Spectral-based thickness profiling of the corpus callosum enhances anomaly detection in fetal alcohol spectrum disorders

Introduction

Fetal alcohol spectrum disorders (FASD) range from fetal alcohol syndrome (FAS) to non-syndromic forms (NS-FASD). The neuroanatomical consequences of prenatal alcohol exposure are mainly the reduction in brain size, but also focal abnormalities such as those of the corpus callosum (CC). We previously showed a narrowing of the CC for brain size, using manual measurement and its usefulness to improve diagnostic certainty. Our aim was to automate these measurements of the CC and identify more recurrent abnormalities in FAS subjects, independently of brain size reduction.

Methods

We developed a fast, automated, and normalization-free method based on spectral analysis to generate thicknesses of the CC continuously and at singular points (genu, body, isthmus, and splenium), and its length (LCC). We applied it on midsagittal section of the CC extracted from T1-anatomical brain MRI of 89 subjects with FASD (52 FAS, 37 NS-FASD) and 126 with typically development (6-20 y-o). After adjusting for batch effect, we compared the mean profiles and thicknesses of the singular points across the 3 groups. For each parameter, we established variations with age (growth charts) and brain size in the control group (scaling charts), then identified participants with abnormal measurements (<10th percentile).

Results

We confirmed the slimming of the posterior half of the CC in both FASD groups, and of the genu section in the FAS group, compared to the control group. We found a significant group effect for the LCC, genu, median body, isthmus, and splenium thicknesses (p < 0.05). We described a body hump whose morphology did not differ between groups. According to the growth charts, there was an excess of FASD subjects with abnormal LCC and isthmus, and of FAS subjects with abnormal genu and splenium. According to the scaling charts, this excess remained only for LCC, isthmus and splenium, undersized for brain size.

Conclusion

We characterized size-independent anomalies of the posterior part of the CC in FASD, with an automated method, confirming and extending our previous study. Our new tool brings the use of a neuroanatomical criterion including CC damage closer to clinical practice. Our results suggest that an FAS signature identified in NS-FASD, could improve diagnosis specificity.

Mapping corpus callosum surface reduction in fetal alcohol spectrum disorders with sulci and connectivity-based parcellation

Introduction

Fetal alcohol spectrum disorders (FASD) range from fetal alcohol syndrome (FAS) to non-syndromic non-specific forms (NS-FASD) that are still underdiagnosed and could benefit from new neuroanatomical markers. The main neuroanatomical manifestation of prenatal alcohol exposure on developmental toxicity is the reduction in brain size, but repeated imaging observations have long driven the attention on the corpus callosum (CC), without being all convergent. Our study proposed a new segmentation of the CC that relies on both a sulci-based cortical segmentation and the "hemispherotopic" organization of the transcallosal fibers.

Methods

We collected a monocentric series of 37 subjects with FAS, 28 with NS-FASD, and 38 with typical development (6 to 25 years old) using brain MRI (1.5T). Associating T1- and diffusion-weighted imaging, we projected a sulci-based cortical segmentation of the hemispheres on the midsagittal section of the CC, resulting in seven homologous anterior-posterior parcels (frontopolar, anterior and posterior prefrontal, precentral, postcentral, parietal, and occipital). We measured the effect of FASD on the area of callosal and cortical parcels by considering age, sex, and brain size as linear covariates. The surface proportion of the corresponding cortical parcel was introduced as an additional covariate. We performed a normative analysis to identify subjects with an abnormally small parcel.

Results

All callosal and cortical parcels were smaller in the FASD group compared with controls. When accounting for age, sex, and brain size, only the postcentral (η² = 6.5%, p_FDR = 0.032) callosal parcel and % of the cortical parcel (η² = 8.9%, p_FDR = 0.007) were still smaller. Adding the surface proportion (%) of the corresponding cortical parcel to the model, only the occipital parcel was persistently reduced in the FASD group (η² = 5.7%, p_FDR = 0.014). In the normative analysis, we found an excess of subjects with FASD with abnormally small precentral and postcentral (peri-isthmic) and posterior-splenial parcels (p_FDR < 0.05).

Conclusion

The objective sulcal and connectivity-based method of CC parcellation proved to be useful not only in confirming posterior-splenial damage in FASD but also in the narrowing of the peri-isthmic region strongly associated with a specific size reduction in the corresponding postcentral cortical region (postcentral gyrus). The normative analysis showed that this type of callosal segmentation could provide a clinically relevant neuroanatomical endophenotype, even in NS-FASD.

Group-level cortical surface parcellation with sulcal pits labeling

Sulcal pits are the points of maximal depth within the folds of the cortical surface. These shape descriptors give a unique opportunity to access to a rich, fine-scale representation of the geometry and the developmental milestones of the cortical surface. However, using sulcal pits analysis at group level requires new numerical tools to establish inter-subject correspondences. Here, we address this issue by taking advantage of the geometrical information carried by sulcal basins that are the local patches of surfaces surrounding each sulcal pit. Our framework consists in two phases. First, we present a new method to generate a population-specific atlas of this sulcal basins organi- zation as a fold-level parcellation of the cortical surface. Then, we address the labeling of individual sulcal pits and corresponding basins with respect to this atlas. To assess their validity, we applied these methodological advances on two different populations of healthy subjects. The first database of 137 adults allowed us to compare our method to the state-of-the-art and the second database of 209 children, aged between 0 and 18 years, illustrates the adaptability and relevance of our method in the context of pediatric data showing strong variations in cortical volume and folding.

Efficacy of Tumor Necrosis Factor Antagonist Treatment in Patients With Refractory Ulcerative Proctitis

BACKGROUND & AIMS

It is a challenge to manage patients with ulcerative proctitis (UP) refractory to standard therapy. We investigated the effectiveness of tumor necrosis factor (TNF) antagonists in a large cohort of patients with refractory UP.

METHODS

We conducted a nationwide retrospective cohort study of 104 consecutive patients with active UP refractory to conventional therapies, treated at 1 of 15 centers in France or 1 center in Belgium (the GETAID cohort). Patients received at least 1 injection of anti-TNF (infliximab, adalimumab, golimumab) from October 2006 through February 2017. Clinical response was defined as significant improvement in UC-related symptoms, and remission as complete disappearance of UC-related symptoms, each determined by treating physicians. We collected demographic, clinical, and treatment data. The median duration of follow-up was 24 months (interquartile range, 13-51 months). The primary outcome was clinical response of UP to anti-TNF treatment.

RESULTS

Overall, 80 patients (77%) had a clinical response to anti-TNF therapy and 52 patients (50%) achieved clinical remission. Extra-intestinal manifestations (odds ratio OR, 0.24; 95% CI, 0.08-0.7), ongoing treatment with topical steroids (OR, 0.14; 95% CI, 0.03-0.73), and ongoing treatment with topical 5-aminosalycilates (OR, 0.21; 95% CI, 0.07-0.62) were significantly associated with the absence of clinical remission. Sixty percent (38/63) of the patients who had endoscopic assessment during follow up had mucosal healing. Among the overall population (n = 104), the cumulative probabilities of sustained clinical remission were 87.6% ± 3.4% at 1 year and 74.7% ± 4.8% at 2 years.

CONCLUSIONS

In a retrospective study of 104 patients with refractory UP, anti-TNF therapy induced clinical remission in 50% and mucosal healing in 60%. About two thirds of the patients were still receiving anti-TNF therapy at 2 years.

Alteration of the Cortex Shape as a Proxy of White Matter Swelling in Severe Cerebral Small Vessel Disease

CADASIL is a monogenic small vessel disease characterized by the accumulation of brain tissue lesions of microvascular origin leading to strokes and cognitive deficits. Both cortical and parenchymal alterations have been described using various MRI markers. However, relationships between cortical and subcortical alterations remain largely unexplored. While brain atrophy is a preponderant feature in cerebral small vessel disease, recent results in CADASIL suggest slightly larger brain volumes and increased white matter water content at early stages of the disease by comparison to controls. We hypothesized in this study that increased water content in gyral white matter balances expected brain atrophy. Direct white matter volume computation is challenging in these patients given widespread subcortical alterations. Instead, our approach was that a gyral white matter swelling would translate into a modification of the shape of cortical gyri. Our goal was then to assess the relationship between subcortical lesions and possible alteration of the cortex shape. More specifically, aims of this work were to assess 1) morphometric differences of the cortex shape between CADASIL patients and controls 2) the relationship between the cortex shape and the volume of white matter hyperintensities (WMH), a reflect of white matter alterations. Twenty-one patients at the early stage of the disease and 28 age- and sex-matched controls were included. Cortical surfaces were reconstructed from 3D-T1-weighted images. Folding power assessed from spectral analysis of gyrification and cortical morphometry using curvedness and shape index were computed as proxies of the cortex shape. Influence of segmentation errors were evaluated through the simulation of WMH in controls. As a result, patients had larger folding power and curvedness compared to controls. They also presented lower shape indices both related to sulci and gyri. In patients, the volume of WMH was associated with decreased gyral shape index. These results suggest that the cortex shape of CADASIL patients is different compared to controls and that the enlargement of gyri is related to the extent of white matter alterations. The study of the cortex shape might be another way to evaluate subcortical swelling or atrophy in various neurological disorders.

Three-Dimensional Probabilistic Maps of Mesial Temporal Lobe Structures in Children and Adolescents' Brains

The hippocampus and the adjacent perirhinal, entorhinal, temporopolar, and parahippocampal cortices are interconnected in a hierarchical MTL system crucial for memory processes. A probabilistic description of the anatomical location and spatial variability of MTL cortices in the child and adolescent brain would help to assess structure-function relationships. The rhinal sulcus (RS) and the collateral sulcus (CS) that border MTL cortices and influence their morphology have never been described in these populations. In this study, we identified the aforementioned structures on magnetic resonance images of 38 healthy subjects aged 7-17 years old. Relative to sulcal morphometry in the MTL, we showed RS-CS conformation is an additional factor of variability in the MTL that is not explained by other variables such as age, sex and brain volume; with an innovative method using permutation testing of the extrema of structures of interest, we showed that RS-SC conformation was not associated with differences of location of MTL sulci. Relative to probabilistic maps, we offered for the first time a systematic mapping of MTL structures in children and adolescent, mapping all the structures of the MTL system while taking sulcal morphology into account. Our results, with the probabilistic maps described here being freely available for download, will help to understand the anatomy of this region and help functional and clinical studies to accurately test structure-function hypotheses in the MTL during development. Free access to MTL pediatric atlas: http://neurovault.org/collections/2381/.

SPANOL (SPectral ANalysis of Lobes): A Spectral Clustering Framework for Individual and Group Parcellation of Cortical Surfaces in Lobes

Understanding the link between structure, function and development in the brain is a key topic in neuroimaging that benefits from the tremendous progress of multi-modal MRI and its computational analysis. It implies, inter alia, to be able to parcellate the brain volume or cortical surface into biologically relevant regions. These parcellations may be inferred from existing atlases (e.g., Desikan) or sets of rules, as would do a neuroanatomist for lobes, but also directly driven from the data (e.g., functional or structural connectivity) with minimum a priori. In the present work, we aimed at using the intrinsic geometric information contained in the eigenfunctions of Laplace-Beltrami Operator to obtain parcellations of the cortical surface based only on its description by triangular meshes. We proposed a framework adapted from spectral clustering, which is general in scope and suitable for the co-parcellation of a group of subjects. We applied it to a dataset of 62 adults, optimized it and revealed a striking agreement between parcels produced by this unsupervised clustering and Freesurfer lobes (Desikan atlas), which cannot be explained by chance. Constituting the first reported attempt of spectral-based fully unsupervised segmentation of neuroanatomical regions such as lobes, spectral analysis of lobes (Spanol) could conveniently be fitted into a multimodal pipeline to ease, optimize or speed-up lobar or sub-lobar segmentation. In addition, we showed promising results of Spanol on smoother brains and notably on a dataset of 15 fetuses, with an interest for both the understanding of cortical ontogeny and the applicative field of perinatal computational neuroanatomy.

The dynamics of cortical folding waves and prematurity-related deviations revealed by spatial and spectral analysis of gyrification

In the human brain, the appearance of cortical sulci is a complex process that takes place mostly during the second half of pregnancy, with a relatively stable temporal sequence across individuals. Since deviant gyrification patterns have been observed in many neurodevelopmental disorders, mapping cortical development in vivo from the early stages on is an essential step to uncover new markers for diagnosis or prognosis. Recently this has been made possible by MRI combined with post-processing tools, but the reported results are still fragmented. Here we aimed to characterize the typical folding progression ex utero from the pre- to the post-term period, by considering 58 healthy preterm and full-term newborns and infants imaged between 27 and 62 weeks of post-menstrual age. Using a method of spectral analysis of gyrification (SPANGY), we detailed the spatial-frequency structure of cortical patterns in a quantitative way. The modeling of developmental trajectories revealed three successive waves that might correspond to primary, secondary and tertiary folding. Some deviations were further detected in 10 premature infants without apparent neurological impairment and imaged at term equivalent age, suggesting that our approach is sensitive enough to highlight the subtle impact of preterm birth and extra-uterine life on folding.

Total midgut volvulus in adults with intestinal malrotation. Report of eleven patients

OBJECTIVE

Total small-intestinal volvulus with malrotation (TSIVM) classically presents in the neonatal period; it occurs much less frequently in the adult and is often misdiagnosed. Prognosis is directly related to the degree and duration of intestinal ischemia. Our goal is to describe our experience with TSIVM in the adult, to identify any specific findings and to discuss its management.

METHOD

Eleven patients who had undergone surgery for TSIVM at three centers between 1992 and 2012 were included. Surgery was performed as an emergency for five patients and surgery was elective for six.

RESULTS

Mean follow-up was 63 months (range: 12-270). Six patients had had previous abdominal surgery. In nine cases, the diagnosis of TSIVM was made preoperatively, mainly by CT scan in eight cases. Seven patients had associated congenital failure of retroperitoneal fixation of the right colon and all of these underwent a Ladd procedure. The mortality rate was zero. Of the five patients who underwent emergency surgery, three required intestinal resections, one of whom developed a short bowel syndrome. The six patients who underwent surgery electively had no surgical complications.

CONCLUSION

TSIVM is a very unusual finding in adult patients. The diagnosis can be made by CT scan with IV and oral contrast, but it often comes to light only at the time of surgery, even though the patients have often had recurrent episodes of abdominal symptomatology that dated back to childhood. The Ladd procedure, consisting of division of Ladd's bands, widening of the mesentery, and incidental appendectomy, remains the standard surgical repair. Digestive surgeons who care for adults should be familiar with this procedure, and it should be performed, as often as possible, with the assistance of a pediatric surgeon.

Are Developmental Trajectories of Cortical Folding Comparable Between Cross-sectional Datasets of Fetuses and Preterm Newborns?

Magnetic resonance imaging has proved to be suitable and efficient for in vivo investigation of the early process of brain gyrification in fetuses and preterm newborns but the question remains as to whether cortical-related measurements derived from both cases are comparable or not. Indeed, the developmental folding trajectories drawn up from both populations have not been compared so far, neither from cross-sectional nor from longitudinal datasets. The present study aimed to compare features of cortical folding between healthy fetuses and early imaged preterm newborns on a cross-sectional basis, over a developmental period critical for the folding process (21-36 weeks of gestational age [GA]). A particular attention was carried out to reduce the methodological biases between the 2 populations. To provide an accurate group comparison, several global parameters characterizing the cortical morphometry were derived. In both groups, those metrics provided good proxies for the dramatic brain growth and cortical folding over this developmental period. Except for the cortical volume and the rate of sulci appearance, they depicted different trajectories in both groups suggesting that the transition from into ex utero has a visible impact on cortical morphology that is at least dependent on the GA at birth in preterm newborns.

Encoding cortical dynamics in sparse features

Distributed cortical solutions of magnetoencephalography (MEG) and electroencephalography (EEG) exhibit complex spatial and temporal dynamics. The extraction of patterns of interest and dynamic features from these cortical signals has so far relied on the expertise of investigators. There is a definite need in both clinical and neuroscience research for a method that will extract critical features from high-dimensional neuroimaging data in an automatic fashion. We have previously demonstrated the use of optical flow techniques for evaluating the kinematic properties of motion field projected on non-flat manifolds like in a cortical surface. We have further extended this framework to automatically detect features in the optical flow vector field by using the modified and extended 2-Riemannian Helmholtz–Hodge decomposition (HHD). Here, we applied these mathematical models on simulation and MEG data recorded from a healthy individual during a somatosensory experiment and an epilepsy pediatric patient during sleep. We tested whether our technique can automatically extract salient dynamical features of cortical activity. Simulation results indicated that we can precisely reproduce the simulated cortical dynamics with HHD; encode them in sparse features and represent the propagation of brain activity between distinct cortical areas. Using HHD, we decoded the somatosensory N20 component into two HHD features and represented the dynamics of brain activity as a traveling source between two primary somatosensory regions. In the epilepsy patient, we displayed the propagation of the epileptic activity around the margins of a brain lesion. Our findings indicate that HHD measures computed from cortical dynamics can: (i) quantitatively access the cortical dynamics in both healthy and disease brain in terms of sparse features and dynamic brain activity propagation between distinct cortical areas, and (ii) facilitate a reproducible, automated analysis of experimental and clinical MEG/EEG source imaging data.

Structural basis for the association of MAP6 protein with microtubules and its regulation by calmodulin

Microtubules are highly dynamic αβ-tubulin polymers. In vitro and in living cells, microtubules are most often cold- and nocodazole-sensitive. When present, the MAP6/STOP family of proteins protects microtubules from cold- and nocodazole-induced depolymerization but the molecular and structure determinants by which these proteins stabilize microtubules remain under debate. We show here that a short protein fragment from MAP6-N, which encompasses its Mn1 and Mn2 modules (MAP6(90-177)), recapitulates the function of the full-length MAP6-N protein toward microtubules, i.e. its ability to stabilize microtubules in vitro and in cultured cells in ice-cold conditions or in the presence of nocodazole. We further show for the first time, using biochemical assays and NMR spectroscopy, that these effects result from the binding of MAP6(90-177) to microtubules with a 1:1 MAP6(90-177):tubulin heterodimer stoichiometry. NMR data demonstrate that the binding of MAP6(90-177) to microtubules involve its two Mn modules but that a single one is also able to interact with microtubules in a closely similar manner. This suggests that the Mn modules represent each a full microtubule binding domain and that MAP6 proteins may stabilize microtubules by bridging tubulin heterodimers from adjacent protofilaments or within a protofilament. Finally, we demonstrate that Ca(2+)-calmodulin competes with microtubules for MAP6(90-177) binding and that the binding mode of MAP6(90-177) to microtubules and Ca(2+)-calmodulin involves a common stretch of amino acid residues on the MAP6(90-177) side. This result accounts for the regulation of microtubule stability in cold condition by Ca(2+)-calmodulin.

Model-driven harmonic parameterization of the cortical surface: HIP-HOP

In the context of inter subject brain surface matching, we present a parameterization of the cortical surface constrained by a model of cortical organization. The parameterization is defined via an harmonic mapping of each hemisphere surface to a rectangular planar domain that integrates a representation of the model. As opposed to previous landmark-based registration methods we do not match folds between individuals but instead optimize the fit between cortical sulci and specific iso-coordinate axis in the model. This strategy overcomes some limitation to sulcus-based registration techniques such as topological variability in sulcal landmarks across subjects. Experiments on 62 subjects with manually traced sulci are presented and compared with the result of the Freesurfer software. The evaluation involves a measure of dispersion of sulci with both angular and area distortions. We show that the model-based strategy can lead to a natural, efficient and very fast (less than 5 min per hemisphere) method for defining inter subjects correspondences. We discuss how this approach also reduces the problems inherent to anatomically defined landmarks and open the way to the investigation of cortical organization through the notion of orientation and alignment of structures across the cortex.

The structure of HasB reveals a new class of TonB protein fold

TonB is a key protein in active transport of essential nutrients like vitamin B12 and metal sources through the outer membrane transporters of Gram-negative bacteria. This inner membrane protein spans the periplasm, contacts the outer membrane receptor by its periplasmic domain and transduces energy from the cytoplasmic membrane pmf to the receptor allowing nutrient internalization. Whereas generally a single TonB protein allows the acquisition of several nutrients through their cognate receptor, in some species one particular TonB is dedicated to a specific system. Despite a considerable amount of data available, the molecular mechanism of TonB-dependent active transport is still poorly understood. In this work, we present a structural study of a TonB-like protein, HasB dedicated to the HasR receptor. HasR acquires heme either free or via an extracellular heme transporter, the hemophore HasA. Heme is used as an iron source by bacteria. We have solved the structure of the HasB periplasmic domain of Serratia marcescens and describe its interaction with a critical region of HasR. Some important differences are observed between HasB and TonB structures. The HasB fold reveals a new structural class of TonB-like proteins. Furthermore, we have identified the structural features that explain the functional specificity of HasB. These results give a new insight into the molecular mechanism of nutrient active transport through the bacterial outer membrane and present the first detailed structural study of a specific TonB-like protein and its interaction with the receptor.

Surface smoothing: a way back in early brain morphogenesis

In this article we propose to investigate the analogy between early cortical folding process and cortical smoothing by mean curvature flow. First, we introduce a one-parameter model that is able to fit a developmental trajectory as represented in a Volume-Area plot and we propose an efficient optimization strategy for parameter estimation. Second, we validate the model on forty cortical surfaces of preterm newborns by comparing global geometrical indices and trajectories of central sulcus along developmental and simulation time.

Larger is twistier: spectral analysis of gyrification (SPANGY) applied to adult brain size polymorphism

The description of cortical folding pattern (CFP) is challenging because of geometric complexity and inter-subject variability. On a cortical surface mesh, curvature estimation provides a good scalar proxy of CFP. The oscillations of this function can be studied using a Fourier-like analysis to produce a power spectrum representative of the spatial frequency composition of CFP. First, we introduce an original method for the SPectral ANalysis of GYrication (Spangy), which performs a spectral decomposition of the mean curvature of the grey/white interface mesh based on the Laplace-Beltrami operator eigenfunctions. Spangy produces an ordered 7 bands power spectrum of curvature (B0-B6) and provides an anatomically relevant segmentation of CFP based on local spectral composition. A spatial frequency being associated with each eigenfunction, the bandwidth design assumes frequency doubling between consecutive spectral bands. Next, we observed that the last 3 spectral bands (B4, 5 and 6) accounted for 93% of the analyzed spectral power and were associated with fold-related variations of curvature, whereas the lower frequency bands were related to global brain shape. The spectral segmentation of CFP revealed 1st, 2nd and 3rd order elements associated with B4, B5 and B6 respectively. These elements could be related to developmentally-defined primary, secondary and tertiary folds. Finally, we used allometric scaling of frequency bands power and segmentation to analyze the relationship between the spectral composition of CFP and brain size in a large adult dataset. Total folding power followed a positive allometric scaling which did not divide up proportionally between the bands: B4 contribution was constant, B5 increased like total folding power and B6 much faster. Besides, apparition of new elements of pattern with increasing size only concerned the 3rd order. Hence, we demonstrate that large brains are twistier than smaller ones because of an increased number of high spatial frequency folds, ramifications and kinks that accommodate the allometric increase of cortical surface.

Microtubule-targeting drugs rescue axonal swellings in cortical neurons from spastin knockout mice

Mutations in SPG4, encoding the microtubule-severing protein spastin, are responsible for the most frequent form of hereditary spastic paraplegia (HSP), a heterogeneous group of genetic diseases characterized by degeneration of the corticospinal tracts. We previously reported that mice harboring a deletion in Spg4, generating a premature stop codon, develop progressive axonal degeneration characterized by focal axonal swellings associated with impaired axonal transport. To further characterize the molecular and cellular mechanisms underlying this mutant phenotype, we have assessed microtubule dynamics and axonal transport in primary cultures of cortical neurons from spastin-mutant mice. We show an early and marked impairment of microtubule dynamics all along the axons of spastin-deficient cortical neurons, which is likely to be responsible for the occurrence of axonal swellings and cargo stalling. Our analysis also reveals that a modulation of microtubule dynamics by microtubule-targeting drugs rescues the mutant phenotype of cortical neurons. Together, these results contribute to a better understanding of the pathogenesis of SPG4-linked HSP and ascertain the influence of microtubule-targeted drugs on the early axonal phenotype in a mouse model of the disease.

The C terminus of tubulin, a versatile partner for cationic molecules: binding of Tau, polyamines, and calcium

The C-terminal region of tubulin is involved in multiple aspects of the regulation of microtubule assembly. To elucidate the molecular mechanisms of this regulation, we study here, using different approaches, the interaction of Tau, spermine, and calcium, three representative partners of the tubulin C-terminal region, with a peptide composed of the last 42 residues of α1a-tubulin. The results show that their binding involves overlapping amino acid stretches in the C-terminal tubulin region: amino acid residues 421-441 for Tau, 430-432 and 444-451 for spermine, and 421-443 for calcium. Isothermal titration calorimetry, NMR, and cosedimentation experiments show that Tau and spermine have similar micromolar binding affinities, whereas their binding stoichiometry differs (C-terminal tubulin peptide/spermine stoichiometry 1:2, and C-terminal tubulin peptide/Tau stoichiometry 8:1). Interestingly, calcium, known as a negative regulator of microtubule assembly, can compete with the binding of Tau and spermine with the C-terminal domain of tubulin and with the positive effect of these two partners on microtubule assembly in vitro. This observation opens up the possibility that calcium may participate in the regulation of microtubule assembly in vivo through direct (still unknown) or indirect mechanism (displacement of microtubule partners). The functional importance of this part of tubulin was also underlined by the observation that an α-tubulin mutant deleted from the last 23 amino acid residues does not incorporate properly into the microtubule network of HeLa cells. Together, these results provide a structural basis for a better understanding of the complex interactions and putative competition of tubulin cationic partners with the C-terminal region of tubulin.

Circulation and suspended sediment transport in a coral reef lagoon: the south-west lagoon of New Caledonia

The south-west lagoon of New Caledonia is a wide semi-open coral reef lagoon bounded by an intertidal barrier reef and bisected by numerous deep inlets. This paper synthesizes findings from the 2000-2008 French National Program EC2CO-PNEC relative to the circulation and the transport of suspended particles in this lagoon. Numerical model development (hydrodynamic, fine suspended sediment transport, wind-wave, small-scale atmospheric circulation) allowed the determination of circulation patterns in the lagoon and the charting of residence time, the later of which has been recently used in a series of ecological studies. Topical studies based on field measurements permitted the parameterisation of wave set-up induced by the swell breaking on the reef barrier and the validation of a wind-wave model in a fetch-limited environment. The analysis of spatial and temporal variability of suspended matter concentration over short and long time-scales, the measurement of grain size distribution and the density of suspended matter (1.27 kg l(-1)), and the estimation of erodibility of heterogeneous (sand/mud, terrigenous/biogenic) soft bottoms was also conducted. Aggregates were shown to be more abundant near or around reefs and a possible biological influence on this aggregation is discussed. Optical measurements enabled the quantification of suspended matter either in situ (monochromatic measurements) or remotely (surface spectral measurements and satellite observations) and provided indirect calibration and validation of a suspended sediment transport model. The processes that warrant further investigation in order to improve our knowledge of circulation and suspended sediment transport in the New Caledonia lagoon as well as in other coral reef areas are discussed, as are the relevance and reliability of the numerical models for this endeavour.

A reaction-diffusion model of human brain development

Cortical folding exhibits both reproducibility and variability in the geometry and topology of its patterns. These two properties are obviously the result of the brain development that goes through local cellular and molecular interactions which have important consequences on the global shape of the cortex. Hypotheses to explain the convoluted aspect of the brain are still intensively debated and do not focus necessarily on the variability of folds. Here we propose a phenomenological model based on reaction-diffusion mechanisms involving Turing morphogens that are responsible for the differential growth of two types of areas, sulci (bottom of folds) and gyri (top of folds). We use a finite element approach of our model that is able to compute the evolution of morphogens on any kind of surface and to deform it through an iterative process. Our model mimics the progressive folding of the cortical surface along foetal development. Moreover it reveals patterns of reproducibility when we look at several realizations of the model from a noisy initial condition. However this reproducibility must be tempered by the fact that a same fold engendered by the model can have different topological properties, in one or several parts. These two results on the reproducibility and variability of the model echo the sulcal roots theory that postulates the existence of anatomical entities around which the folding organizes itself. These sulcal roots would correspond to initial conditions in our model. Last but not least, the parameters of our model are able to produce different kinds of patterns that can be linked to developmental pathologies such as polymicrogyria and lissencephaly. The main significance of our model is that it proposes a first approach to the issue of reproducibility and variability of the cortical folding.

The anatomical variability of the human brain folds remains an unclear and challenging issue. However it is clear that this variability is the product of the brain development. Several hypotheses coexist for explaining the rapid development of cortical sulci and it is of the highest interest that understanding their variability would improve the comparison of anatomical and functional data across cohorts of subjects. In this article we propose to extend a model of cortical folding based on interactions between growth factors that shape the cortical surface. First the originality of our approach lies in the fact that the surface on which these mechanisms take place is deformed iteratively and engenders geometric patterns that can be linked to cortical sulci. Secondly we show that some statistical properties of our model can reflect the reproducibility and the variability of sulcal structures. At the end we compare different patterns produced by the model to different pathologies of brain development.

Optical flow approaches to the identification of brain dynamics

The superior temporal resolution of magneto- and electroencephalography (MEEG) provides unique insight into the dynamics of brain function. The analysis of the spatial dimensions of MEEG recordings can take a multiplicity of approaches: from the original scalp recordings to the identification of their generators through localizing or imaging techniques. Overall, both MEEG native or imaging data may be considered as multidimensional structures with potentially dense information contents. Quantitative analysis of the spatiotemporal flow of information conveyed by MEEG begins with a feature-extraction problem, thereby leading to improved insight in the multidimensional structure of brain dynamics. In this contribution, we approach this endeavor by suggesting that brain dynamic features from local through global spatial scales may be identified using the previously-introduced technique of surface-based optical flow. We illustrate this assertion by the quantitative analysis of time-resolved sequences of brain activity through the identification of episodes of relative topographical stability. In that respect, we revisit the concept of brain microstates with a new approach and distinct operational hypotheses. Local dynamic features from a variety of brain systems may also be explored through this methodology, as illustrated by experimental data on fast responses in the visual system as revealed by MEEG source imaging.

Optimization of patent foramen ovale detection by contrast transthoracic echocardiography using second harmonic imaging

BACKGROUND

Patent foramen ovale is an anomaly responsible for paradoxical embolizations and cerebral ischemic events. Aims. - We want to show second harmonic transthoracic echography sensitized by contrast agent perfusion is as well as transesophageal echography to patent foramen ovale detection.

METHODS

Onene hundred twenty one patients referred for transesophageal echocardiography for patent foramen ovale detection, underwent additive second harmonic transthoracic echocardiography with one of three randomized contrast agents: a mixture A of dextrose and air, mixture B of dextrose and air and blood, or mixture C of hydroxyethylamidon. The severity of atrial shunting was evaluated on recordings by semi-quantitative scoring. Intensity of contrast was also assessed by objective quantitative videodensitometry.

RESULTS

No difference was observed between the two techniques, nor between mixture A, B and C in terms of PFO detection during each exam. However, quantitative contrast analysis showed higher intensity with mixtures B and C with mixture A during transthoracic echography.

CONCLUSIONS

When performed with a contrast agent, second harmonic transthoracic echography and transoesophageal echography are comparable when it comes to patent foramen ovale detection. Although the composition of the contrast agent does not appear to affect the rate of this detection, contrast quality in the right atrium during transthoracic exam is better with mixtures B and C than with mixture A.

Optical flow and advection on 2-Riemannian manifolds: a common framework

Dynamic pattern analysis and motion extraction can be efficiently addressed using optical flow techniques. This article presents a generalization of these questions to non-flat surfaces, where optical flow is tackled through the problem of evolution processes on non-Euclidian domains. The classical equations of optical flow in the Euclidian case are transposed to the theoretical framework of differential geometry. We adopt this formulation for the regularized optical flow problem, prove its mathematical well-posedness and combine it with the advection equation. The optical flow and advection problems are dual: a motion field may be retrieved from some scalar evolution using optical flow; conversely, a scalar field may be deduced from a velocity field using advection. These principles are illustrated with qualitative and quantitative evaluations from numerical simulations bridging both approaches. The proof-of-concept is further demonstrated with preliminary results from time-resolved functional brain imaging data, where organized propagations of cortical activation patterns are evidenced using our approach.

Modeling and detecting deep brain activity with MEG & EEG

We introduce an anatomical and electrophysiological model of deep brain structures dedicated to magnetoencephalography (MEG) and electroencephalography (EEG) source imaging. So far, most imaging inverse models considered that MEG/EEG surface signals were predominantly produced by cortical, hence superficial, neural currents. Here we question whether crucial deep brain structures such as the basal ganglia and the hippocampus may also contribute to distant, scalp MEG and EEG measurements. We first design a realistic anatomical and electrophysiological model of these structures and subsequently run Monte-Carlo experiments to evaluate the respective sensitivity of the MEG and EEG to signals from deeper origins. Results indicate that MEG/EEG may indeed localize these deeper generators, which is confirmed here from experimental MEG data reporting on the modulation of alpha brain waves.

(1)H, (13)C and (15)N resonance assignments of the C-terminal domain of HasB, a specific TonB like protein, from Serratia marcescens

The backbone and side chain resonance assignments of the periplasmic domain of HasB, the energy transducer for heme active transport through the specific receptor HasR of Serratia marcescens, have been determined as a first step towards its structural study. The BMRB accession code is 15440.

Imaging Brain Activation Streams from Optical Flow Computation on 2-Riemannian Manifolds

We report on mathematical methods for the exploration of spatiotemporal dynamics of Magneto- and Electro-Encephalography (MEG / EEG) surface data and/or of the corresponding brain activity at the cortical level, with high temporal resolution. In this regard, we describe how the framework and numerical computation of the optical flow--a classical tool for motion analysis in computer vision--can be extended to non-flat 2-dimensional surfaces such as the scalp and the cortical mantle. We prove the concept and mathematical well-posedness of such an extension through regularizing constraints on the estimated velocity field, and discuss the quantitative evaluation of the optical flow. The method is illustrated by simulations and analysis of brain image sequences from a ball-catching paradigm.

[Use of echocardiography in the diagnosis of carcinoid tumors. Report of 4 cases]

Carcinoid tumours are the most common neuro-endocrine tumours but cardiac involvement is rarely symptomatic although often observed at post-mortem and rarely revelatory of the disease. The authors report 4 cases in which echocardiographic detection of characteristic right ventricular involvement led to the confirmation of the diagnosis of carcinoid tumour leading to the secondary diagnosis of the primary carcinoid tumour. The clinical, physiopathological echocardiographic and therapeutic characteristics of this condition are discussed.

[Criteria of localization of the bundle of Kent]

The high success rate (> 90%) of radiofrequency ablation of accessory pathways is related to accurate mapping. This determines the site of the accessory pathway and the best target for ablation with the object of reducing the number of applications and the associated morbidity. Analysis of the surface ECG is the first step of localisation of a Kent bundle. Different algorithms may be used based on the correlation between the polarity of the delta wave, of the QRS and the site of the accessory pathway confirmed at surgery or during radiofrequency ablation procedures. Some of the recent algorithms allow localisation of certain postero-septal or sub-epicardial pathways, the ablation of which can only be accomplished via the coronary sinus or one of its branches, or in an abnormally dilated coronary sinus, the so-called diverticulum. A relatively accurate localisation of the accessory pathway from the surface ECG reduces the duration of an ablation procedure and may economise the need for left-sided catheterisation. However, the endocavitary electrogrammes determine the precise target of ablation whether this be the ventricular or atrial pole of the bundle of Kent. The association of the criteria obtained by bipolar and unipolar recordings in sinus rhythm, during pacing or reentrant tachycardia enables accurate localisation in the majority of cases. Ablation of some pathways may be more complex because of their site or the presence of associated congenital or acquired cardiac disease which alters the anatomical or electrical markers. In these cases, the electrical criteria, especially those of the surface ECG may be erroneous and non invasive investigations such as Doppler echocardiography, isotopic ventriculography with phase analysis are most valuable with a positive predictive value of over 90%.

Teleonomical optimization of a fractal model of the pulmonary arterial bed

Modeling the pulmonary arterial tree (PAT) is considered here as an optimal synthesis problem. Firstly, a class of candidate models is specified: the three-dimensional symmetric dichotomous fractal trees of elastic tubes described by Womersley's equations. Secondly, the parameters are shown to be constrained by interactions of PAT with the rest of the body; these constraints are used to limit the volume of the parametric space to which attention will be directed in the synthesis step. Thirdly, a teleonomical hypothesis is proposed: a naturally selected PAT must have a minimal input impedance under conditions keeping total arterial volume and distensibility as small as possible. This hypothesis is translated in mathematical terms and the resulting cost-function minimized in the limited parametric volume. The optimal model has parameter values and an impedance spectrum corresponding satisfactorily with real data. Moreover this model gives a clear picture of the internal hemodynamic behavior of PAT as an impedance matching device.

Parvalbumins and muscle relaxation: a computer simulation study

The distribution of Ca2+ and Mg2+ among the 'regulatory' cation binding sites of troponin (T-sites) and the strong, Ca2+-Mg2+ binding sites of troponin and parvalbumins (P-sites) in the sarcoplasm of a muscle was calculated. At rest, 60% of the T-sites were metal free, while 92% of the P-sites were loaded with Mg2+. In response to a Ca2+ pulse, troponin-calcium (T-Ca) complexes were rapidly formed, while the binding of Ca2+ to P-sites was limited by the slow rate of dissociation of the parvalbumin-magnesium (P-Mg) complexes. Muscle activation was not prevented by a high content of parvalbumins. Parvalbumin and the sarcoplasmic reticulum (SR) pump were complementary relaxing factors that removed Ca2+ from the cytosol and from the T-sites. Parvalbumins dominated the first part of relaxation, while the action of the SR was essential to ensure the return to a very low level of free Ca2+ ion and of T-Ca. After relaxation, a large fraction of the Ca2+ pulse was still bound to parvalbumins and returned slowly to the SR during the recovery. When the SR activity was reduced, the presence of parvalbumins preserved a fast rate of relaxation, at least for a few contractions. This may have a high adaptive value in cold-blooded animals.

Free-wall shortening and relaxation during ejection in the canine right ventricle

Relations between shortening, velocity of shortening, and relaxation of inflow and outflow segments of the right ventricular (RV) free wall (FW) were examined during ejection in 12 open-chest dogs after pharmacologic blockade by recording RV pressures, RVFW dimensions (piezoelectric crystals), and pulmonary blood flow. At heart rates of 113 +/0 8 (SD) beats/min, investigated segments remained isometric or even lengthened before the end of ejection. Tension-length data in the outflow tract converged at the time of peak systolic tension toward a common linear relation (average slope 65 +/- 10 cmH2O/mm, average intercept 5.9 +/- 0.9 mm), but markedly deviated from this line at the end of ejection. Consistent relations between peak tension and mean velocity of shortening were only observed during the first part of ejection. In addition the rate of segmental isometric relaxation, estimated from RV pressure fall was load dependent (e.g., +60% increase in relaxation rate when RVFW end-diastolic segment length increased from 12.9 +/- 0.8 to 13.5 +/- 0.8 mm). We conclude that under normal conditions, the tension-velocity-length relations of the RVFW are comparable to those of the left ventricle during the first part of ejection only. We also conclude that RV relaxation is load dependent and that a significant part of RV ejection occurs during RVFW relaxation.

[Isotopic study of fluid and electrolyte disturbances in decompensated chronic respiratory insufficiency (author's transl)]

The study of fluid and electrolyte disturbances by isotope radiodilution method is carried out in 22 patients with chronic respiratory insufficiency and cardiac failure. The simultaneous measurements of hydro-ionic compartments have been carried out with tritiated water (HTO), labelled sodium (22Na), labelled potassium (42K) and labelled bromine (82Br). From these measurements, the various water spaces are calculated: total water (ET) and extracellular fluids (LEC), also exchangeable electrolytes: sodium (NaE), potassium (KE), chlorine (ClE) and derived values. Results are compared to corresponding values in controls with the same obesity index. Patients with respiratory insufficiency show a fluid and sodium rise, similar to that found in cardiac failure and denutrition. The (NaE + KE)/ET ratio is not significantly decreased and the natremia is only slightly lower. There is no real potassium depletion in most patients.