Search PubMed⌕ Search

Biomedical subjects

S Schmidt

Publications and source records attributed to S Schmidt.

At least 325 records · Page 18Linked to original sources
PubMed1993

The accessory bacteriochlorophyll: a real electron carrier in primary photosynthesis.

The primary electron transfer in reaction centers of Rhodobacter sphaeroides is studied by subpicosecond absorption spectroscopy with polarized light in the spectral range of 920-1040 nm. Here the bacteriochlorophyll anion radical has an absorption band while the other pigments of the reaction center have vanishing ground-state absorption. The transient absorption data exhibit a pronounced 0.9-ps kinetic component which shows a strong dichroism. Evaluation of the data yields an angle between the transition moments of the special pair and the species related with the 0.9-ps kinetic component of 26 +/- 8 degrees. This angle compares favorably with the value of 29 degrees expected for the reduced accessory bacteriochlorophyll. Extensive transient absorbance data are fully consistent with a stepwise electron transfer via the accessory bacteriochlorophyll.

Journal Article↗
PubMed1993

Accumulation of unsulphated precursors in Dictyostelium discoideum during selenate inhibition of growth.

Incubation of Dictyostelium discoideum cells with selenate is known to inhibit vegetative growth. In this paper we show that in the presence of selenate macromolecules accumulate which can be converted to sulphated products once the selenate is removed. The presence of cycloheximide, an inhibitor of protein synthesis, during the subsequent incubation does not prevent this conversion but tunicamycin, an inhibitor of glycosylation does. It is concluded that, in the presence of selenate, precursors accumulate as unglycosylated proteins, suggesting that feedback inhibition of glycosylation may be operated.

Animals↗
PubMed1993

Sequence-specific and mechanism-based crosslinking of Dcm DNA cytosine-C5 methyltransferase of E. coli K-12 to synthetic oligonucleotides containing 5-fluoro-2'-deoxycytidine.

The product of the dcm gene is the only DNA cytosine-C5 methyltransferase of Escherichia coli K-12; it catalyses transfer of a methyl group from S-adenosyl methionine (SAM) to the C-5 position of the inner cytosine residue of the cognate sequence CCA/TGG. Sequence-specific, covalent crosslinking of the enzyme to synthetic oligonucleotides containing 5-fluoro-2'-deoxycytidine is demonstrated. This reaction is abolished if serine replaces the cysteine at residue #177 of the enzyme. These results lend strong support to a catalytic mechanism in which an enzyme sulfhydryl group undergoes Michael addition to the C5-C6 double bond, thus activating position C-5 of the substrate DNA cytosine residue for electrophilic attack by the methyl donor SAM. The enzyme is capable of self-methylation in a DNA-independent reaction requiring SAM and the presence of cysteine at position #177.

Base Sequence↗
PubMed1993

Parvalbumin-immunoreactive structures of the adult human entorhinal and transentorhinal region.

Parvalbumin-immunoreactive structures in the entorhinal and transentorhinal region of the adult human brain were studied using the avidin-biotin-peroxidase technique. Parvalbumin-immunoreactive neurons and fibers (axons) were present in all layers (layer nomenclature according to Rose, 1927). The density of fibers was high in the islands of the superficial cell layer pre-alpha and in layer pre-beta and still heavier in pre-gamma. In the subjacent lamina dissecans it diminished abruptly and remained low in all layers of the internal principal stratum (layers pri-alpha, -beta, -gamma). This low density of fibers facilitated recognition of axon cartridges in layers pri-alpha and pri-gamma. Axon cartridges were also present within layers pre-beta and pre-gamma but were obscured by the dense fiber network there. Parvalbumin immunoreactivity was observed in the nerve cell soma and throughout the dendritic tree allowing the distinction of numerous nerve cell types. All parvalbumin-immunoreactive neurons belonged to the class of nonpyramidal neurons. Their lipofuscin pigment patterns differed distinctly from that of the pyramidal and modified pyramidal neurons. Based on their location, soma size, and dendritic arborization, they were grouped as large, medium-sized, and small neurons either of the multipolar or bipolar (vertical or horizontal) type. One type could be identified as an axo-axonic neuron, more specifically as a chandelier neuron generating axon cartridges. The dense fiber net within layer pre-gamma suggested the existence of another neuronal type, probably a neuron with an extended axonal ramification. The identified neurons were compared to neuronal types described in the literature from Golgi studies.

Adult↗
PubMed1993

Biocompatibility of silicon-based electrode arrays implanted in feline cortical tissue.

The passive biocompatibility of silicon-based electrode arrays was studied in feline cortical tissue. Three types of arrays were used: uncoated, coated with polyimide, and coated with polyimide over an adhesion promoter. Fifteen arrays were implanted for 24 h to determine early tissue reaction to the implantation procedure, and twelve arrays were implanted for 6 months to determine structural and material biocompatibility. Edema and hemorrhage were present around the short-term implants, but involved less than 6% of the total area of the tissue covered by the array. With chronic implants, leukocytes were rarely present and macrophages were found around roughly one-third of the tracks. Remnants of foreign material from the electrodes could be identified in less than 10% of the tracks. Gliosis was found around all tracks, forming an annulus between 20 and 40 microns thick. A capsule was not always present, and never exceeded a thickness of 9 microns. These results suggest that the implantation procedure produces limited amounts of tissue damage, and that the arrays are biocompatible. However, the arrays insulated with polyimide over a primer had significantly greater involvement of macrophages, gliosis, and capsule formation than uncoated arrays and arrays insulated with polyimide without printer, perhaps indicating a reaction to aluminum oxide in the primer.

Animals↗
PubMed1993

Effects of pyrantel pamoate on adult and preadult Toxocara canis worms: an electron microscope and autoradiography study.

Adult as well as preadult Toxocara canis isolated from the intestine of a beagle were incubated for 2, 4, and 14 h in medium containing either different concentrations of pyrantel pamoate (23.6, 236, and 2360 micrograms/ml medium) or tritiated pyrantel pamoate (2.36 micrograms/ml medium). These incubations were performed to study the effects of pyrantel pamoate on the morphology of the parasitic nematodes and to obtain information concerning the mode of uptake, the distribution, and the total amount of pyrantel pamoate ingested by T. canis. The results of the ultrastructure studies indicate that the intestine, hypodermis, and muscle cells are the organs that are predominantly affected by the drug. Additionally, it turned out that the duration of the treatment, i.e., the incubation time, was more important in determining the efficacy of pyrantel pamoate against T. canis than was the concentration itself. Autoradiography studies revealed that the adult worms ingest the drug orally, whereas preadults absorb pyrantel pamoate mainly through the whole body surface. Finally, measurements of the total amount of pyrantel pamoate taken up by T. canis indicated that adult worms can limit or even reduce the ingestion of pyrantel for more than 4 h, but then ingest large amounts of the drug. Preadult worms, however, absorb the drug more or less continuously during the first 14 h through the cuticula, albeit in lower concentrations than the adults. The different experiments elucidate differences in the uptake of pyrantel pamoate as well as in the total amount of drug ingested or absorbed by adult or preadult worms, leading to the assumption that repeated treatment with lower concentrations will be more effective than high concentrations given only once.

Aging↗
PubMed1993

Fetal transcutaneous PCO2 measurements during labour.

The departments of Obstetrics and Gynaecology of the Universities of Bonn and Copenhagen and the Free University of Amsterdam cooperated in the European Community Concerted Action Project 'New methods for Perinatal Surveillance'. In 95 patients fetal transcutaneous PCO2 (tcPCO2) recording (measuring temperature 41 degrees C) during labour was evaluated regarding its clinical applicability. During the first stage of labour fetal tcPCO2 was rather stable at a level of 7.3 +/- 1.4 kPa. In the second stage there were marked differences between the three subpopulations. In the first stage of labour the correlation between tcPCO2 and PCO2 in fetal blood samples was 0.38 (P = 0.02) and in the second stage -0.20 (P = 0.36). The correlation of fetal tcPCO2 with umbilical artery PCO2 was 0.30 (P = 0.01) and with pH -0.30 (P = 0.01). Using a fetal tcPCO2 level of 8.0 kPa as a cut-off point to predict an umbilical artery pH less then 7.20, sensitivity was 88%, specificity 65%, positive predictive value 29% and negative predictive value 97%. The likelihood ratio of a positive test was 2.47 and of a negative test 0.13. It is concluded that fetal tcPCO2 possibly can be an additional tool to exclude fetal acidosis. In case of values above 8.0 kPa further evaluation of the fetal acid-base balance is indicated.

Blood Gas Monitoring, Transcutaneous↗
PubMed1993

Psychophysical frequency modulation thresholds in a FM-bat, Tadarida brasiliensis.

Echolocating bats hunting flying insects discriminate complex temporal patterns of acoustic stimuli. For bats using frequency modulated sonar calls (FM bats), there are no behavioral data on the perception of sinusoidally frequency modulated (SFM) stimuli. Discrimination performance for SFM stimuli of varying modulation depth was measured in 4 Tadarida brasiliensis in a two-alternative, forced choice procedure. A center frequency of 40 kHz was modulated with rates between 10 and 2000 Hz. It was found that discrimination performance improved from a mean threshold modulation depth of 3.05 kHz at a modulation rate of 2000 Hz to 1.58 kHz at a modulation rate of 10 Hz. Psychoacoustical modulation depth thresholds of T. brasiliensis are thus distinctly larger than those observed in bat species emitting constant frequency (CF) components followed by an FM-sweep, in active echolocation experiments. The modulation thresholds of T. brasiliensis are discussed in connection with the ability of bats to discriminate insect wingbeats. A comparison between non-echolocating mammals and the FM bat T. brasiliensis shows that the ability to echolocate is not reflected in the modulation thresholds.

Acoustic Stimulation↗
PubMed1993

Screening patients for heterozygous p53 mutations using a functional assay in yeast.

Inherited mutations of the p53 gene significantly increase the risk of developing diverse malignancies, and germline p53 mutations can be detected by assaying the transcriptional activity of the p53 protein in mammalian cells. Here we describe a method starting with lymphocytes that allows detection of germline p53 mutations by 'functional' analysis of p53 protein expressed in Saccharomyces cerevisiae. The p53 PCR products are directly cloned into yeast expression vectors in vivo and subsequently tested for transcriptional activity in a simple growth assay. This technique, functional analysis of separated alleles in yeast (FASAY), requires only a few steps, can be automated readily and should permit screening for germline or somatic heterozygous mutations in any gene whose function can be monitored in yeast.

Animals↗
PubMed1993

The nurse clinician: role conflict in research.

In a recent pilot study focusing on stroke rehabilitation, four clinical nurse specialists (CNSs) experienced role conflict when assuming the nurse researcher-interviewer role. Presenting an overview of the pilot study and the experiences that occurred, the authors question the reliability of the interviews. They propose that outcomes of research can be biased by role conflict when CNSs serve as interviewers and collect data. The authors suggest that interviewing training specifically address role conflict.

Bias↗
PubMed1993

The course of major depressive disorder in adolescents: I. Recovery and risk of manic switching in a follow-up of psychotic and nonpsychotic subtypes.

Fifty-eight adolescents meeting Research Diagnostic Criteria (RDC) for major depressive disorder were observed for 24-months after inpatient admission in a prospective, naturalistic design study to assess time to recovery, risk of manic switching, and level and persistence of psychosocial impairment. Subjects were further categorized as psychotic or nonpsychotic by RDC. The cumulative probability of recovery by 24 months was high (90%); however, the episode was protracted with only 6.9% recovering within 12 weeks and only 29.3% recovering by week 20. Time to recovery did not vary by RDC subtype, but manic switching was observed only among psychotics, at a rate of 28%. Psychotics were more likely than were nonpsychotics to exhibit psychosocial impairment through 6 months of follow-up, but this difference narrows by 24 months. Implications of these findings for understanding developmental effects on the course and treatment of depression in adolescents are discussed.

Adolescent↗
PubMed1993

Polymorphism of the angiotensin I converting enzyme gene is apparently not related to high blood pressure: Dutch Hypertension and Offspring Study.

OBJECTIVE: Studies in genetically hypertensive rats and their normotensive Wistar-Kyoto control rats have revealed a linkage of a chromosomal region containing the angiotensin converting enzyme (ACE) gene with blood pressure. This led to the hypothesis that ACE is a possible candidate gene for primary hypertension in humans. We defined the genotypes and allele frequencies of an insertion-deletion (I/D) polymorphism in parental couples who both had either high or low blood pressure and in their offspring. SUBJECTS: Parents (n = 111) and offspring (n = 75) with defined blood pressure status from the Dutch Hypertension and Offspring Study. METHODS: Genomic DNA was amplified by polymerase chain reaction using primers flanking the polymorphic region in intron 16 of the ACE gene. Alleles were detected on agarose gels stained with ethidium bromide. RESULTS: Allele frequencies for the D-allele were similar in parents with high (0.66) and low blood pressure (0.59) and in their offspring (0.67 and 0.69, respectively). A similar lack of difference was found with respect to the complementary I-allele. CONCLUSIONS: In the present rather large sample we failed to find a significant association between I/D polymorphism of the ACE gene and blood pressure status in subjects with high or low blood pressure and in their offspring.

Adult↗
PubMed1993

Modulation of the effect of humoral-mediated cytotoxicity on isolated rat pancreatic islets by glucose.

Rat islets of Langerhans exposed for 20 h at high glucose (20 mmol/l) to 50% or 20% experimentally raised rabbit anti-rat islet cell surface antiserum (ICSA-positive serum) plus complement exhibited an irreversible loss of glucose-stimulated insulin secretion. In contrast, islets treated with 50% ICSA-positive serum at low glucose (5.5 mmol/l) could overcome this alteration within a subsequent 48 h recovery period at 10 mmol/l glucose in the absence of ICSA, and islets affected at 5.5 mmol/l glucose by 20% ICSA-positive serum even retained the insulin secretory potential and responded on glucose challenge already immediately after the removal of ICSA. The islet insulin content was reduced by the effect of 50% as well as of 20% ICSA-positive serum and complement irrespective of whether the glucose level amounted to 5.5 or 20 mmol/l during serum influence. However, islets altered in a normoglycaemic environment at 5.5 mmol/l glucose by 20% ICSA-positive serum restored their insulin content up to the level of control islets, whereas those islets affected under hyperglycaemic conditions at 20 mmol/l glucose only partially recovered. Thus, beta-cell loss and/or impairment of the insulin secretory mechanisms result from the simultaneous action of humoral-mediated anti-islet cytotoxicity and elevated glucose level, and cause the diminished insulin secretory potential of the islets. These results support the hypothesis that decreasing the insulin secretory activity of beta cells may protect them from cytotoxic immunological attacks.

Animals↗