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Biomedical subjects

J Schmidt

Publications and source records attributed to J Schmidt.

At least 703 records · Page 39Linked to original sources
PubMed1984

An immunochemical approach to the identification of the MBTA binding site of the nicotinic acetylcholine receptor of Torpedo californica.

Monospecific anti-[4-(N-maleimidobenzyl) trimethylammonium] (MBTA) antibodies were prepared from sera of rabbits immunized with an albumin-MBTA conjugate and used to synthesize an MBTA-specific immunosorbent. Torpedo californica acetylcholine receptor was affinity labeled with [3H]-MBTA and proteolyzed extensively with pronase, and the peptide fraction of the digest chromatographed on the anti-MBTA resin. The amino acid composition of the purified MBTA-peptide fraction was compared with the sequences flanking the seven cysteinyl residues of the alpha-subunit. The best fit was observed with the segment containing cysteine 142.

Affinity Labels↗
PubMed1984

The impact of radiodecay on 125I-Tyr-54-alpha-bungarotoxin.

The intramolecular consequences, for the structural and functional integrity of labeled proteins, of the radiodecomposition of covalently bound 125I were analyzed, using the 125I-Tyr-54 derivative of the curarimimetic protein alpha-bungarotoxin (alpha BuTx) as a specific example. Mono- and di-iodinated alpha BuTx derivatives of high specific radioactivity were prepared and monitored for up to ten 125I half-lives. Analysis of the specific activity of a mono-125I-alpha BuTx as a function of storage time was carried out and revealed that at least 95.3% of all radiolabeled alpha BuTx molecules are inactivated by the decay event. Generation of radioactive fragments of low molecular weight was studied in several preparations of di-125I-alpha BuTx; it was found that approximately 89% of all decaying 125I-alpha BuTx molecules undergo fragmentation of the labeled tyrosyl moiety. It has long been known that covalently bound 125I cleaves and inactivates double-stranded DNA with extreme efficiency (see Halpern, A., and Stöcklin, G. (1977) Radiat. Environ. Biophys. 14, 167-183; 257-274); the present findings establish that alpha BuTx, a protein, is similarly disabled by 125I decay.

Animals↗
PubMed1984

Mapping of the protein-coding regions of Rhizobium meliloti common nodulation genes.

An 8.5-kb EcoRI fragment containing the common nod region of the megaplasmid pRme41b of Rhizobium meliloti was recloned in plasmids of Escherichia coli, and a detailed restriction map was established. The region can express at least eight proteins in E. coli minicells and in an in vitro transcription/translation system, prepared from E. coli. Protein coding regions were determined by subcloning of restriction fragments, deletion mutations and by transposon mutagenesis. The coding regions for at least three polypeptide chains (mol. wts. 23 000, 28 500 and 44 000) were mapped on a 3.3-kb nod gene cluster. The 44 000 mol. wt. protein is expressed from a nod region, which is highly conserved in two Rhizobium species. The protein map of the 8.5-kb fragment was correlated to a map of insertion mutations with Nod and Fix phenotypes. The data suggest that the proteins encoded by the nod gene cluster may be involved in early steps of the nodulation process. Nod Fix symbiotic mutations were localized in the coding region for a 33 000 mol. wt. protein, suggesting that this polypeptide might be a fix gene product.

Journal Article↗
PubMed1984

High-resolution hydroxyapatite chromatography of proteins.

Hydroxyapatite chromatography has been used to separate all five isozymes of lactic dehydrogenase, six enzymatically active forms of bovine pancreatic DNase I, and a standard protein mixture. The proteins were eluted with a linear gradient of sodium phosphate. Enzyme activity recoveries were greater than 90%. Packing materials were obtained from commercial fine-particle-sized hydroxyapatite (DNA grade Bio-Gel HTP) by an elutriation procedure. Long columns packed with small crystals were run under low pressure at acceptable flow rates, and were used over prolonged periods.

Bacillus↗
PubMed1984

Elimination of mycoplasmas from cell cultures and establishment of mycoplasma-free cell lines.

Several antibiotics were examined for their potential to eliminate mycoplasmas from contaminated cell cultures. Acholeplasma laidlawii, Mycoplasma arginini, Mycoplasma hyorhinis and Mycoplasma orale were effectively eliminated from experimentally contaminated mouse fibroblasts and mink epithelial cells by the use of the antibiotics minocycline and tiamutin . An elimination procedure was established, which involved the consecutive treatment of the cultures over a period of 3 weeks, followed by cell cloning. This procedure was effective when applied to cell lines which had been contaminated with unidentified and partially non-cultivable strains of mycoplasmas.

Animals↗
PubMed1984

Inhibition of isolation-induced changes in aminergic transmission by chronic lithium treatment.

Social isolation of mice leads to changes in aminergic transmission systems. After 6 weeks of isolation, an increase of apomorphine-stimulated climbing behavior is seen, reflecting an isolation-induced dopaminergic supersensitivity. After 1-3 weeks of isolation, a decrease of clonidine sedation is detectable, suggesting the development of noradrenergic alpha 2-receptor subsensitivity. The isolation-induced changes of both drug effects are prevented by lithium given over the time of isolation.

Animals↗
PubMed1984

A human monoclonal antibody reactive with human prostate.

A human immunoglobulin M monoclonal antibody secreting hybridoma, termed MHG7, has been isolated and characterized for its reactivity against human prostate cells. Lymphocytes isolated from a regional draining lymph node of a patient with prostate carcinoma were fused with murine P3-NS1-Ag4-1 myeloma cells. Supernatants from the generated mouse-human somatic cell hybrids were first screened for human immunoglobulin production by an enzyme immunoassay. The identified human immunoglobulin-secreting hybridomas were expanded for further analysis and their supernatants screened by enzyme immunoassay against a panel of prostate cell lines. The human immunoglobulin M monoclonal antibody MHG7, in addition to reacting with prostate cell lines, also reacted with prostate carcinoma cells and benign prostatic hypertrophy cells on both frozen and paraffin embedded tissue sections. These data suggest that regional draining lymph nodes of prostate carcinoma patients can be used as a source of human lymphocytes for generating human immunoglobulin-secreting hybridomas reactive with human prostate cells.

Animals↗
PubMed1984

Oncogenic retrovirus from spontaneous murine osteomas. I. Isolation and biological characterization.

Spontaneous osteomas in strain 101 mice, a strain which has a high incidence of benign bone tumours, harbour numerous C-type virus-like particles with pleomorphic characteristics. A cell-free extract from osteomas from two mice induced bone tumours, together with osteopetrosis and lymphomas, in newborn mice of the low incidence NMRI strain after a latent period of 12 to 15 months. When C3H embryo fibroblasts were infected with the osteoma extract, the resulting cell line produced virus (OA MuLVC) with a high titre. OA MuLVC was cloned by serial endpoint dilution and NIH 3T3 cells were productively infected. The resulting virus was named OA MuLVN. OA MuLVC and OA MuLVN also induced bone tumours, osteopetrosis and lymphomas 12 to 15 months after injection into newborn NMRI mice. The isolated virus showed typical characteristics of the murine retrovirus group. Fv-1 host range restriction assays classified the viruses as N-ecotropic and XC-positive. Tryptic p30 peptide analysis and RNase T1 fingerprint analysis of OA MuLVC and OA MuLVN indicated that OA MuLVC contains an Akv-like virus as well as additional components, whereas OA MuLVN is closely related to Akv, but not identical to it. Serological analysis of the envelope proteins using monoclonal antibodies also showed the virus to be similar, but not identical, to Akv virus.

Animals↗
PubMed1984

Trifluoperazine stimulates acetylcholine receptor synthesis in cultured chick myotubes.

Acetylcholine receptor appearance rate in the presence of the phenothiazines trifluoperazine and chlorpromazine was measured in cultured embryonic chick myotubes by means of 125I-alpha-bungarotoxin. At drug concentrations of 5 to 10 X 10(-6) M, receptor appearance rate was significantly enhanced while receptor half-life, cellular protein, net protein synthesis rate, and acetylcholinesterase levels were not similarly affected. The sulfoxide derivatives were without effect. At concentrations of 3 X 10(-5) M and above, both trifluoperazine and chlorpromazine caused myotube contracture and cell loss. Drug combination experiments revealed that receptor stimulation caused by phenothiazines is overcome by low concentrations of veratridine and ryanodine, but not by membrane depolarization with 20 mM KCl. These results lend support to the role of calcium as an intracellular messenger in acetylcholine receptor synthesis regulation, but are difficult to reconcile with the notion that cytosolic calmodulin serves as the calcium receptor in this signaling pathway. Since the trifluoperazine effect resembles that caused by the calcium antagonist D-600, phenothiazines may stimulate receptor synthesis by blocking a voltage-gated calcium channel.

Animals↗
PubMed1984

[Development of tolerance to haloperidol in the rat striatum].

Microiontophoretic application of dopamine effects in the rat's striatum a dose-dependent inhibition of the glutamate-induced pulse activities. Acute systemic applications of haloperidol are able to abolish this dopamine-induced inhibition. After chronic pretreatment with haloperidol, however, acute administration of haloperidol can no longer antagonize the dopamine-induced inhibition of the pulse activity. Hence, it is likely that tolerance to haloperidol , as described in individual behavioral studies can develop also on the cellular level.

Animals↗
PubMed1984

[Significance of ultrasound B image diagnosis as a screening method in pregnancy].

Report about the degree of sonographic routine examinations of pregnant women of the town Karl-Marx-Stadt from January 1981 till December 1982. In spite of limited capacity important diagnoses were possible by only one sonography, i.e. malformations, gemini, placental localization and confirmation of duration of pregnancy. One additional examination is necessary to clear term discrepancies or to state fetal growth retardation. A complete and repeated sonographic care of all pregnant women is possible only by formation of locally good alloted examination centres with optimal utilization of equipment.

Congenital Abnormalities↗
PubMed1984

On some mechanisms of antihypoxic actions of nootropic drugs.

The antihypoxic effect of meclofenoxate hydrochloride seen in the accelerated restitution of posthypoxic dopamine release inhibition originates in the alcoholic component of the drug. Via choline dimethylaminoethanol might run, like orotic acid, into a CDP-choline pool, the generation of which is able to be facilitated by piracetam which in turn increases the phosphorylation potential. All these nootropic drugs will in this way increase the biosynthesis of hypoxically vulnerable phospholipids by different mechanisms. Indeed, a combined treatment with piracetam, meclofenoxate hydrochloride and methylglucamineorotate leads to a more rapid restitution of posthypoxic dopamine release inhibition than the drugs are active when applied separately.

Animals↗
PubMed1984

[Effect of nootropic agents on the lowering of the spasm threshold after a single ethanol application].

We used the effect of ethanol on the convulsion threshold as model of injuriousness to analyse the CNS protective efficacy of nootropics. The CD50 of picrotoxine in mice was significantly diminished in comparision with the controls between 5 and 6 hours after 66 mmol/kg ethanol administered intraperitoneally and between 7 and 8 h after 92.4 mmol/kg. In this moment the administered ethanol was already eliminated; the effect is explained as a reversible consequence of the previous ethanol exposition. The influence of nootropics was examined. Piracetam (0.7 mmol/kg i.p.) as well as methylglucaminorotate (MGO) (0.68 mmol/kg-1 i.p.) suppressed the ethanol effect on the convulsibility, pyritinol (0.82 mmol/kg) was ineffective, and meclophenoxate (1.02 mmol/kg) by itself decreased the convulsions threshold.

Animals↗
PubMed1984

Nootropic drugs reduce immobility in behavioural despair test in mice.

The effect of different nootropic drugs (piracetam, pyritinol, meclofenoxate, methylglucamine orotate, dihydroergotoxine, nicergoline, vinpocetine) on the duration of immobility in the behavioural despair test in mice was studied. All tested nootropics exhibited a dose-related reduction in immobility. In connection with the discussed role of monoaminergic processes in the state of immobility our data support the possible participation of central monoaminergic systems in the mechanisms of action of nootropic drugs.

Animals↗
PubMed1984

Effects of piracetam on brain development in newborn rats exposed to hypoxia.

Perinatal hypoxia is one of the main causes of disturbances of the function of the CNS during childhood. In this study the protective effect of the nootropic drug piracetam (oxo-2-pyrrolidinyl-1)-2-acetamide was tested. One-day-old Wistar rats were exposed together with their mothers to hypoxia up to the 10th day of life (11 h daily, pO2 = 9.86 kPa). On the 11th day a 48% decrease of body weight and a 30% decrease of brain weight was found in the hypoxic animals. The protein/DNA ratio and the AChE activity in the brain cortex were decreased indicating retarded brain development. Piracetam (daily 100 mg/kg, s. c., before hypoxic exposure) did not affect the mortality rate, the somatic development of the animals, or the estimated basic neurochemical markers in the cortex of the brain. At the age of 3 months the fractional efflux rate (FER) of dopamine (DA) evoked chemically or electrically as a characteristic functional feature of chemical synaptic transmission, was examined. It was found that postnatal hypoxia induces a long lasting increase of FER of DA of striatum slices. Animals exposed postnatally to hypoxia and treated with piracetam showed an increased FER of DA (potassium as stimulus) by comparison with those animals also exposed postnatally to hypoxia but left untreated with piracetam.

Animals↗
PubMed1984

[Dopamine sensitivity of brain-induced behavior after repeated administration of dopamine agonists and antagonists].

Comparative investigations were carried out on dopamine sensitivity, as judged by the rotational behavior of rats, of different nuclear areas of the central nervous system following repeated application of dopaminergic agonists, or the dopamine antagonist, haloperidol. In the mesolimbic area and in the Nucleus caudatoputamen, repeated pretreatment with amphetamine alone or in combination with another agonist did not result in a change of sensitivity to dopamine. In contrast, dopamine sensitivity of these target areas increased strongly by repeated pretreatment with haloperidol. Pretreatment with dopaminergic agonists distinctly increased the rotation intensity following dopamine injection into the Globus pallidus and Substantia nigra, whereas haloperidole pretreatment reversed the rotational direction after pallidally injected dopamine, and left unaffected the sensitivity of the Substantia nigra. Thus, repeated treatment with dopaminergic agonists produces different patterns of sensibilization. This does lend support to the hypothesis that behavioral facilitation and dopaminergic supersensitivity are mediated differently.

Amphetamine↗