Biomedical subjects

Martin Müller

Publications and source records attributed to Martin Müller.

At least 37 records · Page 2Linked to original sources

PubMed2005

Temporary inactivation of the medial and basolateral amygdala differentially affects TMT-induced fear behavior in rats.

Trimethylthiazoline (TMT) is a component of fox feces and is thought to be a stimulus with innate fear-eliciting properties for rodents. Naive laboratory rats that are exposed to TMT display freezing behavior, a known behavioral sign of fear and anxiety. Early studies examining the neural basis of TMT-induced fear showed that the bed nucleus of the stria terminalis is important for this behavior. In contrast, the central and lateral nuclei of the amygdala does not seem to participate in the neural processing of TMT-induced fear. However, a study investigating c-fos expression in response to TMT-exposure revealed a strong activation of the medial as well as a weak activation of the basolateral amygdala. Therefore, the present study examined the effects of temporary inactivation of the medial and basolateral amygdala on TMT-induced freezing. Temporary inactivation was accomplished by local injections of the GABA(A) receptor agonist muscimol into the areas of interest. TMT-induced freezing was completely blocked by temporary inactivation of the medial amygdala. Temporary inactivation of the basolateral amygdala resulted in a delay of the onset of the freezing response to TMT. These results clearly demonstrate that the medial amygdala is crucial for TMT-induced freezing, whereas the basolateral amygdala seems to play a modulatory role in this type of fear behavior. Since the medial amygdala is also involved in the processing of cat odor-induced fear, the finding of the present study points towards a general role of the medial amygdala in the processing of predator odor-induced fear.

Amygdala↗

PubMed2005

The egghead gene is required for compartmentalization in Drosophila optic lobe development.

The correct targeting of photoreceptor neurons (R-cells) in the developing Drosophila visual system requires multiple guidance systems in the eye-brain complex as well as the precise organization of the target area. Here, we report that the egghead (egh) gene, encoding a glycosyltransferase, is required for a compartment boundary between lamina glia and lobula cortex, which is necessary for appropriate R1-R6 innervation of the lamina. In the absence of egh, R1-R6 axons form a disorganized lamina plexus and some R1-R6 axons project abnormally to the medulla instead of the lamina. Mosaic analysis demonstrates that this is not due to a loss of egh function in the eye or in the neurons and glia of the lamina. Rather, as indicated by clonal analysis and cell-specific genetic rescue experiments, egh is required in cells of the lobula complex primordium which transiently abuts the lamina and medulla in the developing larval brain. In the absence of egh, perturbation of sheath-like glial processes occurs at the boundary region delimiting lamina glia and lobula cortex, and inappropriate invasion of lobula cortex cells across this boundary region disrupts the pattern of lamina glia resulting in inappropriate R1-R6 innervation. This finding underscores the importance of the lamina/lobula compartment boundary in R1-R6 axon targeting.

Animals↗

PubMed2005

The linear behavior of the system middle cerebral artery flow velocity and blood pressure in patients with migraine: lack of autonomic control?

BACKGROUND AND PURPOSE: Migraine is considered a disorder of the autonomic nervous system. We used the frequency analysis of dynamic cerebral autoregulation to assess whether blood flow regulation disturbances can be found at the frequencies at which sympathetic and parasympathetic activity is present. METHODS: We measured simultaneously mean arterial blood pressure (BP) and the mean blood velocity (V) in the middle cerebral artery using transcranial Doppler ultrasound in 33 healthy controls (mean age+/-SD; 36+/-13 years) and in 22 patients with migraine (mean age; 39+/-7 years). Apart from assessing spectral power density for BP and V, we calculated the transfer function parameters gain, phase, and coherence at the frequency range between 0.0 and 0.25 Hz. RESULTS: Compared with the controls, the spectral power density of BP and V exhibited a maximum magnitude of 10(26) in the migraine patients, whereas the maximum magnitude of BP and V in the controls was 10(-3). Coherence showed no difference between patients and controls. Gain between BP and V increased in the controls >0.01 Hz but was approximately 0 or negative in the migraine patients over the whole frequency range (P<0.01). The usually observed phase lead of V against BP was absent in the migraine patients in whom BP leaded V over nearly the whole frequency range (P<0.01). CONCLUSIONS: In terms of phase and gain, dynamic cerebral autoregulation is completely different in migraine patients compared with healthy subjects. Insofar, this can be interpreted as a lack of sympathetic and parasympathetic control of cerebral blood flow.

Adolescent↗

PubMed2005

Preparation of monomodal polyelectrolyte complex nanoparticles of PDADMAC/poly(maleic acid-alt-alpha-methylstyrene) by consecutive centrifugation.

We report on the refinement of anionic and cationic nanoparticles of nonstoichometric polyelectrolyte complexes (PEC) by consecutive centrifugation, which was studied by dynamic light scattering (DLS), atomic force microscopy (AFM), colloid titration and infrared spectroscopy (IR). PEC dispersions were prepared by mixing poly(diallyldimethylammonium chloride) (PDADMAC) and sodium poly(maleic acid-alt-alpha-methylstyrene) (PMA-MS) at the monomolar mixing ratio of n-/n+ = 1.50 (anionic PEC) and 0.66 (cationic PEC), respectively, and the polymer concentration of c(POL) = 0.002 M. The particle size (Rh), titrable charge amount, and IR spectra were determined for both dispersions in the original state, after the first centrifugation and after the second centrifugation. Freshly prepared PEC dispersions contained two different particle sizes: around 10-25 nm (small particles) and around 100 nm (large particles). Consecutive centrifugation of freshly prepared PEC dispersions resulted in the separation of highly charged excess polyelectrolyte (PEL) and small PEC particles from a low charged coacervate phase of the desired larger PEC particles. After the second centrifugation, the coacervate phase of both dispersions PEC-1.50 and PEC-0.66 consisted of monomodal particles sizing around 100 nm. These results were supported by AFM measurements on the respective dispersions deposited on glass plates. PEC-1.50 particles tended to adopt slightly smaller sizes ( approximately 90 nm) in comparison to PEC-0.66 ones (approximately 110 nm). No significant influence of the PDADMAC molecular weight on the particle size was found. IR spectroscopy showed changes in the environment of the carboxylate groups of PMA-MS by consecutive centrifugation. The centrifuged PEC-1.50 dispersions showed remarkable long-term stability over more than a year. The high macroscopic stability of the studied PEC dispersions is presumably due to repulsive electrostatic interparticle interactions and attractive hydrophobic intraparticle interaction. The introduced monomodal PEC particles might be projected as latex analogues or as nanocarriers for drugs and proteins.

Journal Article↗

PubMed2005

4G/5G promoter polymorphism in the plasminogen-activator-inhibitor-1 gene in children with systemic meningococcaemia.

UNLABELLED: Meningococcal disease may present as sepsis, meningitis or a combination of both. Impaired fibrinolysis and massive elevation of the plasminogen activator inhibitor-1 (PAI-1) is a characteristic feature of meningococcal sepsis. Previously, an association between mortality and the functional 4G/5G promoter polymorphism of the PAI-1gene in a cohort of UK and Dutch children with meningococcal sepsis was reported. We carried out a prospective, multicentre study to investigate the association of the 4G/5G PAI-1 polymorphism, diagnosis, and outcome in meningococcal disease in a Central European and UK population. Blood samples and clinical information of 347 previously healthy children with meningococcal infection were collected from 95 paediatric hospitals in Germany, Switzerland, Italy, the United Kingdom, and Austria from 2000 until 2002. Mortality was significantly associated with the 4G/4G genotype (12 of 90 (13%) vs. 15 of 240 (6%), P = 0.037), resulting in an odds ratio of 2.31. The diagnosis of sepsis (independent of symptoms of meningitis) was significantly more frequent in carriers of the 4G/4G genotype (P = 0.01), resulting in an odds ratio of 2.21 to develop sepsis. Meningitis was not associated with the PAI-1 4G/5G polymorphism, and allele frequencies were similar in patient and control groups. CONCLUSION: Our data show a correlation between the 4G/4G genotype in the plasminogen activator inhibitor-1 gene and poor outcome in children with meningococcal infection. In addition, 4G homozygous patients were prone to develop sepsis. We found no influence of the plasminogen activator inhibitor-1 polymorphism on the susceptibility to invasive meningococcal infection.

Adolescent↗

PubMed2005

Characterisation and quantification of equine interferon gamma.

Interferon-gamma (IFN-gamma) is a key cytokine in cell-mediated immunity. To measure IFN-gamma production of equine lymphocytes (eqIFN-gamma), we developed a quantitative ELISA. Monoclonal antibodies (mAb) were produced against bacterially derived eqIFN-gamma. The mAbs recognised recombinant and lymphocyte-derived eqIFN-gamma in ELISA, Western blotting, as well as flow cytometric and microscopic analysis. In contrast to bacterially derived material, mammalian and insect cell-derived eqIFN-gamma was biologically active but could be neutralised by one of the monoclonal antibodies. Unexpectedly, glycosylation seemed to be required for antiviral activity of eqIFN-gamma.

Animals↗

PubMed2005

Codon optimization of papillomavirus genes.

Early and late genes of human and animal papillomaviruses show a codon composition seemingly unfavorable for expression in mammalian cells. It remains unclear how the viruses manage to achieve high levels of late gene expression during the viral life cycle. One possible solution could be that the availability of certain t-RNAs changes with progressing stages of cellular differentiation. Previous studies have demonstrated that modification of codon usage of papillomavirus late (L1 and L2) and early genes (E7) can overcome poor expression of these proteins both in transient and in stable expression systems. This was shown not only for human but also for plant cells. Two strategies can be employed to alter codon usage: elimination of only those codons that are rarely used in a particular expression system, or exchange of all possible codons by the ones most frequently used. Currently, there are two protocols for codon modification--a template-less polymerase chain reaction (PCR)-based protocol, in which very long overlapping oligodeoxynucleotides are used in an overlap-extension reaction, or a ligase chain reaction, in which shorter oligodeoxynucleotides are fused together after an annealing procedure. Both methods are presented and discussed.

Amino Acids↗

PubMed2005

Hypericin: a promising fluorescence marker for differentiating between glioblastoma and neurons in vitro.

The naturally occurring photosensitizer, hypericin, with its high quantum yield of singlet oxygen photogeneration was studied for its ability to differentiate between glioblastoma cells and fetal rat neurons using fluorescence microscopy. Eight human glioma cell lines and twelve primary human glioma cell cultures were compared to human astrocytes and cerebellar granule neurons after incubation with 20 microM hypericin for 5-120 min. Photobleaching effects have been studied by exposing the cell lines to 100 msec of excitation light (510-550 wavelength). Mainly, perinuclear hypericin staining was detected. Neurons can be differentiated from glioblastoma cell lines and astrocytes by a lower fluorescence intensity (Tukey-Kramer HSD test, p < 0.0001). Therefore, hypericin seems to be a promising substance for the photodynamic therapy of malignant brain tumors.

Animals↗

PubMed2004

Generalized epidemic process and tricritical dynamic percolation.

The renowned general epidemic process describes the stochastic evolution of a population of individuals which are either susceptible, infected, or dead. A second order phase transition belonging to the universality class of dynamic isotropic percolation lies between the endemic and pandemic behavior of the process. We generalize the general epidemic process by introducing a fourth kind of individuals, viz., individuals which are weakened by the process but not yet infected. This weakening gives rise to a mechanism that introduces a global instability in the spreading of the process and therefore opens the possibility of a discontinuous transition in addition to the usual continuous percolation transition. The tricritical point separating the lines of first and second order transitions constitutes an independent universality class, namely, the universality class of tricritical dynamic isotropic percolation. Using renormalized field theory we work out a detailed scaling description of this universality class. We calculate the scaling exponents in an epsilon expansion below the upper critical dimension d(c) =5 for various observables describing tricritical percolation clusters and their spreading properties. In a remarkable contrast to the usual percolation transition, the exponents beta and beta(') governing the two order parameters, viz., the mean density and the percolation probability, turn out to be different at the tricritical point. In addition to the scaling exponents we calculate for all our static and dynamic observables logarithmic corrections to the mean-field scaling behavior at d(c) =5.

Cluster Analysis↗

PubMed2004

Codon optimization of the human papillomavirus 11 (HPV 11) L1 gene leads to increased gene expression and formation of virus-like particles in mammalian epithelial cells.

The 505 amino acid L1 protein of the human papillomavirus type 11 (HPV 11) is the major capsid polypeptide that has been shown to self-assemble into virus-like particles (VLPs) in vivo and in vitro. While L1 is essential for viral infection, expression studies in mammalian cells have been hampered by different codon preference between the virus and its host. To optimize L1 gene expression in mammalian cells, we converted wild-type HPV 11 L1 (11 L1wt) codons to those more common in human genes. The modified HPV 11 L1 gene (11 L1h) generated protein levels that were at least 100-fold higher than those of wild-type HPV 11 L1, while no obvious differences were seen in the level of mRNA. HPV 11 L1 protein was detected in mammalian epithelial and fibroblast cells, by immunoblotting and indirect immunofluorescence (IIF) techniques. Unlike the situation in situ, IIF revealed the presence of L1 mainly at perinuclear sites. Virus-like particles assembled intranuclearly only to a low extent, as indicated by transmission electron microscopy. DNA vaccination using the HPV 11 L1h gene yielded a drastic increase in L1-specific antibody production in mice as compared to immunization with the wild-type gene.

Animals↗

PubMed2004

Relation between microstructure and mechanical behavior of concentrated silica gels.

We produce concentrated (40 vol%) gels of uniformly sized silica particles by an in situ process, based on the enzyme-catalyzed hydrolysis of urea in the liquid phase of electrostatically stabilized suspensions. Two different methods are used: Either the pH of the suspensions is shifted toward the isoelectric point of the particles (delta pH method), or the ionic strength is continuously increased at constant pH (deltaI method). We compare the two kinds of gels in terms of elastic and yield behavior as well as microstructure by using rheological measurements in oscillation and high-pressure freezing in combination with cryo-SEM, respectively. Results suggest a strong increase of elastic and yield properties in concentrated particle gels with decreasing homogeneity of their microstructures.

Journal Article↗

PubMed2004

Oxidation-responsive polymeric vesicles.

Vesicles formed in water by synthetic macro-amphiphiles have attracted much attention as nanocontainers having properties that extend the physical and chemical limits of liposomes. We sought to develop ABA block copolymeric amphiphiles that self-assemble into unilamellar vesicles that can be further oxidatively destabilized. We selected poly(ethylene glycol) (PEG) as the hydrophilic A blocks, owing to its resistance to protein adsorption and low toxicity. As hydrophobic B blocks, we selected poly(propylene sulphide) (PPS), owing to its extreme hydrophobicity, its low glass-transition temperature, and most importantly its oxidative conversion from a hydrophobe to a hydrophile, poly(propylene sulphoxide) and ultimately poly(propylene sulphone). This is the first example of the use of oxidative conversions to destabilize such carriers. This new class of oxidation-responsive polymeric vesicles may find applications as nanocontainers in drug delivery, biosensing and biodetection.

Hydrogen Peroxide↗

PubMed2004

Structure and physical properties of [micro-tris(1,4-bis(tetrazol-1-yl)butane-N4,N4')iron(II)] bis(hexafluorophosphate), a new Fe(II) spin-crossover compound with a three-dimensional threefold interlocked crystal lattice.

[micro-Tris(1,4-bis(tetrazol-1-yl)butane-N4,N4')iron(II)] bis(hexafluorophosphate), [Fe(btzb)(3)](PF(6))(2), crystallizes in a three-dimensional 3-fold interlocked structure featuring a sharp two-step spin-crossover behavior. The spin conversion takes place between 164 and 182 K showing a discontinuity at about T(1/2) = 174 K and a hysteresis of about 4 K between T(1/2) and the low-spin state. The spin transition has been independently followed by magnetic susceptibility measurements, (57)Fe-Mössbauer spectroscopy, and variable temperature far and midrange FTIR spectroscopy. The title compound crystallizes in the trigonal space group P3 (No. 147) with a unit cell content of one formula unit plus a small amount of disordered solvent. The lattice parameters were determined by X-ray diffraction at several temperatures between 100 and 300 K. Complete crystal structures were resolved for 9 of these temperatures between 100 (only low spin, LS) and 300 K (only high spin, HS), Z = 1 [Fe(btzb)(3)](PF(6))(2): 300 K (HS), a = 11.258(6) A, c = 8.948(6) A, V = 982.2(10) A(3); 100 K (LS), a = 10.989(3) A, c = 8.702(2) A, V = 910.1(4) A(3). The molecular structure consists of octahedral coordinated iron(II) centers bridged by six N4,N4' coordinating bis(tetrazole) ligands to form three 3-dimensional networks. Each of these three networks is symmetry related and interpenetrates each other within a unit cell to form the interlocked structure. The Fe-N bond lengths change between 1.993(1) A at 100 K in the LS state and 2.193(2) A at 300 K in the HS state. The nearest Fe separation is along the c-axis and identical with the lattice parameter c.

Journal Article↗

PubMed2004

In vitro gene delivery by a novel human calcitonin (hCT)-derived carrier peptide.

Gene therapy still awaits a broader application, since safe and efficient gene delivery is a major problem. Also for the investigation of signal transduction and intracellular trafficking, delivery systems for hydrophilic macromolecules that are easy to use are needed. Several peptide-based delivery systems have been developed during the last years. We present here a novel carrier peptide derived from human calcitonin that is capable of transfecting human neuroblastoma cells by complex formation with a plasmid. Because of the peptide's physiological origin, cytotoxic effects are not expected.

Amino Acid Sequence↗

PubMed2004

Hox gene cross-regulatory interactions in the embryonic brain of Drosophila.

During embryonic development of the Drosophila brain, the Hox gene labial is required for the regionalized specification of the tritocerebral neuromere. In order to gain further insight into the mechanisms of Hox gene action in the CNS, we have studied the molecular and genetic basis of cross-regulatory interactions between labial and other more posterior Hox genes using the GAL4/UAS system for targeted misexpression. Misexpression of posterior Hox genes in the embryonic neuroectoderm results in a labial loss-of function phenotype and a corresponding lack of Labial protein expression in the tritocerebrum. This is due to repression of labial gene transcription in the embryonic brain. Enhancer analysis suggests that this transcriptional repression operates on a 3.65 kb brain-specific labial-enhancer element. A functional analysis of Antennapedia and Ultrabithorax protein domains shows that the transcriptional repression of labial requires homeodomain-DNA interactions but is not dependent on a functional hexapeptide. The repressive activity of a Hox protein on labial expression in the tritocerebrum can, however, be abolished by concomitant misexpression of a Hox protein and the cofactors Homothorax and nuclear-targeted Extradenticle. Taken together, these results provide novel and detailed insight into the cross-regulatory interactions of Hox genes in embryonic brain development and suggest that specification of tritocerebral neuronal identity requires equilibrated levels of a Hox protein and Hth and n-Exd cofactors.

Animals↗

PubMed2004

Rotary F1-ATPase. Is the C-terminus of subunit gamma fixed or mobile?

F-ATP synthase synthesizes ATP at the expense of ion motive force by a rotary coupling mechanism. A central shaft, subunit gamma, functionally connects the ion-driven rotary motor, F(O), with the rotary chemical reactor, F(1). Using polarized spectrophotometry we have demonstrated previously the functional rotation of the C-terminal alpha-helical portion of gamma in the supposed 'hydrophobic bearing' formed by the (alpha beta)(3) hexagon. In apparent contradiction with these spectroscopic results, an engineered disulfide bridge between the alpha-helix of gamma and subunit alpha did not impair enzyme activity. Molecular dynamics simulations revealed the possibility of a 'functional unwinding' of the alpha-helix to form a swivel joint. Furthermore, they suggested a firm clamping of that part of gamma even without the engineered cross-link, i.e. in the wild-type enzyme. Here, we rechecked the rotational mobility of the C-terminal portion of gamma relative to (alpha beta)(3). Non-fluorescent, engineered F(1) (alpha P280C/gamma A285C) was oxidized to form a (nonfluorescent) alpha gamma heterodimer. In a second mutant, containing just the point mutation within alpha, all subunits were labelled with a fluorescent dye. Following disassembly and reassembly of the combined preparations and cystine reduction, the enzyme was exposed to ATP or 5'-adenylyl-imidodiphosphate (AMP-PNP). After reoxidation, we found fluorescent alpha gamma dimers in all cases in accordance with rotary motion of the entire gamma subunit under these conditions. Molecular dynamics simulations covering a time range of nanoseconds therefore do not necessarily account for motional freedom in microseconds. The rotation of gamma within hours is compatible with the spectroscopically detected blockade of rotation in the AMP-PNP-inhibited enzyme in the time-range of seconds.

Adenosine Triphosphate↗

PubMed2004

Nuclear translocation of papillomavirus minor capsid protein L2 requires Hsc70.

Minor capsid protein L2 of papillomaviruses plays an essential role in virus assembly by recruiting viral components to PML bodies, the proposed sites of virus morphogenesis. We demonstrate here that the function of L2 in virus assembly requires the chaperone Hsc70. Hsc70 was found dispersed in naturally infected keratinocytes and cultured cells. A dramatic relocation of Hsc70 from the cytoplasm to PML bodies was induced in these cells by L2 expression. Hsc70-L2 complex formation was confirmed by coimmunoprecipitation. The complex was modulated by the cochaperones Hip and Bag-1, which stabilize and destabilize Hsc70-substrate complexes, respectively. Cytoplasmic depletion of Hsc70 caused retention of wild-type and N-terminally truncated L2, but not of C-terminally truncated L2, in the cytoplasm. This retention was partially reversed by overexpression of Hsc70 fused to green fluorescent protein but not by ATPase-negative Hsc70. Hsc70 associated with L1-L2 virus-like particles (VLPs) but not with VLPs composed either of L1 alone or of L1 and C-terminally truncated L2. Moreover, displacement of Hsc70 from L1-L2 VLPs by encapsidation of DNA, generating pseudovirions, was found. These data indicate that Hsc70 transiently associates with viral capsids during the integration of L2, possibly via the L2 C terminus. Completion of virus assembly results in displacement of Hsc70 from virions.

Active Transport, Cell Nucleus↗

PubMed2003

Cell-wall recovery after irreversible deformation of wood.

The remarkable mechanical properties of biological materials reside in their complex hierarchical architecture and in specific molecular mechanistic phenomena. The fundamental importance of molecular interactions and bond recovery has been suggested by studies on deformation and fracture of bone and nacre. Like these mineral-based materials, wood also represents a complex nanocomposite with excellent mechanical performance, despite the fact that it is mainly based on polymers. In wood, however, the mechanistic contribution of processes in the cell wall is not fully understood. Here we have combined tensile tests on individual wood cells and on wood foils with simultaneous synchrotron X-ray diffraction analysis in order to separate deformation mechanisms inside the cell wall from those mediated by cell-cell interactions. We show that tensile deformation beyond the yield point does not deteriorate the stiffness of either individual cells or foils. This indicates that there is a dominant recovery mechanism that re-forms the amorphous matrix between the cellulose microfibrils within the cell wall, maintaining its mechanical properties. This stick-slip mechanism, rather like Velcro operating at the nanometre level, provides a 'plastic response' similar to that effected by moving dislocations in metals. We suggest that the molecular recovery mechanism in the cell matrix is a universal phenomenon dominating the tensile deformation of different wood tissue types.

Adaptation, Physiological↗