References of "Luxen, André"
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See detailRadiochemical synthesis of p-[18F]desmethyl-MPPF (p-[18F]D-MPPF) for the study of 5-HT1A receptors.
Defraiteur, C.; Plenevaux, Alain ULg; Lemaire, Christian ULg et al

in Journal of Labelled Compounds & Radiopharmaceuticals (2003), 46

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See detailSimple device for the radiosynthesis of [carbonyl-11C]amides, esters and ketones using carbon-11 monoxide.
Brichard, L.; Del Fiore, G.; Lemaire, Christian ULg et al

in Journal of Labelled Compounds & Radiopharmaceuticals (2003), 46

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See detailSynthesis of [18F]fluorinated a-methyl-a-amino acids by phase transfer catalysis for potential PET application.
Wouters, L.; Lemaire, Christian ULg; Plenevaux, Alain ULg et al

in Journal of Labelled Compounds & Radiopharmaceuticals (2003), 46

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See detailDevelopment and evaluation of an automated atlas-based image analysis method for microPET studies of the rat brain.
Rubins, Daniel J.; Melega, William P.; Lacan, Goran et al

in NeuroImage (2003), 20(4), 2100-18

An automated method for placement of 3D rat brain atlas-derived volumes of interest (VOIs) onto PET studies has been designed and evaluated. VOIs representing major structures of the rat brain were ... [more ▼]

An automated method for placement of 3D rat brain atlas-derived volumes of interest (VOIs) onto PET studies has been designed and evaluated. VOIs representing major structures of the rat brain were defined on a set of digitized cryosectioned images of the rat brain. For VOI placement, each PET study was registered with a synthetic PET target constructed from the VOI template. Registration was accomplished with an automated algorithm that maximized the mutual information content of the image volumes. The accuracy and precision of this method for VOI placement was determined using datasets from PET studies of the striatal dopamine and hippocampal serotonin systems. Each evaluated PET study could be registered to at least one synthetic PET target without obvious failure. Registration was critically dependent upon the initial position of the PET study relative to the synthetic PET target, but not dependent on the amount of synthetic PET target smoothing. An evaluation algorithm showed that resultant radioactivity concentration measurements of selected brain structures had errors=2% due to misalignment with the corresponding VOI. Further, radioligand binding values calculated from these measurements were found to be more precise than those calculated from measurements obtained with manually drawn regions of interest (ROIs). Overall, evaluation results demonstrated that this atlas-derived VOI method can be used to obtain unbiased measurements of radioactivity concentration from PET studies. Its automated features, and applicability to different radioligands and brain regions, will facilitate quantitative rat brain PET assessment procedures. [less ▲]

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See detailThe neural substrates of the central executive: Exploration of the updating and shifting processes
Collette, Fabienne ULg; Van der Linden, Martial ULg; Delchambre, Marie et al

Conference (2002, December)

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See detailBrain function in the vegetative state
Laureys, Steven ULg; Antoine, S.; Boly, Mélanie ULg et al

in Acta Neurologica Belgica (2002), 102(4), 177-185

Positron emission tomography (PET) techniques represent a useful tool to better understand the residual brain function in vegetative state patients. It has been shown that overall cerebral metabolic rates ... [more ▼]

Positron emission tomography (PET) techniques represent a useful tool to better understand the residual brain function in vegetative state patients. It has been shown that overall cerebral metabolic rates for glucose are massively reduced in this condition. However, the recovery of consciousness from vegetative state is not always associated with substantial changes in global metabolism. This finding led us to hypothesize that some vegetative patients are unconscious not just because of a global loss of neuronal function, but rather due to an altered activity in some critical brain regions and to the abolished functional connections between them. We used voxel-based Statistical Parametric Mapping (SPM) approaches to characterize the functional neuroanatomy of the vegetative state. The most dysfunctional brain regions were bilateral frontal and parieto-temporal associative cortices. Despite the metabolic impairment, external stimulation still induced a significant neuronal activation (i.e., change in blood flow) in vegetative patients as shown by both auditory click stimuli and noxious somatosensory stimuli. However this activation was limited to primary cortices and dissociated from higher-order associative cortices, thought to be necessary for conscious perception. Finally, we demonstrated that vegetative patients have impaired functional connections between distant cortical areas and between the thalami and the cortex and, more importantly, that recovery of consciousness is paralleled by a restoration of this cortico-thalamo-cortical interaction. [less ▲]

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See detailCortical processing of noxious somatosensory stimuli in the persistent vegetative state
Laureys, Steven ULg; Faymonville, Marie-Elisabeth ULg; Peigneux, Philippe ULg et al

in NeuroImage (2002), 17(2), 732-741

The persistent vegetative state (PVS) is a devastating medical condition characterized by preserved wakefulness contrasting with absent voluntary interaction with the environment. We used positron ... [more ▼]

The persistent vegetative state (PVS) is a devastating medical condition characterized by preserved wakefulness contrasting with absent voluntary interaction with the environment. We used positron emission tomography to assess the central processing of noxious somatosensory stimuli in the PVS. Changes in regional cerebral blood flow were measured during high-intensity electrical stimulation of the median nerve compared with rest in 15 nonsedated patients and in 15 healthy controls. Evoked potentials were recorded simultaneously. The stimuli were experienced as highly unpleasant to painful in controls. Brain glucose metabolism was also studied with [F-18]fluorodeoxyglucose in resting conditions. In PVS patients, overall cerebral metabolism was 40% of normal values. Nevertheless, noxious somatosensory stimulation-activated midbrain, contralateral thalamus, and primary somatosensory cortex in each and every PVS patient, even in the absence of detectable cortical evoked potentials. Secondary somatosensory, bilateral insular, posterior parietal, and anterior cingulate cortices did not show activation in any patient. Moreover, in PVS patients, the activated primary somatosensory cortex was functionally disconnected from secondary somatosensory, bilateral posterior parietal, premotor, polysensory superior temporal, and prefrontal cortices. In conclusion, somatosensory stimulation of PVS patients, at intensities that elicited pain in controls, resulted in increased neuronal activity in primary somatosensory cortex, even if resting brain metabolism was severely impaired. However, this activation of primary cortex seems to be isolated and dissociated from higher-order associative cortices. (C) 2002 Elsevier Science (USA). [less ▲]

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See detailThe neural substrates of the central executive: Exploration of the updating and shifting processes
Collette, Fabienne ULg; Van der Linden, Martial ULg; Delchambre, Marie et al

Conference (2002, September)

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See detailEpimerization study on [18F]FDG produced by an alkaline hydrolysis on solid support under stringent conditions
Mosdzianowski, C.; Lemaire, Christian ULg; Simoens, F. et al

in Applied Radiation & Isotopes (2002), 56(6), 871-875

Since 1998, routine [18F]FDG syntheses are being carried out by alkaline hydrolysis on a solid support, i.e. the labeled intermediate is trapped on a tC18 solid phase extraction cartridge, purified and ... [more ▼]

Since 1998, routine [18F]FDG syntheses are being carried out by alkaline hydrolysis on a solid support, i.e. the labeled intermediate is trapped on a tC18 solid phase extraction cartridge, purified and finally hydrolyzed within the cartridge, at room temperature, using sodium hydroxide. The present study demonstrated that no epimerization of [18F]FDG to [18F]FDM occurs even when 12 N NaOH is used and when the hydrolysis time is extended up to 1 h. The alkaline hydrolysis on solid support appears to be a simple method leading to [18F]FDG with high purity. [less ▲]

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See detailA PET investigation of lexicality and phonotactic frequency in oral language processing
Majerus, Steve ULg; Collette, Fabienne ULg; Van der Linden, Martial ULg et al

in Cognitive Neuropsychology (2002), 19(4), 343-360

Lexicality and phonotactic frequency effects are observed in many cognitive studies on language processing, but little is known about their underlying neural substrates, especially with regard to ... [more ▼]

Lexicality and phonotactic frequency effects are observed in many cognitive studies on language processing, but little is known about their underlying neural substrates, especially with regard to phonotactic frequency effects. Here, we conducted a positron emission tomography (PET) study in which 11 right-handed volunteers had either to repeat or to listen to lists of words, high phonotactic frequency nonwords, and low phonotactic frequency nonwords. The comparison of word versus nonword processing consistently confirmed previous findings of left temporal and prefrontal activations classically ascribed to lexicosemantic processing. Higher activation was found in the right posterior superior temporal gyrus when comparing high phonotactic frequency nonwords to words, but not when comparing low phonotactic frequency nonwords to words. We propose that this region is implicated in the formation of temporary phonological representations for high-probability phonological events, which may support processing of high phonotactic frequency nonwords [less ▲]

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See detailShort- and long-term effects of p-ethynylphenylalanine on brain serotonin levels
Zimmer, Luc; Luxen, André ULg; Giacomelli, Fabrice ULg et al

in Neurochemical Research (2002), 27(4), 269-275

Changes in tissue and extracellular serotonin (5-HT) in raphe dorsalis, raphe medialis and in their main projections areas (hippocampus, striatum and frontal cortex) were investigated at short and long ... [more ▼]

Changes in tissue and extracellular serotonin (5-HT) in raphe dorsalis, raphe medialis and in their main projections areas (hippocampus, striatum and frontal cortex) were investigated at short and long-term times after single injection (5 mg/kg ip) of a novel tryptophan hydroxylase inhibitor, p-ethynylphenylalanine (p-EPA). The 5-HT tissue concentration decreased significantly in raphe nuclei, 30 min post-injection and for 4 days, whereas it decreased from 24 hours post-injection in the 5-HT projections. Normal 5-HT levels reappeared after 12 days post-injection in all areas. Moreover, in the projection areas, the extracellular 5-HT levels decreased rapidly, 90, 40 and 30 min after p-EPA injection, in hippocampus, striatum and frontal cortex, respectively. Decreased accumulation of 5-hydroxytryptophan (5-HTP) under NSD-101 perfusion in the serotoninergic projections after p-EPA injection, confirmed the direct inhibitory effect of the drug on the tryptophan hydroxylase activity. These results demonstrated that p-EPA is a useful pharmacological tool which powerfully, acutely and irreversibly reduces the 5-HT levels. [less ▲]

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See detailEffect of endogenous serotonin on the binding of the 5-HT1A PET ligand 18 F in the rat hippocampus: kinetic b measurements combined with microdialysis
Zimmer, Luc; Mauger, Gweltas; Le Bars, Didier et al

in Journal of Neurochemistry (2002), 80(2), 278-286

By using a combination of an original beta(+)-sensitive intracerebral probe and microdialysis, the effect of increased endogenous serotonin on specific binding of F-18-MPPF [4-(2'-methoxy-phenyl)-1-[2'-[N ... [more ▼]

By using a combination of an original beta(+)-sensitive intracerebral probe and microdialysis, the effect of increased endogenous serotonin on specific binding of F-18-MPPF [4-(2'-methoxy-phenyl)-1-[2'-[N-(2"-pyridinyl)-p-fluorobenzamido]ethyl]piperazine] to the serotonin-1A (5-HT1A) receptors was investigated in the hippocampus of the anaesthetized rat. Our beta-sensitive probe prototype was sensitive enough to obtain Specific F-18-MPPF time-activity curves in the rodent (hippocampus/cerebellum ratio approximate to 2). The serotonin neuronal release was pharmacologically enhanced using fenfluramine at three different doses (1, 2 and 10 mg/kg intravenous) multiplying by 2-15 the extracellular serotonin in the hippocampus. These extracellular variations of extracellular serotonin resulted in dose-ranging decreases in F-18-MPPF-specific binding in the same rat. Our results showed for the first time that F-18-MPPF binding could be modulated by modifications of extracellular serotonin in the rat hippocampus. These results were confirmed by the enhancement of extracellular radioactivity collected in dialysates after the displacement of F-18-MPPF by fenfluramine. After modelization, F-18-MPPF binding could constitute an interesting radiotracer for positron emission tomography in evaluating the serotonin endogenous levels in limbic areas of the human brain. [less ▲]

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See detailModeling [F-18]MPPF positron emission tomography kinetics for the determination of 5-hydroxytryptamine(1A) receptor concentration with multiinjection
Costes, Nicolas; Merlet, I.; Zimmer, L. et al

in Journal of Cerebral Blood Flow & Metabolism (2002), 22

The selectivity of [F-18]MPPF (fluorine-18-labeled 4-(2'-methoxyphenyl)-1-[2'-(N-2"-pirydynyl)-p-fluorobenzamido]ethylpiperazine) for serotonergic 5-hydroxytryptamine(1A) (5-HT1A) receptors has been ... [more ▼]

The selectivity of [F-18]MPPF (fluorine-18-labeled 4-(2'-methoxyphenyl)-1-[2'-(N-2"-pirydynyl)-p-fluorobenzamido]ethylpiperazine) for serotonergic 5-hydroxytryptamine(1A) (5-HT1A) receptors has been established in animals and humans. The authors quantified the parameters of ligand-receptor exchanges using a double-injection protocol. After injection of a tracer and a coinjection dose of [F-18]MPPF, dynamic positron emission tomography (PET) data Were acquired during a 160-minute session in five healthy males. These PET and magnetic resonance imaging data were coregistered for anatomical identification. A three-compartment model was used to determine six parameters: F-v (vascular fraction). K-1, k(2) (plasma/free compartment exchange rate). k(off). k(on)/V-r (association and dissociation rate), B-max (receptor concentration), and to deduce K-d (apparent equilibrium dissociation rate). The model was fitted with regional PET kinetics and arterial input function corrected for metabolites. Analytical distribution volume and binding potential Were compared With indices generated by Logan-Patlak graphical analysis. The 5HT(1A) specificity for MPPF was evidenced. A B-max of 2.9 pmol/mL and a K-d of 2.8 nmol/L were found in hippocampal regions, K-d and distribution volume in the free compartment were regionally stable. and the Logan binding potential was linearly correlated to B-max. This study confirms the value of MPPF in the investigation of normal and pathologic systems involving the limbic network and 5-HT1A receptors. Standard values can be used for the simulation of simplified protocols. [less ▲]

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See detailLanthanide DOTA chelates bearing a methanethiosulfonate group as contrast agents for magnetic resonance imaging
Thonon, David ULg; Paris, Jérôme; Jacques, Vincent et al

Poster (2002)

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See detailEffects of incidental and intentional feature binding on recognition: a behavioural and PET activation study
Lekeu, Françoise ULg; Van der Linden, Martial ULg; Collette, Fabienne ULg et al

in Neuropsychologia (2002), 40(2), 131-144

Using Positron Emission Tomography (PET), we investigated cerebral regions associated with the episodic recognition of words alone and words bound to contextual colours. Two modes of colour encoding were ... [more ▼]

Using Positron Emission Tomography (PET), we investigated cerebral regions associated with the episodic recognition of words alone and words bound to contextual colours. Two modes of colour encoding were tested: incidental and intentional word-to-colour binding. Word-only recognition was associated with brain activation in a lexico-semantic left middle temporal region and in the cerebellum following an incidental colour encoding, and with brain activation in the left posterior middle frontal gyrus, right anterior cingulate and right inferior frontal gyrus following an intentional encoding. Recognition of bound features was associated with activation in left prefrontal and superior parietal regions following an incidental colour encoding, and with preferential right prefrontal cortex activation following an intentional colour encoding. Our results are in line with the hypothesis of a parietal involvement in context processing, and prefrontal areas in monitoring retrieval processes. Our results also support the hypothesis of a 'cortical asymmetry for reflective activity' (CARA). [less ▲]

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See detail18F-MPPF Pharmacokinetics in rat hippocampus imaged with MicroPet.
Rubin, D. J.; Way, B.; Lacan, G. et al

in Journal of Nuclear Medicine : Official Publication, Society of Nuclear Medicine (2002), 43(S1), 209

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See detailInfluence of P-glycoprotein on the tissue distribution in rats of the 5-HT1A antagonist p-[18F]MPPF.
Plenevaux, Alain ULg; Lacan, G.; Defraiteur, C. et al

in Society for Neuroscience / Abstracts (2002)

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See detailFast F-18 FDG synthesis by alkaline hydrolysis on a low polarity solid phase supports
Lemaire, Christian ULg; Damhaut, P.; Lauricella, Benjamino ULg et al

in Journal of Labelled Compounds & Radiopharmaceuticals (2002), 45(5), 435-447

The synthesis of 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) has been simplified by the use of a tC18 Sep Pak cartridge to effect purification and hydrolysis of the tetraacetylated [18F]fluoro-glucose ... [more ▼]

The synthesis of 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) has been simplified by the use of a tC18 Sep Pak cartridge to effect purification and hydrolysis of the tetraacetylated [18F]fluoro-glucose compound ([18F]TAG). After radiolabelling, this derivative was trapped on a solid phase extraction (SPE) cartridge and the residual reaction solvent (CH3CN), reagents (K222, K2CO3,) and by-products removed by washing the support with water. After this cleaning step, the acetyl groups were cleaved on the same tC18 column using 2N sodium hydroxide. This fast reaction proceeded near quantitatively (>98%) at room temperature in less than 2 min. The [18F]FDG was then recovered with a small amount of water, neutralized with a slight excess of 2N hydrochloric acid, buffered for pH with a citrate solution and finally purified on a neutral alumina oxide and a second tC18 column. After filtration, the radiochemical yield of this [18F]FDG isotonic solution after more than 100 production runs was found to be very reliable and reproducible (70±6% decay corrected). The synthesis time was about 22 min. Quality controls showed that the radiochemical purity was higher than 98% and in any case no [18F]FDM was detected. Only traces of 2-chloro-2-deoxy-glucose (ClDG) were found in the final sample (64±9 g/ batch of 16 ml). [18F]FDG specific activity averaged between 1 and 20 Ci/µmol (EOS). No evaporation and use of ion retardation resin (AG11A8) are required. Moreover, this new approach is suitable for complete remote operation using available single use medical components. Copyright © 2002 John Wiley [less ▲]

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See detailNeural and cognitive bases of upper limb apraxia in corticobasal degeneration
Peigneux, Philippe ULg; Salmon, Eric ULg; Garraux, Gaëtan ULg et al

in Neurology (2001), 57(7), 1259-1268

OBJECTIVE: To investigate the neural and cognitive bases of upper limb apraxia in corticobasal degeneration (CBD). METHODS: Eighteen patients with CBD underwent a cognitive neuropsychological assessment ... [more ▼]

OBJECTIVE: To investigate the neural and cognitive bases of upper limb apraxia in corticobasal degeneration (CBD). METHODS: Eighteen patients with CBD underwent a cognitive neuropsychological assessment of apraxia and resting [(18)F]-fluorodeoxyglucose PET scanning. Two complementary measures of apraxia were computed for each modality of gesture production. First, a performance score measured error frequency during gesture execution. Second, as a more stringent test of the integrity of the praxis system, the correction score measured the patient's ability to correct his or her errors on a second attempt. For each measure type, a cut-off score for the presence of apraxia was defined with regard to healthy controls. Using each cut-off score, the regional cerebral glucose metabolism of patients with CBD with apraxia (i.e., performing below cut-off score) was compared with that of patients with CBD without apraxia. RESULTS: Mean performance scores were below normal values in all modalities. Anterior cingulate hypometabolism predominated in patients with CBD who performed below the cut-off performance score. At variance, mean correction scores were below normal values for gesture imitation only. Hypometabolism in superior parietal lobule and supplementary motor area characterized patients with CBD who were unable to correct their errors at the same rate as control subjects did. CONCLUSIONS: Distinct neural networks underlie distinct aspects of the upper limb apraxic deficits in CBD. Extending previous findings of gesture production deficits in CBD, the use of complementary measures of apraxic behavior discloses a visuoimitative upper limb apraxia in CBD, underlain by a metabolic decrease in a parietofrontal neural network. [less ▲]

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See detailGeneration of rapid eye movements during paradoxical sleep in humans
Peigneux, Philippe ULg; Laureys, Steven ULg; Fuchs, Sonia et al

in NeuroImage (2001), 14(3), 701-708

Although rapid eye movements (REMs) are a prominent feature of paradoxical sleep (PS), their origin and functional significance remain poorly understood in humans. In animals, including nonhuman primates ... [more ▼]

Although rapid eye movements (REMs) are a prominent feature of paradoxical sleep (PS), their origin and functional significance remain poorly understood in humans. In animals, including nonhuman primates, REMs during PS are closely related to the occurrence of the so-called PGO waves, i.e., prominent phasic activities recorded throughout the brain but predominantly and most easily in the pons (P), the lateral geniculate bodies (G), and the occipital cortex (O). Therefore, and because the evolution of species is parsimonious, a plausible hypothesis would be that during PS in humans, REMs are generated by mechanisms similar to PGO waves. Using positron emission tomography and iterative cerebral blood flow measurements by H(2)(15)O infusions, we predicted that the brain regions where the PGO waves are the most easily recorded in animals would be differentially more active in PS than in wakefulness, in relation with the density of the REM production [i.e., we looked for the condition (PS versus wakefulness) by performance (REM density) interaction]. Accordingly, we found a significant interaction effect in the right geniculate body and in the primary occipital cortex. The result supports the hypothesis of the existence of processes similar to PGO waves in humans, responsible for REM generation. The interest in the presence of PGO waves in humans is outstanding because the cellular processes involved in, or triggered by, PGO waves might favor brain plasticity during PS. [less ▲]

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