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Biomedical subjects

M R Turner

Publications and source records attributed to M R Turner.

At least 19 recordsLinked to original sources
PubMed2005

[11C]-WAY100635 PET demonstrates marked 5-HT1A receptor changes in sporadic ALS.

The pathogenesis of amyotrophic lateral sclerosis (ALS) remains obscure, but it is now clear that neuronal loss is not confined to the motor cortex, even in cases without dementia. A reliable method of assessing cortical involvement in vivo remains elusive. WAY100635 binds selectively to the 5-hydroxytryptamine (5-HT1A) receptor, which is expressed on pyramidal neurones present throughout the cortex. [11C]-WAY100635 PET is, therefore, a potential marker of cerebral neuronal loss or dysfunction in ALS. Twenty-one ALS subjects and 19 healthy volunteers underwent [11C]-WAY100635 PET of the brain. A cortical template consisting of multiple volumes of interest (VOI) was applied to each individual's [11C]-WAY100635 binding potential (BP) image to determine the regional reduction in binding in ALS patients compared to controls. There was a marked reduction (21%) in both the global cortical and raphe BP of [11C]-WAY100635 in ALS patients (P < 0.001), with regional variations in the VOI analysis that ranged from 16% to 29% decrease compared with the control group, and trends to greater reductions in those with bulbar involvement. To clarify the significance of the global cortical reductions, statistical parametric mapping was used as an alternative method to identify the cortical regions with the most significant decreases in [11C]-WAY100635 binding. SPM analysis revealed the greatest differences between ALS cases and controls in frontotemporal regions, cingulate and lateral precentral gyri. The reductions in cortical [11C]-WAY100635 binding were not related to depression, riluzole or other drug use. We postulate that the reduction of 5-HT1A binding represents loss of, or damage to, neurones bearing these receptors although we cannot exclude the possibility that these reductions reflect alterations in receptor expression or function. Further investigation into the role of the 5-HT1A receptor and the potential of [11C]-WAY100635 PET as a marker of cortical dysfunction in ALS is warranted.

Adult↗
PubMed2004

Evidence of widespread cerebral microglial activation in amyotrophic lateral sclerosis: an [11C](R)-PK11195 positron emission tomography study.

Microglial activation is implicated in the pathogenesis of ALS and can be detected in animal models of the disease that demonstrate increased survival when treated with anti-inflammatory drugs. PK11195 is a ligand for the "peripheral benzodiazepine binding site" expressed by activated microglia. Ten ALS patients and 14 healthy controls underwent [(11)C](R)-PK11195 PET of the brain. Volumes of interest were defined to obtain [(11)C](R)-PK11195 regional binding potential values for motor and "extra-motor" regions. Significantly increased binding was found in motor cortex (P = 0.003), pons (P = 0.004), dorsolateral prefrontal cortex (P = 0.010) and thalamus (P = 0.005) in the ALS patients, with significant correlation between binding in the motor cortex and the burden of upper motor neuron signs clinically (r = 0.73, P = 0.009). These findings indicate that cerebral microglial activation can be detected in vivo during the evolution of ALS, and support the previous observations that cerebral pathology is widespread. They also argue for the development of therapeutic strategies aimed at inflammatory pathways.

Adult↗
PubMed2003

Prolonged survival in motor neuron disease: a descriptive study of the King's database 1990-2002.

Motor neuron disease is a clinically heterogeneous disease with significant differences in survival. The authors have characterised a subset of long term survivors seen in a tertiary clinic over a 12 year period in terms of clinical variables and demographics, comparing them with short term survivors and the remaining population. Thirty of 769 patients survived more than 10 years, corresponding to 4% of the total population. Significantly younger onset of disease symptoms and a predominance of pure upper motor neuron signs at presentation characterised the long term survivors, but factors traditionally regarded as being associated with poor prognosis were also well represented. For a few people with motor neuron disease there remains the hope, whatever the initial presentation, that their subsequent survival will be longer than expected.

Adult↗
PubMed2002

Prognostic modelling of therapeutic interventions in amyotrophic lateral sclerosis.

BACKGROUND: Amyotrophic lateral sclerosis (ALS) is a disease with a widely varying prognosis. The majority of patients survive about 3 years, but a significant number survive for 10 years or more, leading to problems in clinical trial design. OBJECTIVE: To demonstrate that simple clinical variables can be used to construct a robust predictive model for survival, and to assess the effect of a known treatment within this model. METHODS: We carried out a retrospective multivariate modelling of a database of 841 patients with ALS seen over a 10-year period in a specialist motor neuron disorders clinic. The use of riluzole was tested as a prognostic factor within the model. RESULTS: A prognostic score generated from one cohort of patients predicted survival for a second cohort of patients (r(2) = 0.78). Prognostic variables included site of onset, age of onset, time from symptom onset to diagnosis, and El Escorial category at presentation. Riluzole therapy was an independently significant prognostic factor (relative risk of death 0.48, P < 0.0001, model chi(2) 297, P < 0.0001). CONCLUSIONS: Clinical databases can be used to generate multivariate prognostic models in ALS. Such models could be used to predict survival, to improve criteria for matching of patients in future clinical trials, and to test the impact of interventions.

Age of Onset↗
PubMed2001

Clinical trials in ALS: an overview.

Clinical trials in amyotrophic lateral sclerosis (ALS) have been conducted for over half a century now and have incorporated a wide variety of drugs. Most of these trials have had negative results and a cure remains elusive. The explosion in our understanding of molecular biology and parallel developments in clinical epidemiology have opened up a vast number of novel therapeutic strategies. However, advances in statistical analysis, computing, and global communications have also put greater pressure on scientific investigators to improve the design and implementation of clinical trials so that they permit rigorous testing of hypotheses within a solid ethical framework. This article documents the first published trial for all drugs tried clinically in the treatment of ALS, focusing in more detail on the large, multicenter trials of recent years, namely those involving riluzole, ciliary neurotrophic factor, insulin-like growth factor-I, brain-derived neurotrophic factor, and SR57746A. The problems in the design of trials in ALS are discussed, including the selection of end points and surrogate markers of disease progression, and the major parameters in ALS assessment are reviewed.

Amyotrophic Lateral Sclerosis↗
PubMed2001

Role of chloride in constriction of descending vasa recta by angiotensin II.

We investigated the dependence of ANG II (10(-8) M)-induced constriction of outer medullary descending vasa recta (OMDVR) on membrane potential (Psim) and chloride ion. ANG II depolarized OMDVR, as measured by fully loading them with the voltage-sensitive dye bis[1,3-dibutylbarbituric acid-(5)] trimethineoxonol [DiBAC(4)(3)] or selectively loading their pericytes. ANG II was also observed to depolarize pericytes from a resting value of -55.6 +/- 2.6 to -26.2 +/- 5.4 mV when measured with gramicidin D-perforated patches. When measured with DiBAC(4)(3) in unstimulated vessels, neither changing extracellular Cl(-) concentration ([Cl(-)]) nor exposure to the chloride channel blocker indanyloxyacetic acid 94 (IAA-94; 30 microM) affected Psim. In contrast, IAA-94 repolarized OMDVR pretreated with ANG II. Neither IAA-94 (30 microM) nor niflumic acid (30 microM, 1 mM) affected the vasoactivity of unstimulated OMDVR, whereas both dilated ANG II-preconstricted vessels. Reduction of extracellular [Cl(-)] from 150 to 30 meq/l enhanced ANG II-induced constriction. Finally, we identified a Cl(-) channel in OMDVR pericytes that is activated by ANG II or by excision into extracellular buffer. We conclude that constriction of OMDVR by ANG II involves pericyte depolarization due, in part, to increased activity of chloride channels.

Angiotensin II↗
PubMed2001

Neuroleptic malignant-like syndrome after abrupt withdrawal of baclofen.

We present the case of a 36-year-old man who presented with a clinically neuroleptic malignant-like syndrome involving disorientation, signs of autonomic dysfunction, rigidity and raised total creatine kinase level, but in the absence of any neuroleptic medication. He had, however, abruptly stopped taking his long-term baclofen in the days prior to presentation. He improved markedly after the reintroduction of baclofen, and we postulate that his clinical syndrome resulted from the sudden withdrawal of this drug. We concur with the concept that neuroleptic malignant syndrome represents a spectrum of disorders, and add it to the list of possible sequelae after abrupt withdrawal of baclofen.

Adult↗
PubMed2000

Positron emission tomography (PET)--its potential to provide surrogate markers in ALS.

Positron emission tomography (PET) has enabled us to study the human brain with unrivalled sensitivity, and has already established its place in the research of neurological conditions such as Parkinson's disease and epilepsy. PET has been used as a tool in the study of patients with motor neuron disease (MND) for well over ten years now, but its potential in diagnosis and to identify surrogate markers of disease expression (phenotype) and progression has yet to be fully realized. The early studies using 2-18fluoro-2-deoxy-D-glucose to measure regional changes in cerebral metabolic rate for glucose gave the first clues to the more widespread involvement of the brain in MND. Later studies exploited the development of activation studies using 15O-containing tracers, which allowed correlation with neuropsychological measures, and the refinement of mapping techniques to delineate the extra-motor areas involved in the disease process. More recently, studies involving ligands such as 11C-flumazenil have allowed the exploration of functional reorganisation in MND, and inhibitory interneuronal pathways which may be crucial in modulation of disease expression. In the future new ligands will be applied in combination with other modalities of investigation (multimodal magnetic resonance imaging; neurophysiological studies) in order to understand the pathophysiology of this heterogeneous condition. Although the potential of PET has not yet been realized in ALS, it is likely to play a part in defining new diagnostic and surrogate markers of disease extent and severity.

Amyotrophic Lateral Sclerosis↗
PubMed1998

Intrarenal blood flow: microvascular anatomy and the regulation of medullary perfusion.

1. The microcirculation of the kidney is arranged in a manner that facilitates separation of blood flow to the cortex, outer medulla and inner medulla. 2. Resistance vessels in the renal vascular circuit include arcuate and interlobular arteries, glomerular afferent and efferent arterioles and descending vasa recta. 3. Vasoactive hormones that regulate smooth muscle cells of the renal circulation can originate outside the kidney (e.g. vasopressin), can be generated from nearby regions within the kidney (e.g. kinins, endothelins, adenosine) or they can be synthesized by adjacent endothelial cells (e.g. nitric oxide, prostacyclin, endothelins). 4. Vasoactive hormones released into the renal inner medullary microcirculation may be trapped by countercurrent exchange to act upon descending vasa recta within outer medullary vascular bundles. 5. Countercurrent blood flow within the renal medulla creates a hypoxic environment. Relative control of inner versus outer medullary blood flow may play a role to abrogate the hypoxia that arises from O2 consumption by the thick ascending limb of Henle. 6. Cortical blood flow is autoregulated. In contrast, the extent of autoregulation of medullary blood flow appears to be influenced by the volume status of the animal. Lack of medullary autoregulation during volume expansion may be part of fundamental processes that regulate salt and water excretion.

Animals↗
PubMed1997

Hydraulic and diffusional permeabilities of isolated outer medullary descending vasa recta from the rat.

Water permeates many microvessel walls via a pathway shared with small hydrophilic solutes and also via an exclusive water pathway. In outer medullary descending vasa recta (OMDVR), the relationship between diffusional permeabilities to water and sodium indicates the existence of an exclusive water pathway and suggests that of a shared pathway. We investigated the latter possibility by estimating hydraulic permeability (Lp) and diffusional permeability to [3H]raffinose (P(raf)) in isolated, perfused OMDVR. The product of hydraulic permeability and osmotic reflexion coefficient of albumin (Lp sigma a) was 1.56 +/- 0.19 x 10(-6) cm.s-1.mmHg-1 (n = 28), calculated from transmural volume fluxes induced by perfusate-to-bath differences in albumin oncotic pressure (delta IIa). P(raf) in the same vessels was 40.1 +/- 7.5 x 10(-5) cm/s when delta IIa was zero. In separate experiments, sigma a was at least 0.89 +/- 0.10 (n = 17). Lp sigma a correlates with P(raf), indicating that OMDVR contain a shared pathway for convection driven by delta IIa and for diffusion of small hydrophilic solutes.

Animals↗
PubMed1997

Vasopressin constricts outer medullary descending vasa recta isolated from rat kidneys.

Arginine vasopressin (AVP) can selectively decrease blood flow in the renal medulla, but the sites of vasoconstriction are uncertain. We have examined the effects of vasopressin-receptor agonists and antagonists on the diameters of outer medullary descending vasa recta (OMDVR), isolated and perfused in vitro. AVP can constrict OMDVR, apparently via V1a-receptors. Ablumenal AVP (10(-10)-10(-6)M) or the selective V1a-receptor agonist [Phe2, Ile3, Orn8]-vasopressin (PO-VT, 10(-8) M) constricted OMDVR focally and (at higher AVP concentrations) transiently. The V1b agonist ideamino-Cys1,D-3-(pyridyl)Ala2,Arg8)vasopressin (DP-VP; 10(-8) M) and the V2 agonist [deamino-Cys1, D-Arg8]vasopressin (DDAVP; 10(-8) M) did not constrict OMDVR. The V1a antagonist [d(CH2)5(1), O-Me-Tyr2,Arg8]vasopressin (CTM-VP, 10(-10) 10(-8) M) inhibited vasoconstriction by AVP 10(-9 M), whereas the V2 antagonist [d(CH2)5(1), D-Ile2,Ile4 Arg8]vasopressin (II-VP) at low concentration (10(-10) M) did not. V2 stimulation seems to inhibit V1a constriction of OMDVR. DDAVP prevented constriction by PO-VT (10(-8) M) applied at the same time and dilated OMDVR preconstricted with PO-VT.

Animals↗
PubMed1997

Molecular sieving of small solutes by outer medullary descending vasa recta.

Molecular sieving of small solutes by outer medullary descending vasa recta (OMDVR). Descending vasa recta (DVR) plasma equilibrates with the medullary interstitium by volume efflux (Jv), as well as by influx of solutes. Jv is driven by transmural osmotic pressure gradients due to small hydrophilic solutes (delta pi s), NaCl and urea. DVR endothelium probably contains a "water-only" pathway most likely mediated by the aquaporin-1 (AQP1) water channel. We measured the ability of microperfused OMDVR to concentrate lumenal 22Na and [3H]raffinose when Jv was driven by transmural NaCl gradients. Collectate-to-perfusate ratios of 2 x 10(6) M(r) fluorescein isothiocyanate-labeled dextran volume marker (RDx), 22Na (RNa), and [3H]raffinose (Rraf) were measured in the absence and presence of Jv. During volume efflux (Jv > 0), RDx was 1.37 +/- 0.31. RNa increased from 0.64 +/- 0.03 when Jv = 0 to 0.82 +/- 0.05 when Jv > 0 and Rraf increased from 0.83 +/- 0.03 to 1.13 +/- 0.05: Mathematical simulations predict RNa and Rraf most accurately when the OMDVR reflection coefficient to the tracers is assigned a value near unity. This indicates that the OMDVR wall contains a pathway for osmotic volume flux that excludes small hydrophilic solutes, a behavior consistent with that of aquaporins.

Animals↗
PubMed1996

Twenty questions for the consumer: a quality assurance tool for the lactation consultant.

A simple post-service consumer survey is presented with which the lactation consultant can gather and analyze data to determine the extent to which services are meeting the needs of clients. The brief survey can be used to gather data from all clients or from a sample of clients. The survey can be administered by telephone or by postal return form. After analyzing the data obtained, the lactation consultant can identify where improvement in practice is needed. An additional " self assessment questionnaire" enables the lactation consultant to identify areas where personal growth is needed.

Breast Feeding↗
PubMed1992

Liquid flow through monolayers of cultured Madin-Darby canine kidney cells.

The rate of liquid flow per unit area (Jv/A) through Madin-Darby canine kidney cell monolayers has been studied at temperatures between 0 and 38 degrees C and at transmonolayer hydrostatic pressures between 14 and 44 cmH2O. Jv/A decreased exponentially with time during application of a constant pressure to the free surface of each monolayer. This behaviour resembles the sealing of cultured vascular endothelium. For monolayers sealed between 33-38 degrees C and 30-33 cmH2O, the mean (+/- S.E.M.) half-time (t1/2) of sealing was 228 (+/- 88) s (n = 6). The decrease in Jv/A during sealing can be expressed as a fraction of the initial Jv/A. Between 33-38 degrees C and 30-33 cmH2O, the mean (+/- S.E.M.) sealing fraction was 0.58 (+/- 0.06; n = 6). Mean sealing t1/2 was longer at lower temperatures, and longer for glutaraldehyde-fixed than for unfixed monolayers, but did not vary with transmonolayer pressure. Sealing fraction was not affected by variations in temperature or transmonolayer pressure, or by glutaraldehyde fixation of monolayers. It is argued that sealing is a physical, rather than a biological, phenomenon and that monolayers have non-linear mechanical properties.

Animals↗
PubMed1992

Electrical resistances of cultured bovine arterial endothelium in solutions of various resistivities.

Relationships between the electrical resistance (Rm) of cultured endothelium and the resistivity (rho) of the bathing solution have been investigated, using eight monolayers of bovine arterial endothelium. Bathing solutions of differing rho were prepared by mixing culture medium and isosmolar (290 mM) sucrose in various proportions. Relationships between 1/Rm and 1/rho were linear, as predicted, with a mean 1/Rm intercept of zero. The slopes of the relationships give a mean fractional area per unit path length (Ap/delta chi) of 12.7 cm-1 for the paracellular pathways of the cultured endothelium. This resembles previous estimates of Ap/delta chi for mammalian endothelium in arteries. The 1/Rm intercept of zero indicates that the major electrical conducting pathways of cultured arterial endothelium are paracellular.

Animals↗
PubMed1992

Flows of liquid and electrical current through monolayers of cultured bovine arterial endothelium.

1. Monolayers of arterial endothelium on porous membranes were exposed to a constant pressure between 15 and 35 cmH2O. The rates of liquid flow per unit area (Jv/A) through the monolayers were monitored, together with the electrical resistance (Rm) of the endothelium. 2. At constant pressure, Jv/A decreased with an approximately exponential time course, towards a stable baseline value. This behaviour resembles the sealing previously described for cultured vascular endothelium. At 30-35 cmH2O and 37 degrees C, the mean (+/- S.E.M.) half-time (t1/2) of the decrease in Jv/A (the sealing t1/2) was 548 +/- 141 S (n = 5). The difference between the initial and baseline values of Jv/A was expressed as a fraction of the initial value. The mean (+/- S.E.M.) of this sealing fraction was 0.64 +/- 0.03 (n = 5). Mean (+/- S.E.M.) hydraulic permeability (Lp) was 23.9 +/- 6.4 x 10(-7) cm S-1 cmH2O-1 (n = 9), when measured after sealing. Endothelium appeared damaged after sealing at 30-35 cmH2O and 37 degrees C. 3. Sealing was also observed using glutaraldehyde-fixed endothelium at 30-33 cmH2O and 26-28 degrees C. There was no significant difference between the mean sealing t1/2 of these fixed monolayers, and that of unfixed endothelium at 30-35 cmH2O and 37 degrees C. However, mean sealing fraction was significantly larger for the fixed monolayers than for unfixed endothelium at 30-35 cmH2O and 37 degrees C. There were no significant difference between the post-sealing Lps of these fixed and unfixed monolayers, although the fixed monolayers appeared undamaged after sealing. 4. For unfixed endothelium, Rm was lower after sealing at 30-35 cmH2O and 37 degrees C than before pressure application. There was no significant difference between endothelial Rm before and after sealing, for glutaraldehyde-fixed monolayers. 5. Sealing was also observed at 0 degree C, using unfixed endothelium at 30 cmH2O. Mean sealing t1/2 was not significantly different from that of unfixed endothelium at 30 cmH2O and 37 degrees C. However, mean sealing fraction was significantly smaller at 0 degree C than at 37 degrees C. Unfixed endothelium appeared undamaged after sealing at 30 cmH2O and 0 degree C. Despite this, the post-sealing Lp was not significantly different from that of unfixed endothelium sealed at 30 cmH2O and 37 degrees C, after allowance was made for the effect of temperature on Lp. Rm was not measured in these experiments. 6. It is proposed that sealing is due to pressure-induced deformation of monolayers.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗