To Be or Not to Be a Flatworm: The Acoel Controversy

Since first described, acoels were considered members of the flatworms (Platyhelminthes). However, no clear synapomorphies among the three large flatworm taxa - the Catenulida, the Acoelomorpha and the Rhabditophora - have been characterized to date. Molecular phylogenies, on the other hand, commonly positioned acoels separate from other flatworms. Accordingly, our own multi-locus phylogenetic analysis using 43 genes and 23 animal species places the acoel flatworm Isodiametra pulchra at the base of all Bilateria, distant from other flatworms. By contrast, novel data on the distribution and proliferation of stem cells and the specific mode of epidermal replacement constitute a strong synapomorphy for the Acoela plus the major group of flatworms, the Rhabditophora. The expression of a piwi-like gene not only in gonadal, but also in adult somatic stem cells is another unique feature among bilaterians. These two independent stem-cell-related characters put the Acoela into the Platyhelminthes-Lophotrochozoa clade and account for the most parsimonious evolutionary explanation of epidermal cell renewal in the Bilateria. Most available multigene analyses produce conflicting results regarding the position of the acoels in the tree of life. Given these phylogenomic conflicts and the contradiction of developmental and morphological data with phylogenomic results, the monophyly of the phylum Platyhelminthes and the position of the Acoela remain unresolved. By these data, both the inclusion of Acoela within Platyhelminthes, and their separation from flatworms as basal bilaterians are well-supported alternatives.     

Matrix metalloproteinase 2 polymorphisms in a caucasian population with abdominal aortic aneurysm

BACKGROUND: The formation of sporadic abdominal aortic aneurysm (AAA) is explained by remodeling of the extracellular matrix (ECM) and breakdown of structural components of the vascular wall. Matrix metalloproteinase 2 (MMP2) is one of the principal matrix-degrading proteases and is known to play a major role in the remodeling of the extracellular matrix in arterial vessels. Increased MMP2 expression in the extracellular matrix of the walls of AAAs has been shown in several studies. To investigate the possible impact of genetic variants of the MMP2 gene in the etiology of AAA, we conducted this case-control study. PATIENTS AND METHODS: We analyzed MMP2 single-nucleotide polymorphisms (SNPs) in 51 patients with AAA and 48 controls. Differences in genotype and allele frequencies of identified polymorphisms were determined after sequencing the entire coding region and three selected parts of the promoter. RESULTS: Eighteen polymorphisms were identified, 6 of which are newly described, with 3 located in the introns (c.IVS1+31C>G, c.IVS7-18G>A, c.IVS10+26C>T) and 3 located in the coding region (c.124G>A, c.1368C>T, c.1860C>T). There were no statistically significant differences in genotype or allele frequencies between the two groups. CONCLUSIONS: Our analysis of the entire coding region and three parts of the promoter of the MMP2 gene failed to show an association between genetic polymorphisms and AAA, suggesting that variations in the MMP2 gene do not contribute to the development of AAA.     

Characterization of an artificial valve flow using the numerical dye washout visualization technique: application to the monoleaflet valve with purged flow

Until today, no ideal heart valve prosthesis for the replacement of a diseased natural valve or for use in ventricular assist devices exists. Valves still cause thromboembolic complications originating from thrombus formations in the valve's stagnant zones. Optimization of valve design involves avoiding stagnation zones and zones of high shear stresses. This requires detailed flow field investigations. Usually, the regions which are more prone to thrombus formation can be estimated using a dye washout experiment. The method allows an assessment of regions with a high or low residence time that may in turn predict regions with a corresponding thrombus risk. This successful experimental method was simulated using numerical methods with a combination of the computational fluid dynamics program FLUENT (Fluent Inc., Lebanon, NH, USA) and of the visualization tool AMIRA (TGS Inc., San Diego, CA, USA). The numerical dye washout visualization was applied to four monoleaflet valves with varying valve housing geometries. The results show a significant difference in the washout processes of the examined valves. The dye washout was characterized by a time course of the gray value averaged over a defined region of interest. Finally, these curves were quantified by a half dye time. The half dye time in the best optimized valve was only 0.2753 s. The same time in the original valve was 0.6834 s. This study shows that the proposed numerical method of dye washout visualization can be used as an additional tool of the flow characterization in artificial organs.     

Individual olfactory sensory neurons project into more than one glomerulus in Xenopus laevis tadpole olfactory bulb

An essential step in the coding of odorants is the way olfactory sensory neurons (OSNs) convey their information to the olfactory bulb. This projection determines how the specificities of OSNs are mapped onto the spatial activity patterns of the olfactory bulb (OB). Despite the fact that virtually nothing is known about how individual OSN axons project to glomeruli, it is generally believed that OSNs always project to one glomerulus each. Our recent findings in tadpoles of Xenopus laevis challenge this view. By injection of a tracer into individual OSNs, we show for the first time that axons typically project into more than one glomerulus and that they do so in a characteristic way. Upon entering the olfactory bulb, an axon bifurcates to give two primary branches. Each of these branches bifurcates again to give two subbranches, thus resulting in four subbranches per OSN. The two subbranches of each primary branch project into two different glomeruli. Variations of this characteristic innervation pattern include the innervation of three and, occasionally, one glomerulus. In any case, and independent of the number of glomeruli innervated by an OSN, each glomerulus receives at least two axonal branches of the same OSN.     

Therapeutic alternatives in nonunion of hamate hook fractures: personal experience in 8 patients and review of literature

Symptomatic nonunion frequently results after conservative treatment of hamate hook fractures, emphasizing the need of appropriate surgical strategies. A retrospective analysis of 8 patients with nonunions treated by fragment excision or open reduction and internal fixation (ORIF) at 3 centers was performed. The literature was reviewed for treatment options, as bone grafting and low-intensity pulsed ultrasound. Although fragment excision is advocated as the "gold standard" in nonunion, reports on functional results are controversial, and recent anatomic and biomechanical studies of the hook challenge this opinion. In our patients, complete relief of symptoms and comparable functional results were observed after ORIF or fragment excision. Bone grafting could supplement ORIF in selected cases. Low-intensity pulsed ultrasound may evolve as a conservative treatment option. Several alternatives to hook excision are available aiming at complete anatomic and functional recovery of hamate hook nonunion. Further experience is needed before general recommendations can be formulated.     

Seizure suppression by adenosine A1 receptor activation in a mouse model of pharmacoresistant epilepsy

PURPOSE: Because of the high incidence of pharmacoresistance in the treatment of epilepsy (20-30%), alternative treatment strategies are needed. Recently a proof-of-principle for a new therapeutic approach was established by the intraventricular delivery of adenosine released from implants of engineered cells. Adenosine-releasing implants were found to be effective in seizure suppression in a rat model of temporal lobe epilepsy. In the present study, activation of the adenosine system was applied as a possible treatment for pharmacoresistant epilepsy. METHODS: A mouse model for drug-resistant mesial temporal lobe epilepsy was used, in which recurrent spontaneous seizure activity was induced by a single intrahippocampal injection of kainic acid (KA; 200 ng in 50 nl). RESULTS: After injection of the selective adenosine A1-receptor agonist, 2-chloro-N6-cyclopentyladenosine (CCPA; either 1.5 or 3 mg/kg, i.p.), epileptic discharges determined in EEG recordings were completely suppressed for a period of 相似文献   

Amino acid composition of brain cysts: levels of excitatory amino acids in cyst fluid fail to predict seizures

A recent study describing two epileptic patients with brain cysts has suggested that elevated concentrations of excitatory amino acids in cysts may play a role in induction and maintenance of epileptogenesis [Epilepsy Res. 28 (1997) 245]. Here, we report that only in 3 out of 22 patients with brain cysts undergoing brain surgery cyst fluids displayed highly increased amounts of the excitatory amino acids aspartate and/or glutamate. Two of these patients experienced epileptic seizures prior to neurosurgical intervention. Thus, highly increased excitatory amino acid levels are present only in a subset of patients with brain cysts. Our observation that one patient with highly increased glutamate and aspartate concentrations in the cyst did not display seizures or typical epileptiform potentials in the EEG questions that these excitatory amino acids in the cyst fluid are directly involved in epileptogenicity. This patient displayed an increased level of adenosine in the cyst fluid, which is known to have anticonvulsant properties and might provide protection from seizures. In summary, there is no evidence for a close correlation between excitatory amino acids in brain cysts and the occurrence of seizures.