Biomedical subjects

G Mohr

Publications and source records attributed to G Mohr.

At least 55 records · Page 3Linked to original sources

PubMed1996

Correlation of chloroethylnitrosourea resistance with ERCC-2 expression in human tumor cell lines as determined by quantitative competitive polymerase chain reaction.

We have developed a method to quantitate ERCC-2 gene expression in tumor cell lines. A mutant ERCC-2 DNA fragment (1-bp mutation) is used as a competitive DNA template in a coamplification PCR reaction with cDNA obtained by reverse transcribing DNase-free total RNA from six human tumor cell lines. The PCR products are separated on agarose gel by virtue of their differential banding pattern upon restriction enzyme digestion. Densitometric readings of the PCR products from a negative film of the gel are used to establish a linear regression curve, which in turn is used to quantitate ERCC-2 levels. Beta-actin expression is similarly quantitated. Normalized ERCC-2 gene expression (either to beta-actin or to total RNA) correlates with cytotoxicity of 1,3-bis-(2-chloroethyl)-1-nitrosourea or (2-chloroethyl)-3-sarcosinamide-1-nitrosourea, suggesting that ERCC-2 may play an important role in drug resistance in these cell lines. This method is reliable and can be used to quantitate gene expression in clinical tumor specimens.

Antineoplastic Agents↗

PubMed1996

A tyrosyl-tRNA synthetase protein induces tertiary folding of the group I intron catalytic core.

The Neurospora crassa mitochondrial tyrosyl-tRNA synthetase (CYT-18 protein) functions in splicing group I introns. We have used chemical-structure mapping and footprinting to investigate the interaction of the CYT-18 protein with the N. crassa mitochondrial large subunit ribosomal RNA (mt LSU) and ND1 introns, which are not detectably self-splicing in vitro. Our results show that both these non-self-splicing introns form most of the short range pairings of the conserved group I intron secondary structure in the absence of CYT-18, but otherwise remain largely unfolded, even at high Mg2+ concentrations. The binding of CYT-18 promotes the formation of the extended helical domains P6a-P6-P4-P5 (P4-P6 domain) and P8-P3-P7-P9 (P3-P9 domain) and their interaction to form the catalytic core. In iodine-footprinting experiments, CYT-18 binding results in the protection of regions of the phosphodiester backbone expected for tertiary folding of the catalytic core, as well as additional protections that may reflect proximity of the protein. In both introns, most of the putative CYT-18 protection sites are in the P4-P6 domain, the region of the SU intron previously shown to bind CYT-18 as a separate RNA molecule, but additional sites are found in the other major helical domain in P8 and P9 in both introns and in L9 and P7.1/P7.1a in the mt LSU intron. Protease digestion of the CYT-18/intron RNA complexes results in the loss of CYT-18-induced RNA tertiary structure and splicing activity. Considered together with previous studies, or results suggest that CYT-18 binds initially to the P4-P6 region of group I introns to form a scaffold for the assembly of the P3-P9 domain, which may contain additional binding sites for the protein. A three-dimensional model structure of the CYT-18 binding site in group I introns indicates that CYT-18 interacts with the surface of the catalytic core on the side opposite the active-site cleft and may primarily recognize a specific three-dimensional geometry of the phosphodiester backbone of group I introns.

Base Sequence↗

PubMed1996

Mapping of the basal forebrain cholinergic system of the dog: a choline acetyltransferase immunohistochemical study.

In an effort to produce a canine model of basal forebrain ischemia with memory deficits, we have shown that dogs possess a medial striate artery that perfuses basal forebrain territory, homologous to the human recurrent artery of Heubner. In the present study, we set out to delineate the precise topography of the cholinergic neurons in the canine forebrain, a neuronal system implicated in cognitive and memory functions. Floating coronal sections, derived from the head of the caudate nucleus to the rostral border of the hippocampus, were stained for choline acetyltransferase using a monoclonal antibody. Representative sections from one dog brain were drawn. These outlines were used for measurement of cell density, cell size, number of processes, and cell roundness. Choline acetyltransferase-positive neurons constituted four major subdivisions within the basal forebrain. A relatively dense population of cholinergic neurons was present in the medial septal nucleus (Ch1). A continuum of densely packed cells was also delineated within the vertical (Ch2) and horizontal (Ch3) nuclei of the diagonal band of Broca. A fourth group of heterogeneously packed cholinergic neurons represented the nucleus basalis magnocellularis (Ch4). Except for the caudal component of the Ch4 population, the forebrain cholinergic corticopetal system was located within the perfusion territory of the medial striate arteries. The Ch4 cell group in dogs is better defined than that of rodents but is not as sharply demarcated as in human and nonhuman primates. Our findings indicate that the dog may serve as an excellent model for assessing neurological and memory deficits, which, in humans, results from hypoperfusion of the recurrent artery of Heubner.

Analysis of Variance↗

PubMed1996

Microvascular anatomy of striate vessels in dogs: contribution to an experimental model of forebrain ischemia.

Basal perforating vessels such as Heubner's artery are involved in various arteriopathic conditions resulting in cognitive and memory deficits. In order to evaluate if a model of focal forebrain ischemia can be obtained in dogs, a systematic study of the microvascular anatomy of the striate vessels was performed using intravascular injections of acrylic paint and/or India ink. Medial and lateral striate arteries were identified and found distinct either by their superficial anatomy as well as their deep perfusion territories. One medial striate artery emerging consistently from the junction of the A1 segment of the anterior cerebral artery and the ethmoidal artery resembles the human recurrent artery of Heubner. Therefore, the dog may provide a suitable model of forebrain ischemia involving solely the perfusion territory of the medial striate arteries.

Anatomy, Artistic↗

PubMed1996

Pulsation-pressure relationship in experimental aneurysms: observation of aneurysmal hysteresis.

In this study the pulsation-pressure relationship in an experimental model of aneurysms was analyzed. In addition, we have examined pulsatility of the aneurysmal wall reinforced by Guglielmi Detachable Coils (GDC). Bifurcation (BAn), aneurysms (LAn) and bilobar (BiA) aneurysms were produced in 15 mongrel dogs. The aneurysmal dome was constructed from a segment of the external jugular vein which was sutured to the window performed on the apex of bifurcation of the ECA and lingual artery (BAn) or on the ECA (LAn). One set of the GDC (diameter 5 mm, length 20 cm) were inserted into the aneurysm. Intra-aneurysmal pressure, aneurysmal pulsation, ECG and femoral artery pressure were recorded. Results showed that an experimental aneurysm pulsates in synchrony with the intra-aneurysmal pressure and aneurysmal pulsation is proportional to the aneurysmal size. Pulsation profile also depends on the aneurysmal type (BAn, LAn, BiA). The looped pressure-pulsation curve indicates that aneurysms exhibit property of hysteresis. For the same pressure the aneurysm is smaller during the ascending (systolic) portion of the blood pressure wave. Insertion of catheter into the aneurysm and subsequent release of the GDC did not elicit any measurable changes of the intra-aneurysmal pressure. Aneurysm reinforced by GDC showed smaller pulsation and the hysteresis was reduced as well. It was concluded that aneurysmal hysteresis could be an important factor resulting in degeneration of aneurysmal wall since it is known that hysteresis accelerates degeneration of all fibrous elements, predominantly of elastic fibers. GDC seems to buffer the intra-aneurysmal hemodynamic forces and hence they might have a stabilizing effect on the aneurysmal wall.

Aneurysm↗

PubMed1996

Microencapsulation for cell implants into the central nervous system: the importance of alginate viscosity and related factors.

We have developed microcapsules using sodium alginate and poly-L-lysine with optimal combinations of experimental parameters and also used different autoclave times to evaluate the impact of sterilization on the property of capsules. We found that an autoclave time of 20 min was sufficient for sterilization of the alginate, and the optimal concentration of the alginate of low and high viscosity was 1.75 and 1.25% respectively. The capsules made with those optimal parameters remained intact for 6 months in an environment resembling that of the brain. Our results suggest that it is important to optimally combine experimental parameters in order to obtain reliable microcapsules, which may be used for many secretory cell implantats into the central nervous system in vivo.

Alginates↗

PubMed1996

Production of highly homogeneous and structurally intact recombinant von Willebrand factor multimers by furin-mediated propeptide removal in vitro.

Recombinant human von Willebrand Factor (rvWF), a multimeric glycoprotein essential to haemostasis, has been developed as a potential therapeutic agent for treatment of von Willebrand disease (vWD). Permanent Chinese-hamster ovary (CHO)-rvWF cell clones co-expressing recombinant furin (rfurin) were established in order to ensure complete rvWF propeptide removal [Fischer, Schlokat, Mitterer, Reiter, Mundt, Turecek, Schwarz and Dorner (1995) FEBS Lett. 375, 259-262]. Large quantities of material are required for in vivo tests and clinical studies. This demand is commonly met by achieving high-yield expression of the desired protein via amplification. Co-amplification of rfurin, necessary to completely process increasing amounts of rvWF precursor, could not be accomplished, presumably due to lethal effects of overexpressed rfurin for the host cells [Creemers (1994) Ph.D. Thesis, University of Leuven]. Recent reports have inferred that rfurin can only mediate rvWF processing intracellularly [Rehemtulla and Kaufman (1992) Blood 79, 2349-2355; Rehemtulla, Dorner and Kaufman (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 8235-8239]. We report here that rvWF-precursor processing, however, occurs predominantly extracellularly upon rfurin co-expression. Mixing experiments employing rfurin- as well as rvWF-precursor-containing conditioned media demonstrate that rvWF precursors are accessible and cleavable by rfurin in vitro. Exposure to rfurin in vitro converts the heterogeneous multimer pattern typical of incompletely processed rvWF multimers into highly homogeneous and structurally intact multimers superior to the ones exhibited by plasma-derived vWF. These findings thus demonstrate the feasibility of large-scale production of a completely processed, intact and homogeneous rvWF preparation, based on individual rvWF-precursor high-yield expression and subsequent propeptide removal by rfurin in vitro.

Animals↗

PubMed1995

Placebo-controlled trial of safety and efficacy of intraoperative controlled delivery by biodegradable polymers of chemotherapy for recurrent gliomas. The Polymer-brain Tumor Treatment Group.

Chemotherapy for brain tumours has been limited because of difficulty in achieving adequate exposure to the tumour without systemic toxicity. We have developed a method for local sustained release of chemotherapeutic agents by their incorporation into biodegradable polymers. Implantation of the drug-impregnated polymer at the tumour site allows prolonged local exposure with minimal systemic exposure. We conducted a randomised, placebo-controlled, prospective study to evaluate the effectiveness of biodegradable polymers impregnated with carmustine to treat recurrent malignant gliomas. In 27 medical centres, 222 patients with recurrent malignant brain tumours requiring re-operation were randomly assigned to receive surgically implanted biodegradable polymer discs with or without 3.85% carmustine. Randomisation balanced the treatment groups for all of the prognostic factors examined. Median survival of the 110 patients who received carmustine polymers was 31 weeks compared with 23 weeks for the 112 patients who received only placebo polymers (hazard ratio = 0.67, p = 0.006, after accounting for the effects of prognostic factors). Among patients with glioblastoma, 6-month survival in those treated with carmustine-polymer discs was 50% greater than in those treated with placebo (mortality = 32 of 72 [44%] vs 47 of 73 [64%], p = 0.02). There were no clinically important adverse reactions related to the carmustine polymer, either in the brain or systemically. Interstitial chemotherapy delivered with polymers directly to brain tumours at the time of surgery seems to be a safe and effective treatment for recurrent malignant gliomas.

Biodegradation, Environmental↗

PubMed1995

Study of microencapsulation for pituitary transplantation: capsule preparation and in vitro study.

We have developed microcapsules using sodium alginate (SA) and Poly-L-Lysine (PLL). A factorial design method of screening was chosen to study influences of different experimental parameters on size and stability of the capsules. We found that air flow affects initial size of the capsules significantly, while the molecular weight (MW) of PLL and incubation time have a positive impact on the expansion when capsules are incubated in sodium citrate (SC). When the capsules were continuously shaken in an attempt to mimic in vivo environmental conditions, those capsules made with optimal parameters (0.1% PLL, 42,000 MW, incubated for 6 minutes; 1.5% SA, incubated for 4 minutes; SC bath 4 minutes; 25# needle; air flow 14L/min) were still intact after 30 days and not totally ruptured until 90 days, while those developed with less strict parameters were ruptured within 2 hours in 50%. We also encapsulated human pituitary adenoma cells using PLL of 80,000 MW and cultured them for 9 days. Adenoma cells, both encapsulated or non-encapsulated, secreted the same amount of hormones. Our preliminary study suggests that selecting optimal combinations of experimental parameters is essential in developing durable microcapsules, which may be potentially used for pituitary transplantation in vivo.

Adenoma↗

PubMed1995

The clinical introduction of a third generation lithotriptor: Modulith SL 20.

The Modulith SL 20* was designed as a third generation lithotriptor with outstanding disintegrative efficacy in vitro, and equipped with a combined fluoroscopic and ultrasound localization system integrated in a multifunctional table. Its introduction to clinical extracorporeal shock wave lithotripsy took place in 3 phases. In phase 1 (49 patients) only in line ultrasound localization was possible. The many caliceal stones were adequately disintegrated with restricted generator voltage. In phase 2 (81 patients) fluoroscopic localization with the virtual focus of an adapted x-ray C-arm unit enabled in situ lithotripsy of ureteral stones in 33% of all patients. Phase 3 (549 patients) was characterized by additionally increasing the generator voltage to 20 kv. This development of the lithotriptor by improving the localization system and shock wave energy resulted in the possibility for successful disintegration of stones in the entire upper urinary tract (including the complete ureter), decreased treatment time (52 to 39 minutes) and an improved efficiency quotient (0.45 to 0.67). During phase 3 auxiliary measures were performed before lithotripsy in 24% of the cases. After 1.8% of the treatments minor or moderate perirenal fluid collection or bleeding was detected by routine followup sonography. A 91% stone-free rate was achieved with only 9.3% curative auxiliary measures after extracorporeal shock wave lithotripsy, including a 23% retreatment rate. Thus, the Modulith device had a high efficacy quotient compared with other lithotriptors.

Adult↗

PubMed1994

A tyrosyl-tRNA synthetase can function similarly to an RNA structure in the Tetrahymena ribozyme.

Group I introns are highly structured RNAs which catalyse their own splicing by guanosine-initiated transesterification reactions. Their catalytic core is generally stabilized by RNA-RNA interactions within the core and with peripheral RNA structures. Additionally, some group I introns require proteins for efficient splicing in vivo. The Neurospora CYT-18 protein, the mitochondrial tyrosyl-transfer RNA synthetase (mt TyrRS), promotes splicing of the Neurospora mitochondrial large ribosomal RNA (LSU) and other group I introns by stabilizing the catalytically active structure of the intron core. We report here that CYT-18 functions similarly to a peripheral RNA structure, P5abc, that stabilizes the catalytic core of the Tetrahymena LSU intron. The CYT-18 protein and P5abc RNA bind to overlapping sites in the intron core, inducing similar conformational changes correlated with splicing activity. Our results show that a protein can play the role of an RNA structure in a catalytic RNA, a substitution postulated for the evolution of nuclear pre-messenger RNA introns from self-splicing introns.

Animals↗

PubMed1994

Measuring activation patterns of the heart at a microscopic size scale with thin-film sensors.

To study the spread of excitation in ventricular heart preparations we have designed a fast, high-resolution recording and mapping system. Papillary muscles were dissected from the isolated guinea pig hearts. The preparation was fixed in a tissue bath and superfused with Tyrode solution. Linear and two-dimensional arrays of Ag/AgCl electrodes were made on glass with a thin-film technique. The transparent sensors with up to 24 electrodes (spaced 50, 90, or 180 microns apart) were positioned close to the surface of the preparation with a custom-designed three-dimensional micromanipulator. Extracellular signals were simultaneously recorded by a 24-channel data acquisition system with a 200 kHz per channel sample rate, with 12-bit amplitude resolution and a maximum data length of up to 3 MB. Digitized video images of the electrode array and the underlaying preparation were used to identify the locations of the recording sites. A UNIX-based computer system with a custom-designed data acquisition and database program was used to control the instruments and to manage the experimental data. This technique gave signals with excellent signal-to-noise ratios (up to 65 dB) and permitted accurate evaluation of the time and the site of the local activation with high resolution (to within 5 microseconds, 50 microns). We describe the spread of excitation within the area of a few cells and found a substantial dispersion of conduction velocities. Beat-to-beat comparison of activation patterns showed relatively small variations in the spread of excitation (a few microseconds).

Action Potentials↗

PubMed1994

Memory of self-performed tasks: self-performing during recognition.

Two experiments focused on whether performing actions described by to-be-remembered phrases during recognition enhances recognition compared with results of a standard verbal recognition test. The enhancement was predicted when the actions described by the phrases had been performed during study, but not when the phrases were verbally encoded by simply listening to and memorizing the material. Both experiments showed that enactment prior to recognition improved memory performance, but only when subjects had encoded by enactment. Experiment 1 also demonstrated that this test-procedure effect was independent of a bizarreness effect, which was observed only with the verbal encoding task. Experiment 2 showed that the effect of enactment during recognition was reduced when subjects used different hands for performing the actions during study and recognition. The findings support the assumption that some kind of motor memory record underlies the enactment effect that occurs when actions are performed during recognition.

Acoustic Stimulation↗

PubMed1994

Intratemporal vascular malformations (angiomas): particular clinical features.

Vascular malformations (angiomas) represent 1% of all pathologies of the temporal bone, including those of the cerebellopontine angle (CPA). We report six new cases of angiomas and compare them to the 48 cases listed in the literature published since 1949. Angiomas develop more frequently in the internal auditory canal (IAC) and at the geniculate ganglion (GG). When present in the IAC, rapidly progressive hearing loss is found in 88% of the patients reported in the literature and in 100% of patients in our series; facial nerve dysfunction is found in 72% and 60% of cases, respectively. The average tumour size is less than 10 mm. Acoustic neuroma, the most frequent tumour of this area, causes a slowly progressive sensorineural hearing loss in 75% of cases and facial weakness in 0.8%, according to the literature. Only 10% of acoustic neuromas measure less than 10 mm. Angiomas differ from acoustic neuromas in their rapid onset of sensorineural deafness and much greater incidence of facial nerve dysfunction despite a smaller tumour size.

Adult↗

PubMed1994

Ureteral stone. Treatment using the Modulith SL 20 and Lithostar plus.

The treatment of ureteric calculi by extra-corporeal shock waves was found to have an 80% success rate by Mannheim authors, regardless of the site of the calculus. The authors compared two 3rd generation apparatuses: 1--the Siemens Lithostar Plus, in which waves are produced by a electromagnetic cylinder and focussed by a parabolic electromagnetic cylinder and focussed by a parabolic reflector: 2--the Storz Medical Modulith SL 10, in which waves produced by an electromagnetic coil are focussed by acoustic lenses. Both apparatuses are based upon image-intensification and ultrasonography concepts. No difference in efficacy was found between the two apparatuses. A second shock wave session was necessary in 16% of cases and some other type of additional treatment in 7% of cases.

Acoustics↗

PubMed1994

Endoscopic repair of anterior skull base cerebrospinal fluid fistulas: an emphasis on postoperative nasal function maximization.

Endoscopic repair of cerebrospinal fluid (CSF) fistulas has been proposed as an alternative to the traditional intracranial and extracranial approaches. This study reports on four consecutive adult cases of anterior skull base CSF fistulas. The technique used for endoscopic repair, which was designed to maximize postoperative nasal function, is described in detail. The results and complications recorded, using this technique, are reported. Endoscopic repair appears to be a safe and successful approach in the surgical treatment of CSF fistulas while preserving nasal function.

Adult↗

PubMed1993

Evolutionary relationships among group II intron-encoded proteins and identification of a conserved domain that may be related to maturase function.

Many group II introns encode reverse transcriptase-like proteins that potentially function in intron mobility and RNA splicing. We compared 34 intron-encoded open reading frames and four related open reading frames that are not encoded in introns. Many of these open reading frames have a reverse transcriptase-like domain, followed by an additional conserved domain X, and a Zn(2+)-finger-like region. Some open reading frames have lost conserved sequence blocks or key amino acids characteristic of functional reverse transcriptases, and some lack the Zn(2+)-finger-like region. The open reading frames encoded by the chloroplast tRNA(Lys) genes and the related Epifagus virginiana matK open reading frame lack a Zn(2+)-finger-like region and have only remnants of a reverse transcriptase-like domain, but retain a readily identifiable domain X. Several findings lead us to speculate that domain X may function in binding of the intron RNA during reverse transcription and RNA splicing. Overall, our findings are consistent with the hypothesis that all of the known group II intron open reading frames evolved from an ancestral open reading frame, which contained reverse transcriptase, X, and Zn(2+)-finger-like domains, and that the reverse transcriptase and Zn(2+)-finger-like domains were lost in some cases. The retention of domain X in most proteins may reflect an essential function in RNA splicing, which is independent of the reverse transcriptase activity of these proteins.

Amino Acid Sequence↗

PubMed1993

[Significance of psychological stress, absence of stress and resources for health promotion at the workplace].

Stress is defined as a lasting, averse situation, the avoidance of which appears to be subjectively important and where the individual is not sure of having enough ability to control it. Eustress, contrary to this, is characterized by the individual's confidence of being able to master given demands successfully. Therefore eustress can not equated with stress. One may assume that the repeated experience of mastering given demands constitutes a resource in coping with stressors. Empirical findings have shown psychic stressors to be systematically linked with individual discomfort preceding clinical symptoms. Therefore alterations to psychic stressors may be a mean of prophylaxis. Data from surveys on blue-collar workers moreover have suggested that two working conditions themselves may provide resources for coping with stressors: decision latitude and social support. Hence enlarging decision latitude and enhancing social support may be possibilities for prevention, especially in such cases, where stressors cannot (yet) be directly changed.

Adaptation, Psychological↗