Biomedical subjects
M R Turner
Publications and source records attributed to M R Turner.
Effects of hypoxia, anoxia, and metabolic inhibitors on KATP channels in rat femoral artery myocytes.
Vascular ATP-sensitive potassium (KATP) channels have an important role in hypoxic vasodilation. Because KATP channel activity depends on intracellular nucleotide concentration, one hypothesis is that hypoxia activates channels by reducing cellular ATP production. However, this has not been rigorously tested. In this study we measured KATP current in response to hypoxia and modulators of cellular metabolism in single smooth muscle cells from the rat femoral artery by using the whole cell patch-clamp technique. KATP current was not activated by exposure of cells to hypoxic solutions (Po2 approximately 35 mmHg). In contrast, voltage-dependent calcium current and the depolarization-induced rise in intracellular calcium concentration ([Ca2+]i) was inhibited by hypoxia. Blocking mitochondrial ATP production by using the ATP synthase inhibitor oligomycin B (3 microM) did not activate current. Blocking glycolytic ATP production by using 2-deoxy-D-glucose (5 mM) also did not activate current. The protonophore carbonyl cyanide m-chlorophenylhydrazone (1 microM) depolarized the mitochondrial membrane potential and activated KATP current. This activation was reversed by oligomycin B, suggesting it occurred as a consequence of mitochondrial ATP consumption by ATP synthase working in reverse mode. Finally, anoxia induced by dithionite (0.5 mM) also depolarized the mitochondrial membrane potential and activated KATP current. Our data show that: 1) anoxia but not hypoxia activates KATP current in femoral artery myocytes; and 2) inhibition of cellular energy production is insufficient to activate KATP current and that energy consumption is required for current activation. These results suggest that vascular KATP channels are not activated during hypoxia via changes in cell metabolism. Furthermore, part of the relaxant effect of hypoxia on rat femoral artery may be mediated by changes in [Ca2+]i through modulation of calcium channel activity.
Wasp sting induced autoimmune neuromyotonia.
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Distinct cerebral lesions in sporadic and 'D90A' SOD1 ALS: studies with [11C]flumazenil PET.
Five to ten percent of amyotrophic lateral sclerosis (ALS) cases are associated with mutations of the superoxide dismutase-1 (SOD1) gene, and the 'D90A' mutation is associated with a unique phenotype and markedly slower disease progression (mean survival time 14 years). Relative sparing of inhibitory cortical neuronal circuits might be one mechanism contributing to the slower progression in patients homozygous for the D90A mutation (homD90A). The GABA(A) receptor PET ligand [11C]flumazenil has demonstrated motor and extra-motor cortical changes in sporadic ALS. In this study, we used [11C]flumazenil PET to explore differences in the pattern of cortical involvement between sporadic and genetically homogeneous ALS groups. Twenty-four sporadic ALS (sALS) and 10 homD90A patients underwent [11C]flumazenil PET of the brain. In addition, two subjects homozygous for the D90A mutation, but without symptoms or signs ('pre-symptomatic', psD90A), also underwent imaging. Results for each group were compared with those for 24 healthy controls of similar age. Decreases in the binding of [11C]flumazenil in the sALS group were found within premotor regions, motor cortex and posterior motor association areas. In the homD90A group of ALS patients, however, decreases were concentrated in the left fronto-temporal junction and anterior cingulate gyrus. In the two psD90A subjects, a small focus of reduced [11C]flumazenil binding at the left fronto-temporal junction was seen, similar to the pattern seen in the clinically affected patients. Within the sALS group, there was no statistically significant association between decreases in cortical [11C]flumazenil binding and revised ALS functional rating scale (ALSFRS-R score), whereas the upper motor neuron (UMN) score correlated with widespread and marked cortical decreases over the dominant hemisphere. In the homD90A group, there was a stronger statistical association between reduced cortical [11C]flumazenil binding and the ALSFRS-R, rather than the UMN, score, and also with disease duration. This study provides evidence for differences in the distribution of reduced cortical [11C]flumazenil binding in homD90A compared with sALS patients. We hypothesize that this might reflect differences in cortical neuronal vulnerability.
[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.
Mills' and other isolated upper motor neurone syndromes: in vivo study with 11C-(R)-PK11195 PET.
(11)C-(R)-PK11195 positron emission tomography (PET) was used to explore and delineate in vivo the cortical lesion in three clinically isolated upper motor neurone syndromes of similar presentation, with reference to the syndrome of progressive spastic hemiparesis first described by Mills. Three patients with isolated UMN syndromes underwent (11)C-(R)-PK11195 PET of the brain. One patient fulfilled criteria for PLS. Two others had clinical features similar to the cases described by Mills; one of these had a high cervical cord inflammatory lesion previously noted on magnetic resonance imaging. The patient with PLS showed focal increase in the binding of (11)C-(R)-PK11195, indicating microglial activation, in the motor cortex contralateral to the predominantly affected limbs. Of the other two patients, one demonstrated marked increases in binding in the superior frontal region (supplementary motor region) contralateral to the affected limbs. In contrast, no focal areas of increased binding were seen in the cerebral cortex of the third patient, who had a high cervical cord lesion and was presumed to have extra-cerebral inflammatory disease. (11)C-(R)-PK11195 PET demonstrates in vivo that active pathology may be detectable many years after the onset of symptoms, and that it can occur in disparate sites with clinically similar presentations. We conclude that Mills' syndrome is a purely clinical description that should be reserved for patients with a progressive spastic hemiparesis for which no other explanation can be found.
Abnormal cortical excitability in sporadic but not homozygous D90A SOD1 ALS.
BACKGROUND: Excitotoxicity is one pathogenic mechanism proposed in amyotrophic lateral sclerosis (ALS), and loss of cortical inhibitory influence may be contributory. Patients with ALS who are homozygous for the D90A superoxide dismutase-1 (SOD1) gene mutation (homD90A) have a unique phenotype, associated with prolonged survival compared with patients with sporadic ALS (sALS). In this study, transcranial magnetic stimulation (TMS) was used to explore cortical excitation and inhibition. Flumazenil binds to the benzodiazepine subunit of the GABA(A) receptor, and (11)C-flumazenil positron emission tomography (PET) was used as a marker of cortical neuronal loss and/or dysfunction, which might in turn reflect changes in cortical inhibitory GABAergic mechanisms. METHODS: Cortical responses to single and paired stimulus TMS were compared in 28 patients with sALS and 11 homD90A patients versus 24 controls. TMS measures included resting motor threshold, central motor conduction time, silent period, intracortical inhibition (ICI), and facilitation. (11)C-flumazenil PET of the brain was performed on 20 patients with sALS and nine with homD90A. Statistical parametric mapping was used to directly compare PET images from the two patient groups to identify those areas of relatively reduced cortical (11)C-flumazenil binding that might explain differences in cortical excitability seen using TMS. RESULTS: Increased cortical excitability, demonstrated by reduction in ICI, was seen in the patients with sALS but not the homD90A patients. A relative reduction in cortical (11)C-flumazenil binding was found in the motor and motor association regions of the superior parietal cortices of the patients with sALS. CONCLUSIONS: A cortical inhibitory deficit in sALS was not demonstrable in a homogeneous genetic ALS population of similar disability, suggesting a distinct cortical vulnerability. (11)C-flumazenil PET demonstrated that neuronal loss/dysfunction in motor and motor association areas may underlie this difference. The corollary, that there may be relative preservation of neuronal function in these areas in the homD90A group, has implications for understanding the slower progression of disease in these patients.
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.
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.
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.
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.
Widespread cerebral cavernous haemangiomata found after 24 years of intermittent symptoms.
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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.
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.
Starting a research post: some considerations for ward-based doctors.
Starting a research post after ward-based work can be a leap of faith and, as rewarding as it ultimately is, the initial transition can be a difficult one. This article addresses some of the questions which someone considering research should ask.
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.
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.
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.