BLA) plays a crucial role for the acquisition of fear memories, sensory cortices are involved in their long-term storage in rats. However, the time course of their respective involvement has received little investigation. Here we assessed the role of the glutamatergic N-methyl-d-aspartate (NMDA) receptors in the BLA and olfactory cortex at discrete moments of an odor fear conditioning session. We showed that NMDA receptors in BLA are critically involved in odor fear acquisition during the first association but not during the next ones. In the cortex, NMDA receptor activation at encoding is not necessary for recent odor fear memory while its role in remote memory storage needs further investigation

Dorsal striatum and the temporal expectancy of an aversive event in Pavlovian odor fear learning

International audienceInterval timing, the ability to encode and retrieve the memory of intervals from seconds to minutes, guides fundamental animal behaviors across the phylogenetic tree. In Pavlovian fear conditioning, an initially neutral stimulus (conditioned stimulus, CS) predicts the arrival of an aversive unconditioned stimulus (US, generally a mild foot-shock) at a fixed time interval. Although some studies showed that temporal relations between CS and US events are learned from the outset of conditioning, the question of the memory of time and its underlying neural network in fear conditioning is still poorly understood. The aim of the present study was to investigate the role of the dorsal striatum in timing intervals in odor fear conditioning in male rats. To assess the animal’s interval timing ability in this paradigm, we used the respiratory frequency. This enabled us to detect the emergence of temporal patterns related to the odor-shock time interval from the early stage of learning, confirming that rats are able to encode the odor-shock time interval after few training trials. We carried out reversible inactivation of the dorsal striatum before the acquisition session and before a shift in the learned time interval, and measured the effects of this treatment on the temporal pattern of the respiratory rate. In addition, using intracerebral microdialysis, we monitored extracellular dopamine level in the dorsal striatum throughout odor-shock conditioning and in response to a shift of the odor-shock time interval. Contrary to our initial predictions based on the existing literature on interval timing, we found evidence suggesting that transient inactivation of the dorsal striatum may favor a more precocious buildup of the respiratory frequency’s temporal pattern during the odor-shock interval in a manner that reflected the duration of the interval. Our data further suggest that the conditioning and the learning of a novel time interval were associated with a decrease in dopamine level in the dorsal striatum, but not in the nucleus accumbens. These findings prompt a reassessment of the role of the striatum and striatal dopamine in interval timing, at least when considering Pavlovian aversive conditioning

Study of metabolites from lichen-associated bacterial communities

International audienceLichens are complex organisms resulting from the symbiosis between fungus, microalga and/or cyanobacteria and are source of metabolites of interest. As other living organisms harboring bacterial communities they could be considered as a mini-ecosystem. These bacterial communities most often belong to different phyla: Actinobacteria, Proteobacteria, with a dominance of Alphaproteobacteria and Firmicutes. In this study, we focused on the bacterial communities present on six lichens from Brittany coast (France) (Roccella fuciformis, R. phycopsis, Lichina confinis, L. pygmaea, Xanthoria aureola and X. calcicola). Abundance and diversity of these communities are dependent on several extrinsic factors (environmental) and/or intrinsic parameters including the chemical composition of their substrates (lichens). So, our aims are to elucidate the chemical composition of the studied lichens (extraction, isolation and structural identification) as well as those of associated bacterial communities. Some bacterial species were isolated from these lichens, identified by molecular fingerprints and their culture were optimized (media composition, pH and temperature). Due to the existence of chemical interactions between symbionts we target molecules with antibiotic properties