The appearance of a second genotype of Japanese encephalitis virus in the Australasian region

In mid-January 2000, the reappearance of Japanese encephalitis (JE) virus activity in the Australasian region was first demonstrated by the isolation of JE virus from 3 sentinel pigs on Badu Island in the Torres Strait. Further evidence of JE virus activity was revealed through the isolation of JE virus from Cidex gelidus mosquitoes collected on Badu Island and the detection of specific JE virus neutralizing antibodies in 3 pigs from Saint Pauls community on Moa Island. Nucleotide sequencing and phylogenetic analyses of the premembrane and envelope genes were performed which showed that both the pig and mosquito JE virus isolates (TSOO and TS4152, respectively) clustered in genotype I, along with northern Thai, Cambodian, and Korean isolates. All previous Australasian JE virus isolates belong to genotype II, along with Malaysian and Indonesian isolates. Therefore, for the first time, the appearance and transmission of a second genotype of JE virus in the Australasian region has been demonstrated.

Corneal endothelial response to induced myopia in the chicken

Purpose: To investigate the role of corneal endothelial surface enlargement in the chicken myopia model in inducing corneal endothelial changes. Methods: Lid suture was performed on one eye of 1-day-old cockerels. Five chickens were killed at 1 week, and four chickens killed at each of 3 weeks, 6 weeks, and 10 weeks postnatal. The endothelial morphology was obtained by flat mounting the endothelial surface and the subsequent digitisation. Comparisons were undertaken between the control unsutured eye and the lid-sutured eye endothelium, and between the central endothelial areas compared to the peripheral endothelial areas in both the myopic and the normal corneas. Calculation of the contribution to the endothelial change by hypertrophy and mitosis were calculated using Bahn's formula. Results: Total endothelial surface area increased significantly over time in the myopic model compared to control eyes but the mean cell area of endothelial cells remained the same for both the enlarged myopic endothelial surface area and in the normal controls. Sampling from the central and the peripheral corneal endothelial surface also disclosed no difference. The mean cell area did increase steadily with age but was the same for both normal and myopic corneas. Conclusions: It would appear that there are equal contributions from hypertrophy and mitosis in the myopic group and the normal corneal group with a slightly increasing trend towards mitotic activity in the myopic corneal endothelial layer.

Autosomal dominant hypocalcemia: A novel activating mutation (E604K) in the cysteine-rich domain of the calcium-sensing receptor

We report a novel activating mutation (E604K) of the calcium-sensing receptor in a family with autosomal dominant hypocalcemia. Whereas all affected individuals exhibited marked hypocalcemia, some cases with untreated hypocalcemia exhibited seizures in infancy, whereas others were largely asymptomatic from birth into adulthood. The missense mutation E604K (G2182A, GenBank accession no. U20759), which affects an amino acid residue in the C terminus of the cysteine-rich domain of the extracellular head, co-segregated with hypocalcemia in all seven individuals for whom DNA was available. Two unaffected, normocalcemic members of the family did not exhibit the mutation. The molecular impact of the mutation on two key components of the signaling response was assessed in HEK-293 cells transiently transfected with cDNA corresponding to either the wild-type calcium-sensing receptor or the E604K mutation derived by site-directed mutagenesis. There was a significant leftward shift in the concentration response curves for the effects of extracellular Ca2+ on both intracellular Ca2+ mobilization (determined by aequorin luminescence) and MAPK activity (determined by luciferase expression). The C terminus of the cysteine-rich domain of the extracellular head may normally act to suppress receptor activity in the presence of low extracellular Ca2+ concentrations.

Stress affects theta activity in limbic networks and impairs novelty-induced exploration and familiarization

Exposure to a novel environment triggers the response of several brain areas that regulate emotional behaviors. Here, we studied theta oscillations within the hippocampus (HPC)-amygdala (AMY)-medial prefrontal cortex (mPFC) network in exploration of a novel environment and subsequent familiarization through repeated exposures to that same environment; in addition, we assessed how concomitant stress exposure could disrupt this activity and impair both behavioral processes. Local field potentials were simultaneously recorded from dorsal and ventral hippocampus (dHPC and vHPC respectively), basolateral amygdala (BLA) and mPFC in freely behaving rats while they were exposed to a novel environment, then repeatedly re-exposed over the course of 3 weeks to that same environment and, finally, on re-exposure to a novel unfamiliar environment. A longitudinal analysis of theta activity within this circuit revealed a reduction of vHPC and BLA theta power and vHPC-BLA theta coherence through familiarization which was correlated with a return to normal exploratory behavior in control rats. In contrast, a persistent over-activation of the same brain regions was observed in stressed rats that displayed impairments in novel exploration and familiarization processes. Importantly, we show that stress also affected intra-hippocampal synchrony and heightened the coherence between vHPC and BLA. In summary, we demonstrate that modulatory theta activity in the aforementioned circuit, namely in the vHPC and BLA, is correlated with the expression of anxiety in novelty-induced exploration and familiarization in both normal and pathological conditions.

N-acetyl-�� -d-glucosaminidase activity in feral Carcinus maenasexposed to cadmium

Cadmium is a priority hazardous substance, persistent in the aquatic environment, with the capacity to interfere with crustacean moulting. Moulting is a vital process dictating crustacean growth, reproduction and metamorphosis. However, for many organisms, moult disruption is difficult to evaluate in the short term, what limits its inclusion in monitoring programmes. N-acetyl-��-d-glucosaminidase (NAGase) is an enzyme acting in the final steps of the endocrine-regulated moulting cascade, allowing for the cast off of the old exoskeleton, with potential interest as a biomarker of moult disruption. This study investigated responses to waterborne cadmium of NAGase activity of Carcinus maenas originating from estuaries with different histories of anthropogenic contamination: a low impacted and a moderately polluted one. Crabs from both sites were individually exposed for seven days to cadmium concentrations ranging from 1.3 to 2000 ��g/L. At the end of the assays, NAGase activity was assessed in the epidermis and digestive gland. Detoxification, antioxidant, energy production, and oxidative stress biomarkers implicated in cadmium metabolism and tolerance were also assessed to better understand differential NAGase responses: activity of glutathione S-transferases (GST), glutathione peroxidase (GPx) glutathione reductase (GR), levels of total glutathiones (TG), lipid peroxidation (LPO), lactate dehydrogenase (LDH), and NADP+-dependent isocitrate dehydrogenase (IDH). Animals from the moderately polluted estuary had lower NAGase activity both in the epidermis and digestive gland than in the low impacted site. NAGase activity in the epidermis and digestive gland of C. maenas from both estuaries was sensitive to cadmium exposure suggesting its usefulness for inclusion in monitoring programmes. However, in the digestive gland NAGase inhibition was found in crabs from the less impacted site but not in those from the moderately contaminated one. Altered glutathione levels were observed in cadmium-treated crabs from the contaminated site possibly conferring enhanced tolerance to these animals through its chelator action. Investigation of enhanced tolerance should thus be accounted for in monitoring programmes employing NAGase as biomarker to avoid data misinterpretation.

Human Tissue Kallikrein Activity in Angiographically Documented Chronic Stable Coronary Artery Disease

AbstractBackground:Human tissue kallikrein (hK1) is a key enzyme in the kallikrein–kinin system (KKS). hK1-specific amidase activity is reduced in urine samples from hypertensive and heart failure (HF) patients. The pathophysiologic role of hK1 in coronary artery disease (CAD) remains unclear.Objective:To evaluate hK1-specific amidase activity in the urine of CAD patientsMethods:Sixty-five individuals (18–75 years) who underwent cardiac catheterism (CATH) were included. Random midstream urine samples were collected immediately before CATH. Patients were classified in two groups according to the presence of coronary lesions: CAD (43 patients) and non-CAD (22 patients). hK1 amidase activity was estimated using the chromogenic substrate D-Val-Leu-Arg-Nan. Creatinine was determined using Jaff��’s method. Urinary hK1-specific amidase activity was expressed as ��M/(min �� mg creatinine) to correct for differences in urine flow rates.Results:Urinary hK1-specific amidase activity levels were similar between CAD [0.146 ��M/(min ��mg creatinine)] and non-CAD [0.189 ��M/(min . mg creatinine)] patients (p = 0.803) and remained similar to values previously reported for hypertensive patients [0.210 ��M/(min . mg creatinine)] and HF patients [0.104 ��M/(min . mg creatinine)]. CAD severity and hypertension were not observed to significantly affect urinary hK1-specific amidase activity.Conclusion:CAD patients had low levels of urinary hK1-specific amidase activity, suggesting that renal KKS activity may be reduced in patients with this disease.

Cortical origin of functional recovery in the somatosensory cortex of the adult mouse after thalamic lesion

R��sum�� L'accident vasculaire c��r��bral sensoriel pur est un des syndromes lacunaires, d�� �� l'occlusion de petits vaisseaux c��r��braux, souvent dans le cadre d'une l��sion int��ressant le noyau ventro-caudal du thalamus. Il produit un h��misyndrome sensitif pur, et parfois un syndrome douloureux se d��veloppe �� distance de l'��v��nement aigu. Afin d'��tudier la r��cup��ration fonctionnelle dans le cortex somatosensoriel (SI) apr��s une telle l��sion dans le thalamus, un mod��le de l��sion excitotoxique a ��t�� d��velopp�� dans le syst��me somatosensoriel de la souris adulte, caract��ris�� par la pr��sence de formations cytoarchitectoniques dans SI appel��es "tonneaux". Chacun de ces tonneaux correspond �� la repr��sentation corticale d'une vibrisse du museau. L'activit�� m��tabolique a ��t�� mesur��e dans SI �� diff��rents intervalles apr��s la l��sion, �� l'aide de d��oxyglucose marqu�� radioactivement. Dans les deux premiers jours suivant celle-ci, l'activit�� m��tabolique diminue de mani��re importante dans toutes les couches corticales, avec une atteinte plus marqu��e dans la couche IV, principale projection des axones thalamo-corticaux. Une r��cup��ration de l'activit�� m��tabolique se produit ensuite, d'autant plus marqu��e que le d��lai apr��s la l��sion est grand. Cette r��cup��ration s'observe dans toutes les couches coticales, les couches I et Vb r��cup��rant plus rapidement que les couches II, III, IV, Va et VI. Cinq semaines apr��s la l��sion, l'absence des vibrisses correspondant �� la partie d��aff��rent��e de SI diminue l'activit�� m��tabolique corticale de 32% et d��montre l'activation par la p��riph��rie de cette partie de l'��corce, malgr�� la perte des axones thalamo-corticaux provenant du noyau ventro-caudal. Des exp��riences de tra��age r��trograde ont montr�� une augmentation des projections intracorticales sur la partie d��aff��rent��e de l'��corce, en particulier de longue distance, ainsi que des projections interh��misph��riques, mais n'ont pas permis de mettre en ��vidence de nouvelle projection thalamique, indiquant une origine corticale �� la r��cup��ration fonctionnelle observ��e. Abstract To study the degree and time course of the functional recovery in the somatosensory cortex (SI) after an excitotoxic lesion in the adult mouse thalamus, metabolic activity was determined in SI at various times points post lesion. Immediately after the lesion, metabolic activity in the thalamically deafferented part of SI was at its lowest value but increased progressively at subsequent time points. This was seen in all cortical layers, however, layers I and Vb recover more rapidly than layers II, III, IV, Va and VI. Removal of the mystacial whiskers corresponding to the deafferented area, 5 weeks after cortical recovery, produced a subsequent 32% drop in metabolic activity, demonstrating peripheral sensory activation of this part of the cortex. Tracing experiments revealed that the deafferented cortex did not receive a novel thalamic input, but cortico-cortical and contralateral barrel cortex projections to this area were reinforced. We conclude that the cortical functional recovery after a thalamic lesion is, at least partially, due to modified cortico-cortical and callosal projections to the deafferented cortical area.

Genetic diversity and differentiation processes in the ploidy series of Olea europaea L.: a multiscale approach from subspecies to insular populations.

Geographical isolation and polyploidization are central concepts in plant evolution. The hierarchical organization of archipelagos in this study provides a framework for testing the evolutionary consequences for polyploid taxa and populations occurring in isolation. Using amplified fragment length polymorphism and simple sequence repeat markers, we determined the genetic diversity and differentiation patterns at three levels of geographical isolation in Olea europaea: mainland-archipelagos, islands within an archipelago, and populations within an island. At the subspecies scale, the hexaploid ssp. maroccana (southwest Morocco) exhibited higher genetic diversity than the insular counterparts. In contrast, the tetraploid ssp. cerasiformis (Madeira) displayed values similar to those obtained for the diploid ssp. guanchica (Canary Islands). Geographical isolation was associated with a high genetic differentiation at this scale. In the Canarian archipelago, the stepping-stone model of differentiation suggested in a previous study was partially supported. Within the western lineage, an east-to-west differentiation pattern was confirmed. Conversely, the easternmost populations were more related to the mainland ssp. europaea than to the western guanchica lineage. Genetic diversity across the Canarian archipelago was significantly correlated with the date of the last volcanic activity in the area/island where each population occurs. At the island scale, this pattern was not confirmed in older islands (Tenerife and Madeira), where populations were genetically homogeneous. In contrast, founder effects resulted in low genetic diversity and marked genetic differentiation among populations of the youngest island, La Palma.

Climate change in the Atlantic Ocean since the 1940's and the effects on the global climate

En aquest projecte s���ha estudiat la relaci�� entre els canvis en les temperatures superficials de l���Oce�� Atl��ntic i els canvis en la circulaci�� atmosf��rica en el segle XX. Concretament s���han analitzat dos per��odes de estudi: el primer des del 1940 al 1960 i el segon des del 1980 fins al 2000. S���ha posat especial inter��s en les anomalies en les temperatures superficials del mar en la regi�� tropical de l���Oce�� Atl��ntic i la possible interconnexi�� amb els canvis clim��tics observats i predits. Per a la realitzaci�� de l���estudi s���han dut a terme una s��rie d���experiments utilitzant el model clim��tic elaborat a la universitat d���UCLA (UCLA���AGCM model). Els resultats obtinguts han estat analitzats en forma de mapes i figures per a cada variable d���estudi. Tamb�� s���ha fet una comparaci�� entre els resultats obtinguts i altres trobats en altres treballs publicats sobre el mateix tema de recerca. Els resultats obtinguts s��n molt amplis i poden tenir diverses interpretacions. Tot i aix�� algunes de les conclusions a les quals s���ha arribat s��n: les difer��ncies m��s significatives per a les variables estudiades i trobades a partir dels resultats obtinguts del model per als dos per��odes d���estudi s��n en els mesos d���hivern i a la zona dels tr��pics; concretament a parts del nord de sud Am��rica i a parts del nord d�����frica. S���han trobat tamb�� canvis significatius en els patrons de precipitaci�� sobre aquestes mateixes zones. Tamb�� s���ha observant un moviment cap al nord de la zona d���interconverg��ncia tropical i pot ser degut a l���an��mal gradient trobat a la zona equatorial en les temperatures superficial de l���Oce��. Tot i aix�� per a una definitiva discussi�� i conclusions sobre els resultats dels experiments, seria necessari un estudi m��s ampli i profund.

Induction of Glutathione S-transferase Activity in Triatoma infestans

Several synthetic pesticides and allelochemicals used to treat Triatoma infestans adults by topic application showed some degree of cytosolic glutathione S-transferase (GST) induction. General inducers of detoxication systems such as phenobarbital and 3-methylcholantrene topically applied on T. infestans resulted in no GST induction. Meanwhile, general insecticide synergist such as piperonyl butoxide (160 mg/insect) increased the GST-activity in the range of 120-140%. Insects injected with reduced glutathione (300 mg/insect) presented at the forth day elevated GST activity

Dengue in the State of Rio de Janeiro, Brazil, 1986-1998

This paper presents epidemiological, laboratory, and clinical data on 12 years of dengue virus activity in the State of Rio de Janeiro from the time the disease was first confirmed virologically in April 1986 through April 1998. DEN-1 and DEN-2 viruses are the serotypes circulating in the state and were responsible for the epidemics reported during the last 12 years. The results published here show both the impact of dengue virus infections on the population and laboratory advances that have improved dengue diagnosis.

The expression of GABA receptors in the human auditory cortex

Abstract : GABA, the primary inhibitory neurotransmitter, and its receptors play an important role in modulating neuronal activity in the central nervous system and are implicated in many neurological disorders. In this study, GABAA and GABAB receptor subunit expression was visualized by immunohistochemistry in human auditory areas TC (= primary auditory area), TB, and TA. Both hemispheres from nine neurologically normal subjects and from four patients with subacute or chronic stroke were included. In normal brains, GABAA receptor subunit (α1, α2, & β2/3) labeling produced neuropil staining throughout all cortical layers as well as labeling fibers and neurons in layer VI for all auditory areas. Densitometry profiles displayed differences in GABAA subunit expression between primary and non-primary areas. In contrast to the neuropil labeling of GABAA subunits, GABAB1 and GABAB2 subunit immunoreactivity was revealed on neuronal somata and proximal dendritic shafts of pyramidal and non-pyramidal neurons in layers II-III, more strongly on supra- than in infragranular layers. No differences were observed between auditory areas. In stroke cases, we observed a downregulation of the GABAA receptor α2 subunit in granular and infragranular layers, while the other GABAA and the two GABAB receptor subunits remained unchanged. Our results demonstrate a strong presence of GABAA and GABAB receptors in the human auditory cortex, suggesting a crucial role of GABA in shaping auditory responses in the primary and non-primary auditory areas. The differential laminar and area expression of GABAA subunits that we have found in the auditory areas and which is partially different from that in other cortical areas speaks in favor of a fine turning of GABA-ergic transmission in these different compartments. In contrast, GABAB expression displayed laminar, but not areal differences; its basic pattern was also very similar to that of other cortical areas, suggesting a more uniform role within the cerebral cortex. In subacute and chronic stroke, the selective GABAA α2 subunit downregulation is likely to influence postlesional plasticity and susceptibility to medication. The absence of changes in the GABAB receptors suggests different regulation than in other pathological conditions, such as epilepsy, schizophrenia or bipolar disorder, in which a downregulation has been reported. R��sum�� : GABA, le principal neurotransmetteur inhibiteur, et ses r��cepteurs jouent un r��le important en tant que modulateur de l'activit�� neuronale dans le syst��me nerveux central et sont impliqu��s dans de nombreux d��sordres neurologiques. Dans cette ��tude, l'expression des sous-unit��s des r��cepteur GABAA et GABAB a ��t�� visualis��e par immunohistochimie dans les aires auditives du cortex humains: le TC (= aire auditif primaire), le TB, et le TA. Les deux h��misph��res de neuf sujets consid��r��s normaux du point de vue neurologique et de quatre patients ayant subis un accident c��r��bro-vasculaire et se trouvant dans la phase subaigu�� ou chronique ��taient inclues. Dans les cerveaux normaux, les immunohistochimies contre les sous-unit��s α1, α2, & β2/3 du r��cepteur GABAA ont marqu�� le neuropil dans toutes les couches corticales ainsi que les fibres et les neurones de la couche VI dans toutes les aires auditives. Le profile densitom��trique montre des diff��rences dans l'expression des sous-unit��s du r��cepteur GABAA entre les aires primaires et non-primaires. Contrairement au marquage de neuropil par les sous-unit��s du recepteur GABAA, 1'immunor��activit�� des sous-unit��s GABAB1 et GABAB2 a ��t�� r��v��l��e sur les corps cellulaires neuronaux et les dendrites proximaux des neurones pyramidaux et non-pyramidaux dans les couches II-III et est plus dense dans les couches supragranulaires que dans les couches infragranulaires. Aucune diff��rence n'a ��t�� observ��e entre les aires auditives. Dans des cas l��sionnels, nous avons observ�� une diminution de la sous-unit�� α2 du r��cepteur GABAA dans les couches granulaires et infragranulaires, alors que le marquage des autres sous-unit��s du r��cepteur GABAA et des deux sous-unit��s de r��cepteur GABAB reste inchang��. Nos r��sultats d��montrent une pr��sence forte des r��cepteurs GABAA et GABAB dans le cortex auditif humain, sugg��rant un r��le crucial du neurotransmetteur GABA dans la formation de la r��ponse auditive dans les aires auditives primaires et non-primaires. L'expression diff��rentielle des sous-unit��s de GABAA entre les couches corticales et entre les aires auditives et qui est partiellement diff��rente de celle observ��e dans d'autres aires corticales pr��conise une modulation fine de la transmission GABA-ergic en ces diff��rents compartiments. En revanche, l'expression de GABAB a montr�� des diff��rences laminaires, mais non r��gionales ; son motif d'expression de base est ��galement tr��s semblable �� celui d'autres aires corticales, sugg��rant un r��le plus uniforme dans le cortex c��r��bral. Dans les phases subaigu�� et chronique des accidents c��r��bro-vasculaires, la diminution s��lective de la sous-unit�� α2 du recepteur GABAA est susceptible d'influencer la plasticit�� et la susceptibilit�� postl��sionnelle au m��dicament. L'absence de changement pour les r��cepteurs GABAB sugg��re que le r��cepteur est r��gul�� diff��remment apr��s un accident cerebro-vasculaire par rapport �� d'autres conditions pathologiques, telles que l'��pilepsie, la schizophr��nie ou le d��sordre bipolaire, dans lesquels une diminution de ces sous-unit��s a ��t�� rapport��e.

Severity of chronic experimental Chagas' heart disease parallels tumour necrosis factor and nitric oxide levels in the serum: models of mild and severe disease

Heart tissue inflammation, progressive fibrosis and electrocardiographic alterations occur in approximately 30% of patients infected by Trypanosoma cruzi, 10-30 years after infection. Further, plasma levels of tumour necrosis factor (TNF) and nitric oxide (NO) are associated with the degree of heart dysfunction in chronic chagasic cardiomyopathy (CCC). Thus, our aim was to establish experimental models that mimic a range of parasitological, pathological and cardiac alterations described in patients with chronic Chagas’ heart disease and evaluate whether heart disease severity was associated with increased TNF and NO levels in the serum. Our results show that C3H/He mice chronically infected with the Colombian T. cruzi strain have more severe cardiac parasitism and inflammation than C57BL/6 mice. In addition, connexin 43 disorganisation and fibronectin deposition in the heart tissue, increased levels of creatine kinase cardiac MB isoenzyme activity in the serum and more severe electrical abnormalities were observed in T. cruzi-infected C3H/He mice compared to C57BL/6 mice. Therefore, T. cruzi-infected C3H/He and C57BL/6 mice represent severe and mild models of CCC, respectively. Moreover, the CCC severity paralleled the TNF and NO levels in the serum. Therefore, these models are appropriate for studying the pathophysiology and biomarkers of CCC progression, as well as for testing therapeutic agents for patients with Chagas’ heart disease.

S��lection et suivi pr��transplantation des patients candidats �� la greffe cardiaque en Suisse romande [Selection and preoperative follow-up of heart transplantation candidates in the French part of Switzerland].

Heart transplantation (HTx) started in 1987 at two university hospitals (CHUV, HUG) in the western part of Switzerland, with 223 HTx performed at the CHUV until December 2010. Between 1987 and 2003, 106 HTx were realized at the HUG resulting in a total of 329 HTx in the western part of Switzerland. After the relocation of organ transplantation activity in the western part of Switzerland in 2003, the surgical part and the early postoperative care of HTx remained limited to the CHUV. However, every other HTx activity are pursued at the two university hospitals (CHUV, HUG). This article summarizes the actual protocols for selection and pre-transplant follow-up of HTx candidates in the western part of Switzerland, permitting a uniform structure of pretransplant follow-up in the western part of Switzerland.

Gliotransmission in the hippocampus, mechanisms and interaction with synaptic functions

SUMMARYAstrocytes represent the largest cell population in the human brain. In addition to a well established role as metabolic support for neuronal activity, in the last years these cells have been found to accomplish other important and, sometimes, unexpected functions. The tight enwrapping of synapses by astrocytic processes and the predominant expression of glutamate uptake carriers in the astrocytic rather than neuronal plasma membranes brought to the definition of a critical involvement of astrocytes in the clearance of glutamate from synaptic junctions. Moreover, several publications showed that astrocytes are able to release chemical transmitters (gliotransmitters) suggesting their active implication in the control of synaptic functions. Among gliotransmitters, the best characterized is glutamate, which has been proposed to be released from astrocytes in a Ca2+ dependent manner via exocytosis of synaptic-like microvesicles.In my thesis I present results leading to substantial advancement of the understanding of the mechanisms by which astrocytes modulate synaptic activity in the hippocampus, notably at excitatory synapses on dentate granule cells. I show that tumor necrosis factor- alpha (TNFa), a molecule that is generally involved in immune system functions, critically controls astrocyte-to-synapse communication (gliotransmission) in the brain. With constitutive levels of TNFa present, activation of purinergic G protein-coupled receptors in astrocytes, called P2Y1 receptors, induces localized intracellular calcium ([Ca2+]j) elevation in astrocytic processes (measured by two-photon microscopy) followed by glutamate release and activation of pre-synaptic NMDA receptors resulting in synaptic potentiation. In preparations lacking TNFa, astrocytes respond with identical [Ca2+]i elevations but fail to induce neuromodulation. I find that TNFa specifically controls the glutamate release step of gliotransmission. Addition of very low (picomolar) TNFa concentrations to preparations lacking the cytokine, promptly reconstitutes both normal exocytosis in cultured astrocytes and gliotransmission in hippocampal slices. These data provide the first demonstration that gliotransmission and its synaptic effects are controlled not only by astrocyte [Ca2+]i elevations but also by permissive/homeostatic factors like TNFa.In addition, I find that higher and presumably pathological TNFa concentrations do not act just permissively but instead become direct and potent triggers of glutamate release from astrocytes, leading to a strong enhancement of excitatory synaptic activity. The TNFa action, like the one observed upon P2Y1R activation, is mediated by pre-synaptic NMDA receptors, but in this case the effect is long-lasting, and not reversible. Moreover, I report that a necessary molecular target for this action of TNFa is TNFR1, one of the two specific receptors for the cytokine, as I found that TNFa was unable to induce synaptic potentiation when applied in slices from TNFR1 knock-out (Tnfrlv") mice. I then created a double transgenic mouse model where TNFR1 is knocked out in all cells but can be re-expressed selectively in astrocytes and I report that activation of the receptors in these cells is sufficient to reestablish TNFa-dependent long-lasting potentiation of synaptic activity in the TNFR1 knock-out mice.I therefore discovered that TNFa is a primary molecule displaying both permissive and instructive roles on gliotransmission controlling synaptic functions. These reports might have profound implications for the understanding of both physiological and pathological processes associated to TNFa production, including inflammatory processes in the brain.R��SUM��Les astrocytes sont les cellules les plus abondantes du cerveau humain. Outre leur r��le bien ��tabli dans le support m��tabolique de l'activit�� neuronale, d'autres fonctions importantes, et parfois inattendues de ces cellules ont ��t�� mises en lumi��re au cours de ces derni��res ann��es. Les astrocytes entourent ��troitement les synapses de leurs fins processus qui expriment fortement les transporteurs du glutamate et permettent ainsi aux astrocytes de jouer un r��le critique dans l'��limination du glutamate de la fente synaptique. N��anmoins, les astrocytes semblent ��tre capables de jouer un r��le plus int��gratif en modulant l'activit�� synaptique, notamment par la lib��ration de transmetteurs (gliotransmetteurs). Le gliotransmetteur le plus ��tudi�� est le glutamate qui est lib��r�� par l'exocytose r��gul��e de petites v��sicules ressemblant aux v��sicules synaptiques (SLMVs) via un m��canisme d��pendant du calcium.Les r��sultats pr��sent��s dans cette th��se permettent une avanc��e significative dans la compr��hension du mode de communication de ces cellules et de leur implication dans la transmission de l'information synaptique dans l'hippocampe, notamment des synapses excitatrices des cellules granulaires du gyrus dentel��. J'ai pu montrer que le �� facteur de n��crose tumorale alpha �� (TNFa), une cytokine commun��ment associ��e au syst��me immunitaire, est aussi fondamentale pour la communication entre astrocyte et synapse. Lorsqu'un niveau constitutif tr��s bas de TNFa est pr��sent, l'activation des r��cepteurs purinergiques P2Y1 (des r��cepteurs coupl��s �� prot��ine G) produit une augmentation locale de calcium (mesur��e en microscopie bi-photonique) dans l'astrocyte. Cette derni��re d��clenche ensuite une lib��ration de glutamate par les astrocytes conduisant �� l'activation de r��cepteurs NMDA pr��synaptiques et �� une augmentation de l'activit�� synaptique. En revanche, dans la souris TNFa knock-out cette modulation de l'activit�� synaptique par les astrocytes n'est pas bien qu'ils pr��sentent toujours une excitabilit�� calcique normale. Nous avons d��montr�� que le TNFa contr��le sp��cifiquement l'exocytose r��gul��e des SLMVs astrocytaires en permettant la fusion synchrone de ces v��sicules et la lib��ration de glutamate �� destination des r��cepteurs neuronaux. Ainsi, nous avons, pour la premi��re fois, prouv�� que la modulation de l'activit�� synaptique par l'astrocyte n��cessite, pour fonctionner correctement, des facteurs �� permissifs �� comme le TNFa, agissant sur le mode de s��cr��tion du glutamate astrocytaire.J'ai pu, en outre, d��montrer que le TNFa, �� des concentrations plus ��lev��es (celles que l'on peut observer lors de conditions pathologiques) provoque une tr��s forte augmentation de l'activit�� synaptique, agissant non plus comme simple facteur permissif mais bien comme d��clencheur de la gliotransmission. Le TNFa provoque 1'activation des r��cepteurs NMD A pr��-synaptiques (comme dans le cas des P2Y1R) mais son effet est �� long terme et irr��versible. J'ai d��couvert que le TNFa active le r��cepteur TNFR1, un des deux r��cepteurs sp��cifiques pour le TNFa. Ainsi, l'application de cette cytokine sur une tranche de cerveau de souris TNFR1 knock-out ne produit aucune modification de l'activit�� synaptique. Pour v��rifier l'implication des astrocytes dans ce processus, j'ai ensuite mis au point un mod��le animal doublement transg��nique qui exprime le TNFR1 uniquement dans les astrocytes. Ce dernier m'a permis de prouver que l'activation des r��cepteurs TNFR1 astrocytaires est suffisante pour induire une augmentation de l'activit�� synaptique de mani��re durable.Nous avons donc d��couvert que le TNFa poss��de un double r��le, �� la fois un r��le permissif et actif, dans le contr��le de la gliotransmission et, par cons��quent, dans la modulation de l'activit�� synaptique. Cette d��couverte peut potentiellement ��tre d'une extr��me importance pour la compr��hension des m��canismes physiologiques et pathologiques associ��s �� la production du TNFa, en particulier lors de conditions inflammatoires.R��SUM�� GRAND PUBLICLes astrocytes repr��sentent la population la plus nombreuse de cellules dans le cerveau humain. On sait, n��anmoins, tr��s peu de choses sur leurs fonctions. Pendant tr��s longtemps, les astrocytes ont uniquement ��t�� consid��r��s comme la colle du cerveau, un substrat inerte permettant seulement de lier les cellules neuronales entre elles. Il n'y a que depuis peu que l'on a d��couvert de nouvelles implications de ces cellules dans le fonctionnement c��r��bral, comme, entre autres, une fonction de support m��tabolique de l'activit�� neuronale et un r��le dans la modulation de la neurotransmission. C'est ce dernier aspect qui fait l'objet de mon projet de th��se.Nous avons d��couvert que l'activit�� des synapses (r��gions qui permettent la communication d'un neurone �� un autre) qui peut ��tre potentialis��e par la lib��ration du glutamate par les astrocytes, ne peut l'��tre que dans des conditions astrocytaires tr��s particuli��res. Nous avons, en particulier, identifi�� une mol��cule, le facteur de n��crose tumorale alpha (TNFa) qui joue un r��le critique dans cette lib��ration de glutamate astrocytaire.Le TNFa est surtout connu pour son r��le dans le syst��me immunitaire et le fait qu'il est massivement lib��r�� lors de processus inflammatoires. Nous avons d��couvert qu'en concentration minime, correspondant �� sa concentration basale, le TNFa peut n��anmoins exercer un r��le indispensable en permettant la communication entre l'astrocyte et le neurone. Ce mode de fonctionnement est assez probablement repr��sentatif d'un processus physiologique qui permet d'int��grer la communication astrocyte/neurone au fonctionnement g��n��ral du cerveau. Par ailleurs, nous avons ��galement d��montr�� qu'en quantit�� plus importante, le TNFa change son mode de fonctionnement et agit comme un stimulateur direct de la lib��ration de glutamate par l'astrocyte et induit une activation persistante de l'activit�� synaptique. Ce mode de fonctionnement est assez probablement repr��sentatif d'un processus pathologique.Nous sommes ��galement arriv��s �� ces conclusions gr��ce �� la mise en place d'une nouvelle souche de souris doublement transg��niques dans lesquelles seuls les astrocytes (etnon les neurones ou les autres cellules c��r��brales) sont capables d'��tre activ��s par le TNFa.