Biomedical subjects

M Ludwig

Publications and source records attributed to M Ludwig.

At least 181 records · Page 10Linked to original sources

PubMed1997

Atomic force microscope imaging contrast based on molecular recognition.

The contrast in atomic force microscope images arises from forces between the tip and the sample. It was shown recently that specific molecular interaction forces may be measured with the atomic force microscope; consequently, we use such forces to map the distribution of binding partners on samples. Here we demonstrate this concept by imaging a streptavidin pattern with a biotinylated tip in a novel imaging mode called affinity imaging. In this mode topography, adhesion, and sample elasticity are extracted online from local force scans. We show that this technique allows the separation of these values and that the measured binding pattern is based on specific molecular interactions.

Adhesiveness↗

PubMed1997

A new indication for an intracytoplasmic sperm injection procedure outside the cases of severe male factor infertility.

OBJECTIVE: To show the success of intracytoplasmic sperm injection (ICSI) in cases of a low number of oocytes retrieved. STUDY DESIGN: 715 microinjection cycles, which were performed at our center, were analyzed retrospectively. RESULTS: Within the analyzed cycles, there were 50 cycles with less than four oocytes retrieved. Twelve, 18, and 20 cases were treated with one, two, and three oocytes, respectively. The rate of metaphase II oocytes injected and subsequently fertilized, and intact oocytes was similar in the three groups. The transfer rate was not significantly different from those cases with more than three oocytes (84% vs. 94%). Therefore, the rate of fertilization failure was not higher in the low-number group. The number of embryos transferred was statistically significantly lower in the group with one and two oocytes compared to the group with three oocytes (1, and 1.31 vs. 2.27; P < 0.01) and the group of all patients (2.63; P < 0.01), as well as between the group of less than four oocytes and all patients (1.63 vs. 2.63; P < 0.01). There was no statistically significant difference between the pregnancy rates of the three groups (36.4% vs. 20% vs. 22.2%), and also no difference was found between the group with less than four oocytes and the data of all patients (22% vs. 26.9%). CONCLUSION: In our opinion, these data show that ICSI guarantees a successful treatment even if only as many oocytes are present as embryos are planned to be transferred, i.e. three embryos. This has been accepted to be a new indication in our center. Therefore it should be possible to stimulate patients mildly, with e.g. clomiphene citrate, to avoid unnecessary hyperstimulation syndromes, and to lower the cost of hormonal superstimulation.

Adult↗

PubMed1997

The embryonic development of sensory organs and the skull in the trisomy 16 mouse, an animal model for Down's syndrome.

The trisomy 16 mouse is a widely accepted animal model for the study of the embryonic development of human trisomy 21. While the development of the brain and heart has been thoroughly studied, there are hardly any data on the development of sensory organs like the eye, nose and ear. By studying scanning electron microscopic pictures and semithin sections from the tenth to the 15th day of development, we found delayed development of the nose, and, in particular, of the vomer. Sensory structures of the otic vesicle also showed a marked developmental delay. Pigmentation of the outer layer of the otic cup starts later in trisomic animals. Cleared specimens on day 16 showed retarded development of ossification centres in all areas of the skull. These findings correspond with the abnormal facial morphology found in Down's syndrome and may also provide new insights into the hearing impairment commonly found. The observations in the eye and skull bones indicate that neural crest tissue maldevelopment is not the sole cause of malformations.

Animals↗

PubMed1997

Long-term in vivo alterations of polyester vascular grafts in humans.

OBJECTIVES: To examine the influence of in vivo hydrolysis on the physical properties of polyester grafts and their correlation to the period of implantation in the human body. MATERIALS AND METHODS: Sixty-five explanted vascular grafts were obtained after 0-23 years of implantation due to suture aneurysms (18), occlusion (12), graft infection (12), failure of graft material (7) and post-mortem (16). The surface was examined by scanning electron microscopy, the molecular integrity by infra-red spectroscopy and physical strength by probe puncture. RESULTS: Scission of macromolecular chains and loss of strength were shown. It was demonstrated that hydrolytic degradation of polyester takes place with increasing time of implantation in humans. Analysis by linear regression showed that polyester grafts lose 31.4% of their bursting strength in 10 years and 100% in 25-39 years after implantation. CONCLUSIONS: Regular follow-ups of patients with aged vascular grafts and the precise documentation of implanted materials are necessary to estimate graft degradation.

Blood Vessel Prosthesis↗

PubMed1997

Autoinhibition of supraoptic nucleus vasopressin neurons in vivo: a combined retrodialysis/electrophysiological study in rats.

To examine the role of endogenous vasopressin on the electrical activity of vasopressin neurons within the supraoptic nucleus of the rat brain in vivo, we have developed a novel technical approach for administering neuroactive drugs directly into the extracellular environment of the neuronal dendrites. A microdialysis probe was used for controlled local drug administration into the dendritic area of the nucleus during extracellular recording of single neurons in vivo. Vasopressin or selective V1 receptor antagonists were administered for between 10 and 30 min via a U-shaped microdialysis probe placed flat on the surface of the supraoptic nucleus after transpharyngeal exposure of the nucleus in urethane-anaesthetized rats. Microdialysis administration (retrodialysis) of vasopressin inhibited vasopressin neurons by reducing their firing rate, sometimes to total inactivity. Retrodialysis of V1-receptor antagonists partially reversed the effect of vasopressin, and a subsequent vasopressin administration was not effective in reducing the activity of these neurons, suggesting a receptor-mediated action of endogenous vasopressin. In addition, the duration of the periods of activity and the mean frequency during the active phase were increased in vasopressin neurons after retrodialysis of V1-receptor antagonist, indicating a physiological role of endogenous vasopressin. Neither vasopressin nor the antagonists altered the activity of continuously firing oxytocin neurons. Thus, vasopressin released within the supraoptic nucleus may act via V1 receptors located specifically on vasopressin neurons to regulate their phasic activity by an auto-inhibitory action. Since vasopressin release from the dendrites of vasopressin neurons is increased and prolonged after various forms of stimulation, it is proposed that this mechanism will act to limit excitation of vasopressin neurons, and hence secretion from the neurohypophysis. In addition, combined in vivo retrodialysis/ single cell recording allows controlled introduction of neuroactive substances into the extracellular fluid in the immediate vicinity of recorded neurons. This is shown to provide a novel approach to study neurotransmitter actions on supraoptic neurons in vivo.

Action Potentials↗

PubMed1997

Effects of antisense oligodeoxynucleotides on peptide release from hypothalamoneurohypophysial explants.

Rapid effects of antisense oligodeoxynucleotides (AODNs) on the function of the neurohypophysial system have been reported previously. The present studies were designed to determine the effects of vasopressin (VP) and oxytocin (OT) AODNs on osmotically or potassium-stimulated VP and OT release from perifused hypothalamoneurohypophysial (HNS) explants. The AODNs were 18-mer phosphorothioate forms targeted toward the translation initiation sites of either VP or OT mRNA, or a mixed base sequence (4 microM). The explants were exposed to a ramp increase in NaCl (either 20 or 30 mosmol/6 h) or to 25 mM KCl. VP and OT release was measured by radioimmunoassay in sequential 20-min fractions of the perifusate. There was a peptide-specific inhibition by the AODNs of osmotically stimulated VP and OT release. VP AODN inhibited VP, but not OT release, and vice vorsa. However, the AODNs had no effect on potassium-stimulated peptide release, demonstrating that depolarization-secretion coupling was still intact. Furthermore, there were no significant differences in VP and OT mRNA and peptide content after antisense treatment. Thus these observations indicate that acute exposure to peptide AODNs interrupts osmotically stimulated VP and OT release in a peptide-specific manner.

Animals↗

PubMed1997

Baroreceptor input regulates osmotic control of central vasopressin secretion.

Sinoaortic baroreceptor denervation (SAD) results in increased osmotically induced secretion of vasopressin (VP) and oxytocin (OT) and increased cardiovascular responses to many centrally acting pressor agents. Studies were conducted to determine whether SAD increases the cardiovascular and endocrine responses to direct and peripheral osmotic stimulation of the supraoptic nucleus (SON). SON microdialysis was performed in urethane-anesthetized male rats with measurement of dialysate peptides, mean arterial pressure (MAP) and heart rate. Experiment 1 tested the effect of direct stimulation of the SON with hypertonic NaCl in SAD, sham-operated (control) and intake-matched (matched) rats. Osmotically induced VP release into the SON was significantly greater in SAD than in control or matched groups. VP release peaked at 36 +/- 13 and 15 +/- 7 pg in SAD and controls, respectively, with no increase observed in the matched group. Plasma VP was significantly elevated after SON osmotic stimulation with no differences observed among the groups. The pressor response to osmotic stimulation was greater in SAD (29 +/- 4 mm Hg) than in control (20 +/- 3 mm Hg) and matched animals (15 +/- 3 mm Hg). Experiment 2 tested the effect of intraperitoneal injection of hypertonic NaCl on SON VP and OT release. SAD rats showed an increased central VP response to peripheral osmotic stimulation, a 64-fold increase in SAD as compared to a 4-fold one in controls. Central OT release was not significantly altered (peak of 22 +/- 6 vs. 11 +/- 4 pg, SAD vs. control). A direct SON osmotic challenge given 3.5 h after the intraperitoneal test confirmed an increased VP responsiveness in the SAD group. Plasma VP and OT were significantly increased after intraperitoneal hypertonic saline with no difference observed between groups. The MAP response to intraperitoneal hypertonic saline was greater in the SAD group with an elevation of 37 +/- 4 versus 18 +/- 3 mm Hg observed in SAD versus control subjects. These results demonstrate that baroreceptor denervation produces a state of heightened osmotic sensitivity for VP neurons, with evidence for increased central VP release to both direct and peripheral hypertonic NaCl stimulation.

Animals↗

PubMed1997

[An overview of ovarian hyperstimulation syndrome: a reproductive medicine-iatrogenic disease picture with internal medicine consequences].

The ovarian hyperstimulation syndrome is a complication of the controlled ovarian hyperstimulation in assisted reproduction procedures. It has become more widespread, since the techniques of ovarian hyperstimulation has become more frequent. The potentially life-threatening complication of this condition is a hemoconcentration with subsequent thrombo-embolic complications and death. In this article the pathophysiology, prevention strategies, treatment guidelines and more theoretical approaches for the therapy are reviewed and discussed.

Death, Sudden↗

PubMed1996

The structure of the C-terminal domain of methionine synthase: presenting S-adenosylmethionine for reductive methylation of B12.

BACKGROUND: In both mammalian and microbial species, B12-dependent methionine synthase catalyzes methyl transfer from methyltetrahydrofolate (CH3-H4folate) to homocysteine. The B12 (cobalamin) cofactor plays an essential role in this reaction, accepting the methyl group from CH3-H4folate to form methylcob(III)alamin and in turn donating the methyl group to homocysteine to generate methionine and cob(I)alamin. Occasionally the highly reactive cob(I)alamin intermediate is oxidized to the catalytically inactive cob(II)alamin form. Reactivation to sustain enzyme activity is achieved by a reductive methylation, requiring S-adenosylmethionine (AdoMet) as the methyl donor and, in Esherichia coli, flavodoxin as an electron donor. The intact system is controlled and organized so that AdoMet, rather than methyltetrahydrofolate, is the methyl donor in the reactivation reaction. AdoMet is not wasted as a methyl donor in the catalytic cycle in which methionine is synthesized from homocysteine. The structures of the AdoMet binding site and the cobalamin-binding domains (previously determined) provide a starting point for understanding the methyl transfer reactions of methionine synthase. RESULTS: We report the crystal structure of the 38 kDa C-terminal fragment of E.coli methionine synthase that comprises the AdoMet-binding site and is essential for reactivation. The structure, which includes residues 901-1227 of methionine synthase, is a C-shaped single domain whose central feature is a bent antiparallel betasheet. Database searches indicate that the observed polypeptide has no close relatives. AdoMet binds near the center of the inner surface of the domain and is held in place by both side chain and backbone interactions. CONCLUSIONS: The conformation of bound AdoMet, and the interactions that determine its binding, differ from those found in other AdoMet-dependent enzymes. The sequence Arg-x-x-x-Gly-Tyr is critical for the binding of AdoMet to methionine synthase. The position of bound AdoMet suggests that large areas of the C-terminal and cobalamin-binding fragments must come in contact in order to transfer the methyl group of AdoMet to cobalamin. The catalytic and activation cycles may be turned off and on by alternating physical separation and approach of the reactants.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗

PubMed1996

Salt loading abolishes osmotically stimulated vasopressin release within the supraoptic nucleus.

Central and systemic osmotic stimulation increase vasopressin (VP) release within the supraoptic nucleus (SON) and into the general circulation. We examined whether changes in water/electrolyte balance affect the neurosecretory responses to these stimuli. Urethane-anesthetized control, salt-loaded (2% NaCl for 2 days) or water-deprived (for 2 days) male rats were implanted with an arterial catheter and bilateral microdialysis probes into the SON. Plasma and SON VP levels were measured before and after acute osmotic stimuli were administered intraperitoneally (i.p.) and then directly into the SON. Water deprivation resulted in elevated basal intranuclear and plasma VP levels. Intraperitoneal hypertonic saline (HS) and direct osmotic stimulation of the SON increased VP release into the SON in both the control and water-deprived groups. Salt loading abolished the intranuclear VP response to both stimuli. Osmotically induced release of VP into plasma was not different between the three groups. These data demonstrate that salt loading, but not water deprivation, alters the central neurosecretory VP response to acute osmotic stimulation.

Animals↗

PubMed1996

Induction of apoptosis and secondary necrosis in rat dorsal root ganglion cell cultures by oxidized low density lipoprotein.

Neural cell degeneration underlies central and peripheral nervous system disorders. In this study we examined the influence of oxidized low density lipoprotein (Ox-LDL) on rat dorsal root ganglion (DRG) cells in culture. Methods used were cell morphology, lactate dehydrogenase (LDH) release, the TUNEL-reaction and DNA fragmentation. Exposure of DRG cells to Ox-LDL for 24 h led to elevation of LDH in the culture medium; short term exposure (4 h) induced apoptosis, evidenced by DNA fragmentation and a positive TUNEL-reaction. DRG cells modified LDL in the presence of Cu2+ to mildly oxidized and to a small extent to fully oxidized forms; these in situ-generated LDL oxidation products were strongly toxic. These results suggest that Ox-LDL is a neurotoxin; it initiates apoptotic cell injury which progresses to necrosis and cell death.

Animals↗

PubMed1996

A 50 KDa protein modulates guanine nucleotide binding of transglutaminase II.

Regulation of cellular response is an important mechanism for controlling cellular functions. The transmembrane signaling of the hormone receptors is regulated by GTP-binding proteins (GTPases) and their associated proteins. Our previous studies demonstrated that the bifunctional GTP-binding protein, G alpha h (transglutaminase II), consistently copurified with an approximately 50 kDa protein (G Beta h) which is dissociated from G alpha h upon activation with GTP gamma S or AlF4-. Present immunological and biochemical studies on the regulation of the GTPase cycle of G alpha h, which involves the alpha 1-adrenoceptor and 50 KDa G beta h, reveal that the 50 kDa protein is indeed a G alpha h-associated protein and down regulates functions of G alpha h. Thus, polyclonal antibody against G Beta h coimmunoprecipitates GDP-bound G alpha h but not the GDP-AlF4--bound form. The GTP gamma S binding and GTPase activity of G alpha h are inhibited in a G beta h concentration dependent manner. Supporting this notion, G beta h accelerated GTP gamma S release from G alpha h and changes the affinity of G alpha h from GTP to GDP. Moreover, the ternary complex preparation exhibits TGase activity that is inhibited in the presence of the alpha 1-agonist and GTP. The GTP gamma S binding by the ternary complex, consisting of the alpha 1-agonist, the receptor, and Gh, is also inhibited by G beta h. The inhibition of GTP gamma S binding with the ternary complex requires a > or = 2.7-fold higher concentration of G beta h than the G alpha h alone, indicating that the receptor enhances the affinity of G alpha h for GTP. In addition, G beta h copurifies with an alpha 1-agonist, adrenoceptor, and G alpha h ternary complex, showing that the complex is a heterotetramer. Our data also suggest that G beta h does not directly interact with alpha 1-adrenoceptor. These findings clearly demonstrate that G alpha h associates with a novel protein which modulates the affinity of G alpha h for guanine nucleotides and that the GDP-bound Gh is the ground state for the counterpart activator, the alpha 1-adrenoceptor, in this signaling system.

Animals↗

PubMed1996

Haemophilia B (sixth edition): a database of point mutations and short additions and deletions.

The sixth edition of the haemophilia B database lists in easily accessible form all known factor IX mutations due to small changes (base substitutions and short additions and/or deletions of <30 bp) identified in haemophilia B patients. The 1380 patient entries are ordered by the nucleotide number of their mutation. Where known, details are given on factor IX activity, factor IX antigen in circulation and origin of mutation. References to published mutations are given and the laboratories generating the data are indicated.

Databases, Factual↗

PubMed1996

Behavioral consequences of intracerebral vasopressin and oxytocin: focus on learning and memory.

Since the pioneering work of David de Wied and his colleagues, the neuropeptides arginine vasopressin and oxytocin have been thought to play a pivotal role in behavioral regulation in general, and in learning and memory in particular. The present review focuses on the behavioral effects of intracerebral arginine vasopressin and oxytocin, with particular emphasis on the role of these neuropeptides as signals in interneuronal communication. We also discuss several methodological approaches that have been used to reveal the importance of these intracerebral neuropeptides as signals within signaling cascades. The literature suggests that arginine vasopressin improves, and oxytocin impairs, learning and memory. However, a critical analysis of the subject indicates the necessity for a revision of this generalized concept. We suggest that, depending on the behavioral test and the brain area under study, these endogenous neuropeptides are differentially involved in behavioral regulation; thus, generalizations derived from a single behavioral task should be avoided. In particular, recent studies on rodents indicate that socially relevant behaviors triggered by olfactory stimuli and paradigms in which the animals have to cope with an intense stressor (e.g., foot-shock motivated active or passive avoidance) are controlled by both arginine vasopressin and oxytocin released intracerebrally.

Animals↗

PubMed1996

Comparison of cryopreservation of supernumerary pronuclear human oocytes obtained after intracytoplasmic sperm injection (ICSI) and after conventional in-vitro fertilization.

A comparison was made of pronuclear stage human oocytes obtained either after classical in-vitro fertilization (IVF) or after intracytoplasmic sperm injection (ICSI). After ICSI or IVF, three fertilized oocytes from each patient were kept in culture for a further 24 h before embryo transfer. The surplus oocytes were cryopreserved using the 'open freezing system' and 1,2-propanediol and sucrose as cryoprotectants. A cohort of 817 and 1626 oocytes in pronuclear stage were frozen after IVF and ICSI respectively. Of these, 333 and 744 zygotes have been thawed, of which 78 and 76.5% were morphologically intact zygotes after IVF and ICSI respectively. From the 204 (ICSI) and 89 (IVF) zygote transfers performed, 34 (17%) and 18 (20%) pregnancies were established. Both groups showed a similar abortion rate of approximately 20%. It is concluded that pronuclear stage oocytes resulting from ICSI can be successfully frozen/thawed and the survival and pregnancy rates achieved are comparable to those for zygotes obtained after IVF.

Cryopreservation↗

PubMed1996

The combination of two semen preparation techniques (glass wool filtration and swim-up) and their effect on the morphology of recovered spermatozoa and outcome of IVF-ET.

The aim of this prospective study was to relate sperm quality, especially sperm morphology, to the outcome of IVF results, when glass wool filtration (GWF) and swim-up were used in combination for the preparation of spermatozoa. A total of 60 ejaculates were analysed. GWF was compared with glass wool filtration/swim-up (GWF-SU) by using aliquots from the same semen samples to increase the precision of the comparison and to establish the cumulative effect of these two semen preparation methods on the morphology of the recovered spermatozoa. Sperm parameters were examined in native semen, in semen preparation samples after GWF and GWF-SU. The mean percentages for motility, morphology and velocity were improved significantly over those in fresh semen only when GWF-SU was used. GWF alone resulted only in a significantly higher recovery of motile spermatozoa. In semen preparation, 10% of spermatozoa with normal morphology appeared to be the cut-off point as there was a significantly higher recovery in fresh semen samples containing > 10% morphologically normal spermatozoa after GWF-SU. Outcome of IVF-ET following preparation with GWF-SU showed better results in comparison to the swim-up procedure alone, though this difference was not statistically significant. The cut-off point was also > 10% morphologically normal spermatozoa. Improvement in all aspects of IVF-ET occurred when native semen contained > 10% morphologically normal spermatozoa. It is concluded that GWF alone did not produce significantly better results but, in combination with swim-up, it resulted in significantly better sperm morphology and in an improved outcome of IVF-ET for fresh semen samples with > 10% morphologically normal spermatozoa.

Adult↗

PubMed1996

Neural input modulates osmotically stimulated release of vasopressin into the supraoptic nucleus.

The effects of lesioning of the anteroventral third ventricle (AV3V) region on vasopressin (VP) release into the supraoptic nucleus (SON) and blood in response to central and systemic osmotic stimulation were determined. Microdialysis probes were implanted bilaterally within the SON of male urethan-anesthetized rats with sham or AV3V lesions. Osmotic stimuli were administered intraperitoneally (3.5 M NaCl, 600 microliters/100 g body wt) and then via the microdialysis probes (1 M NaCl-artificial cerebrospinal fluid). AV3V lesions attenuated the response to systemic osmotic stimulation. The lesioned rats showed no increase in intranuclear VP release and reduced plasma VP (increase of 42.6 +/- 8.4 vs. 78.0 +/- 16.4 pg/ml) and blood pressure responses (7.1 +/- 2.3 vs. 19.6 +/- 3.2 mmHg) to intraperitoneal NaCl. In contrast, the endocrine and cardiovascular responses to direct osmotic stimulation of the nucleus were as seen in previous studies and seemed to be unaffected by the lesion. These results show that lesion of the AV3V region interrupts neuronal inputs which trigger VP secretion from the posterior pituitary as well as release into the extracellular compartment of the SON.

Analysis of Variance↗

PubMed1996

Human papillomavirus in tissue of bladder and bladder carcinoma specimens. A preliminary study.

OBJECTIVE: To evaluate the significance of HPV type 6b, 11, 16 and 18 together with type-specific antibodies in the serum of bladder carcinoma. METHODS: The prevalence of HPV type 6b, 11, 16 and 18 in bladder tumor, normal bladder and urethra together with type-specific antibodies in serum was investigated in 23 patients with bladder cancer and 9 patients with chronic cystitis. HPV DNA analysis was done by polymerase chain reaction (PCR). Open reading frames of HPV were expressed in Escherichia coli as beta-galactosidase fusion proteins. RESULTS: HPV 6b was demonstrated in the tumor tissue of 6 patients (19%), and in the nonmalignant specimens of 6 further patients (19%). HPV 16/18 was only found in the urethral swabs of 2 patients (6%). Anti-HPV antibodies were positive in 7 patients (22%). There was no association between the demonstration of HPV 6b and the occurrence of bladder tumor in this study. CONCLUSION: Though, in this study, HPV was not associated with bladder cancer, further investigation is necessary to elucidate the role of HPV 6b in bladder tissue possibly by a semiquantitative PCR in tissue samples and of anti-HPV antibodies in serum.

Adenocarcinoma↗