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Biomedical subjects

A E Johnson

Publications and source records attributed to A E Johnson.

At least 91 records · Page 5Linked to original sources
PubMed1995

Interval cancers in the National Health Service Breast Screening Programme.

The National Health Service (NHS) Breast Screening Programme defines objectives with acceptable and, where possible, achievable standards. This paper examines the problem of interval cancers. Slopes due to shrinkage of primary breast cancers in response to primary systemic therapy are used as surrogates for growth slopes. From the distribution of these slopes the proportion of tumours which might reach particular sizes in any time interval may be estimated. For specific differences in size between screen and clinical detection levels the number of interval cancers which could appear in 1, 2 and 3 years after screening is estimated. The justification for these predictions is evaluated. The literature in relation to growth is reviewed; we add three growth slopes from our own measurements. The range of volume doubling times and volume halving times is the same whereas the mean value derived from the literature is about 90 days in contrast to only 26 days for inferred growth rates. Because of the difficulties inherent in the measurement of growth, it is concluded that the literature defines the left half of a distribution; the right hand side is completed by shrinkage data. The observed rates for interval cancers from different sources vary widely; there is an underlying assumption that interval cancers are an index of failure. These calculations suggest that there is an irreducible minimum of interval cancers, which will depend upon the screening interval and the size at which tumours are detected. The interval cancers will contain more poorly differentiated tumours. The anticipated achievable standards appear to be over optimistic.

Anthropometry↗
PubMed1995

Identification of the elongation factor Tu binding site on 70S E. coli ribosomes by chemical crosslinking.

Elongation factor Tu (EF-Tu), in the presence of Phe-tRNA, GMPPCP, and Poly (U), binds to 70S ribosomes at the recognition (R) site. In order to identify the ribosomal proteins adjacent to the EF-Tu occupying the R site, EF-Tu:Phe-tRNA:GMPPCP:ribosome complexes were crosslinked by modification with 2-iminothiolane and mild oxidation to form disulfide bridges between neighbouring proteins whose endogenous or introduced SH groups were appropriately located. The binding of Phe-tRNA to the ribosome was shown to be largely dependent on the presence of Poly(U). The total protein from the complexes was extracted and separated by two-dimensional gel electrophoresis by non-equilibrium pH gradient electrophoresis (NEpHGE) in the first dimension, followed by gradient SDS gel electrophoresis in the second dimension. Comparison of control samples crosslinked without Poly(U) to those crosslinked with Poly(U) present showed a single crosslinked complex in the region of the gel near EF-Tu. No cross-links in the vicinity of EF-Tu were visible in the absence of Poly(U). The crosslinked proteins in this region were recovered by electroelution, radiolabeled and their identity was confirmed by 2D gel electrophoresis and immunoblot analyses. Two major 50S ribosomal proteins, L7/L12 and L10 were found to be covalently linked to EF-Tu. The isolated crosslinked complex did not contain any protein from the 30S subunit. These results demonstrate that L7/L12 and L10 are the major, if not only, ribosomal protein cross-links to EF-Tu in the R site. In contrast to previous crosslinking results obtained by others, our results define a unique location for the EF-Tu binding site, one compatible with functional data and near that of the EF-G binding site on the ribosome.

Binding Sites↗
PubMed1994

Characterization of dopamine receptor binding sites in the subthalamic nucleus.

Experiments were undertaken to determine the distribution and binding profile of dopamine (DA) receptors within a key extra-striatal region of the rat basal ganglia, the subthalamic nucleus (STh). Analysis of [125I]NCQ-298 autoradiograms showed that binding sites of the D2-receptor family are abundant in the STh. Competition studies indicated that these sites were specifically of the D2 subtype. However, contrary to previously published data, [125I]SCH-23982 autoradiograms failed to reveal D1 receptor binding in the STh. These data suggest that DA acting at D2 receptors may directly modulate STh neural activity and furthermore that the antagonism of STh D2 receptor binding by neuroleptics may be involved in the expression of extrapyramidal motor disturbances.

Animals↗
PubMed1994

Secretory proteins move through the endoplasmic reticulum membrane via an aqueous, gated pore.

The environment of secretory proteins undergoing translocation across the ER membrane was determined by incorporating fluorescent probes into nascent chains during translation. Dyes were positioned at various locations across the entire bilayer and inside the ribosome, and in each case the probes were in an aqueous milieu, as shown both by their fluorescence lifetimes and by collisional quenching of their fluorescence by iodide ions introduced into the ER lumen. The nascent chain therefore occupies an aqueous pore that spans the entire membrane. Since the pore is sealed off from the cytoplasm, cotranslational translocation is effected topographically. This pore is not open to the lumen after targeting is completed; it opens only after the nascent chain length reaches about 70 residues.

Animals↗
PubMed1994

Chronic treatment with a classical neuroleptic alters excitatory amino acid and GABAergic neurotransmission in specific regions of the rat brain.

The purpose of the following experiments was to describe some of the neurochemical changes that occur in the basal ganglia of rats exposed chronically to a classical neuroleptic, fluphenazine, and to relate these changes to extrapyramidal motor dysfunction. For these studies a combination of behavioural, receptor autoradiographic and in situ hybridization methods were employed. Preliminary pharmacological studies on GABA receptors showed that incubation in Tris-acetate rather than Tris-citrate buffer increased the number of binding sites labelled by [3H]muscimol by over 120% without affecting binding affinity or selectivity. The results of experiments with fluphenazine showed that treatment for six months increased the frequency of vacuous chewing movements compared to controls. In the striatum, changes in GABA transmission were observed in fluphenazine-treated rats with increases in glutamate decarboxylase mRNA levels in the caudate nucleus, dorsal shell and core of the accumbens and decreases in [3H]muscimol binding in the caudate and dorsal shell regions. These data suggest that fluphenazine treatment increased GABA transmission in specific subregions of the caudate and accumbens nuclei. In addition, glutamate decarboxylase mRNA levels were elevated in the entopeduncular nucleus of fluphenazine-treated animals. Autoradiographic analysis of excitatory amino acid binding showed that fluphenazine exposure decreased [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid binding in entopeduncular nucleus and in the ventrolateral thalamic nucleus and decreased [3H]dizocilpine maleate binding in the medial geniculate nucleus. These experiments show that in addition to altering GABA transmission, chronic neuroleptic exposure alters excitatory amino acid transmission in specific regions of the basal ganglia-thalamocortical motor system. The neuroleptic dependent increases in glutamate decarboxylase mRNA levels in the entopeduncular nucleus may reflect changes in neurotransmission in the indirect pathway connecting the major input and output nuclei of the basal ganglia. Changes in some of these brain regions may be related to the occurrence of extrapyramidal motor disturbances.

Animals↗
PubMed1994

Glutamate inhibits ingestive behaviour.

Male rats treated with reserpine were motionless and ingested only a few of ten consecutive intraoral injections of a 1 M solution of sucrose. While injection of apomorphine, a dopamine agonist, stimulated locomotion and stereotyped sniffing in reserpinized rats, it did not reactivate ingestive responses. The non-competitive N-methyl-D-aspartate receptor antagonist MK801, however, stimulated locomotion as well as ingestion suggesting involvement of glutamate in the suppressive effect of resperpine on ingestive responses. A series of experiments was therefore undertaken to investigate the possible physiological role of glutamate in feeding. For this purpose, we used Grill's intraoral intake test, in which the rat is infused intraorally with a sucrose solution and the amount ingested measured. In untreated rats, MK801 dose-dependently facilitated ingestion of the sucrose solution and antagonized inhibition of ingestion by cholecystokinin octapeptide. Administration of cholecystokinin octapeptide or ingestion of sucrose increased the concentration of glutamate in the nucleus of the solitary tract, a brain stem relay transmitting sensory information from the gastrointestinal tract to the forebrain. MK801 was found to bind specifically to this brain area and block the elevation of glutamate and dopamine levels which occurred after treatment with cholecystokinin octapeptide in this neural site. Together these data suggest that dopamine and glutamate may interact within the nucleus of the solitary tract in controlling ingestive behaviour.

Animals↗
PubMed1994

Cross-sectional analysis of the differences between patients with systemic lupus erythematosus in England, Brazil and Sweden.

This study is a cross-sectional analysis of the differences between SLE outpatients seen in Rheumatology departments at University centres in England, Brazil and Sweden, using a standard protocol. The demographic characteristics, extent and activity of disease of 209 patients with SLE were studied; 112 patients were seen in England, 33 in Brazil and 64 in Sweden. The median age of disease onset of Brazilian and English patients was 25 years and of Swedish patients 31.5 years. Disease activity was measured by the BILAG index. In most systems Brazilian patients experienced more activity than English patients and English patients more activity than Swedish patients. Non-Caucasians experienced more active disease than Caucasians. No sex or occupational differences were observed in disease activity. English patients were the most likely to have experienced photosensitivity, oral ulcers and haematological disorders, Brazilian patients renal disorders and Swedish patients discoid rashes. Brazilian patients were the most likely to be prescribed only one drug for treatment of SLE and to be taking steroids and the highest dose of steroids, in contrast to the European patients who were often prescribed steroids and an antimalarial agent or azathioprine. The results of this cross-sectional assessment of disease activity using a standardized instrument indicate that there are real differences in the extent and degree of activity of SLE in different national groups. This reflects a combination of genetic, environmental and social influences on disease expression and has implications for treatment and monitoring of SLE patients.

Adolescent↗
PubMed1993

Serotonergic lesions decrease mu- and delta-opiate receptor binding in discrete areas of the hypothalamus and in the midbrain central gray.

Serotonergic nerve terminals in the brain were lesioned by intraventricular infusion of the selective neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) and levels of mu- and delta-opiate binding were measured in brain areas implicated in reproductive behavior and gonadotropin secretion. The lesion decreased mu-receptor binding in the preoptic area (mPOA) and the midbrain central gray, while delta-receptor binding was decreased in the mPOA and the dorsomedial nucleus of the hypothalamus. Hypothalamic serotonergic lesions also attenuated morphine inhibition of female sexual behavior. These results indicate the existence of serotonergic-opiate interactions in select regions of the brain and suggest that these interactions may be important in the regulation of lordosis behavior.

Animals↗
PubMed1993

Localization and characterization of vasopressin binding sites in the rat brain using an iodinated linear AVP antagonist.

The binding characteristics and central distribution of 125I-Linear AVP antagonist, a new ligand for vasopressin binding sites, are described in the following studies. Saturation studies performed on rat brain septal membranes demonstrated that 125I-Linear AVP antagonist binds to a single class of sites with high affinity (55 pM) and limited capacity (88 fmol/mg protein). In autoradiographic studies, 125I-Linear AVP antagonist labeled brain areas known to contain vasopressin receptors without binding to neurophysins. 125I-Linear AVP antagonist also labeled sites in cortex, hypothalamus, ventral tegmental area and substantia nigra. In competition studies, 125I-Linear AVP antagonist binding was most readily blocked by AVP and a selective V1a agonist. Oxytocin and a selective V2 ligand were effective only in micromolar concentrations. A selective oxytocin agonist was virtually ineffective in blocking 125I-Linear AVP antagonist binding. In regions that contain a high density of oxytocin binding sites, however, oxytocin-displaceable binding was observed. In agreement with studies on peripheral tissues, the binding profile generated from these studies indicates that 125I-Linear AVP antagonist binds to vasopressin receptors of the V1a subtype. These results suggest that 125I-Linear AVP antagonist is a valuable ligand for the study of central AVP receptors.

Amino Acid Sequence↗
PubMed1993

The signal sequence moves through a ribosomal tunnel into a noncytoplasmic aqueous environment at the ER membrane early in translocation.

The signal sequence is in an aqueous milieu at an early stage in the translocation of a nascent secretory protein across the endoplasmic reticulum membrane. This was determined using fluorescent probes incorporated into the signal sequence of fully assembled ribosome-nascent chain-membrane complexes: the fluorescence lifetimes revealed that the probes were in an aqueous environment rather than buried in the nonpolar core of the membrane. Since these membrane-bound probes were not susceptible to collisional quenching by iodide ions, the space containing the signal sequence is sealed off from the cytoplasm by a tight ribosome-membrane junction. The nascent chain inside the ribosome is also not exposed to the cytoplasm and apparently passes through an aqueous tunnel in the ribosome.

Animals↗
PubMed1993

The chondroitin sulfate moiety of thrombomodulin binds a second molecule of thrombin.

The role of the chondroitin sulfate moiety of thrombomodulin (TM) in the binding of thrombin to TM has been examined using fluorescent derivatives of thrombin. An anilinonaphthalene-6-sulfonic acid (ANS) dye was attached covalently to the active site histidine of thrombin via a D-Phe-Pro-Arg (FPR) linkage to form ANS-FPR-thrombin. When ANS-FPR-thrombin was titrated with TM lacking the chondroitin sulfate moiety (csf-TM), a monotonic and saturable increase in ANS emission intensity was observed that was consistent with the formation of a high affinity 1:1 thrombin-csf-TM complex. In contrast, titration of ANS-FPR-thrombin with intact TM containing the chondroitin sulfate resulted in a biphasic change in ANS-FPR-thrombin emission intensity that was consistent with each molecule of TM binding at least two molecules of ANS-FPR-thrombin with different affinities. This suggested that the second thrombin binds to TM via the chondroitin sulfate moiety. A direct interaction between thrombin and chondroitin sulfate was demonstrated by showing that chondroitin sulfate, cleaved and purified from TM, caused a saturable increase in ANS emission intensity upon addition to an ANS-FPR-thrombin sample. This spectral change was reversed by adding an excess of unmodified thrombin. The minimum Kd for the ANS-FPR-thrombin-chondroitin sulfate complex was approximately 20 nM, consistent with chondroitin sulfate being the lower affinity binding site on TM for thrombin. The titration of chondroitin sulfate into ANS-FPR-thrombin samples in the absence and presence of a TM fragment containing the fifth and sixth growth factor-like domains (GF5-6) showed that GF5-6 did not block chondroitin sulfate binding and that a GF5-6-thrombin-chondroitin sulfate ternary complex was formed. Thus, the chondroitin sulfate binds to thrombin somewhere other than anion-binding exosite I, and in doing so, alters the structure and/or environment of the active site more than 15A from the active site serine without detectably changing the conformation near Ser-195. Since excess TM and excess csf-TM increased the ANS emission intensity of ANS-FPR-thrombin to different extents (approximately 15 and approximately 80%, respectively), the chondroitin sulfate also influences the environment of the active site probe even when thrombin is bound to the higher affinity site on TM (GF5-6).

Antithrombin III↗