Structure, fonctionnement, évolution des communautés benthiques des fonds meubles exploités du plateau continental Nord Gascogne

Dans le double cadre de la conservation des écosystèmes soumis à l'exploitation et du développement durable d'une pêcherie, cette étude intégrée d'écologie benthique concerne la structure, le fonctionnement et l'évolution des communautés benthiques du plateau continental Nord Gascogne. Deux communautés distinctes ont été mises en évidence : une première dans la partie centrale de la Grande Vasière et une autre au niveau de la marge externe. Les divergences structurelles au sein de ces communautés traduisent un fonctionnement différent de ces deux écosystèmes contraints par des apports trophiques, des relations biotiques et des régimes de perturbations très différents. Des différences remarquables, notamment sur l'épifaune, ont été détectées en relation avec les perturbations engendrées par le passage des engins traînants. La comparaison des communautés à 35 ans d'intervalle révèle une évolution à long terme des entités biosédimentaires. La structure du réseau d'interactions trophiques a été précisée, en termes de niveaux trophiques et d'origine de la nourriture. Les apports trophiques par sédimentation ont été quantifiés. Aux échelles spatio-temporelles considérées, ils montrent une forte variabilité traduisant le rôle majeur des forçages physiques. Les données acquises au cours de cette étude ont été utilisées pour développer un modèle de réseau trophique à l'état stable de l'écosystème benthodémersal de la Grande Vasière. A l'échelle annuelle, ce modèle révèle que la majeure partie des apprts trophiques par sédimentation n'est pas consommée, que la pression de prédation exercée sur les consommateurs primaires benthiques est forte et que l'incidence des rejets de pêche dans le fonctionnement trophique de cet écosystème est faible. La définition de stratégies de gestion des pêcheries en terme de préservation des écosystèmes soumis à l'exploitation et de développement durable de ces activités doit prendre en compte l'ampleur et le rythme de ces modifications.In the double context of the conservation of ecosystems exposed to exploitation and in the sustainable use of a fishery, this integrated benthic ecology study concerns the structure, functioning and evolution of the benthic communities of the North Bay of Biscay continental shelf. Two distinct communities were separated : the first one in the central part of the Grande Vasière and the second one offshore, on the external margin. The structural divergences within these communities reflect a different functioning of these two ecosystems forced by different trophic inputs, biotic relationships and disturbance sources. Remarkable differences, mainly on the epifauna, were detected in relation to the disturbances generated by the bottom-trawling gears. The comparison of the benthic communities separated by 35 years revealed a long term evolution of the biosedimentary units. The interactions within the trophic webs have been specified, in terms of trophic levels and food sources. The trophic inputs from the pelagic sedimentation were quantified. At the different spatio-temporal scales considered, they showed a strong variability highlighting the major role of the physical forcing. The data collected in this study was used to develop a steady state trophic web model of the benthic-demersal ecosystem of the central part of the Grande Vasière. At the annual scale, this model reveals that the major part of the particle sedimentation imports is not consumed, the predation pressure exerted on the benthic primary consumers is important and that the consequences of the fishing discards in the trophic webs are weak. The definition of fisheries management strategy in term of preservation of the exploited ecosytems and sustainable use of these activities must take into account the amplitude width and rates of these modifications.BORDEAUX1-Lab.Océanogr.Arcacho (330092101) / SudocBREST-BU Droit-Sciences-Sports (290192103) / SudocPLOUZANE-Bibl.La Pérouse (290195209) / SudocSudocFranceF

Kinetics of the norepinephrine analog [76Br]-metabromobenzylguanidine in isolated working rat heart

A related set of kinetic studies of the norepinephrine analog [Br-76]-meta-bromobenzylguanidine (MBBG) were performed with an isolated working rat heart preparation. A series of constant infusion studies over a wide range of MBBG concentrations allowed estimation of the Michaelis-Menten constants for transport by the neuronal norepinephrine transporter (uptake(1)) and the extraneuronal uptake system (uptake(2)). Pharmacological blocking studies with inhibitors of uptake(1), uptake(2) and vesicular uptake were performed to delineate the relative importance of these norepinephrine handling mechanisms on the kinetics of MBBG in the rat heart. Bolus injection studies were done to assess the ability of compartmental modeling techniques to characterize the kinetics of MBBG. These studies demonstrate that MBBG shares many of the same uptake mechanisms as norepinephrine in the rat heart. PET imaging studies with MBBG would be useful for assessing sympathetic nerve status in the living human heart. (C) 1998 Elsevier Science Inc

Preparation and pharmacological characterization of [76Br]-meta-bromobenzylguanidine ([76Br]MBBG)

[76Br]-meta-Bromobenzylguanidine ([76Br]MBBG) was prepared from the iodinated analog (MIBG) and [76Br]NH4 using a Cu+-assisted halogen exchange reaction. [76Br]MBBG was produced in a 60–65% radiochemical yield with a specific activity of 20 MBq/nmol. In rats, biodistribution kinetic studies showed a high uptake of [76Br]MBBG in heart tissues with its maximum of 5% ID/g at 2 h p.i.; whereas 4 h p.i., the maximum of the heart-to-lung concentration ratio of 8 was observed. Metabolic studies in rats indicated that [76Br]MBBG was rapidly metabolized in plasma. However in heart tissue, 25 h p.i., 85% of the radioactivity still represented unchanged radiotracer. Pharmacological studies in rats showed that the myocardial uptake of [76Br]MBBG was similar to that of norepinephrine. After pretreatment of the rats, the uptake of [76Br]MBBG was reduced 4 h p.i. to the following values: after desipramine (DMI) to 37%, after dexamethasone (DXM) to 88% and after 6-hydroxydopamine (6-OHDA) to 16%. These preliminary results suggest that [76Br]MBBG can be useful for the assessment of heart catecholamine reuptake disorders with PET

Assessing intratumor distribution and uptake with MBBG versus MIBG imaging and targeting xenografted PC12-pheochromocytoma cell line

The heterogeneity of tumor uptake is likely to substantially limit the effectiveness of metaiodobenzylguanidine (MIBG) therapy. This study was done to establish whether metabromobenzyl-guanidine (MBBG) can target neuroendocrine tumors and to provide intratumor biodistribution and uptake information in comparison to MIBG. Methods: MBBG and MIBG tumor uptake and kinetic studies were performed in experimental PC-12 pheochromocytoma grown in nude mice. Intratumor distribution studies were performed using autoradiography and secondary ion mass spectrometry (SIMS) microscopy, because the latter technique can detect and potentially quantify both drugs concomitantly within the same tumor specimen. Results: MBBG uptake in PC12 tumors was early (2 hr) and intense (80% ID/g). Retention values were similar for both drugs 24 hr postinjection. At the cellular level, MBBG mostly accumulated in the cytosol. At the multicellular level, cells exhibited staining, but in many areas, SIMS images of both drugs were not spatially correlated. Conclusion: MBBG targeted experimental pheochromocytoma efficiently with high early uptake values. Bromine-76-MBBG is a promising means of imaging and quantifying tumor uptake with PET. Both drugs were localized in the cytosol, but the correlation between the two distributions, as assessed by the values of the standardized local concentrations, was weak although significant multicellularly

Bromine-76-Metabromobenzylguanidine: A PET Radiotracer for Mapping Sympathetic Nerves of the Heart

Iodine-123-metaiodobenzylguanidine (MIBG) is used to qualitatively assess heart innervation with single-photon emission computed tomography (SPECT). This approach is clinically useful in the prognostic evaluation of congestive heart failure. To improve quantification of uptake of the tracer using positron emission tomography (PET), we studied the characteristics of the bromoanalog of MIBG. Bromine-76-metabromobenzylguanidine (76Br-MBBG) was prepared from a heteroisotopic exchange between radioactive bromine atoms (noncarrier-added (76Br) BrNH4) and the cold iodine atoms of the precursor metaiodobenzylguanidine. Biodistribution was studied in rats and PET cardiac imaging performed in dogs. Myocardial uptake was high and prolonged in both species (mean half-life in dogs: 580 min). In rats, myocardial uptake was inhibited by desipramine by 64%, whereas after pretreatment with 6- hydroxydopamine uptake was reduced by 84%. In dogs pretreated with 6- hydroxydopamine or with desipramine, a steep washout of the tracer occurred (mean half-life: 136 min and 118 min, respectively). The non-specific uptake plus the passive neuronal diffusion of the tracer could be estimated at about 25%-30% of the total fixation. In dogs, analysis of unchanged 76Br-MBBG in plasma showed that radiotracer metabolism was slow: 60 min after injection, 80% of the radioactivity was related to unchanged 76Br-MBBG. These preliminary findings suggest that 76Br-MBBG could be used to quantitatively assess adrenergic innervation in heart disease using PET. When combined with use of 11C-CGP 12177, cardiac adrenergic neurotransmission can be assessed