Quantification de l’activité dopaminergique striatale en TEP à la 18F-DOPA : quels paramètres choisir en routine ?

Aim of the studyFunctional assessment of the nigrostriatal dopaminergic pathway (NSDP) is still largely dominated by SPECT imaging of presynaptic dopamine transporters. Because of greater performance characteristics and a potential medico-economic added value, 18F-DOPA PET may advantageously replace SPECT procedures. Clinical analysis of 18F-DOPA PET images is mainly based on visual assessment, a parameter which may be empirically affected by a low reproducibility. We assessed several reproducible semi-quantitative parameters applicable in clinical routine.Material and methodsSeventy-two patients (18 control subjects, 55.2 ± 13.4 years; 54 patients without confirmed Parkinson's disease (no-PD patients): 74.0 ± 9.9 years) were prospectively referred for a 18F-DOPA PET brain study. 18F-DOPA striatal uptake, which reflects the activity level of L-DOPA decarboxylase (DDC), was quantified using calculation methods of SUV in several striatal VOI. Background activity in occipital VOI (non specific uptake) was taken into consideration to assess specific uptake.ResultsDespite the absence of standard of truth regarding the medical status of no-PD patients, the most effective quantitative parameter to assess specific striatal dopaminergic activity was the putamen-to-occipital ratio. According to our data, activity level of DCC might decrease with age.ConclusionAn accurate and early in-vivo detection of NSDP alteration is a critical issue at the earliest stages of PD. Despite limits of this preliminary study, simple semi-quantitative parameters appear to be valuable tools to address problems of classification reproducibility in clinical practice.     

Asymptotic Relative Efficiency of Some Jackknife Estimators of a Common Odds Ratio

In the situation of several 2 × 2 tables the asymptotic relative efficiencies of certain jackknife estimators of a common odds ratio are investigated in the case that the number of tables is fixed while the sample sizes within each table tend to infinity. The estimators show very good results over a wide range of parameters. Some situations in which the estimators have low asymptotic relative efficiency are pointed out:.     

Enhancing native chemical ligation for challenging chemical protein syntheses

Native chemical ligation has enabled the chemical synthesis of proteins for a wide variety of applications (e.g., mirror-image proteins). However, inefficiencies of this chemoselective ligation in the context of large or otherwise challenging protein targets can limit the practical scope of chemical protein synthesis. In this review, we focus on recent developments aimed at enhancing and expanding native chemical ligation for challenging protein syntheses. Chemical auxiliaries, use of selenium chemistry, and templating all enable ligations at otherwise suboptimal junctions. The continuing development of these tools is making the chemical synthesis of large proteins increasingly accessible.     

Role of Asp297 of the AT2 receptor in high-affinity binding to different peptide ligands

To determine how ligand-receptor interaction is affected by the charges of the amino acids at position 2 of the ligands and position 297 of the AT2 receptor, we generated the Asp297Lys mutant of AT2 and a ligand SarAsp²Ile. Asp297Lys mutant lost affinity to Ang II and SarIle however retained partial affinity to ¹²⁵I-CGP42112A. The SarAsp²Ile had high affinity to Asp297Lys (IC₅₀3.5nM) and partial affinity to the AT2 (IC₅₀15nM). Therefore, not only the charge, but also the length of the side arms of the amino acids at position 2 of the ligand and position 297 of the receptor affect their interaction.     

Male-biased sex ratios in mature damselfly populations: real or artefact?

1. There is ongoing controversy about whether biased sex ratios in diploid insect populations are real or an artefact caused by different behaviours and/or different catchability of the sexes. This was tested by monitoring two field and three semi-natural populations of the damselfly Lestes sponsa. 2. Capture–mark–recapture data showed that population size estimates were about twice as large for males as for females at both field sites. Independent estimates of the sex ratios based on total numbers of males and females captured supported the male bias. 3. Males had higher recapture probabilities than females due to longer times between successive visits in females. Because the same pattern was found in the semi-natural populations, the longer intervals in females are no artefact due to their lower detectability. 4. Theoretical models show that the strong temporary emigration of females tends, if anything, to overestimate female population sizes and that the heterogeneity of recapture probabilities observed in males tends to underestimate male population sizes. Hence, behavioural differences between the sexes do not cause an artificially male-biased sex ratio. 5. Spatial data show that operational sex ratios are male biased at the pond but become female biased in the plots further away from the shoreline; however because of the decrease in densities away from the shoreline, this does not result in a global even sex ratio. 6. Spatial data, temporary emigration patterns, and independent estimates suggest strongly that the male-biased sex ratios in mature damselfly populations are real.     

Fire effects on ecosystem nitrogen cycling in a Californian bishop pine forest

Fire can cause severe nitrogen (N) losses from grassland, chaparral, and temperate and boreal forest ecosystems. Paradoxically, soil ammonium levels are markedly increased by fire, resulting in high rates of primary production in re-establishing plant communities. In a manipulative experiment, we examined the influence of wild-fire ash residues on soil, microbial and plant N pools in a recently burned Californian bishop pine (Pinus muricata D. Don) forest. Ash stimulated post-fire primary production and ecosystem N retention through direct N inputs from ash to soils, as well as indirect ash effects on soil N availability to plants. These results suggest that redistribution of surface ash after fire by wind or water may cause substantial heterogeneity in soil N availability to plants, and could be an important mechanism contributing to vegetation patchiness in fire-prone ecosystems. In addition, we investigated the impact of fire on ecosystem N cycling by comparing ¹⁵N natural abundance values from recently burned and nearby unburned P. muricata forest communities. At the burned site, ¹⁵N natural abundance in recolonising species was similar to that in bulk soil organic matter. By contrast, there was a marked ¹⁵N depletion in the same species relative to the total soil N pool at the unburned site. These results suggest that plant uptake of nitrate (which tends to be strongly depleted in ¹⁵N because of fractionation during nitrification) is low in recently burned forest communities but could be an important component of eco- system N cycling in mature conifer stands. Received: 29 June 1999 / Accepted: 24 October 1999