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Biomedical subjects

D Parker

Publications and source records attributed to D Parker.

At least 127 records · Page 7Linked to original sources
PubMed1996

Low-cost high-resolution fast spin-echo MR of acoustic schwannoma: an alternative to enhanced conventional spin-echo MR?

PURPOSE: To determine whether unenhanced high-resolution T2-weighted fast spin-echo MR imaging provides an acceptable and less expensive alternative to contrast-enhanced conventional T1-weighted spin-echo MR techniques in the diagnosis of acoustic schwannoma. METHODS: We reviewed in a blinded fashion the records of 25 patients with pathologically documented acoustic schwannoma and of 25 control subjects, all of whom had undergone both enhanced conventional spin-echo MR imaging and unenhanced fast spin-echo MR imaging of the cerebellopontine angle/internal auditory canal region. The patients were imaged with the use of a quadrature head receiver coil for the conventional spin-echo sequences and dual 3-inch phased-array receiver coils for the fast spin-echo sequences. RESULTS: The size of the acoustic schwannomas ranged from 2 to 40 mm in maximum dimension. The mean maximum diameter was 12 mm, and 12 neoplasms were less than 10 mm in diameter. Acoustic schwannoma was correctly diagnosed on 98% of the fast spin-echo images and on 100% of the enhanced conventional spin-echo images. Statistical analysis of the data using the kappa coefficient demonstrated agreement beyond chance between these two imaging techniques for the diagnosis of acoustic schwannoma. CONCLUSIONS: There is no statistically significant difference in the sensitivity and specificity of unenhanced high-resolution fast spin-echo imaging and enhance T1-weighted conventional spin-echo imaging in the detection of acoustic schwannoma. We believe that the unenhanced high-resolution fast spin-echo technique provides a cost-effective method for the diagnosis of acoustic schwannoma.

Adult↗
PubMed1995

Long-lasting potentiation of a direct central connection between identified motor neurons in the locust.

The plasticity of the direct central connection between the fast extensor and the posterior fast flexor tibiae motor neurons in the locust (Schistocerca gregaria) metathoracic ganglion was studied. An action potential in the fast extensor results in a monosynaptic excitatory postsynaptic potential (EPSP) in the flexor motor neuron. Antidromic stimulation of the fast extensor at 100 Hz for 3.5 s resulted in a long-lasting potentiation of the EPSP amplitude. The potentiation was not dependent on feedback caused by movement of the tibia, and was associated with an increase in the input resistance of the flexor motor neuron. The potentiation was heterosynaptic, and was not affected by bath application of the N-methyl-D-aspartate receptor antagonist 2-amino-5-phosphonovaleric acid. The potentiation was voltage dependent, as hyperpolarizing the flexor motor neuron during the stimulation blocked the development of the potentiation whereas depolarizing the flexor in the absence of presynaptic activity caused potentiation of subsequent fast extensor-evoked EPSPs. The depolarization-induced potentiation was calcium dependent. Antidromic stimulation of the fast extensor at 100 Hz for 3.5 s also caused modulation of the presynaptic action potential. The spike duration was increased and the amplitude of the afterhyperpolarization reduced. These effects were dependent on movement of the tibia. Bath application of the 5-hydroxytryptamine (5-HT) receptor antagonist ketanserin blocked the changes in the presynaptic spike. The modulation was probably due to the release of 5-HT from proprioceptive afferents that monitor movement of the tibia about the femur. The modulation of the presynaptic action potential increases transmitter release onto the flexor motor neurons, and this acts in synergy with the postsynaptic modulation to potentiate the connection.

Action Potentials↗
PubMed1995

Behavioural characteristics and involvement in different types of traffic accident.

Recent research has shown risk of road traffic accident involvement to be associated with the tendency to commit driving violations, fast driving, and a lack of thoroughness in decision making. It has also been shown that three broad types of accident can be used to categorise more than 70% of drivers' brief written descriptions of their accidents. These categories are "shunts" (rear-end collisions), right-of-way violations, and loss-of-control accidents. Furthermore, for each accident type the role of the reporting driver may be defined as active (striking) or passive (struck) depending on the position of his/her vehicle. This paper reports two studies examining the extent to which measures of tendency to commit violations (measured by the Driver Behaviour Questionnaire (DBQ)), frequency of fast driving (measured by the Driving Style Questionnaire (DSQ)) and thoroughness in decision making (measured by the Decision Making Questionnaire (DMQ)) are associated specifically with involvement in each of the main accident types. The results showed that a high DBQ-violation score was associated with accidents in general, both active and passive, and specifically with active loss-of-control accidents and passive right-of-way accidents. High DSQ-speed and low DMQ-thoroughness were associated with active but not passive accidents, high DSQ-speed with active right-of-way violations, and low DMQ-thoroughness was specifically associated with active shunts and active right-of-way violations. The implications of these results are discussed.

Accidents, Traffic↗
PubMed1995

Multiple binding sites for bacterial superantigens on soluble class II MHC molecules.

We used surface plasmon resonance to study the binding of a set of soluble mouse I-E class II major histocompatibility molecules, each occupied by a different single peptide, to the staphylococcal enterotoxin superantigens, SEA and SEB. The rates of association and dissociation to SEA varied greatly depending on the I-E-bound peptide. By contrast, binding to SEB yielded fast association and dissociation rates, which were relatively peptide independent. The results also indicated nonoverlapping binding sites for SEB and SEA on class II and raised the possibility of enhanced SAg presentation to T cells by cross-linking of cell surface class II.

Amino Acid Sequence↗
PubMed1995

Academic rigour in the lived experience of researchers using phenomenological methods in nursing.

In its quest for knowledge, nursing has relied heavily on the positivist approach to scientific enquiry. Phenomenological enquiry identifies the essence of a phenomenon and accurately describes it through the lived experience. Through consistency in the use of the methodology, and avoidance of method slurring, academic rigour can be maintained. It is advocated that the phenomenological method is congruent with nursing ideals where humanistic knowledge is valued. Nurses and phenomenologists share skills in observation, interviewing, interaction and interpersonal relationships in the appreciation of the individual's perception of an experience. Through the development of professional practice, nurses thus gain the tools to assist them in phenomenological research. It is suggested that, given appropriate attention to rigour, phenomenological methodology could become the basic instrument in the reform of nursing research as it moves from the positivist to the humanist paradigm.

Humans↗
PubMed1995

Pharmacokinetics of ifosfamide and its enantiomers following a single 1 h intravenous infusion of the racemate in patients with small cell lung carcinoma.

Ifosfamide is a chiral pro-drug which is administered clinically in its racemic form. Serum concentrations of rac-ifosfamide and its enantiomers were measured in 12 patients with lung carcinoma following a mean (+/- s.d.) intravenous dose of 4.2 (0.83) g infused over 1 h. The mean (+/- s.d.) volumes of distribution (VSS) of rac, (R)- and (S)-ifosfamide were 0.61 (0.17), 0.60 (0.16) and 0.61 (0.19) l kg-1, respectively. The mean (+/- s.d.) half-lives and clearances were 6.57 (1.69), 7.12 (1.92) and 5.98 (1.52) h and 0.065 (0.013), 0.060 (0.013) and 0.072 (0.014) l h-1 kg-1 for rac, (R)- and (S)-ifosfamide, respectively. The half-life of (S)-ifosfamide was significantly (P < 0.001) shorter than that of (R)-ifosfamide and it had a significantly higher clearance (P < 0.001). There was no significant difference in the volumes of distribution of the enantiomers. The clinical significance of the faster elimination of (S)-ifosfamide is not known.

Aged↗
PubMed1995

Cholinergic synaptic transmission between proprioceptive afferents and a hind leg motor neuron in the locust.

1. The physiology and pharmacology of the connections made by stress-sensitive campaniform sensilla on the proximal dorsal tibia of a locust hind leg with a fast extensor tibiae motor neuron (FETi) have been examined. 2. Mechanical stimulation of a campaniform sensillum on the anterior surface of the tibia elicited bursts of spikes in its afferent and a depolarization in FETi. Each afferent spike was followed at short and constant latency by an excitatory postsynaptic potential (EPSP) in FETi, even at high-frequency stimulation. Electrical stimulation of the extensor tibiae muscle with the tibia fixed elicited an antidromic spike in FETi followed by a compound potential which resulted from the activation of the campaniform sensillum afferent. The connections between the campaniform sensillum and FETi was monosynaptic and chemically mediated. 3. Ionophoresis of ACh into the neuropil depolarized FETi, as did the application of the cholinesterase inhibitor physostigmine. Bath application of the cholinergic agonists, nicotine and muscarine, also depolarized FETi, with nicotine causing a reduction in input resistance, while muscarine caused no detectable change in input resistance. Muscarine and the muscarinic agonist oxotremorine also caused rhythmic depolarizations and bursts of spikes in FETi. These effects were seen in low calcium/high magnesium saline to block synaptic transmission and are therefore due to direct effects on FETi. FETi therefore appears to have both nicotinic and muscarinic receptors. 4. The compound potential in FETi, caused by activation of the campaniform sensillum, was reduced by bath application of nicotinic cholinergic antagonists. However, the muscarinic antagonist scopolamine increased the amplitude of the compound potential.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Serotonergic modulation of locust motor neurons.

1. The effects of the putative endogenous neuromodulator serotonin (5-HT) on the fast extensor and flexor tibiae motor neurons in the locust (Schistocerca gregaria) metathoracic ganglion, were analyzed. 2. 5-HT consistently increased the duration of the fast extensor spike and usually reduced the afterhyperpolarization, although this effect was less consistent. The spike broadening in the fast extensor was associated with an increase in the amplitude of the excitatory postsynaptic potential (EPSP) evoked monosynaptically in the flexor motor neurons by fast extensor stimulation. 5-HT also increased the membrane resistance of the fast extensor and flexor tibiae motor neurons. 3. The effects of 5-HT were mimicked by bath application of the 5-HT uptake inhibitor imipramine, and blocked by the 5-HT receptor antagonist ketanserin. The effects were also mimicked by dibutryl cyclic AMP, a membrane permeant analogue of cyclic AMP, and by the phosphodiesterase inhibitor 3-isobutyl-1-methyl-xanthine, but not by dibutryl cyclic GMP. The 5-HT-dependent modulation was blocked by the protein kinase A inhibitor H8. In addition, injection of cyclic AMP into the fast extensor or a flexor motor neuron could mimic the effects of 5-HT on these neurons. 4. 5-HT probably broadened the FETi action potential by modulating potassium conductances responsible for spike repolarization. 5. These results show that 5-HT modulates both the fast extensor and flexor tibiae motor neurons, resulting in potentiation of synaptic transmission between these neurons. In addition, the increase in flexor membrane resistance will potentiate other inputs onto these cells, which will affect the output of the motor neurons during locomotion.

1-Methyl-3-isobutylxanthine↗
PubMed1995

Depression of synaptic connections between identified motor neurons in the locust.

1. The fast extensor tibiae motor neuron makes direct excitatory central connections with the posterior group of flexor tibiae motor neurons in the locust metathoracic ganglion. The flexor group has a slow, a fast, and an intermediate motor neuron. The motor neurons are involved in the motor program for kicking and jumping, the defensive and escape behaviors of the locust. An antidromic action potential in fast extensor tibiae motor neuron (FETi) results in a monosynaptic, glutamatergic excitatory postsynaptic potential (EPSP) in each of the flexor motor neurons. 2. A train of 10 antidromic spikes in FETi at frequencies of 1-20 Hz resulted in depression of the amplitude of the EPSP in each of the flexor motor neurons. The depression was not significantly different in the different flexor motor neurons. The depression was greater with higher frequency stimulation and was reduced in low calcium saline. 3. After stimulation at 20 Hz, the EPSP amplitude was depressed by approximately 80%. This did not change when the number of stimuli was increased to 20, when stimulation was done in high calcium saline, or when the frequency of stimulation was increased to 50 or 100 Hz. The recovery from depression was greater after 20-Hz stimulation than at lower frequencies, although the recovery was reduced when the number of stimuli was increased, and also in high calcium saline. 4. In normal saline the depression of the EPSP amplitude was associated with a reduction of the presynaptic spike amplitude at frequencies of > or = 5 Hz. In tetraethylammonium (TEA) saline the width of a TEA-broadened spike was also reduced. The reduction in spike amplitude and spike width correlated with the depression of the EPSP. 5. Certain of these results are consistent with a depletion model of synaptic depression, whereas others are not consistent with this model. The depression may be partly due to an initial depletion of transmitter stores, and partly to modulation of the presynaptic action potential that reduces calcium entry, and therefore transmitter release. The significance of the depression on the motor program for kicking and jumping is discussed.

Animals↗
PubMed1995

Potentiometric, enantioselective sensors for alkyl and aryl ammonium ions of pharmaceutical significance, based on lipophilic cyclodextrins.

Lipophilic alpha, beta and gamma cyclodextrins (CDs) have been systematically analysed in order to establish their selective binding to onium ions. They have been identified as excellent ionophores for a range of ions of vital importance in clinical, pharmaceutical and forensic analysis. From the results obtained we found the following. A peroctylated cyclodextrin provides a size-selective cavity for the binding and detection of onium ions. Potentiometric alpha, beta and gamma cyclodextrin-based electrodes selectively sense NH4+, NMe4+ and NEt4+ ions respectively. These experiments were performed in order to enable us to understand the nature of analyte recognition by the lipophilic cyclodextrins. Peroctylated alpha CD is a suitable ionophore for dopamine hydrochloride, -log[C] = 5.4, -log K = 2.0 (in serum level of Na+, K+, Ca2+) whereas peroctylated and 2,6 didodecyl beta CD sense acetylcholine chloride, -log[C] = 5.0, -log K = 4.2 (in serum level of Na+, K+, Ca2+) and creatinine hydrochloride, -log K = 2.7 (in serum level of Na+, K+, Ca2+), respectively. The 2,6 didodecyl beta CD responds to more bulky aryl ammonium ions such as the anaesthetics procaine, prilocaine and lignocaine hydrochlorides, -log K = 4.2 (in serum level of Na+, K+, Ca2+). Partially octylated alpha CD has been identified as an enantioselective sensor for ephedrine hydrochloride, -log K = 4.5 (in serum level of Na+, K+, Ca2+), -log Kpot+/- = 2.6, and related compounds such as amphetamine hydrochloride. The 2,6 didodecyl beta CD is enantioselective for propranalol hydrochloride, -log K = 4.2 (in serum level of Na+, K+, Ca2+), -log Kpot+/- = 2.7. Complexation has also been studied by electrospray mass spectrometry (ESMS).

Acetylcholine↗
PubMed1995

Plasma concentrations of fentanyl with subcutaneous infusion in palliative care patients.

1. Plasma concentrations of fentanyl were measured by g.c. in 20 patients (median age: 75 years and range: 54-86 years; eight females) in palliative care receiving the drug by continuous s.c. infusion (median rate: 1200 micrograms day-1 and range: 100-5000 micrograms day-1). 2. The infusion rate was significantly related to the duration of therapy (Spearman rho = 0.56, P < 0.05). The total steady-state plasma concentrations of fentanyl ranged between 0.1 and 9 ng ml-1, with a median of 1 ng ml-1. The unbound fraction of fentanyl in the plasma ranged from 17.8 to 44.4%, with a median value of 33.6%. Infusion rates and both total and unbound plasma concentrations of fentanyl were correlated (Spearman rho = 0.92, P < 0.05 in each case). Even with standardization for dosage, there was an eightfold variation in total plasma concentrations and 3.5-fold variation in unbound plasma concentrations of fentanyl. 3. There is considerable inter-patient variability in the pharmacokinetics of fentanyl with s.c. infusion in the palliative care setting, which necessitates careful titration of dosage according to individual clinical response.

Aged↗
PubMed1994

Don't eat it.

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Animals↗
PubMed1994

Oxidation of 2-methoxynaphthalene by toluene, naphthalene and biphenyl dioxygenases:structure and absolute stereochemistry of metabolites.

2-Methoxynaphthalene was subjected to biooxidation by whole cells of six organisms: Pseudomonas putida F39/D containing toluene dioxygenase, Escherichia coli JM109(pDTG601), containing recombinant toluene dioxygenase from Pp F39/D, Pseudomonas sp. NCIB 9816/11, containing naphthalene dioxygenase. E. coli JM109(pDTG141), containing recombinant naphthalene dioxygenase from NCIB 98161/11, E. coli C534(ProR/Sac) containing recombinant naphthalene dioxygenase from Pp G7, and Beijerinckia sp. B8/36, containing biphenyl dioxygenase. The major product of oxidation by the naphthalene and biphenyl dioxygenases has been isolated and identified as (1R,2S)-dihydroxy-7-methoxy-1,2-dihydronaphthalene, 2c. A minor product, (1R,2S)-dihydroxy-6-methoxy-1,2-dihydronaphthalene, 3c, has also been detected. Oxidation by the toluene dioxygenase-containing organisms led to the isolation of 3c as the major product. Minor products detected in these reactions were 2c, and a third compound, (1S,2S)-dihydroxy-3-methoxy-1,2-dihydronaphthalene, 4c. Structural studies and dehydration of the diols to a mixture of naphthols are described. The absolute stereochemistry of these new diols has been established by correlation with known compounds. The organisms' potential in the production of new metabolites as useful chiral synthons by biooxidation of 2-substituted naphthalenes is indicated.

Bacteria↗
PubMed1994

The contribution of immunization to economic development.

Immunization received intensive support during the 1980s in light of its demonstrable value, relatively low cost, and established infrastructure. The goal of universal childhood immunization was achieved in 1990 on the basis of a strategy of expanding coverage, technological improvements, and social mobilization. Although its impact is difficult to quantify precisely, the Expanded Programme on Immunization (EPI) has had significant positive effects on national and household economies as a result of the reduction of morbidity and mortality. It also has contributed to the development of the managerial and operational capacity of health systems and to the generation of widespread social and political support for health actions through a variety of different mechanisms. Priorities for the next decade include attention to policies to ensure the maintenance of high levels of coverage, continued technical development, and further strengthening of EPI planning and management.

Child Health Services↗