462 research outputs found
Simulation and evaluation of a new PET system based on liquid xenon as detection medium
présenté par J.P. CussoneauDue to its intrinsic physical properties, high density and atomic number, fast scintillation, high scintillation light yield and low ionization potential, liquid xenon is an excellent medium for the tracking and the accurate energy measurement of γ-rays in the MeV energy domain. The use of liquid xenon associated to a micro gap structure device[1] to measure 511 keV γ-rays in PET system is under investigation at Subatech. A Geant3 simulation of a full PET design made of lXe-TPC modules has been developed and the first estimations of the performances from a realistic detector are very promising: good overall sensitivity to 511 keV γ's (~ 93% for a 9 cm lXe module), good three-dimensional spatial resolution (250 µm FWHM, for first interaction vertex localization). The measurement of the 3 coordinates of the interaction vertices and the energy loss associated allow to reconstruct the correct Compton sequence of correlated annihilation γ-rays. Hence the capability to identify the first interaction vertex leads to major progresses in PET imaging: a parallax free PET tomograph with high detection sensitivity and spatial resolution. Moreover, such lXe-PET camera have an excellent rejection power on scattered events in 3D reconstruction mode
Sistema dopaminérgico y muerte neuronal
The mechanism involved in dopaminergic neuronal death remains unknown. Increased oxidative stress, inhibition of mitochondrial respiratory chain and apoptosis have been suggested as possible factors mediating cellular death. This article reviews the most important findings reported in parkinsonian brains related to nigral neuronal death
Exogenous LRRK2G2019S induces parkinsonian-like pathology in a nonhuman primate
Parkinson’s disease (PD) is the second most prevalent neurodegenerative disease among the elderly. To understand pathogenesis and to test therapies, animal models that faithfully reproduce key pathological PD hallmarks are needed. As a prelude to developing a model of PD, we tested the tropism, efficacy, biodistribution, and transcriptional impact of canine adenovirus type 2 (CAV-2) vectors in the brain of Microcebus murinus, a nonhuman primate that naturally develops neurodegenerative lesions. We show that introducing helper-dependent (HD) CAV-2 vectors results in long-term, neuron-specific expression at the injection site and in afferent nuclei. Although HD CAV-2 vector injection induced a modest transcriptional response, no significant adaptive immune response was generated. We then generated and tested HD CAV-2 vectors expressing LRRK2 (leucine-rich repeat kinase 2) and LRRK2 carrying a G2019S mutation (LRRK2G2019S), which is linked to sporadic and familial autosomal dominant forms of PD. We show that HD-LRRK2G2019S expression induced parkinsonian-like motor symptoms and histological features in less than 4 months
A proposal for a high performance -camera based on liquid Xenon converter and gaseous photomultiplier for PET
présenté par D. Ther
Combining Gene Transfer and Nonhuman Primates to Better Understand and Treat Parkinson’s Disease
Parkinson's disease (PD) is a progressive CNS disorder that is primarily associated with impaired movement. PD develops over decades and is linked to the gradual loss of dopamine delivery to the striatum, via the loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). While the administration of L-dopa and deep brain stimulation are potent therapies, their costs, side effects and gradual loss of efficacy underlines the need to develop other approaches. Unfortunately, the lack of pertinent animal models that reproduce DA neuron loss and behavior deficits-in a timeline that mimics PD progression-has hindered the identification of alternative therapies. A complementary approach to transgenic animals is the use of nonhuman primates (NHPs) combined with the overexpression of disease-related genes using viral vectors. This approach may induce phenotypes that are not influenced by developmental compensation mechanisms, and that take into account the personality of animals. In this review article, we discuss the combination of gene transfer and NHPs to develop "genetic" models of PD that are suitable for testing therapeutic approaches
Detection of cannabinoid receptors CB1 and CB2 within basal ganglia output neurons in macaques: changes following experimental parkinsonism
Abstract Although type 1 cannabinoid receptors (CB1-
Rs) are expressed abundantly throughout the brain, the
presence of type 2 cannabinoid receptors (CB2Rs) in neurons
is still somewhat controversial. Taking advantage of
newly designed CB1R and CB2R mRNA riboprobes, we
demonstrate by PCR and in situ hybridization that transcripts
for both cannabinoid receptors are present within
labeled pallidothalamic-projecting neurons of control and
MPTP-treated macaques, whereas the expression is markedly
reduced in dyskinetic animals. Moreover, an in situ
proximity ligation assay was used to qualitatively assess
the presence of CB1Rs and CB2Rs, as well as CB1R–CB2R
heteromers within basal ganglia output neurons in all
animal groups (control, parkinsonian and dyskinetic
macaques). A marked reduction in the number of CB1Rs,
CB2Rs and CB1R–CB2R heteromers was found in dyskinetic
animals, mimicking the observed reduction in CB1R
and CB2R mRNA expression levels. The fact that chronic
levodopa treatment disrupted CB1R–CB2R heteromeric
complexes should be taken into consideration when
designing new drugs acting on cannabinoid receptor
heteromers
Influence of Temperature and Humidity on Bakelite Resistivity
Presentation made at RPC99 and submitted to Elsevier PreprintThe use of phenolic or melaminic bakelite as RPC electrodes is widespread. The electrode resistivity is an important parameter for the RPC performance. As recent studies have pointed out, the bakelite resistivity changes with temperature and is influenced by humidity. In order to gain a quantitative understanding on the influence of temperature and humidity on RPC electrodes, we assembled an apparatus to measure resistivity in well-controlled conditions. A detailed description of the experimental set-up as well as the first resistivity measurements for various laminates in different environmental conditions are presented
Interferometry of Direct Photons in Central 280Pb+208Pb Collisions at 158A GeV
Two-particle correlations of direct photons were measured in central
208Pb+208Pb collisions at 158 AGeV. The invariant interferometric radii were
extracted for 100<K_T<300 MeV/c and compared to radii extracted from charged
pion correlations. The yield of soft direct photons, K_T<300 MeV/c, was
extracted from the correlation strength and compared to theoretical
calculations.Comment: 5 pages, 4 figure
Study of the Resistive Plate Chambers for the ALICE Dimuon Arm
Presentation made at RPC99 and submitted to Elsevier PreprintThe trigger system for the ALICE Dimuon Arm will be based on Resistive Plate Chambers. An RPC prototype, with electrodes made of low resistivity bakelite (rho ~ 3.109 Ωcm) has been tested both at the SPS and at the GIF. The results for operation in streamer mode are presented here
Event-by-Event Fluctuations in Particle Multiplicities and Transverse Energy Produced in 158.A GeV Pb+Pb collisions
Event-by-event fluctuations in the multiplicities of charged particles and
photons, and the total transverse energy in 158 GeV Pb+Pb collisions
are studied for a wide range of centralities. For narrow centrality bins the
multiplicity and transverse energy distributions are found to be near perfect
Gaussians. The effect of detector acceptance on the multiplicity fluctuations
has been studied and demonstrated to follow statistical considerations. The
centrality dependence of the charged particle multiplicity fluctuations in the
measured data has been found to agree reasonably well with those obtained from
a participant model. However for photons the multiplicity fluctuations has been
found to be lower compared to those obtained from a participant model. The
multiplicity and transverse energy fluctuations have also been compared to
those obtained from the VENUS event generator.Comment: To appear in Physical Review C; changes : more detailed discussion on
errors and few figures modifie
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