Search PubMed⌕ Search

Biomedical subjects

A M Thomson

Publications and source records attributed to A M Thomson.

At least 55 records · Page 3Linked to original sources
PubMed1997

Community midwives' and general practitioners' perspectives, of antenatal care in the community.

OBJECTIVE: to ascertain who was providing antenatal care in the community in a defined geographical area in the north of England, and whether the care could achieve the government objectives presented in Changing Childbirth (DoH 1993). DESIGN: a questionnaire was used to obtain demographic information and semi-structured interviews were held with care providers in order to assess the perspective of those providing care. PARTICIPANTS: a purposive sample of nine community midwives and six general practitioners (GPs). FINDINGS: the midwife was the professional undertaking most of the antenatal care although in most instances there was a GP available on site if required. GPs saw the midwife as the main provider of care with themselves as 'back up'. Conflict over responsibility for care was an issue in some instances. Whilst changes in antenatal care provision had been, or were about to be made, only one midwife expressed a clear positive feeling towards midwife-led care. Giving women the opportunity for choice provoked an overwhelming feeling of helplessness for midwives. Midwives and GPs believed their education adequately prepared them to provide antenatal care in the community, however, GPs did not attend regular updating sessions. IMPLICATIONS FOR PRACTICE: whilst it was recognised that midwives are taking increasing responsibility for antenatal care, GPs still believe that overall responsibility lies with them; therefore, there is a need to clarify roles. The majority of midwives expressed reservations about midwife-led care.

Adult↗
PubMed1997

Synaptic interactions in neocortical local circuits: dual intracellular recordings in vitro.

Properties of local synaptic connections in neocortex, studied with dual intracellular recordings in vitro and correlated with cell and synaptic morphology are summarized. The different durations and sensitivities to somatic membrane potential of pyramid-pyramid excitatory postsynaptic potentials (EPSPs) apparently reflect the positions of the synapses on the postsynaptic dendrites. Their time-, frequency- and voltage-dependent properties enable supra-linear summation of several low-frequency inputs arising in the same dendritic region, even if only loosely coincident, but they depress during repetitive firing in any one input. Pyramidal input to classical fast spiking and low threshold spiking interneurones are strikingly different. Here low presynaptic firing rates results in many transmission failures. EPSPs are brief and inputs must be near coincident for summation. However, these synapses display pronounced. frequency-dependent, incrementing facilitation at higher presynaptic frequencies. Once initiated by a brief high-frequency burst, this facilitation is maintained at lower frequencies. GABAA receptor-mediated inhibitory postsynaptic potentials (IPSPs) arising proximally are of very different durations depending on the type of interneurone activated and can prevent and subsequently synchronize firing in their many postsynaptic partners with very different delays (eg. 10-100 ms). Low threshold spiking interneurones, in contrast, generate brief IPSPs only in more distal dendritic regions and have little effect on somatic excitability acting to shunt input distally.

Animals↗
PubMed1997

Stereotactic biopsy of nonpolar tumors in the dominant hemisphere: a prospective study of effects on language functions.

A prospective study of patients undergoing computerized tomography (CT)-guided stereotactic biopsy of nonpolar tumors in the dominant hemisphere was undertaken to determine if stereotactic biopsy caused a deterioration of language functions. Language was assessed using the Western Aphasia Battery (WAB) and the Boston Naming Test (BNT) before and after a biopsy sample was obtained. Of 16 patients studied, five (31%) were dysphasic preoperatively. After the biopsy the Aphasia Quotient (AQ), derived from the WAB, had significantly deteriorated in four (80%) of these patients, whereas in the fifth it remained relatively unchanged. One of these patients with an extensive infiltrating hemispheric oligoastrocytoma subsequently recovered normal language function after radiotherapy. In 10 of the 11 patients who had normal language function preoperatively there were no deleterious changes after biopsy in either the WAB subtest or BNT scores. In the other patient whose WAB score was normal preoperatively, there was a significant deterioration in postoperative AQ. This patient, who declined steroid therapy before and after biopsy, had a glioblastoma multiforme in Wernicke's area. A postoperative CT scan revealed no changes from what was shown on preoperative scan. This clinical study shows that CT-guided stereotactic biopsy of nonpolar tumors in the dominant hemisphere using the Brown-Roberts-Wells system and the Sedan-Nashold biopsy cannula carries a 9% risk (95% confidence intervals 0-26%) of impairing language functions if the patient is not dysphasic preoperatively. If the patient is dysphasic preoperatively, there is a very high risk of aggravating the dysphasia with stereotactic biopsy.

Adult↗
PubMed1997

The utility of the Right Hemisphere Language Battery in patients with brain tumours.

The Right Hemisphere Language Battery (RHLB) (Bryan, 1989) was devised to assess the presence of language disorders in patients with damage to the right cerebral hemisphere and to permit an evaluation of the efficacy of therapeutic techniques. To evaluate the utility and sensitivity of the RHLB in patients with solitary right hemispheric brain tumours 20 patients were assessed before and after neurosurgery. Twenty control subjects with no signs or symptoms of brain disease who were undergoing lumbar spinal surgery were also assessed. On six of the seven RHLB subtests there was no significant difference between the scores obtained preoperatively by patients with right hemispheric brain tumours and the control subjects. There was also no significant change in the scores of the patients with tumours before and after resection of the lesion. The RHLB is therefore not recommended for either evaluating communication deficits or for measuring the efficacy of therapeutic techniques in patients with right hemisphere brain tumours. This study does, however, show that there are statistically significant differences between the control and brain tumour groups on the discourse analysis subtest preoperatively. The implications of the study are discussed together with possible reasons for the findings.

Adult↗
PubMed1996

Single axon IPSPs elicited in pyramidal cells by three classes of interneurones in slices of rat neocortex.

1. Using dual intracellular recordings in slices of adult rat neocortex, twenty-four IPSPs activated by single presynaptic interneurones were studied in simultaneously recorded pyramidal cells. Fast spiking interneurones inhibited one in four or five of their close pyramidal neighbours. No reciprocal connections were observed. After recordings neurones were filled with biocytin. 2. Interneurones that elicited IPSPs were classified as classical fast spiking (n = 10), as non-classical fast spiking (n = 3, including one burst-firing interneurone), as unclassified, or slow interneurones (n = 8), or as regular spiking interneurones (n = 3), i.e. interneurones whose electrophysiological characteristics were indistinguishable from those of pyramidal cells. 3. All of the seven classical fast spiking cells anatomically fully recovered had aspiny, beaded dendrites. Their partially myelinated axons ramified extensively, varying widely in shape and extent, but randomly selected labelled axon terminals typically innervated somata and large calibre dendrites on electron microscopic examination. One 'autapse' was demonstrated. One presumptive regular spiking interneurone axon made four somatic and five dendritic connections with unlabelled targets. 4. Full anatomical reconstructions of labelled classical fast spiking interneurones and their postsynaptic pyramids (n = 5) demonstrated one to five boutons per connection. The two recorded IPSPs that were fully reconstructed morphologically (3 and 5 terminals) were, however, amongst the smallest recorded (< 0.4 mV). Some connections may therefore involve larger numbers of contacts. 5. Single axon IPSPs were between 0.2 and 3.5 mV in average amplitude at -55 to -60 mV. Extrapolated reversal potentials were between -70 and -82 mV. IPSP time course correlated with the type of presynaptic interneurone, but not with IPSP latency, amplitude, reversal potential, or sensitivity to current injected at the soma. 6. Classical fast spiking interneurones elicited the fastest IPSPs (width at half-amplitude 14.72 +/- 3.83 ms, n = 10) and unclassified, or slow interneurones the slowest (56.29 +/- 23.44 ms, n = 8). Regular spiking interneurone IPSPs had intermediate half-widths (27.3 +/- 3.68 ms, n = 3). 7. Increasingly brief presynaptic interspike intervals increased the peak amplitude of, but not the area under, the summed IPSP. Only at interspike intervals between 10 and 20 ms did IPSP integrals exhibit paired pulse facilitation. Paired pulse depression was apparent at < 10 and 20-60 ms. During longer spike trains, summing IPSPs decayed to a plateau potential that was relatively independent of firing rate (100-250 Hz). Thereafter, the voltage response could increase again. 8. Summed IPSPs elicited by two to fifteen presynaptic spike trains decayed as, or more rapidly than, single-spike IPSPs. Summed IPSPs elicited by > 20 spikes (> 150 Hz), however, resulted in an additional, more slowly decaying component (latency > 50 ms, duration > 200 ms). The possible involvement of GABAB receptors in this component is discussed. 9. It is suggested that three broad classes of interneurones may activate GABAA receptors on relatively proximal portions of neocortical pyramidal neurones. The different time courses of the IPSPs elicited by the three classes may reflect different types of postsynaptic receptor rather than dendritic location. An additional class, burst firing, spiny interneurones appear to activate GABAA receptors on more distal sites.

Animals↗
PubMed1996

CA1 pyramid-pyramid connections in rat hippocampus in vitro: dual intracellular recordings with biocytin filling.

In adult rat hippocampus, simultaneous intracellular recordings from 989 pairs of CA1 pyramidal cells revealed nine monosynaptic, excitatory connections. Six of these pairs were sufficiently stable for electrophysiological analysis. Mean excitatory postsynaptic potential amplitude recorded at a postsynaptic membrane potential between -67 and -70 mV was 0.7 +/- 0.5 mV (0.17-1.5 mV), mean 10-90% rise time was 2.7 +/- 0.9 ms (1.5-3.8 ms) and mean width at half-amplitude was 16.8 +/- 4.1 ms (11.6-25 ms). Cells were labelled with biocytin and identified histologically. For one pair that was fully reconstructed morphologically, excitatory postsynaptic potential average amplitude was 1.5 mV, 10-90% rise time 2.8 ms and width at half-amplitude 11.6 ms (at -67 mV). In this pair, correlated light and electron microscopy revealed that the presynaptic axon formed two synaptic contacts with third-order basal dendrites of the postsynaptic pyramid, one with a dendritic spine, the other with a dendritic shaft. In the four pairs tested, postsynaptic depolarization increased excitatory postsynaptic potential amplitude and duration. In two, D-2-amino-5-phosphonovalerate (50 microM) reduced the amplitude and duration of the excitatory postsynaptic potential. The remainder of the excitatory postsynaptic potential now increased with postsynaptic hyperpolarization and was abolished by 20 microM 6-cyano-7-nitroquinoxaline-2,3-dione (n = 1). Paired-pulse depression was evident in the four excitatory postsynaptic potentials tested. This depression decreased with increasing inter-spike interval. These results provide the first combined electrophysiological and morphological illustration of synaptic contacts between pyramidal neurons in the hippocampus and confirm that connections between CA1 pyramidal neurons are mediated by both N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate/kainate receptors.

2-Amino-5-phosphonovalerate↗
PubMed1996

Women's satisfaction with antenatal care in a changing maternity service.

OBJECTIVES: 1) to provide a descriptive analysis of women's views of the antenatal care provided in the study centre; 2) to identify which aspects of antenatal care were important to women; 3) to assess whether or not women 'booked' for delivery at the study centre would welcome the formal introduction of a midwifery-led service and 4) to audit sources of satisfaction and dissatisfaction identified in the survey. DESIGN: descriptive survey using a self-administered questionnaire, and a self-administered audit questionnaire using a modified Measure of Satisfaction. SETTING: the antenatal clinic of one teaching hospital in the north of England between July 1993 and August 1993. The audit was conducted between December 1994 and February 1995. PARTICIPANTS: 110 women attending four 'follow up' antenatal clinics participated in the survey and 151 women participated in the audit. FINDINGS: many women felt they were already having midwifery-led care and that it was important to them to see a doctor during pregnancy. Generally the women were satisfied with antenatal care. Factors which caused dissatisfaction were, lack of continuity of care, quality of advice, waiting time and these were the focus of the audit. IMPLICATIONS FOR PRACTICE: local needs should be assessed before implementing changes in service. Elements of good practice should be identified to ensure that they are not compromised in a changing service. Further evaluation of the changing maternity service is needed to monitor satisfaction and dissatisfaction.

Adolescent↗
PubMed1995

Single axon fast inhibitory postsynaptic potentials elicited by a sparsely spiny interneuron in rat neocortex.

Many of the different morphological types of interneurons in mammalian neocortex are presumed to be inhibitory, but to date, conclusive functional data have been lacking. Using paired intracellular recordings in slices of adult rat somatosensory cortex, we present a sparsely spiny, burst firing interneuron that elicits in a simultaneously recorded pyramid a fast inhibitory postsynaptic potential, reversing at -78 mV. Neither inhibitory postsynaptic potential time course, nor paired pulse depression (inter-spike interval 15-120 ms), was affected by addition of the GABAB antagonist/partial agonist 2-OH-Saclofen (250 microM), but increasing extracellular [Ca2+] enhanced inhibitory postsynaptic potential amplitude at low firing rates and increased paired pulse depression at higher rates. Light microscopic examination of the biocytin-filled neurons revealed the presynaptic cell to be a sparsely spiny interneuron and the postsynaptic to be a small pyramidal neuron, both in layer II. Ultrastructural examination of 16 terminals of the presynaptic interneuron revealed that they formed symmetric contacts with unlabelled neurons, four with neuronal somata, 10 with dendritic shafts and two with spine shafts. This, therefore, is the first report of the properties of a single axon inhibitory postsynaptic potential in neocortex resulting from action potentials in an electro-physiologically and morphologically identified interneuron. We propose that at least some of the sparsely spiny, burst firing interneurons inhibit pyramidal neurons via GABAA receptors.

Animals↗
PubMed1995

Properties of single axon excitatory postsynaptic potentials elicited in spiny interneurons by action potentials in pyramidal neurons in slices of rat neocortex.

In slices of adult rat somatomotor cortex, paired intracellular recordings determined the properties of a novel class of excitatory connection, that of presynaptic pyramidal axon collaterals onto burst firing, spiny inhibitory interneurons. Single axon excitatory postsynaptic potentials were brief in time course and displayed conventional voltage relations, increasing in amplitude with membrane hyperpolarization with no change in time course. Excitatory postsynaptic potential amplitude distributions were not skewed. Paired pulse facilitation was profound at interspike intervals < 50 ms, but not altered by raising extracellular [Ca2+] from 2.5 to 5 mM, despite an apparent increase in release probability. Raising presynaptic firing frequency did however produce an increase in excitatory postsynaptic potentials elicited by first spikes that was associated with a decline in excitatory postsynaptic potentials elicited by second and third spikes in brief trains of presynaptic spikes. That this pattern of synaptic activity may result from low probabilities of transmitter release is discussed. It is proposed that while raising Ca2+ and increasing presynaptic firing both increase release probability, repetitive presynaptic firing raises probability more effectively than does raising extracellular [Ca2+]. However, concomitant exhaustion of readily releasable transmitter at higher firing rates may partially obscure this effect. It is concluded that the major differences in the firing rate- and firing pattern-dependent properties of pyramid-pyramid and pyramid-interneuron connections are due to the typically lower release probability at synapses onto interneurons. The accompanying paper describes the morphology of these connections.

Action Potentials↗
PubMed1995

Innervation of burst firing spiny interneurons by pyramidal cells in deep layers of rat somatomotor cortex: paired intracellular recordings with biocytin filling.

Intracellular recordings were obtained from a class of neuron defined electrophysiologically as burst firing interneurons in layers V and VI in slices of adult rat somatomotor cortex. Four of these cells were recovered histologically. These four cells had resting membrane potentials between -68 and -80 mV, a mean input resistance of 77 +/- 16.2 M omega (measured from the voltage deflection produced by a 100 ms, 0.5 nA hyperpolarizing pulse delivered from a membrane potential of -80 mV) and responded to injections of depolarizing current from membrane potentials negative of -70 to -75 mV with an initial burst of action potentials followed by a complex afterhyperpolarization. In response to injection of larger (0.5-1.5 nA) hyperpolarizing current pulses from membrane potentials between -60 and -70 mV, 15 of 20 burst firing cells (three of four recovered histologically) that were tested displayed delayed inward rectification, and in all 20 cells of this type, responses to large negative current pulses were followed by a rebound depolarization that could initiate action potentials. Filling of four of these cells with biocytin and subsequent histological processing revealed that they were bitufted with sparsely to medium spiny dendrites and extensive local axon ramifications. These neurons are similar to low threshold spiking cells [Kawaguchi (1993) J. Neurophysiol. 69, 416-431]. Ultrastructural examination of the axons of three cells revealed that of 53 labelled terminals studied, the majority formed synaptic contacts with dendritic shafts. Filling neurons with biocytin during paired intracellular recordings resulted in three well labelled interneurons, each of which was postsynaptic to a simultaneously recorded pyramidal neuron. In these pairs both cells were identified, but the presynaptic axon was poorly labelled in one. In one of the two pairs in which the pre- and postsynaptic neurons were fully recovered, light microscopic assessment indicated that the axon of the presynaptic pyramid formed 12 close appositions with dendrites of the postsynaptic interneuron. Six of these appositions were examined at the electron microscopic level and were identified as possible synaptic contacts. In the other pair three of six close appositions observed at the light level were verified as possible synaptic connections at the ultrastructural level. These correlated electrophysiological and anatomical studies provide the first evidence for connections from pyramid to burst firing interneurons in the neocortex and indicate that these connections can be mediated by multiple synaptic contacts. The accompanying paper describes the functional properties of these connections.

Animals↗
PubMed1995

Maternal behaviour during spontaneous and directed pushing in the second stage of labour.

It has become custom and practice within the midwifery and obstetric professions in the English-speaking western world for women to be required to follow very specific instructions on how to push in the second stage of labour. There is very little literature on the behaviour of women using spontaneous pushing in the second stage of labour. In a pilot study of a randomized controlled trial comparing spontaneous (n = 15) with directed (n = 17) pushing, the behaviour of the women was observed and recorded. The findings from the observational part of the study are reported in this paper. When pushing spontaneously women do not instinctively take a deep breath, they do not start expulsive effort with the commencement of the contraction, and they use both open and closed glottis pushing. In order to assist women in the second stage of labour, those caring for them should be aware of what is normal behaviour when women are using spontaneous expulsive effort.

Adult↗
PubMed1995

A gene-targeting suicide vector for Streptococcus bovis.

A gene-targeting suicide vector for Streptococcus bovis has been constructed using the Escherichia coli/Streptococcus shuttle plasmid, pMU1328, and a region derived from the broad host-range, Gram-positive transposon, Tn916. This suicide plasmid replicates autonomously in E. coli, but not in Strep. bovis or Strep. bovis Tn916. Under positive selection, the plasmid was shown to integrate into Strep. bovis Tn916 chromosomal DNA at a frequency of 3 x 10(-8) cell-1 and was stably maintained for at least 100 generations in the absence of selection. This is the first report of a recombination system in ruminal bacteria. The ability to target genes, knock out specific functions or introduce novel genes into these micro-organisms will allow ruminal species to be manipulated and may eventually lead to improved animal production.

Bacterial Proteins↗
PubMed1994

Relationships between morphology and physiology of pyramid-pyramid single axon connections in rat neocortex in vitro.

1. Double intracellular recordings were made from 1163 pairs of pyramidal neurones in layer V-VI of the rat somatomotor cortex in vitro using sharp electrodes filled with biocytin. Monosynaptically connected pairs of cells were identified when an action potential in one could elicit a constant latency excitatory postsynaptic potential (EPSP) in the other and the cells were filled with biocytin. Labelled cells were subsequently identified histologically with avidin-horseradish peroxidase. 2. Thirty-four pairs of cells were found to be monosynaptically connected. Fifteen of these pairs were sufficiently stable for electrophysiological recordings and three of these were recovered sufficiently to permit full morphological reconstruction. 3. The EPSP recorded between the first pair of pyramids varied in amplitude between 0 and 3 mV (mean 1.33 +/- 1.06 mV) and fluctuated considerably (coefficient of variation, 0.796). This was largely due to a high incidence of apparent failures of transmission. On reconstruction two boutons from the presynaptic pyramid axon were in close apposition to the proximal portions of basal dendrites of the postsynaptic cell. 4. In the second pair of pyramids the EPSP had a mean amplitude of 1.06 mV, and displayed a 10-90% rise time of 2.8 ms and a width at half-amplitude of 23 ms. This EPSP did not alter significantly with changes in membrane potential at the soma. The presynaptic axon closely apposed the distal apical dendrite of the postsynaptic cell in eight places. 5. In the third pair of pyramids, the EPSPs, recorded at a relatively depolarized membrane potential, were long lasting and could elicit slow dendritic spikes with long and variable latencies. These slow spikes suggested that the postsynaptic recording site was dendritic and on reconstruction a possible location was identified on the apical dendrite. A total of five presynaptic boutons closely apposed three separate, proximal branches of the postsynaptic apical dendrite. 6. These results provide the first illustration of a morphological basis for variations in functional properties of pyramid-pyramid connections in the neocortex.

Animals↗
PubMed1994

Temporal and spatial properties of local circuits in neocortex.

A large body of anatomical data has detailed many complexities of neocortical circuitry, and physiological studies have indicated some roles for this circuitry in the complex functions of the cortex. Until recently, however, we have little precise information about the spatio-temporal properties of synaptic connections between individual neocortical neurones. Studies of synaptic responses elicited in one neocortical neurone by action potentials in another, and parallel morphological studies that have identified these neurones and the synaptic connections between them, have now described these parameters for certain types of local circuit connection in the neocortex. Some of these studies confirmed previous observations and inferences, but others provided major surprises. Evidence indicates that the class of both the presynaptic and postsynaptic neurone together determine a wide range of synaptic properties, such as the type of postsynaptic receptors involved and the temporal pattern of transmitter release, so that each type of synapse displays unique properties. A role for retrograde diffusable messages in determining the temporal properties of these circuits is postulated.

Animals↗
PubMed1994

A re-evaluation of the effect of pethidine on the length of labour.

In a pilot study of a randomized controlled trial comparing pushing techniques in the second stage of labour, a surprise finding was that there was a positive correlation between the amount of pethidine used for analgesia in the first stage of labour and an increasing length of both the first (r = 0.5687, P = 0.0001, CI = 0.33 to 0.74) and second stages (r = 0.3204, P = 0.037, CI = 0.03 to 0.56). In order to investigate this further a review of the literature on the effect of pethidine on the length of labour was undertaken. The literature searched was the English-language literature, and MEDLINE and Index Medicus were used to identify pertinent papers. Studies selected were randomized controlled trials of pethidine given for pain relief in labour compared with placebo. As only five studies were identified other pertinent studies using the drug were scrutinized. The findings of this review are that, due to methodological flaws and studies with small sample sizes, the effect of pethidine on the length of labour in women has not been adequately assessed. However, there is a strong suggestion in the literature that the use of this drug is associated with a lengthening of labour and this association is dose-related. Studies in animals support this view. Those caring for women in labour should be aware of this side-effect of the analgesic most frequently given in labour in North America and the United Kingdom. As pethidine frequently does not provide adequate analgesia and has other side-effects, the search for an alternative analgesia should continue.

Animals↗