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Biomedical subjects

A Schmitt

Publications and source records attributed to A Schmitt.

At least 19 recordsLinked to original sources
PubMed2002

Constant bond breakup probability model for reversible aggregation processes.

Reversible aggregation processes were simulated for systems of freely diffusing sticky particles. Reversibility was introduced by allowing that all bonds in the system may break with a given probability per time interval. In order to describe the kinetics of such aggregation-fragmentation processes, a fragmentation kernel was developed and then used together with the Brownian aggregation kernel for solving the corresponding kinetic master equation. The deduced fragmentation kernel considers a single characteristic lifetime for all bonds and accounts for the cluster morphology by averaging over all possible configurations for clusters of a given size. It became evident that the simulated cluster-size distributions could be described only when an additional fragmentation effectiveness was considered. Doing so, the stochastic solutions were in good agreement with the simulated data.

Journal Article↗
PubMed2002

A splice variant of glutamate transporter GLT1/EAAT2 expressed in neurons: cloning and localization in rat nervous system.

Rapid uptake of synaptically released glutamate via the high affinity glutamate transporter 1 (GLT1; EAAT2) is important for limiting transmitter signalling and prevents a harmful receptor overstimulation. So far, in the adult brain GLT1 protein has only been detected in astrocytes. Here, we describe the cDNA cloning of a variant of GLT1 from rat brain which is generated by alternative splicing at the 3'-end of the GLT1 cDNA. Reverse transcription-polymerase chain reaction revealed that the GLT1 variant message was present not only in brain, but also in peripheral organs. Northern blot analysis showed that in brain the mRNA of GLT1 (approximately 11 kb) is predominant while in the retina the mRNA of GLT1 variant (approximately 12.5 kb) prevails. In situ hybridization using cRNA and oligonucleotide probes, and immunocytochemistry using an antibody against a synthetic GLT1v peptide were applied in order to identify the cell types expressing GLT1 variant in the adult rat nervous system. GLT1 variant is preferentially expressed in neurons of the CNS and PNS, but is also detected in glial cells (oligodendrocytes, ependymal cells, epithelial cells of the plexus choroideus, satellite cells, and Schwann cells). In contrast to GLT1, GLT1 variant was only occasionally detected in astrocytes. Immunolabelling revealed a preferentially cytoplasmic (frequently granular) staining of neurons and glial cells, suggesting a localization of GLT1 variant protein in vesicle membranes. The studies provide evidence that the cellular expression of the GLT1 variant in the CNS is almost complementary to that of GLT1 and that the GLT1 variant does not seem to be restricted to the CNS.

Alternative Splicing↗
PubMed2001

Identification of PML oncogenic domains (PODs) in human megakaryocytes.

Megakaryocytes (Mks) are unique cells in the human body in that they carry a single and polyploid nucleus. It is therefore of interest to understand their nuclear ultrastructure. PML oncogenic domains (PODs) were described in several types of eukaryotic cells using human autoantibodies which recognize nuclear antigens with a specific speckled pattern (dots) in indirect immunofluorescence (IF). Two main antigens, PML and Sp 100, usually colocalize and concentrate in these nuclear subdomains. We investigated the presence of PODs using IF and immunoelectron microscopy (IEM) in cells from megakaryocytic lineage: the HEL cell line and human cultured Mks. Antibodies against PML, Sp100, and anti-nuclear dots were used in single and double labeling. PODs were identified in HEL cells and in human Mks, and their ultrastructure was characterized. We then used IF to quantify PODs within Mks and showed that their number increased proportionally to nuclear lobularity. In summary, we report the identification of PODs in human Mks at an ultrastructural level and an increase in PODs number in parallel with Mk ploidy. We show that endomitosis not only leads to DNA increase but also to the multiplication of at least one of the associated nuclear structures.

Antigens, Nuclear↗
PubMed2001

Newly recognized cellular abnormalities in the gray platelet syndrome.

The gray platelet syndrome (GPS) is a rare congenital bleeding disorder in which thrombocytopenia is associated with increased platelet size and decreased alpha-granule content. This report describes 3 new pediatric cases presenting with the classical platelet abnormalities of GPS within one family with normal parents. Examination of blood smears of the 3 patients demonstrated not only gray platelets, but also gray polymorphonuclear neutrophils (PMNs) with decreased or abnormally distributed components of secretory compartments (alkaline phosphatase, CD35, CD11b/CD18). Secondary granules were also decreased in number as assayed by immunoelectron microscopy. These data confirm that the secretory compartments in neutrophils were also deficient in this family. Megakaryocytes (MKs) were cultured from the peripheral blood CD34+ cells of the 3 patients for 14 days, in the presence of thrombopoietin and processed for immunoelectron microscopy. Although von Willebrand factor (vWF) was virtually undetectable in platelets, vWF immunolabeling was conspicuous in cultured maturing MKs, particularly within Golgi saccules, but instead of being packaged in alpha-granules, it was released into the demarcation membrane system. In contrast, P-selectin followed a more classical pathway. Double-labeling experiments confirmed that vWF was following an intracellular pathway distinct from the one of P-selectin. In these 3 new cases of GPS, the MKs appeared to abnormally process vWF, with secretion into the extracellular space instead of normal alpha-granule packaging. Furthermore, the secretory compartment of another blood cell line, the neutrophil, was also affected in this family of GPS.

Alkaline Phosphatase↗
PubMed2001

Lifetime measurements of metastable states in Fe+.

The lifetime of two metastable levels in Fe+ has been measured by laser probing of a stored ion beam. In the dense spectrum of Fe+, the metastable levels a (6)S(5/2) and b (4)D(7/2) were selected and their lifetimes were determined to be 230 +/- 30 and 530 +/- 30 ms, respectively. The lifetimes are compared with previous theoretical results. Metastable lifetime measurements of Fe+ are of great importance for interpretation of spectra from astronomical objects. The present experiment opens for the possibilities to investigate lifetimes of metastable states in complex atomic ions, which have, so far, been unexplored.

Journal Article↗
PubMed2001

Two novel Xenopus homologs of mammalian LP(A1)/EDG-2 function as lysophosphatidic acid receptors in Xenopus oocytes and mammalian cells.

Lysophosphatidic acid (LPA) induces diverse biological responses in many types of cells and tissues by activating its specific G protein-coupled receptors (GPCRs). Previously, three cognate LPA GPCRs (LP(A1)/VZG-1/EDG-2, LP(A2)/EDG-4, and LP(A3)/EDG-7) were identified in mammals. By contrast, an unrelated GPCR, PSP24, was reported to be a high affinity LPA receptor in Xenopus laevis oocytes, raising the possibility that Xenopus uses a very different form of LPA signaling. Toward addressing this issue, we report two novel Xenopus genes, xlp(A1)-1 and xlp(A1)-2, encoding LP(A1) homologs (approximately 90% amino acid sequence identity with mammalian LP(A1)). Both xlp(A1)-1 and xlp(A1)-2 are expressed in oocytes and the nervous system. Overexpression of either gene in oocytes potentiated LPA-induced oscillatory chloride ion currents through a pertussis toxin-insensitive pathway. Injection of antisense oligonucleotides designed to inhibit xlp(A1)-1 and xlp(A1)-2 expression in oocytes eliminated their endogenous response to LPA. Furthermore, retrovirus-mediated heterologous expression of xlp(A1)-1 or xlp(A1)-2 in B103 rat neuroblastoma cells that are unresponsive to LPA conferred LPA-induced cell rounding and adenylyl cyclase inhibition. These results indicate that XLP(A1)-1 and XLP(A1)-2 are functional Xenopus LPA receptors and demonstrate the evolutionary conservation of LPA signaling over a range of vertebrate phylogeny.

Adenylate Cyclase Toxin↗
PubMed2001

Modulation of serotonin transporter function by interleukin-4.

Serotonin (5-HT) is an important mediator of interactions between the nervous and immune systems. 5-HT signaling is regulated by the 5-HT transporter (5-HTT), which determines the magnitude and duration of serotonergic responses. Due to this important role, regulation of the 5-HTT by cytokines has been the focus of recent interest. A number of proinflammatory cytokines, including interleukin-1beta, tumor necrosis factor-alpha, and interferon-gamma, have been shown to upregulate the 5-HTT. In the present study we investigated the influence of interleukin-4 (IL-4), which acts as an anti-inflammatory cytokine in the central nervous system, on the 5-HTT. As a model system we used immortalized B lymphocytes, which not only express the 5-HTT, but also allow testing the co-modulatory influence of a recently described polymorphism in the 5-HTT gene promoter (5-HTTLPR) that is associated with anxiety- and depression-related behavioral traits. The results show that IL-4 induces a dose-dependent reduction of 5-HT uptake. This effect is preferentially seen in cell lines homozygous for the long, high-activity allele of the 5-HTTLPR. In conclusion, a picture of differential modulation of the 5-HTT by proinflammatory and anti-inflammatory cytokines is emerging, which may represent a fine-tuned mechanism to communicate the state of an immune response to the central nervous system.

Alleles↗
PubMed2001

Identification of novel molecular components of the photoreceptor connecting cilium by immunoscreens.

The connecting cilium of photoreceptor cells is the only intracellular link between the morphologically, functionally and biochemically different compartments of the inner and outer segments. The non-motile modified cilium plays an important role in the organization and the function of photoreceptor cells, namely in delivery and turnover of enzymes and substrates of the visual transduction cascade, and the photosensitive membranes of the outer segment. The protein components of the cilium participate in the intracellular transport through the cilium, in the outer segment disk morphogenesis and in the maintenance of discrete membrane domains. In order to identify yet unknown cytoskeletal components of the connecting cilium, a combined biochemical and molecular biological strategy was applied. For this purpose, antibodies were raised against proteins of photoreceptor cell axonemes. Using this AX-4-antiserum, a rat retina cDNA expression library was immunoscreened and clones encoding partial sequences of (i) already known photoreceptor specific proteins; (ii) ubiquitously expressed proteins; (iii) clones with homologies to retinal ESTs; and (iv) clones coding for cytoskeletal proteins were isolated. Further analysis revealed that these candidate clones have homologies to Drosophila flightless I, mouse APC-binding protein EB2, human microtubule associated protein 4 (MAP4), human centrin 3, human cytoplasmic dynein intermediate chain 2C, and human dynamitin.The immunoscreening approach used here was successfully applied to isolate genes encoding yet unknown cytoskeletal proteins of photoreceptor cell axonemes. The obtained information will provide further insight into the role of the connecting cilium in photoreceptor cell function.

Adenomatous Polyposis Coli Protein↗
PubMed2001

Effects of antipsychotic treatment on membrane phospholipid metabolism in schizophrenia.

Several studies have shown an increased membrane phospholipid turnover in brain and blood cells of schizophrenic patients. However the specificity of these findings for schizophrenia and the effects of longterm antipsychotic treatment had yet to be demonstrated. In the present study we measured the concentrations of phospholipids in platelet membranes from 67 neuroleptic-free schizophrenic patients compared to both healthy and psychiatric controls, followed by repeated measurements during a 6 months antipsychotic treatment period. At baseline, levels of the main phospholipid components phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were decreased and lysophosphatidylcholine (LPC), a major breakdown product of phospholipid metabolism, was increased in schizophrenic patients compared to healthy and to psychiatric controls, suggesting a specificity of the findings for schizophrenia. During the first 3-weeks on antipsychotic drug treatment LPC levels decreased to control values, but increased again during the following 6 months, reaching significantly higher levels than controls at the end of this period. Thus, at least in peripheral cells an increased breakdown of phospholipids in schizophrenia appears to be present during the acute episode, being influenced only by initial antipsychotic treatment, but without evidence of a long lasting treatment effect on membrane metabolism.

Adult↗
PubMed2001

Of mice and men: comparison of the ultrastructure of megakaryocytes and platelets.

OBJECTIVE: Mice provide an excellent model for studying platelet and megakaryocyte (Mk) biology in vivo. Given the increasing use of transgenic and knockout mice, it is important that any similarities and differences between murine and human platelet/Mk biology be well defined. Therefore the objective of this study was to compare and contrast in detail any significant morphological differences between Mks, platelets, and mechanisms of thrombopoiesis in humans and mice. METHODS: The distinctive structural and ultrastructural features of murine and human platelets and Mks are reviewed. Several platelet and Mk glycoproteins were also localized in murine cells by immunoelectron microscopy using polyclonal antibodies directed against human platelet proteins and compared to existing human data. Finally, the ultrastructure of maturing murine and human Mks in culture and bone marrow were examined in detail to facilitate a comparison of either in vivo or in vitro platelet production. RESULTS: Human and murine platelets exhibit significant but well-established morphological differences. Murine platelets are smaller and more numerous and display much greater granule heterogeneity than their human counterparts. Immunoelectron microscopy also demonstrated that murine platelet alpha-granules are highly compartmentalized. In fact, they are remarkably similar to human alpha-granules, with asymmetrical distribution of von Willebrand factor (vWF), and labeling of alpha(IIb)beta(3) and P-selectin (CD62P) in the granule limiting membrane. In vivo, murine but not human Mks are also consistently localized within the spleen. Subcellular events accompanying platelet formation and release by murine Mks are presented for the first time, and compared to human. Consistent differences were found in the pathway of redistribution of demarcation membranes preceding platelet formation, which may be important for the clarification of the mechanism of platelet release. CONCLUSION: Human and murine platelets and Mks display several characteristic ultrastructural differences (size, number, histological distribution, platelet shedding) which have been emphasized and analyzed in this report. Nevertheless, since there are also many close similarities (organelle and glycoprotein subcellular distribution) mice offer an excellent in vivo model to study various aspects of human Mk and platelet biology.

Animals↗
PubMed2001

Allelic variation of serotonin transporter expression is associated with depression in Parkinson's disease.

Idiopathic Parkinson's disease (PD) is a common neurodegenerative disorder with prominent motor symptoms. However, depression is common in PD, affecting about 40% of PD patients. Since there is extensive evidence of degeneration of serotonin (5HT) neurons and loss of the 5HT transporter (5HTT) in PD, we assessed whether a functional polymorphism in the promoter of the 5HTT gene (5HTT gene-linked polymorphic region, 5HTTLPR), which determines high or low 5HT uptake, is associated with depressive symptomatology in PD patients. We found that patients with the short allele of the 5HTTLPR had significantly higher scores on the Hamilton Depression Scale. A functional promoter polymorphism of the monoamine oxidase A (MAOA) gene showed no association. Thus, the 5HTTLPR but not the MAOA gene promoter-associated polymorphism may be a risk factor for depression in PD patients, while neither polymorphism increases the risk for development of Parkinson's disease itself.

Alleles↗
PubMed2001

A missense mutation in a novel gene encoding a putative cation channel is associated with catatonic schizophrenia in a large pedigree.

Schizophrenia is a common and etiologically heterogeneous disorder. Although inheritance of schizophrenic syndromes is complex with genetic and environmental factors contributing to the clinical phenotype, periodic catatonia, a familial subtype of catatonic schizophrenia, appears to be transmitted in an autosomal dominant manner. We report here that a Leu309Met mutation in WKL1, a positional candidate gene on chromosome 22q13.33 encoding a putative non-selective cation channel expressed exclusively in brain, co-segregates with periodic catatonia in an extended pedigree. Structural analyses revealed that this missense mutation results in conformational changes of the mutant protein. Our results not only underscore the importance of genetic mechanisms in the etiology of schizophrenic syndromes, but also provide a better understanding of the pathogenesis and incapacitating course of catatonic schizophrenia and related disorders.

Amino Acid Sequence↗
PubMed2001

Efficient detection of hereditary nonpolyposis colorectal cancer gene carriers by screening for tumor microsatellite instability before germline genetic testing.

BACKGROUND & AIMS: The optimal strategy for the detection of hereditary nonpolyposis colorectal cancer (HNPCC) gene carriers remains uncertain. We evaluated whether microsatellite instability (MSI) analysis or MSH2 and MLH1 protein immunostaining of tumors will screen individuals efficiently for germline MSH2 and MLH1 testing. METHODS: We performed a case-series study of 114 eligible families enrolled in our high-risk colorectal cancer (CRC) registry. Medical history data were collected on probands and relatives. MSI analysis was performed on proband tumors, and MSH2 and MLH1 protein immunostaining was assessed. Denaturing gradient gel electrophoresis was used to identify germline MSH2 or MLH1 mutations in probands found to have tumors with high-frequency MSI. RESULTS: Tumor tissue and adequate clinical data were available in 109 of the 114 families. Amsterdam criteria and Bethesda guidelines were met by 23% and 70% of the families, respectively. High-frequency MSI was identified in the proband tumors in 47 of the 109 families (43%). Germline MSH2 and MLH1 gene testing was carried out in the probands of 32 of 47 families with MSI-H tumors. Mutations were detected in 16 families (9 in MSH2 and 7 in MLH1) and sequence variants of uncertain significance in 5 families (1 in MSH2 and 4 in MLH1). Germline mutations or sequence variants of uncertain significance were detected in 15 of 19 (79%) of our Amsterdam families and in 6 of 13 (46%) of our non-Amsterdam families with MSI-H tumors. MSH2 and MLH1 protein immunostaining was assessed in 38 of the 47 MSI-H tumors. Unequivocal loss of hMLH1 expression was found in 20 tumors and loss of MSH2 expression in 9 tumors. Corresponding loss of protein expression was seen in 17 of 18 (94%) of tumors from probands with germline mutations or variants. CONCLUSIONS: The detection of high-frequency MSI or the loss of MSH2 or MLH1 immunostaining in CRCs are both useful criteria for selecting high-risk patients who should be tested for germline mutations in MSH2 or MLH1.

Colorectal Neoplasms, Hereditary Nonpolyposis↗
PubMed2001

[Current overview of structural magnetic resonance imaging in schizophrenia].

Non-invasive morphologic imaging (computer tomography, magnetic resonance imaging, MRT) has contributed significantly to our understanding of schizophrenic disorders as diseases of the brain. Improved MRT techniques enable us to analyse anatomical substructures. The present overview evaluates peer-reviewed MRT studies published between 1994 and July 2000 and provides a comparison with our own results. Chronic schizophrenic patients most frequently show an enlargement in the ventricular system along with a reduction in grey matter. A more detailed subdivision into cortical and subcortical regions additionally shows the noted volume reduction to be limited to specific areas within the brain rather than being distributed equally throughout the brain. Within the area of the temporal lobes the two most frequently affected areas are the hippocampus and the gyrus temporalis superior. Alterations within these areas correlate with clinical symptoms such as hallucinations or thought disorders. Within the frontal cortex nearly 70% of all studies show a decrease in overall volume, while 63% note a reduction in size within the thalamus and 60% in the cerebellum. Morphologically speaking these structures therefore play the greatest role in the pathophysiology of schizophrenia and the onset of clinical symptoms. More recent studies also showed a specific progression in subgroups of patients pointing toward a neurodegenerative process. Additionally there are a number of differential antipsychotic effects following longterm treatment with typical neuroleptics as compared to atypical antipsychotics. Based on these findings future longitudinal studies should examine to what extent such a progressive decrease in volume might be influenced by treatment with modern antipsychotics.

Humans↗
PubMed2001

[Antipsychotics and phospholipid metabolism in schizophrenia].

To date numerous in-vivo (31)P-MRS and in-vitro studies in schizophrenic patients have been able to demonstrate changes in their membrane phospholipid metabolism, which might be relevant for the cause and the therapeutic responsiveness of this disorder. Thus far, however, only limited studies exist regarding the specificity of these findings for schizophrenia and the effect of antipsychotic medication. The present study examined the composition of membrane phospholipids in platelets of 67 neuroleptic-free schizophrenic patients compared to healthy and psychiatric controls. In a subsample of the schizophrenic patients we determined the effect of antipsychotic treatment on the phospholipid metabolism during six-months follow up. While untreated patients showed a decrease in major membrane phospholipid components, i.e. phosphatidylcholine and phosphatidylethanolamine, when compared to control subjects, as well as an increase in their breakdown-product lysophosphatidylcholine (LPC), there was a significant reduction in LPC during three weeks of pharmacotherapy with haloperidol. After six months treatment with different antipsychotics some divergent effects on phospholipid metabolism in schizophrenic patients could be demonstrated. While in the long-term course LPC remained decreased under continuous therapy with typical neuroleptics, patients being treated with the atypical drug zotepine showed an increase in LPC compared to their baseline level before therapy. Thus, specific mechanisms of the different antipsychotic therapies on phospholipid metabolism might serve to explain the divergent findings of (31)P-MRS in medicated patients.

Adult↗
PubMed2000

[Effective treatment of depressive disorder with psychotic symptoms by olanzapine combination therapy].

HISTORY AND ADMISSION FINDINGS: Four days after swallowing lithium and amitriptyline tablets with suicidal intent, a 48-year-old man was admitted. He was known to be suffering from recurrent depression which had led to 7 previous hospital admissions. At psychiatric assessment he appeared to be depressed with reduced ability of affective changes and impaired formal reasoning. He exhibited delusions of guilt and reference. His sleep was impaired and appetite diminished. INVESTIGATIONS: Serum lithium level was 1.98 mmol/l (therapeutic range 0.8-1.0 mmol/l). An ECG demonstrated sinus tachycardia, the EEG showed theta waves with mild general changes. DIAGNOSIS, TREATMENT AND COURSE: He was diagnosed as suffering from severe depressive syndrome with psychotic symptoms. He was given both antidepressive and neuroleptic drugs: mirtazapine 30 mg daily (p.d.) and halperidol 10 mg p.d.. When both the depressive and psychotic symptoms were treatment-resistant, even after a change from mirtazapine to venlafaxine (300 mg p.d.), the drug regimen was changed to sertraline, 150 mg p.d., and olanzapine, 20 mg p.d.. While this brought about improvement, his condition deteriorated when olanzapine was withdrawn. But all symptoms completely disappeared when olanzapine was again given. Spontaneous remission in the future thus seems unlikely to occur. CONCLUSION: This case illustrates that the atypical antipsychotic drug olanzapine has some advantages over such typical antipsychotic drug olanzapine has some advantages over such typical antipsychotic medication as butyrophenone. The underlying mechanism for this greater efficacy is probably the difference in receptor-binding capacity between these drugs, the former inhibiting some serotonin receptors so that it is synergistic with antidepressives that inhibit serotonin transport.

Antidepressive Agents, Second-Generation↗