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Biomedical subjects

B Schmitz

Publications and source records attributed to B Schmitz.

At least 145 records · Page 8Linked to original sources
PubMed1993

In vitro comparison of bileaflet aortic heart valve prostheses. St. Jude Medical, CarboMedics, modified Edwards-Duromedics, and Sorin-Bicarbon valves.

The hydrodynamic performance of four currently used bileaflet heart valve prostheses (St. Jude Medical, CarboMedics, modified Edwards-Duromedics, and Sorin-Bicarbon) with a nominal tissue anulus diameter of 27 mm were measured in the aortic position. All experiments were performed in nonpulsatile flow and in an electrohydraulic, computer-controlled pulse duplicator simulating the left side of the human circulatory system. Testing conditions were set at cardiac outputs of 3.0, 4.5, 6.5, and 8.0 L/min at a constant heart rate of 70 beats/min. The Sorin-Bicarbon valve had the lowest pressure difference with regard to nonpulsatile (mean 5.4 mm Hg at 30 L/min) and pulsatile (mean 2.2 mm Hg at 8 L/min) flow, followed by the St. Jude Medical, CarboMedics, and modified Edwards-Duromedics valves. The leakage volumes under static and pulsatile flow conditions were lowest for the modified Edwards-Duromedics and Sorin-Bicarbon valves. The energy loss in pulsatile flow was lowest for the Sorin-Bicarbon valve, mainly because its systolic, closure, and leakage energy losses were low. Systolic sequential velocity profiles showed the most even flow distribution pattern for the St. Jude Medical and Sorin-Bicarbon valves. These findings correspond with lower overall Reynolds shear stress levels for the St. Jude Medical and the Sorin-Bicarbon valves than for the modified Edwards-Duromedics and CarboMedics valves.

Aortic Valve↗
PubMed1992

L2/HNK-1 carbohydrate and protein-protein interactions mediate the homophilic binding of the neural adhesion molecule P0.

The neural adhesion molecule P0, the most abundant glycoprotein in peripheral myelin of mammals, is a member of the immunoglobulin superfamily and expresses the L2/HNK-1 and L3 oligosaccharides at a single N-glycosylation site. It acts in both homophilic and heterophilic binding mechanisms. To investigate the molecular requirements for homophilic interaction, we have used P0 from human sciatic nerve and the extracellular domain of P0 expressed in bacteria to determine binding of P0 to P0 in solid phase and bead aggregation assays. The binding of P0 to P0 could be partially inhibited in both assays by antibodies to the L2/HNK-1 epitope and by the L2/HNK-1 carbohydrate, but not by L3 antibodies or other carbohydrates. Inhibition of binding was also seen with polyclonal antibodies reacting with the protein backbone of P0. These observations indicate that both carbohydrate and protein structures are involved in the binding of P0 to P0 and that P0 acts as a presenter of and a receptor for a functionally important carbohydrate.

Animals↗
PubMed1992

Directionality of phase locking in auditory nerve fibers of the leopard frog Rana pipiens pipiens.

A dorsal approach to the eighth nerve and free-field stimulation were used to investigate the effect of sound direction and intensity on phase locking in auditory nerve fibers of the leopard frog Rana pipiens pipiens. Tuning curves of 75 auditory neurons were analyzed (Fig. 2). Amphibian papillar neurons, but not basilar papillar neurons, exhibit significant phase locking to short tone bursts at the characteristic frequency (CF), the degree of phase locking (vector strength) decreasing with the neuron's CF (Figs. 3, 4 and 10E). Vector strength increases with sound pressure level to saturate about 20 dB above threshold, while the preferred firing phase is only slightly affected (Figs. 5 and 6). In contrast, sound direction hardly affects vector strength (Figs. 7, 8, 9A and 10A and C), but has a strong influence on the preferred firing phase (Figs. 7, 8, 9B and C, 10B and D): With respect to anterior tone presentation there are phase lags for ipsilateral and phase leads for posterior and contralateral presentation. Phase differences between both ears show a sinusoidal or cardioid/ovoidal directional characteristic; maximum differences are found with antero-lateral tone presentation (Fig. 11). The directionality of phase locking decreases with the neuron's CF (Fig. 10F) and only slightly changes with sound pressure level (Fig. 12). Thus, phase locking of amphibian papilla neurons can potentially provide intensity-independent information for sound localization.

Acoustic Stimulation↗
PubMed1992

Range of motion after total condylar knee arthroplasty.

In this study the function of the knee measured at a medium-follow-up of 5-6 years was correlated with influencing factors concerning the implant of total condylar knee prosthesis in 90 patients. The only variable affecting postoperative extension was the preoperative range of extension whereas postoperative flexion was influenced by the preoperative flexion, valgus deviation of the preoperative AP tibial-femoral angle, position of the patella, and thickness of the resection of the distal femur cut.

Humans↗
PubMed1992

Use of large-scale hydrazinolysis in the preparation of N-linked oligosaccharide libraries: application to brain tissue.

In this report, we describe the preparation of a library of N-linked glycans from whole murine brain obtained by the large-scale hydrazinolysis of an acetone powder of the tissue followed by chromatographic procedures. 84% of the characterized oligosaccharides were found to be anionic, the remainder neutral. The anionic species were successively neutralized by neuraminidase (29%), aq. hydrofluoric acid (30%), and methanolysis (26%), indicating that approximately equal portions were sensitive to desialylation, dephosphorylation and desulfation, respectively. The presence of the sulfated fraction was confirmed by direct 35SO4 metabolic labelling. A residual partially characterized fraction was found to be anionic through possession of carboxylic acid groups, unrelated to sialic acid. The purified oligosaccharides, in the absence of their original protein conjugates, were shown to retain those immunological characteristics essential for recognition by a specific monoclonal antibody, LS (412), that is known to recognize a carbohydrate epitope present on a number of neural adhesion molecules and functional in neural cell adhesion. These properties confirm the viability of scaling up the size of the hydrazinolysis procedure and adapting it to whole tissue for the production of glycan libraries and for the probing of structures of interest.

Animals↗
PubMed1992

Cell-mediated immunity and its glucocorticoid-sensitivity after clinical recovery from severe major depressive disorder.

This follow-up study investigated lymphocyte blastogenesis induced by concanavalin A, phytohemagglutinin A, and pokeweed mitogen and their sensitivity to in vitro dexamethasone administration in 12 patients clinically recovered from severe major depression. Although cortisol-levels at 4.00 p.m. decreased significantly after clinical remission, mitogen-driven lymphocyte proliferative responses were unchanged when assessed intra-individually. No impairment of in vitro glucocorticoid-sensitivity of lectin-induced lymphocyte blastogenesis could be observed in clinically recovered patients. The inhibitory potency of in vitro dexamethasone was found to be inversely correlated with in vivo adrenal cortical hormone levels. There were no correlations with age, weight, sex, antidepressant medication, severity or duration of depression. No differences from age- and sex-matched healthy individuals were found. These results indicate that reduced glucocorticoid receptor sensitivity occurs only during the acute depressive illness.

Adrenocorticotropic Hormone↗
PubMed1992

Detection of multisulphated N-linked glycans in the L2/HNK-1 carbohydrate epitope expressing neural adhesion molecule P0.

P0, the most abundant glycoprotein of PNS myelin, is a homophilic and heterophilic adhesion molecule. P0 is known to contain a glycoform population that expresses the L2/HNK-1 carbohydrate epitope found on other neural adhesion molecules, and to be functionally implicated centrally in neural cell adhesion and neurite outgrowth. This carbohydrate epitope has been characterized previously from glycolipid structures and contains a sulphated glucuronic acid residue. However, the L2/HNK-1 carbohydrate epitope has not been characterized in glycoproteins. Because P0 possesses only one glycosylation sequon, the number of P0 glycoforms is equal to the heterogeneity of the glycan species. Here we report that the carbohydrate analysis of L2/HNK-1-reactive P0 showed the presence of anionic structures containing sialic acid and sulphate in various combinations. At least one sulphate residue was present in 80% of the monosaccharide sequences, and 20% contained three sulphates. High-resolution P4 gel chromatography of the desialylated and desulphated oligosaccharides showed substantial heterogeneity of monosaccharide sequences. Sequential exoglycosidase digestions indicated that the majority of the structures were of the hybrid class, although the sulphated structures were found to be endoglycosidase H-resistant.

Antigens, Differentiation↗
PubMed1992

Directional dependence of auditory sensitivity and frequency selectivity in the leopard frog.

Direction-dependent changes in frequency selectivity were documented in three populations of neurons in the auditory periphery of the leopard frog: low-, mid-, and high-frequency sensitive fibers. These changes were most pronounced in the mid-frequency (720-1199 Hz) sensitive fibers which exhibited positive shifts in characteristic frequencies (CFs) and concomitant narrowed bandwidths from posterior speaker presentations. Maximum sensitivities were observed for ipsilateral speaker presentations in these fibers. Low-frequency (63-500 Hz) sensitive fibers exhibited mean threshold shifts at their CFs of up to -7 dB with posterior speaker presentations. Low- and high-frequency sensitive fibers whose CFs closely correspond to the peaks of spectral energy of the species' mating call were the most sensitive (exhibited lowest thresholds) but showed little directional-dependent frequency selectivity. Directional-dependent variation in frequency selectivity and sensitivity in low- and mid-frequency sensitive fibers was attributed to pressure and phase differences impinging on the inner surface of the eardrum.

Animals↗
PubMed1991

Patterns of DNA methylation in selected human genes in different Hodgkin's lymphoma and leukemia cell lines and in normal human lymphocytes.

The human genome, like many other genomes, harbors highly specific patterns of DNA methylation which have not yet been systematically studied. In a limited investigation on the genes for tumor necrosis factors-alpha and -beta, a surprising interindividual concordance in the patterns of DNA methylation at the nucleotide level has been demonstrated earlier by using the genomic sequencing method on DNA from individuals of very different ethnic origins. Patterns of DNA methylation could perhaps serve as indicators for genetic activities. These activities would not have to be restricted to gene transcription but could relate to other genetic activities in the cell. DNA methylation patterns are known to be cell type-specific. We have now initiated a study of these DNA patterns in human lymphocytes and in human cell lines of different malignant origins. Several of the proto-oncogenes, parts of the genes for tumor necrosis factor-alpha and -beta, the insulin receptor and lamin C have been used as hybridization probes. We have relied to some extent on the documented observation that the methylation patterns at 5'-CCGG-3' (HpaII/MspI) sequences yield a reflection of patterns at all 5'-CG-3' sequences. Three main types of patterns have been observed. Some of the probed segments are completely unmethylated; others are fully methylated, most of the areas are partly methylated exhibiting complex patterns at the 5'-CCGG-3' sites. In different tumor cell lines, different DNA methylation patterns are apparent for the same DNA probes. Comparisons of the methylation patterns in a given DNA segment between DNA from primary normal human lymphocytes and DNA from different tumor cell lines reveal changes in these patterns in several instances.

Base Sequence↗
PubMed1991

In vivo and in vitro effects of glucocorticoids on lymphocyte proliferation in depression.

Twelve severely depressed patients and 13 healthy controls were studied under baseline, metyrapone and metyrapone plus dexamethasone pretreated conditions. Lymphocyte proliferation data were obtained by concanavalin A, phytohaemagglutinin and pokeweed mitogen (PWM) stimulation. There was a decrease in PWM-induced B-cell proliferation and an increase in inhibition of spontaneous leucocyte proliferation by dexamethasone added in vitro following metyrapone administration in vivo, in healthy controls, which was not present in the depressed patients. These data support the concept of a decreased functional plasticity of the glucocorticoid receptor in depression also at the cellular level.

Adolescent↗
PubMed1991

Normal lymphocyte responsiveness to lectins but impaired sensitivity to in vitro glucocorticoids in major depression.

The mitogen-induced lymphocyte proliferative response and its sensitivity to in vitro (10(-10)-10(-6) M) dexamethasone (DEX) administration were investigated in 12 severely depressed patients and 13 healthy controls. Patients with major depressive disorder exhibited no impairment of lectin-induced blastogenesis, but a significantly weaker suppressive effect of in vitro DEX on 1.0 microgram/ml phytohemagglutinin A-induced proliferation. The inhibitory potency of in vitro DEX was inversely correlated with in vivo adrenal cortical hormone levels at 4.00 p.m. These effects were not observed with pokeweed mitogen- and concanavalin A-stimulated cells. There were no correlations with age, weight, sex or severity of depression. These results do not support the hypothesis of a primarily impaired cell-mediated immunity, but might be indicative of reduced glucocorticoid receptor sensitivity in major depressive disorder.

Adrenocorticotropic Hormone↗
PubMed1991

Persistence or loss of preimposed methylation patterns and de novo methylation of foreign DNA integrated in transgenic mice.

In cultured mammalian cells, foreign DNA can be integrated into the host genome. Foreign DNA is frequently de novo methylated in specific patterns with successive cell generations. The sequence-specific methylation of promoter sequences in integrated foreign DNA is associated with the long-term inactivation of eukaryotic genes. We have now extended these experiments to studies on transgenic mice. As in previous work, a construct (pAd2E2AL-CAT) has been used which consists of the late E2A promoter of adenovirus type 2 (Ad2) DNA fused to the prokaryotic gene for chloramphenicol acetyltransferase (CAT). This construct has been integrated in the non-methylated in the 5'-CCGG-3' premethylated form in the genomes of transgenic mice. DNA from various organs was analyzed by HpaII/MspI cleavage to assess the state of methylation in 5'-CCGG-3' sequences. The results demonstrate that the transgenic construct is in general stable. Non-methylated constructs have remained partly non-methylated for four generations or can become de novo methylated at all or most 5'-CCGG-3' sequences in the founder animal. Preimposed patterns of 5'-CCGG-3' methylation have been preserved for up to four generations beyond the founder animal. In the testes of two different founder animals and two F1 males, the transgenic DNA has become demethylated by an unknown mechanism. In all other organs, the transgenic DNA preserves the preimposed 5'-CCGG-3' methylation pattern. In the experiments performed so far we have not observed differences in the transmission of methylation patterns depending on whether the transgene has been maternally or paternally inherited. The 5'-CCGG-3' premethylated transgene does not catalyze CAT activity in several organs, except in one example of the testes of an animal in which the transgenic construct has become demethylated. In contrast, when the nonmethylated construct has been integrated and remained largely non-methylated, CAT activity has been detected in extracts from some of the organs.

Adenoviridae↗
PubMed1990

Carbohydrate epitopes involved in neural cell recognition are conserved between vertebrates and leech.

We are reporting on the evolutionary conservation of carbohydrate epitope families from vertebrate to leech. 1) The sulfated L2/HNK-1 carbohydrate epitope (Abo T, Balch CM (1981): J Immunol 127:1024-1029; Kruse J, Mailhammer R, Wernecke H, Faissner A, Timpl R, Schachner M (1984): Nature 311:153-155) is detected on glycoproteins of leech neurons using monoclonal antibodies (mAbs) L2 (336) and HNK-1. 2) Three rat mAbs, L3, L4, and L5, bind to leech nerve and muscle. The L3, L4, and L5 epitopes are localized to a group of mannosidic leech glycoproteins originally identified through mAbs Lan3-2 (Hogg N, Flaster M, Zipser B (1983): J Neurosci Res 9:445-457 and Laz6-189 (McRorie JW III, Zipser B (1988): "Cell Culture Approaches to Invertebrate Neuroscience." London: Academie Press, pp 33-52. MAb Lan3-2, which binds to a mannosidic epitope of the 130 kD sensory protein, has recently been shown to perturb the penetration of sensory afferents into the synaptic area of the central neuropile (Zipser B, Morell R, Bajt ML (1989): Neuron 3:621-630). The L3, L4, and L5 mAbs have been described to recognize different mannosidic epitopes on glycoproteins, some of which have been identified as neural cell adhesion molecules, and on astrocyte-specific proteoglycan from mouse brain (Kücherer A, Faissner A, Schachner M (1987): J Cell Biol 104:1597-1602; Fahrig T, Schmitz B, Weber D, Kücherer-Ehret A, Faissner A, Schachner M (1990): Eur J Neurosci 2:153-161; Streit A, Faissner A, Gehrig B, Schachner M (1990): J Neurochem In Press). The superposition of five different mannosidic epitopes on the axons of sensory afferents suggests complex, concerted participation of mannosidic epitopes in neuronal pathfinding and target recognition.

Animals↗
PubMed1990

[Eosinophilic granulocytes in the cerebrospinal fluid].

The first section of the paper presents the morphology, structure and function of the eosinophilic granulocytes, while the second part deals with major neurologic diseases in which eosinophils are present or represent significant findings. These data are compared with the results of the author's own examinations of 1,000 unselected cerebrospinal fluid (CSF) samples. Eosinophils appeared usually in conjunction with infection, followed by foreign body inflammation. If the proportion of eosinophils exceeds 4%, the condition is termed CSF-eosinophilia, which usually develops in the presence of foreign bodies. However, infection may produce similar findings, especially in parasitic disease, and tumours of the central nervous system occasionally present with CSF eosinophilia.

Encephalitis↗