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P Styles

Publications and source records attributed to P Styles.

At least 19 recordsLinked to original sources
PubMed2005

Detection of the inhibitory neurotransmitter GABA in macrophages by magnetic resonance spectroscopy.

Macrophages are key components of the inflammatory response to tissue injury, but their activities can exacerbate neuropathology. High-resolution magnetic resonance spectroscopy was used to identify metabolite levels in perchloric acid extracts of cultured cells of the RAW 264.7 murine macrophage line under resting and lipopolysaccharide-activated conditions. Over 25 metabolites were identified including gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter not previously reported to be present in macrophages. The presence of GABA was also demonstrated in extracts of human peripheral blood monocyte-derived macrophages. This finding suggests that there may be communication between damaged central nervous system (CNS) tissue and recruited macrophages and resident microglia, which could help orchestrate the immune response. On activation, lactate, glutamine, glutamate, and taurine levels were elevated significantly, and GABA and alanine were reduced significantly. Strong resonances from glutathione, evident in the macrophage two-dimensional 1H spectrum, suggest that this may have potential as a noninvasive marker of macrophages recruited to the CNS, as it is only present at low levels in normal brain. Alternatively, a specific combination of spectroscopic changes, such as lactate, alanine, glutathione, and polyamines, may prove to be the most accurate means of detecting macrophage recruitment to the CNS.

Amino Acids↗
PubMed2005

Confounding effects of anesthesia on functional activation in rodent brain: a study of halothane and alpha-chloralose anesthesia.

Functional magnetic resonance imaging (fMRI) in animal models provides a platform for more extensive investigation of drug effects and underlying physiological mechanisms than is possible in humans. However, it is usually necessary for the animal to be anesthetized. In this study, we have used a rat model of direct cortical stimulation to investigate the effects of anesthesia in rodent fMRI. Specifically, we have sought to answer two questions (i) what is the relationship between baseline neuronal activity and the BOLD response to stimulation under halothane anesthesia? And (ii) how does the BOLD response change after transferring from halothane to the commonly used anesthetic alpha-chloralose? In the first set of experiments, we found no significant differences in the amplitude of the BOLD response at the different halothane doses studied, despite electroencephalography (EEG) recordings indicating a dose-dependent reduction in baseline neuronal activity with increasing halothane levels. In the second set of experiments, a reduction in the spatial extent of the BOLD response was apparent immediately after transfer from halothane to alpha-chloralose anesthesia, although no change in the peak signal change was evident. However, several hours after transfer to alpha-chloralose, a significant increase in both the spatial extent and peak height of the BOLD response was observed, as well as an increased sensitivity to secondary cortical and subcortical activation. These findings suggest that, although alpha-chloralose anesthesia is associated with a greater BOLD response for a fixed stimulus relative to halothane, there is substantial variation in the extent and magnitude of the response over time that could introduce considerable variability in studies using this anesthetic.

Anesthesia, General↗
PubMed2005

MRS reveals additional hexose N-acetyl resonances in the brain of a mouse model for Sandhoff disease.

Sandhoff disease, one of several related lysosomal storage disorders, results from the build up of N-acetyl-containing glycosphingolipids in the brain and is caused by mutations in the genes encoding the hexosaminidase beta-subunit. Affected individuals undergo progressive neurodegeneration in response to the glycosphingolipid storage. (1)H magnetic resonance spectra of perchloric acid extracts of Sandhoff mouse brain exhibited several resonances ca 2.07 ppm that were not present in the corresponding spectra from extracts of wild-type mouse brain. High-performance liquid chromatography and mass spectrometry of the Sandhoff extracts post-MRS identified the presence of N-acetylhexosamine-containing oligosaccharides, which are the likely cause of the additional MRS resonances. MRS of intact brain tissue with magic angle spinning also showed additional resonances at ca 2.07 ppm in the Sandhoff case. These resonances appeared to increase with disease progression and probably arise, for the most part, from the stored glycosphingolipids, which are absent in the aqueous extracts. Hence in vivo MRS may be a useful tool for detecting early-stage Sandhoff disease and response to treatment.

Animals↗
PubMed2004

Quantitative proton magnetic resonance spectroscopy of the cervical spinal cord.

Proton MR spectroscopy ((1)H-MRS) provides indices of neuronal damage in the central nervous system (CNS); however, it has not been extensively applied in the spinal cord. This work describes an optimized proton spectroscopy protocol for examination of the human cervical spinal cord. B(0) field mapping of the cord revealed periodic inhomogeneities due to susceptibility differences with surrounding tissue. By combining field maps and experimental data, we found that the optimum voxel size was 9 x 7 x 35 mm(3) placed with the inferior end of the voxel above vertebral body C2. Metabolite concentrations were determined in the cervical cord in six healthy controls by short-echo point-resolved spectroscopy (PRESS) volume localization. The results were compared with metabolite concentrations in the brainstem, cerebellum, and cortex in the same individuals. The concentrations in the cervical cord were as follows: N-acetyl-aspartate (NAA) 17.3 +/- 0.5, creatine (Cr) 9.5 +/- 0.9, and choline 2.7 +/- 0.5 mmol/l. The NAA concentration was significantly lower in the cord than in the brainstem (Mann-Whitney, P < 0.025), and higher than in the cortex (P < 0.005) and cerebellum (P < 0.005). Cr was significantly lower in the cord than in the cerebellum (P < 0.05). There were no significant differences between Cr concentrations in the spinal cord compared to the cortex and brainstem.

Adult↗
PubMed2004

Effects of carnitine supplementation on muscle metabolism by the use of magnetic resonance spectroscopy and near-infrared spectroscopy in end-stage renal disease.

BACKGROUND/AIM: A defect in skeletal muscle mitochondrial metabolism develops in patients with chronic renal failure on haemodialysis. Treatment with carnitine, a compound essential for normal mitochondrial function, has been suggested to have significant benefits in such patients, so we carried out a study to see if carnitine acts by improving muscle bioenergetics and function. METHODS: In a phase II randomised double-blind trial, patients with end-stage renal disease received placebo or intravenous L-carnitine (20 mg/kg dry body weight three times weekly after haemodialysis) for 16 weeks (n = 13 in each group). 31P magnetic resonance spectroscopy, 1H magnetic resonance imaging and near-infrared spectroscopy were used to measure muscle bioenergetics and function at baseline and at 16 weeks. RESULTS: There were no significant differences between groups at baseline. Mean plasma carnitine rose 10-fold in the carnitine group but was unchanged in the placebo group. L-carnitine had no statistically significant effect on any of the parameters measured. The rate of proton efflux from muscle, as a measure of tissue perfusion, was low in both groups and was not affected by treatment. CONCLUSIONS: The study failed to show any significant effect of 16 weeks' L-carnitine supplementation on these objective measures of muscle metabolism and function. Slow proton efflux from muscle provides evidence supporting low blood flow and, therefore, decreased oxygen availability, as an underlying mechanism for muscle mitochondrial dysfunction in this disorder.

Blood Chemical Analysis↗
PubMed2003

Differences in the BOLD fMRI response to direct and indirect cortical stimulation in the rat.

Functional MRI (fMRI) exploits a relationship between neuronal activity, metabolism, and cerebral blood flow to functionally map the brain. We have developed a model of direct cortical stimulation in the rat that can be combined with fMRI and used to compare the hemodynamic responses to direct and indirect cortical stimulation. Unilateral electrical stimulation of the rat hindpaw motor cortex, via stereotaxically positioned carbon-fiber electrodes, yielded blood oxygenation level-dependent (BOLD) fMRI signal changes in both the stimulated and homotypic contralateral motor cortices. The maximal signal intensity change in both cortices was similar (stimulated = 3.7 +/- 1.7%; contralateral = 3.2 +/- 1.0%), although the response duration in the directly stimulated cortex was significantly longer (48.1 +/- 5.7 sec vs. 19.0 +/- 5.3 sec). Activation of the contralateral cortex is likely to occur via stimulation of corticocortical pathways, as distinct from direct electrical stimulation, and the response profile is similar to that observed in remote (e.g., forepaw) stimulation fMRI studies. Differences in the neuronal pool activated, or neurovascular mediators released, may account for the more prolonged BOLD response observed in the directly stimulated cortex. This work demonstrates the combination of direct cortical stimulation in the rat with fMRI and thus extends the scope of rodent fMRI into brain regions inaccessible to peripheral stimulation techniques.

Animals↗
PubMed2003

Beta-Interferon treatment does not always slow the progression of axonal injury in multiple sclerosis.

Progression of disability in multiple sclerosis (MS) appears related to axonal damage, which is at least in part associated with white matter lesions. Beta-interferon (BIFN) substantially reduces new inflammatory activity in MS and a recent report suggested that it may reverse a component of axonal injury. To test the generalisability of this conclusion, particularly in a population with relatively active disease, we used magnetic resonance spectroscopy measures to test whether BIFN can reverse or arrest progression of axonal injury in patients with MS. Eleven patients with a history of active (median, 1.5 relapses/year) relapsing-remitting MS were treated with BIFN and responses to treatment were monitored with serial MRI and single voxel magnetic resonance spectroscopic measurements of relative concentrations of brain N-acetylaspartate (NAA), a measure of axonal integrity from a central, predominantly white matter brain region. BIFN treatment was associated with a significant reduction in relapse rate (p = 0.007) and white matter water T2 relaxation time (p = 0.047) over 12 months. Also consistent with a treatment effect, white matter T2-hyperintense lesion loads did not increase. However, the central white matter NAA/creatine ratio (NAA/Cr, which was reduced over 16 % in patients relative to healthy controls at the start of treatment), continued to decrease in the patients over the period of observation (mean 6.2 % decrease, p = 0.02). For individual patients the magnitude of the NAA/Cr decrease was correlated with the frequency of relapses over the two years prior to treatment (r = -0.76, p = 0.006). These data suggest that reduction of new inflammatory activity with BIFN does not invariably halt progression of axonal injury. Nonetheless, there appears to be a relationship between the rate of progression of axonal injury and relapse rate over the previous two years. The consequences of reduced inflammation on pathological progression relevant to disability therefore may be present, but substantially delayed. Alternatively, distinct mechanisms may contribute to the two processes.

Adult↗
PubMed2002

Swelling-activated taurine and creatine effluxes from rat cortical astrocytes are pharmacologically distinct.

Primary cultures of rat cortical astrocytes undergo a swelling-activated loss of taurine and creatine. In this study, the pharmacological characteristics of the taurine and creatine efflux pathways were compared, and significant differences were shown to exist between the two. Both taurine and creatine effluxes were rapidly activated upon exposure of astrocytes to hypo-osmotic media, and rapidly inactivated upon their return to iso-osmotic media. The relative rates of taurine and creatine efflux depended upon the magnitude of the hypo-osmotic shock. Anion-transport inhibitors strongly inhibited taurine efflux, with the order of potency being NPPB > DIDS > niflumic acid. DIDS and NPPB had less of an inhibitory effect on creatine efflux, whereas tamoxifen and niflumic acid actually stimulated creatine efflux. These data are consistent with separate pathways for taurine and creatine loss during astrocyte swelling.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2002

A quantitative study of bioenergetics in skeletal muscle lacking utrophin and dystrophin.

Muscle energetics and function were investigated in the hindlimb of mice lacking dystrophin (mdx), utrophin and dystrophin (utr-dys) and controls (C57Bl/10) using 31P and 1H magnetic resonance techniques, electrical nerve stimulation and direct biochemical analysis. At rest, [adenosine triphosphate] and [total creatine] were lowest in utr-dys, while [inorganic phosphate] was elevated. Calculated [adenosine diphosphate] was 3-fold higher in mdx and 5-fold higher in utr-dys than in controls, consistent with an increased adenosine triphosphate requirement for ion pump activity. During stimulation, force production was low only in utr-dys, and this was reflected in the bioenergetic changes. Initial recovery rates of [phosphocreatine] and [adenosine diphosphate] after stimulation were rapid in all groups, indicative of normal mitochondrial adenosine triphosphate production in utr-dys and mdx. Recovery of pH was slow in utr-dys. The data indicate that the severe abnormalities which are present in the absence of utrophin and dystrophin leave basic muscle energetics intact and appear confined to processes involving the sarcolemma.

Adenosine Diphosphate↗
PubMed2002

Mitochondrial dysfunction in Friedreich's ataxia: from pathogenesis to treatment perspectives.

Friedreich's ataxia (FRDA), the most common inherited ataxia, is an autosomal recessive degenerative disorder caused by a GAA triplet expansion or point mutations in the FRDA gene on chromosome 9q13. The FRDA gene product, frataxin, is a widely expressed mitochondrial protein, which is severely reduced in FRDA patients. The demonstration that deficit of frataxin in FRDA is associated with mitochondrial iron accumulation, increased sensitivity to oxidative stress, deficit of respiratory chain complex activities and in vivo impairment of cardiac and skeletal muscle tissue energy metabolism, has established FRDA as a "new" nuclear encoded mitochondrial disease. Pilot studies have shown the potential effect of antioxidant therapy based on idebenone or coenzyme Q10 plus Vitamin E administration in this condition and provide a strong rationale for designing larger randomized clinical trials.

Antioxidants↗
PubMed2001

No correlation between muscle A3243G mutation load and mitochondrial function in vivo.

The authors studied the relationship between the percentage level of A3243G mitochondrial DNA mutation and the degree of mitochondrial dysfunction in vivo in nine individuals from four pedigrees using phosphorus MRS in muscle. There was no significant correlation between mutation load and maximum rate of adenosine triphosphate production (V(max)). V(max) was normal in a subject with 32% A3243G in muscle, which is in contrast with a previous observation of markedly reduced V(max) in a patient with only 6% A3243G in muscle. Factors besides mutation load, such as nuclear genes, influence expression of the A3243G mutation in vivo.

Adenosine Triphosphate↗
PubMed2001

Cardiac energetics are abnormal in Friedreich ataxia patients in the absence of cardiac dysfunction and hypertrophy: an in vivo 31P magnetic resonance spectroscopy study.

OBJECTIVE: Friedreich ataxia (FRDA), the commonest form of inherited ataxia, is often associated with cardiac hypertrophy and cardiac dysfunction is the most frequent cause of death. In 97%, FRDA is caused by a homoplasmic GAA triplet expansion in the FRDA gene on chromosome 9q13 that results in deficiency of frataxin, a mitochondrial protein of unknown function. There is evidence that frataxin deficiency leads to a severe defect of mitochondrial respiration associated with abnormal mitochondrial iron accumulation. To determine whether bioenergetics deficit underlies the cardiac involvement in Friedreich ataxia (FRDA) we measured cardiac phosphocreatine to ATP ratio non-invasively in FRDA patients. METHODS AND RESULTS: Eighteen FRDA patients and 18 sex- and age-matched controls were studied using phosphorus MR spectroscopy and echocardiography. Left ventricular hypertrophy was present in eight FRDA patients while fractional shortening was normal in all. Cardiac PCr/ATP in FRDA patients as a group was reduced to 60% of the normal mean (P<0.0001). In the sub-group of patients with no cardiac hypertrophy PCr/ATP was also significantly reduced (P<0.0001). CONCLUSION: Cardiac bioenergetics, measured in vivo, is abnormal in FRDA patients in the absence of any discernible deterioration in cardiac contractile performance. The altered bioenergetics found in FRDA patients without left ventricle hypertrophy implies that cardiac metabolic dysfunction in FRDA precedes hypertrophy and is likely to play a role in its development.

Adenosine Triphosphate↗
PubMed2001

Daytime liver glycogen accumulation, measured by 13C magnetic resonance spectroscopy, in young children with Type 1 diabetes mellitus.

AIM: To examine daytime liver glycogen accumulation in prepubertal children with Type 1 diabetes mellitus (Type 1 DM) compared with non-diabetic controls. METHODS: Liver glycogen content was ascertained in the fasting (morning) and fed (afternoon) state using 13C magnetic resonance (MR) spectroscopy. Data were analysed from six children with Type 1 DM (median (range) age 8.7 (6.3-12.2) years), who were all on conventional insulin regimens, and six healthy controls (age 8.9 (7-10.2) years). RESULTS: Children with diabetes tended to have lower fasting glycogen values than controls but this did not reach statistical significance (median (range) 154 (70-177) vs. 178 (120-203) mM glycosyl units, Type 1 DM vs. controls respectively; P = 0.06). Glycogen increased in all children with diabetes during the day and concentrations were similar to those in controls by the afternoon (175 (157-299) vs. 172 (136-238) mM glycosyl units; P = 0.7). CONCLUSIONS: The ability of young children with Type 1 DM to replace liver glycogen depleted after an overnight fast was at least as good as that in control subjects, suggesting that impaired glycogen storage is not a contributory factor in nocturnal hypoglycaemia.

Activity Cycles↗
PubMed2001

Hypo-osmotic swelling-activated release of organic osmolytes in brain slices: implications for brain oedema in vivo.

A decrease in the intracellular levels of osmotically active species has invariably been seen after swelling of mammalian brain tissue preparations. The exact identity of the species, and the manner of their decrease, remain to be described. We investigated the swelling-activated decrease of organic osmolytes in rat cortical brain slices using (1)H- and (31)P-magnetic resonance spectroscopy. We found that acute hypo-osmotic shock causes decreases in the levels of a range of intracellular amino acids and amino acid derivatives, N-acetyl-aspartate, creatine, GABA, glutamate, hypotaurine, and also in the levels of the methylamines glycerol-phosphorylcholine, phosphorylcholine and choline. Incubation of cortical slices with the anion channel blockers niflumic acid and tamoxifen caused inhibition of organic osmolyte efflux, suggesting that such osmolyte efflux occurs through anion channels. Intracellular phosphocreatine was also seen to decrease during acute hypo-osmotic superfusion, although intracellular ATP remained constant. In addition, the acidification of an intracellular compartment was observed during hypo-osmotic superfusion. Our results suggest a link between brain energy reserve and brain osmoregulation.

Adenosine Triphosphate↗
PubMed2001

Developmental and regional distribution of aspartoacylase in rat brain tissue.

The function of N-acetyl-aspartate (NAA), a predominant molecule in the brain, has not yet been determined. However, NAA is commonly used as a putative marker of viable neurones. To investigate the possible function of NAA, we determined the anatomical, developmental and cellular distribution of aspartoacylase, which catalyses the hydrolysis of NAA. Levels of aspartoacylase activity were measured during postnatal development in several brain regions. The differential distribution of aspartoacylase activity in purified populations of cells derived from the rat CNS was also investigated. The developmental and anatomical distribution of aspartoacylase correlated with the maturation of white matter tracts in the rat brain. Activity increased markedly after 7 days and coincided with the time course for the onset of myelination in the rat brain. Gray matter showed little activity or developmental trend. There was a 60-fold excess in optic nerve (a white matter tract) when compared with cortex at 21 days of development. In the adult brain there was a 18-fold difference in corpus callosum compared with cortex (stripped of corpus callosum). Cellular studies demonstrated that purified cortical neurons and cerebellar granular neurones have no activity. Primary O-2A progenitor cells had moderate activity, with three-fold higher activity in immature oligodendrocyte and 13-fold increase in mature oligodendrocytes (myelinating cells of the CNS). The highest activity was seen in type-2 astrocytes (20-fold difference compared with O-2A progenitors) derived from the same source. Aspartoacylase activity increased with time in freshly isolated astrocytes, with significantly higher activity after 15 days in culture. We conclude that aspartoacylase activity in the developing postnatal brain corresponds with maturation of myelination, and that the cellular distribution is limited to glial cells.

Amidohydrolases↗
PubMed2001

Altered cellular metabolism following traumatic brain injury: a magnetic resonance spectroscopy study.

Experimental studies have reported early reductions in pH, phosphocreatine, and free intracellular magnesium following traumatic brain injury using phosphorus magnetic resonance spectroscopy. Paradoxically, in clinical studies there is some evidence for an increase in the pH in the subacute stage following traumatic brain injury. We therefore performed phosphorus magnetic resonance spectroscopy on seven patients in the subacute stage (mean 9 days postinjury) following traumatic brain injury to assess cellular metabolism. In areas of normal-appearing white matter, the pH was significantly alkaline (patients 7.09 +/- 0.04 [mean +/- SD], controls 7.01 +/- 0.04, p = 0.008), the phosphocreatine to inorganic phosphate ratio (PCr/Pi) was significantly increased (patients 4.03 +/- 1.18, controls 2.64 +/- 0.71, p = 0.03), the inorganic phosphate to adenosine triphosphate ratio (Pi/ATP) was significantly reduced (patients 0.37 +/- 0.10, controls 0.56 +/- 0.19, p = 0.04), and the PCr/ATP ratio was nonsignificantly increased (patients 1.53 +/- 0.29, controls 1.34 +/- 0.19, p = 0.14) in patients compared to controls. Furthermore, the calculated free intracellular magnesium was significantly increased in the patients compared to the controls (patients 0.33 +/- 0.09 mM, controls 0.22 +/- 0.09 mM, p = 0.03)). Proton spectra, acquired from similar regions showed a significant reduction in N-acetylaspartate (patients 9.64 +/- 2.49 units, controls 12.84 +/- 2.35 units, p = 0.03) and a significant increase in choline compounds (patients 7.96 +/- 1.02, controls 6.67 +/- 1.01 units, p = 0.03). No lactate was visible in any patient or control spectrum. The alterations in metabolism observed in these patients could not be explained by ongoing ischemia but might be secondary to a loss of normal cellular homeostasis or a relative alteration in the cellular population, in particular an increase in the glial cell density, in these regions.

Adenosine Triphosphate↗