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Biomedical subjects

A M Thomson

Publications and source records attributed to A M Thomson.

At least 19 recordsLinked to original sources
PubMed2003

Modulation of inhibitory autapses and synapses on rat CA1 interneurones by GABA(A) receptor ligands.

To determine whether autaptic inhibition plays a functional role in the adult hippocampus, the action potential afterhyperpolarisations (spike AHPs) of CA1 interneurones were investigated in 25 basket, three bistratified and eight axo-axonic cells. The spike AHPs showed two minima in all regular-spiking (5), burst-firing (3) and in many fast-spiking cells (17:28). The fast component had a time-to-peak (TTP) of 1.2 +/- 0.5 ms, the slower TTP was very variable (range of 3.3-103 ms). The AHP width at half-amplitude (HW) was 12.5 +/- 5.7 ms in fast-spiking, 29.3 +/- 18 ms in regular-spiking and 99.7 +/- 42 ms in burst-firing cells. Axo-axonic cells never establish autapses, and the fast-spiking variety showed narrow (HW: 3.9 +/- 0.7 ms) spike AHPs with only one AHP minimum (TTP: 0.9 +/- 0.1 ms). When challenged with GABA(A) receptor modulators, spike AHPs in basket and bistratified cells were enhanced by zolpidem (HW by 18.4 +/- 6.2 % in 10:15 cells tested), diazepam (45.2 +/- 0.5 %, 6:7), etomidate (43.9 +/- 36 %, 6:8) and pentobarbitone sodium (41 %, 1:1), and were depressed by bicuculline (-41 +/- 5.7 %, 5:8) and picrotoxin (-54 %, 1:1), and the enhancement produced by zolpidem was reduced by flumazenil (-31 +/- 13 %, relative to the AHP HW during exposure to zolpidem, 3:4). Neuronal excitability was modulated in parallel. The spike AHPs of three axo-axonic cells tested showed no sensitivity to etomidate, pentobarbitone or diazepam. Interneurone-to-interneurone inhibitory postsynaptic potentials (IPSPs), studied with dual intracellular recordings, had time courses resembling those of the spike AHPs. The IPSP HW was 13.4 +/- 2.8 ms in fast-spiking (n = 16) and 28.7 +/- 5.8 ms in regular-spiking/burst-firing cells (n = 6), and the benzodiazepine1-selective modulator zolpidem strongly enhanced these IPSPs (45 +/- 28 %, n = 5). Interneurones with spike AHPs affected by the GABA(A) receptor ligands exhibited 3.8 +/- 1.9 close autaptic appositions. In three basket cells studied at the ultrastructural level 6 of 6, 1 of 2 and 1 of 2 close appositions were confirmed as autapses. Therefore, in the hippocampus autaptic connections contribute to spike AHPs in many interneurones. These autapses influence neuronal firing and responses to GABA(A) receptor ligands.

Action Potentials↗
PubMed2001

Mammalian class Sigma glutathione S-transferases: catalytic properties and tissue-specific expression of human and rat GSH-dependent prostaglandin D2 synthases.

GSH-dependent prostaglandin D(2) synthase (PGDS) enzymes represent the only vertebrate members of class Sigma glutathione S-transferases (GSTs) identified to date. Complementary DNA clones encoding the orthologous human and rat GSH-dependent PGDS (hPGDS and rPGDS, respectively) have been expressed in Escherichia coli, and the recombinant proteins isolated by affinity chromatography. The purified enzymes were both shown to catalyse specifically the isomerization of prostaglandin (PG) H(2) to PGD(2). Each transferase also exhibited GSH-conjugating and GSH-peroxidase activities. The ability of hPGDS to catalyse the conjugation of aryl halides and isothiocyanates with GSH was found to be less than that of the rat enzyme. Whilst there is no difference between the enzymes with respect to their K(m) values for 1-chloro-2,4-dinitrobenzene, marked differences were found to exist with respect to their K(m) for GSH (8 mM versus 0.3 mM for hPGDS and rPGDS, respectively). Using molecular modelling techniques, amino acid substitutions have been identified in the N-terminal domain of these enzymes that lie outside the proposed GSH-binding site, which may explain these catalytic differences. The tissue-specific expression of PGDS also varies significantly between human and rat; amongst the tissues examined, variation in expression between the two species was most apparent in spleen and bone marrow. Differences in catalytic properties and tissue-specific expression of hPGDS and rPGDS appears to reflect distinct physiological roles for class Sigma GST between species. The evolution of divergent functions for the hPGDS and rPGDS is discussed in the context of the orthologous enzyme from chicken.

Amino Acid Sequence↗
PubMed2001

Women's expectations and experiences of childbirth.

OBJECTIVE: to explore, describe and understand the expectations during pregnancy and subsequent experiences of childbirth in primiparae. DESIGN: a qualitative study using a phenomenological approach. Data were collected using unstructured, tape-recorded interviews in late pregnancy and at two weeks post birth. SETTING: the north of England. PARTICIPANTS: eight pregnant women, expecting their first baby. FINDINGS: the women all wanted to take an active part in their labour and the feeling of being 'in control' was the main finding and the 'essence' of this study. This was achieved through support from partners, the positive attitudes of the midwives caring for them during pregnancy and labour, information giving during pregnancy and labour and being able to make and be included in decision making during labour. IMPLICATIONS FOR PRACTICE: if women are to be empowered by making choices for childbirth and feeling 'in control', then it is important for midwives to explore and discover the wishes and feelings of women in their care so that realistic expectations can be promoted and then hopefully fulfilled.

Adult↗
PubMed2001

A comparison of information retention at an initial orthodontic consultation.

The exchange of information is an everyday part of orthodontic treatment. However, the amount of information that is understood and retained, by patients and their parents, is not known. There has been very little research in the area of information retention in dentistry. This has implications with the demands for improved provision of information for patients. This questionnaire-based study, compared the effectiveness of written, verbal, and visual methods of providing orthodontic information. It assessed the retention of this information, by patients and parents, in both the short- and long-term. Twenty-eight patients and their parents, were allocated alternately into one of three groups, receiving written, verbal, or visual information. Short-term retention of knowledge was assessed 10-15 minutes after receiving the information and long-term retention rated by a second questionnaire mailed 8 weeks later. Overall, little difference was found between the three methods. The findings suggested that verbal information should not be given to patients unless supplemented by written and/or visual information, and that parents were more attentive to verbal instructions than their children.

Adolescent↗
PubMed2001

Identification of a novel AU-Rich element in the 3' untranslated region of epidermal growth factor receptor mRNA that is the target for regulated RNA-binding proteins.

The epidermal growth factor receptor (EGF-R) plays an important role in the growth and progression of estrogen receptor-negative human breast cancers. EGF binds with high affinity to the EGF-R and activates a variety of second messenger pathways that affect cellular proliferation. However, the underlying mechanisms involved in the regulation of EGF-R expression in breast cancer cells are yet to be described. Here we show that the EGF-induced upregulation of EGF-R mRNA in two human breast cancer cell lines that overexpress EGF-R (MDA-MB-468 and BT-20) is accompanied by stabilization (>2-fold) of EGF-R mRNA. Transient transfections using a luciferase reporter identified a novel EGF-regulated approximately 260-nucleotide (nt) cis-acting element in the 3' untranslated region (3'-UTR) of EGF-R mRNA. This cis element contains two distinct AU-rich sequences (~75 nt), EGF-R1A with two AUUUA pentamers and EGF-R2A with two AUUUUUA extended pentamers. Each independently regulated the mRNA stability of the heterologous reporter. Analysis of mutants of the EGF-R2A AU-rich sequence demonstrated a role for the 3' extended pentamer in regulating basal turnover. RNA gel shift analysis identified cytoplasmic proteins (~55 to 80 kDa) from breast cancer cells that bound specifically to the EGF-R1A and EGF-R2A cis-acting elements and whose binding activity was rapidly downregulated by EGF and phorbol esters. RNA gel shift analysis of EGF-R2A mutants identified a role for the 3' extended AU pentamer, but not the 5' extended pentamer, in binding proteins. These EGF-R mRNA-binding proteins were present in multiple human breast and prostate cancer cell lines. In summary, these data demonstrate a central role for mRNA stabilization in the control of EGF-R gene expression in breast cancer cells. EGF-R mRNA contains a novel complex AU-rich 260-nt cis-acting destabilizing element in the 3'-UTR that is bound by specific and EGF-regulated trans-acting factors. Furthermore, the 3' extended AU pentamer of EGF-R2A plays a central role in regulating EGF-R mRNA stability and the binding of specific RNA-binding proteins. These findings suggest that regulated RNA-protein interactions involving this novel cis-acting element will be a major determinant of EGF-R mRNA stability.

3' Untranslated Regions↗
PubMed2000

Thyrotropin-releasing hormone and epidermal growth factor regulate iron-regulatory protein binding in pituitary cells via protein kinase C-dependent and -independent signaling pathways.

Intracellular iron homeostasis is regulated, in part, by interactions between iron-regulatory proteins (IRP1 and IRP2) and iron-responsive elements (IREs) in ferritin and transferrin receptor mRNAs. In addition to iron, cellular oxidative stress induced by H(2)O(2), nitric oxide, and hypoxia, and hormonal activation by thyroid hormone and erythropoeitin have each been shown to regulate IRP binding to IREs. Hormonal signals, in particular mediated through protein kinase C (PKC), play a central role in the modulation of IRP/IRE interactions since phorbol esters were shown to activate IRP binding (Eisenstein, R. S., Tuazon, P. T., Schalinske, K. L., Anderson, S. A., and Traugh, J. A. (1993) J. Biol. Chem. 268, 27363-27370). In pituitary thyrotrophs (TtT97), we found that thyrotropin releasing hormone (TRH) and epidermal growth factor (EGF) increased IRP binding to a ferritin IRE, dependent on PKC and mitogen-activated protein kinase (MAPK) activity. In contrast, TRH and EGF decreased IRP binding in pituitary lactotrophs (GH3), despite activation of PKC and MAPK. IRP1 and IRP2 levels remained constant and IRP2 binding was predominant throughout. TRH and EGF markedly decreased IRP binding in MAPK kinase inhibitor-treated GH3 cells, whereas, they increased IRP binding in phosphatase inhibitor-treated GH3 cells. IRE-dependent CAT reporter translational expression closely reflected IRP binding to the ferritin IRE in both GH3 and TtT97 cells. Interestingly, ferritin protein levels were regulated similarly by TRH in both cell lines. These data link two different cell receptor systems to common signaling pathways that regulate IRP binding and ferritin expression. Remarkably, for TRH and EGF, these effects may be PKC-dependent or -independent determined by the cell type.

Animals↗
PubMed2000

Double immunofluorescence, peroxidase labelling and ultrastructural analysis of interneurones following prolonged electrophysiological recordings in vitro.

Inhibitory hippocampal and neocortical interneurones comprise a physiologically, morphologically and neurochemically heterogenous cell population. To identify the roles each class of interneurone plays within a given circuit it is necessary to correlate the electrophysiological properties of individual cells with their neurochemistry and morphology at both the light and electron microscopic level. However, the optimal conditions required for any one part of the protocol typically compromise the results from another. We have developed a protocol which allows the neurochemical content, gross morphology and ultrastructure details of biocytin-filled neurones to be recovered following long, dual intracellular recordings in thick mature slices maintained in an interface recording chamber, helping define sub-populations which could not otherwise be determined. Dual immunofluorescence is performed by incubating the tissue in monoclonal and polyclonal antibodies simultaneously, prior to visualization of biocytin-labelling with precipitation of a peroxidase reaction product. By using a biotinylated anti-avidin D antibody (Vector Laboratories), the intensity of this precipitation can be enhanced further where necessary. It is envisaged that this protocol can not only help determine the neurochemical content of cells recorded in similar in vivo studies, but that the ability to amplify peroxidase labelling in poorly filled cells is also of interest.

Animals↗
PubMed2000

Neurotransmission: Chemical and electrical interneuron coupling.

Recent studies have described the coupling between pairs of neocortical interneurons involving both electrical and chemical transmission; these new results may have important implications for the mechanisms underlying neuronal synchrony and rhythmic activity in the brain.

Animals↗
PubMed2000

Facilitation, augmentation and potentiation at central synapses.

Release probability (P) appears to be a major factor that influences the pattern of transmitter release. At cortical pyramidal axon inputs onto different classes of target cells, very different release patterns are observed, patterns that correlate with release probability. Simplistically, 'low P' synapses display facilitation and augmentation, whereas 'high P' synapses supplied by the same axon exhibit paired-pulse and frequency-dependent depression. Different combinations of factors probably contribute to release probability at different terminals, during development and under different experimental conditions. The recent advances made by molecular biological studies of the release machinery do, however, provide candidate proteins and protein-protein interactions whose differential distributions might be important factors in determining the patterns of transmitter release.

Animals↗
PubMed2000

Molecular frequency filters at central synapses.

During the 1950s to 70s most of the mechanisms that control transmitter release from presynaptic nerve terminals were described at the neuromuscular junction. It was not, however, until the 1990s that the multiplicity of protein-protein interactions that govern this process began to be identified. The sheer numbers of proteins and the complexity of their interactions at first appears excessive, even redundant. However, studies of identified central synapses indicate that this molecular diversity may underlie a important functional diversity. The task of the neuromuscular junction is to relay faithfully the rate and pattern code generated by the motoneurone. To demonstrate phenomena such as facilitation and augmentation that are apparent only when the probability of release is low, experimental manipulation is required. In the cortex, however, low probability synapses displaying facilitation can be recorded in parallel with high probability synapses displaying depression. The mechanisms are largely the same as those displayed by the neuromuscular junction, but some are differentially expressed and controlled. Central synapses demonstrate exquisitely fine tuned information transfer, each of the many types displaying its own repertoire of pattern- and frequency-dependent properties. These appear tuned to match both the discharge pattern in the presynaptic neurone and the integrative requirements of the postsynaptic cell. The molecular identification of these differentially expressed frequency filters is now just coming into sight. This review attempts to correlate these two aspects of synaptic physiology and to identify the components of the release process that are responsible for the diversity of function.

Animals↗
PubMed2000

Does evidenced-based practice medicalize midwifery care? Part 1.

In this paper evidence-based care is defined. The evidence to support the provision of care by midwives is presented, as is the evidence to support home birth for those women at low obstetric risk. In conclusion midwives are challenged to be political and use this evidence to support changes to improve the quality of care provided to women and their families.

Evidence-Based Medicine↗
PubMed2000

Does evidenced-based practice medicalise midwifery care? Part 2.

In this paper evidence-based care is defined. The evidence to support the provision of care by midwives is presented, as is the evidence to support home birth for those women at low obstetric risk. In conclusion midwives are challenged to be political and use this evidence to support changes to improve the quality of care provided to women and their families.

Delivery, Obstetric↗
PubMed2000

Differential sensitivity to Zolpidem of IPSPs activated by morphologically identified CA1 interneurons in slices of rat hippocampus.

Hippocampal pyramidal cells express several alpha-subunits, which determine the affinity of GABAA (gamma-aminobutyric acid) receptors for benzodiazepine site ligands. This study asked whether inhibitory postsynaptic potentials (IPSPs) elicited by specific interneuronal subclasses were differentially sensitive to the alpha1-preferring agonist Zolpidem, i.e. whether different receptors mediate different inhibitory connections. Paired intracellular recordings in which the presynaptic cell was an interneuron and the postsynaptic cell a CA1 pyramid were performed in slices of adult rat hippocampus. Resultant IPSPs were challenged with Zolpidem, cells filled with biocytin and identified morphologically. IPSPs elicited by fast spiking (FS) basket cells (n = 9) were enhanced more than IPSPs elicited by regular spiking (RS) basket cells (n = 10). At FS basket cell synapses the efficacy of Zolpidem was equivalent to that of Diazepam, while RS basket cell IPSPs are enhanced 50% less by Zolpidem than by Diazepam. Thus, while alpha1 subunits may dominate at synapses supplied by FS basket cells, RS basket cell synapses also involve alpha2/3 subunits. Two bistratified cell IPSPs tested with Zolpidem did not increase in amplitude, despite powerful enhancements of bistratified cell IPSPs by Diazepam, consistent with previous indications that these synapses utilize alpha5-containing receptors. Enhancements of basket cell IPSPs by Zolpidem and Diazepam were bi- or triphasic with steep amplitude increases separated by plateaux, occurring 10-15, 25-30 and 45-55 min after adding the drug to the bath. The entire enhancement was, however, blocked by the antagonist Flumazenil (n = 7). Flumazenil, either alone (n = 3), or after Zolpidem, reduced IPSP amplitude to approximately 90% of control, suggesting that alpha4-containing receptors were not involved.

Animals↗
PubMed2000

Hormonal regulation of mRNA stability and RNA-protein interactions in the pituitary.

Regulating gene expression from DNA to protein is a complex multistage process with multiple control mechanisms. Transcriptional regulation has been considered the major control point of protein production in eukaryotic cells; however, there is growing evidence of pivotal posttranscriptional regulation for many genes. This has prompted extensive investigations to elucidate the mechanisms controlling RNA processing, mRNA nuclear export and localization, mRNA stability and turnover, in addition to translational rates and posttranslational events. The regulation of mRNA stability has emerged as a critical control step in determining the cellular mRNA level, with individual mRNAs displaying a wide range of stability that has been linked to discrete sequence elements and specific RNA-protein interactions. This review will focus on current knowledge of the determinants of mRNA stability and RNA-protein interactions in the pituitary. This field is rapidly expanding with the identification of regulated cis-acting stability-modifying elements within many mRNAs, and the cloning and characterization of trans-acting proteins that specifically bind to their cognate cis elements. We will present evidence for regulation of multiple pituitary genes at the level of mRNA stability and some examples of the emerging data characterizing RNA-protein interactions.

Animals↗
PubMed1999

Release-independent depression at pyramidal inputs onto specific cell targets: dual recordings in slices of rat cortex.

1. Paired intracellular recordings were performed in slices of adult rat neocortex and hippocampus to examine presynaptic depression. A novel form of depression that occurs even in the absence of transmitter release during conditioning activity was observed at a subset of synaptic connections. 2. In each pair studied, a pyramidal neurone was presynaptic and inputs onto a range of morphologically identified postsynaptic target cells were analysed; high probability connections exhibiting the more traditional forms of release-dependent depression, as well as low probability connections exhibiting facilitation, were tested (n = 35). 3. Connections were tested with presynaptic spike pairs and trains of spikes with a range of interspike intervals. Sweeps in which the first action potential elicited no detectable response (apparent failures of transmission) and sweeps in which the first action potential elicited large EPSPs were selected. Second EPSPs that followed apparent failures were then compared with second EPSPs that followed large first EPSPs. 4. Release-independent depression was apparent when second EPSPs at brief interspike intervals (<10-15 ms) were on average smaller than second EPSPs at longer interspike intervals, even following apparent failures and when the second EPSP amplitude at these short intervals was independent of the amplitude of the first EPSP. 5. Release-independent depression appeared selectively expressed. Depressing inputs onto some interneurones, such as CA1 basket-like and bistratified cells, and facilitating inputs onto others, such as some fast spiking neocortical interneurones, exhibited this phenomenon. In contrast, depressing inputs onto 10/10 neocortical pyramids and facilitating inputs onto 7/7 oriens-lacunosum moleculare and 5/5 burst firing, sparsely spiny neocortical interneurones did not.

Action Potentials↗
PubMed1999

Dual intracellular recordings and computational models of slow inhibitory postsynaptic potentials in rat neocortical and hippocampal slices.

Dual intracellular recordings in slices of adult rat neocortex and hippocampus investigated slow, putative GABA(B) receptor-mediated inhibitory postsynaptic potentials. In most pairs tested in which the interneuron elicited a fast inhibitory postsynaptic potential in the pyramid, this GABA(A) receptor mediated inhibitory postsynaptic potential was entirely blocked by bicuculline or picrotoxin (3:3 in neocortex, 6:8 in CA1, all CA1 basket cells), even when high-frequency presynaptic spike trains were elicited. However, in three of 85 neocortical paired recordings involving an interneuron, although no discernible response was elicited by single presynaptic interneuronal spikes, a long latency (> or =20 ms) inhibitory postsynaptic potential was elicited by a train of > or =3 spikes at frequencies > or =50-100 Hz. This slow inhibitory postsynaptic potential was insensitive to bicuculline (one pair tested). In neocortex, slow inhibitory postsynaptic potential duration reached a maximum of 200 ms even with prolonged presynaptic spike trains. In contrast, summing fast, GABA(A) inhibitory postsynaptic potentials, elicited by spike trains, lasted as long as the train. Between four and 10 presynaptic spikes, mean peak slow inhibitory postsynaptic potential amplitude increased sharply to 0.38, 2.6 and 2.9 mV, respectively, in the three neocortical pairs (membrane potential -60 to -65 mV). Thereafter increases in spike number had little additional effect on amplitude. In two of eight pairs in CA1, one involving a presynaptic basket cell and the other a putative bistratified interneuron, the fast inhibitory postsynaptic potential was blocked by bicuculline revealing a slow inhibitory postsynaptic potential that was greatly reduced by 100 microM CGP 35348 (basket cell pair). The sensitivity of this slow inhibitory postsynaptic potential to spike number was similar to that of neocortical 'pure' slow inhibitory postsynaptic potentials, but was of longer duration, its plateau phase outlasting 200 ms spike trains and its maximum duration exceeding 400 ms. Computational models of GABA release, diffusion and uptake suggested that extracellular accumulation of GABA cannot alone account for the non-linear relationship between spike number and inhibitory postsynaptic potential amplitude. However, cooperativity in the kinetics of GABA(B) transduction mechanisms provided non-linear relations similar to experimental data. Different kinetic models were considered for how G-proteins activate K+ channels, including allosteric models. For all models, the best fit to experimental data was obtained with four G-protein binding sites on the K+ channels, consistent with a tetrameric structure for the K+ channels associated with GABA(B) receptors. Thus some inhibitory connections in neocortex and hippocampus appear mediated solely by fast GABA(A) receptors, while others appear mediated solely by slow, non-ionotropic, possibly GABA(B) receptors. In addition, some inhibitory postsynaptic potentials arising in proximal portions of CA1 pyramidal cells are mediated by both GABA(A) and GABA(B) receptors. Our data indicate that the GABA released by a single interneuron can saturate the GABA(B) receptor mechanism(s) accessible to it and that 'spillover' to extrasynaptic sites need not necessarily be proposed to explain these slow inhibitory postsynaptic potential properties.

Algorithms↗
PubMed1999

Iron-regulatory proteins, iron-responsive elements and ferritin mRNA translation.

Iron plays a central role in the metabolism of all cells. This is evident by its major contribution to many diverse functions, such as DNA replication, bacterial pathogenicity, photosynthesis, oxidative stress control and cell proliferation. In mammalian systems, control of intracellular iron homeostasis is largely due to posttranscriptional regulation of binding by iron-regulatory RNA-binding proteins (IRPs) to iron-responsive elements (IREs) within ferritin and transferrin receptor (TfR) mRNAs. the TfR transports iron into cells and the iron is subsequently stored within ferritin. IRP binding is under tight control so that it responds to changes in intracellular iron requirements in a coordinate manner by differentially regulating ferritin mRNA translational efficiency and TfR mRNA stability. Several different stimuli, as well as intracellular iron levels and oxidative stress, are capable of regulating these RNA-protein interactions. In this mini-review, we shall concentrate on the mechanisms underlying modulation of the interaction of IRPs and the ferritin IRE and its role in regulating ferritin gene expression.

Animals↗