Search PubMed⌕ Search

Biomedical subjects

R E Brown

Publications and source records attributed to R E Brown.

At least 37 records · Page 2Linked to original sources
PubMed2001

Cholesterol decreases the interfacial elasticity and detergent solubility of sphingomyelins.

The interfacial interactions of cholesterol with sphingomyelins (SMs) containing various homogeneous acyl chains have been investigated by Langmuir film balance approaches. Low in-plane elasticity among the packed lipids was identified as an important physical feature of the cholesterol-sphingomyelin liquid-ordered phase that correlates with detergent resistance, a characteristic property of sphingolipid-sterol rafts. Changes in the in-plane elastic packing, produced by cholesterol, were quantitatively assessed by the surface compressional moduli (C(s)(-1)) of the monolayer isotherms. Of special interest were C(s)(-1) values determined at high surface pressures (>30 mN/m) that mimic the biomembrane situation. To identify structural features that uniquely affect the in-plane elasticity of the sphingomyelin-cholesterol lateral interaction, comparisons were made with phosphatidylcholine (PC)-cholesterol mixtures. Cholesterol markedly decreased the in-plane elasticity of either SM or PC regardless of whether they were fluid or gel phase without cholesterol. The magnitude of the reduction in in-plane elasticity induced by cholesterol was strongly influenced by acyl chain structure and by interfacial functional groups. Liquid-ordered phase formed at lower cholesterol mole fractions when SM's acyl chain was saturated rather than monounsaturated. At similar high cholesterol mole fractions, the in-plane elasticity within SM-cholesterol liquid-ordered phase was significantly lower than that of PC-cholesterol liquid-ordered phase, even when PCs were chain-matched to the SMs. Sphingoid-base functional groups (e.g., amide linkages), which facilitate or strengthen intermolecular hydrogen bonds, appear to be important for forming sphingomyelin-cholesterol, liquid-ordered phases with especially low in-plane elasticity. The combination of structural features that predominates in naturally occurring SMs permits very effective resistance to solubilization by Triton X-100.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2001

Stoichiometry of cholesterol-sphingomyelin condensed complexes in monolayers.

Some binary mixtures of cholesterol and phospholipids in monolayers have thermodynamic phase diagrams with two upper miscibility critical points. This feature has been interpreted in terms of 'condensed complexes' between the phospholipid and cholesterol. The present work gives evidence for the formation of complexes with a common simple integral stoichiometry in binary mixtures of cholesterol and a series of five sphingomyelins where the amide-linked acyl chain length is varied. This indicates that these complexes have a distinct geometry even though they form a liquid phase.

Cholesterol↗
PubMed2001

Involvement of the acid sphingomyelinase pathway in uva-induced apoptosis.

The sphingomyelin-ceramide pathway is an evolutionarily conserved ubiquitous signal transduction system that regulates many cell functions including apoptosis. Sphingomyelin (SM) is hydrolyzed to ceramide by different sphingomyelinases. Ceramide serves as a second messenger in mediating cellular effects of cytokines and stress. In this study, we find that acid sphingomyelinase (SMase) activity was induced by UVA in normal JY lymphoblasts but was not detectable in MS1418 lymphoblasts from Niemann-Pick type D patients who have an inherited deficiency of acid SMase. We also provide evidence that UVA can induce apoptosis by activating acid SMase in normal JY cells. In contrast, UVA-induced apoptosis was inhibited in MS1418 cells. Exogenous SMase and its product, ceramide (10-40 micrometer), induced apoptosis in JY and MS1418 cells, but the substrate of SMase, SM (20-80 micrometer), induced apoptosis only in JY cells. These results suggest that UVA-induced apoptosis by SM is dependent on acid SMase activity. We also provide evidence that induction of apoptosis by UVA may occur through activation of JNKs via the acid SMase pathway.

Animals↗
PubMed2001

Effects of chronic and acute methylphenidate hydrochloride (Ritalin) administration on locomotor activity, ultrasonic vocalizations, and neuromotor development in 3- to 11-day-old CD-1 mouse pups.

The present study examined the effects of chronic and acute treatment with methylphenidate hydrochloride (Ritalin) on isolation-induced ultrasonic vocalizations, spontaneous locomotor activity, and neuromotor coordination in 3- to 11-day-old CD-1 mouse pups. In Experiment 1, 3- to 11-day-old pups received daily injections of saline, 5 mg/kg or 20 mg/kg of methylphenidate hydrochloride, or no injection and were tested on postnatal Days 3, 5, 7, 9, and 11. Both doses of methylphenidate resulted in significant increases in locomotor activity at all ages, but had no significant effect on body weight, neuromotor development, or emission of ultrasonic vocalizations. In Experiment 2, pups were given a single dose of methylphenidate (5 or 20 mg/kg), saline, or no injection on one of postnatal Days 5, 7, 9, or 11. This acute methylphenidate treatment increased locomotor activity, but had no significant effects on ultrasonic vocalizations or neuromotor coordination. These results indicate that short-term, chronic methylphenidate treatment elevates locomotor responses, but has no immediate effects on anxietylike responses or on the development of neuromotor behavior of CD-1 mice in the first 11 days of life.

Animals↗
PubMed2001

Interfacial interactions of ceramide with dimyristoylphosphatidylcholine: impact of the N-acyl chain.

The mixing behavior of dimyristoylphosphatidylcholine (DMPC) with either N-palmitoyl-sphingosine (C16:0-ceramide) or N-nervonoyl-sphingosine (C24:1-ceramide) was examined using monomolecular films. While DMPC forms highly elastic liquid-expanded monolayers, both neat C16:0-ceramide and C24:1-ceramide yield stable solid condensed monomolecular films with small areas and low interfacial elasticity. Compression isotherms of mixed C16:0-ceramide/DMPC films exhibit an apparent condensation upon increasing X(cer16:0) at all surface pressures. The average area isobars, coupled with the lack of a liquid-expanded to condensed phase transition as X(cer16:0) is increased, are indicative of immiscibility of the lipids at all surface pressures. In contrast, isobars for C24:1-ceramide/DMPC mixtures show surface pressure-dependent apparent condensation or expansion and surface pressure-area isotherms show a composition and surface pressure-dependent phase transition. This suggests miscibility, albeit non-ideal, of C24:1-ceramide and DMPC in both liquid and condensed surface phases. The above could be verified by fluorescence microscopy of the monolayers and measurements of surface potential, which revealed distinctly different domain morphologies and surface potential values for the DMPC/C16:0- and DMPC/C24:1-ceramide monolayers. Taken together, whereas C16:0-ceramide and DMPC form immiscible pseudo-compounds, C24:1-ceramide and DMPC are partially miscible in both the liquid-expanded and condensed phases, and a composition and lateral pressure-dependent two-phase region is evident between the liquid-expanded and condensed regimes. Our results provide novel understanding of the regulation of membrane properties by ceramides and raise the possibility that ceramides with different acyl groups could serve very different functions in cells, relating to their different physicochemical properties.

Acylation↗
PubMed2001

Histamine H(3) receptors depress synaptic transmission in the corticostriatal pathway.

The effect of histamine on the main input to the striatum - the corticostriatal pathway - was studied using electrophysiological techniques in brain slices from rats and mice. Field potentials (FPs) were recorded in the striatum following stimulation at the border of the striatum and the cortex. Bath application of histamine caused a pronounced and long-lasting depression of FPs in rat slices with an IC(50) of 1.6 microM and a maximal depression of around 40%. In mouse slices histamine also depressed FPs, but to a lesser extent and more transiently. Further experiments in rat slices showed that histamine H(3) receptors were responsible for this depression since the selective H(3) receptor agonist R-alpha-methylhistamine (1 microM) mimicked the action of histamine whilst the selective H(3) receptor antagonist, thioperamide (10 microM) blocked the depression caused by histamine application. The histaminergic depression was probably not mediated indirectly through interneurons since blockade of GABA(A), GABA(B), nicotinic and muscarinic receptors or nitric oxide synthase did not prevent the histamine effect. Intracellular recordings from medium spiny neurons in the striatum revealed that histamine did not affect postsynaptic membrane properties but increased paired-pulse facilitation of excitatory synaptic responses indicating a presynaptic locus of action.

Animals↗
PubMed2001

Orexin A excites serotonergic neurons in the dorsal raphe nucleus of the rat.

Orexin A (10-300 nM) strongly excited dorsal raphe serotonergic neurons maintained in vitro. The depolarization persisted in the presence of tetrodotoxin (TTX, 0.5 microM) and was associated with an increase in input resistance. These results have relevance in the context of food intake regulation and the disease, narcolepsy.

Action Potentials↗
PubMed2001

The physiology of brain histamine.

Histamine-releasing neurons are located exclusively in the TM of the hypothalamus, from where they project to practically all brain regions, with ventral areas (hypothalamus, basal forebrain, amygdala) receiving a particularly strong innervation. The intrinsic electrophysiological properties of TM neurons (slow spontaneous firing, broad action potentials, deep after hyperpolarisations, etc.) are extremely similar to other aminergic neurons. Their firing rate varies across the sleep-wake cycle, being highest during waking and lowest during rapid-eye movement sleep. In contrast to other aminergic neurons somatodendritic autoreceptors (H3) do not activate an inwardly rectifying potassium channel but instead control firing by inhibiting voltage-dependent calcium channels. Histamine release is enhanced under extreme conditions such as dehydration or hypoglycemia or by a variety of stressors. Histamine activates four types of receptors. H1 receptors are mainly postsynaptically located and are coupled positively to phospholipase C. High densities are found especially in the hypothalamus and other limbic regions. Activation of these receptors causes large depolarisations via blockade of a leak potassium conductance, activation of a non-specific cation channel or activation of a sodium-calcium exchanger. H2 receptors are also mainly postsynaptically located and are coupled positively to adenylyl cyclase. High densities are found in hippocampus, amygdala and basal ganglia. Activation of these receptors also leads to mainly excitatory effects through blockade of calcium-dependent potassium channels and modulation of the hyperpolarisation-activated cation channel. H3 receptors are exclusively presynaptically located and are negatively coupled to adenylyl cyclase. High densities are found in the basal ganglia. These receptors mediated presynaptic inhibition of histamine release and the release of other neurotransmitters, most likely via inhibition of presynaptic calcium channels. Finally, histamine modulates the glutamate NMDA receptor via an action at the polyamine binding site. The central histamine system is involved in many central nervous system functions: arousal; anxiety; activation of the sympathetic nervous system; the stress-related release of hormones from the pituitary and of central aminergic neurotransmitters; antinociception; water retention and suppression of eating. A role for the neuronal histamine system as a danger response system is proposed.

Animals↗
PubMed2001

Tyrosine hydroxylase protein content in the medulla oblongata of the foetal sheep brain increases in response to acute but not chronic hypoxia.

We have investigated the effect of lowering foetal arterial PO(2) either acutely or chronically on tyrosine hydroxylase (TH) protein content in the dorsal and ventral medullary regions of the brainstem of the sheep foetus during late gestation. TH protein content increased in both the dorsal and ventral medullary regions of the foetal brainstem after exposure to acute hypoxia when compared to normoxia. In contrast there was no increase in the TH protein content of either the dorsal or ventral medullary regions in the brainstem of foetal sheep which were chronically hypoxaemic throughout late gestation as a consequence of experimental restriction of placental growth. The differences between the TH responses to acute and chronic hypoxaemia in the foetal sheep brainstem may be important in the mediation of physiological adaptations to these intrauterine stimuli and for the generation of an appropriate physiological response to hypoxia in the newborn period.

Acute Disease↗
PubMed2001

Basic fibroblast growth factor induced angiogenesis and prefabricated flap survival.

Prefabrication of a latissimus dorsi myocutaneous flap was performed in adult male Landrace pigs. Gelfoam sponges were used as a delivery system for basic fibroblast growth factor (bFGF) at the muscle-subcutaneous tissue interface. Skin survival and angiogenesis were augmented in the growth-factor-treated animals. These data support the use of basic fibroblast growth factor to enhance flap prefabrication.

Animals↗
PubMed2001

Cost effectiveness of treatment options in advanced breast cancer in the UK.

OBJECTIVE: To compare clinical and economic study data for docetaxel, paclitaxel and vinorelbine in the treatment of anthracycline-resistant advanced breast cancer. STUDY DESIGN AND METHODS: A Markov decision-analysis model to simulate the clinical course of a 'typical' patient with advanced breast cancer during salvage chemotherapy was updated with response rates and adverse effect rates from phase III clinical trial data for docetaxel, paclitaxel and vinorelbine. Costs were taken from UK national databases and hospitals. Utilities were estimated from 30 oncology nurses in the UK using the standard gamble method. PERSPECTIVE: National Health Service. RESULTS: When compared with other chemotherapeutic agents, docetaxel has been shown to increase response rate, time to progression and survival in patients with advanced breast cancer. In the base-case analysis, the incremental cost-utility ratio for docetaxel versus paclitaxel was pound1995 per quality-adjusted life year (QALY) gained (1998 values). The incremental cost-utility ratio for docetaxel versus vinorelbine was pound14 055 per QALY gained. In the comparison with vinorelbine, docetaxel provided the equivalent of an additional 92 days of perfect health. Sensitivity analyses confirmed the robustness of the model and the validity of the base-case analysis results. Even in the worst case scenarios, docetaxel remained cost effective compared with paclitaxel and vinorelbine. CONCLUSIONS: These findings support the use of the taxoids, notably docetaxel, in the management of advanced breast cancer.

Antineoplastic Agents, Phytogenic↗
PubMed2001

Of mice and men: virtual Hebb-Williams mazes permit comparison of spatial learning across species.

We developed a computer-generated virtual environment to test humans, for the first time, on the Hebb-Williams mazes. The goal was to provide a standardized test that could be used to directly compare human performance with that of C57BL/6J mice performing in real versions of the mazes. Such a comparison seems crucial if conclusions regarding genetic manipulations of rodents are to be mapped onto human cognitive disorders. The learning curves across species were strikingly similar, lending support to the rodent model of human spatial memory. Humans learned faster than rodents in both the acquisition and the test portions of the protocol, and females of both species were less efficient in solving these problems than males. These results represent the first modern comparison of human and rodent learning that uses the same test of spatial problem solving.

Adult↗
PubMed2000

Interactions between N-methyl-D-aspartate and nitric oxide in the modulation of ultrasonic vocalizations of infant rats.

The effects of interactions between N-methyl-D-aspartate (NMDA) and nitric oxide on ultrasonic vocalizations, motor activity and body temperature was investigated in 9-10-day-old rat pups. The competitive NMDA receptor antagonist, 3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP), and the nitric oxide synthase inhibitor, nitro-L-arginine-methyl ester (L-NAME), decreased the emission of ultrasonic vocalizations while NMDA and the nitric oxide precursor, L-arginine, produced a trend toward increased emission of ultrasonic vocalizations. CCP also attenuated the geotaxic response. Co-administration of CPP with L-NAME virtually abolished the emission of ultrasonic vocalizations and the ability to show the geotaxic response while co-administration of NMDA with L-arginine increased the emission of ultrasonic vocalizations and decreased body temperature with no effect on the geotaxic response. NMDA and L-arginine reversed the effects of L-NAME, but not of CPP, on ultrasonic vocalizations. L-arginine but not NMDA antagonized the effect of CPP on the geotaxic response. Our results confirmed the functional coupling between NMDA receptor activation and nitric oxide in modulating anxiety-like behavior and motor coordination in infant rats.

Animals↗
PubMed2000

Involvement of nuclear factor of activated T cells activation in UV response. Evidence from cell culture and transgenic mice.

Mammalian cells respond to UV radiation by signaling cascades leading to activation of transcription factors, such as activated protein 1, NFkappaB, and p53, a process known as the "UV response." Nuclear factor of activated T cells (NFAT) was first identified as an inducible nuclear factor in immune response and subsequently found to be expressed in other tissues and cells. To date, however, the regulation and function of NFAT in tissues and cells, other than the immune system, are not well understood. In this study, we demonstrate that UV radiation activates NFAT-dependent transcription through a calcium-dependent mechanism in mouse epidermal JB6 cell lines, as well as in the skin of NFAT-luciferase reporter transgenic mice. Exposure of JB6 cells to UV radiation leads to the transactivation of NFAT in a dose-dependent manner. A23187 had a synergistic effect with UV for NFAT induction, whereas pretreatment of cells with nifedipine, a calcium channel blocker, dramatically impaired the NFAT activity induced by either UV or UV plus A23187. Calcium-dependent activation of NFAT by UV was further confirmed by an in vivo study using NFAT-luciferase reporter transgenic mice. These results demonstrated that UV radiation is a strong activator for skin NFAT transactivation through calcium-dependent pathways, suggesting that NFAT activation may be a part of the UV response.

Animals↗
PubMed2000

Cloning and expression of glycolipid transfer protein from bovine and porcine brain.

Glycolipid transfer protein (GLTP) is a small (23-24 kDa), basic protein (pI congruent with 9.0) that accelerates the intermembrane transfer of various glycolipids. Here, we report the first cloning of cDNAs that encode the bovine and porcine GLTPs. The cDNA open reading frame for bovine GLTP was constructed by bridge-overlapping extension polymerase chain reaction (PCR) after obtaining partial coding cDNA clones by hot start, seminested, and rapid amplification of cDNA ends-PCR. The cDNA open reading frame for porcine GLTP was constructed by reverse transcriptase-PCR. The encoded amino acid sequences in the full-length bovine and porcine cDNAs were identical, consisting of 209 amino acid residues, and were nearly the same as the published sequence determined by Edman degradation. The cDNA encoded one additional amino acid at the N terminus (methionine), arginine at positions 10 and 200 instead of lysine, and threonine at position 65 instead of alanine. Expression of GLTP-cDNA in Escherichia coli using pGEX-6P-1 vector resulted in glutathione S-transferase (GST)-GLTP fusion protein. Regulation of growth and induction conditions led to approximately 50% of expressed fusion protein being soluble and active. Proteolytic cleavage of GST-GLTP fusion protein (bound to GST-Sepharose) and affinity purification resulted in fully active GLTP. Northern blot analyses of bovine tissues showed a single transcript of approximately 2.2 kilobases and the following hierarchy of mRNA levels: cerebrum > kidney > spleen congruent with lung congruent with cerebellum > liver > heart muscle. Reverse transcriptase-PCR analyses of mRNA levels supported the Northern blot results.

Amino Acid Sequence↗
PubMed2000

Charged membrane surfaces impede the protein-mediated transfer of glycosphingolipids between phospholipid bilayers.

A lipid transfer protein that facilitates the transfer of glycolipids between donor and acceptor membranes has been investigated using a fluorescence resonance energy transfer assay. The glycolipid transfer protein (23-24 kDa, pI 9.0) catalyzes the high specificity transfer of lipids that have sugars beta-linked to either a ceramide or a diacylglycerol backbone, such as simple glycolipids and gangliosides, but not the transfer of phospholipids, cholesterol, or cholesterol esters. In this study, we examined the effect of different charged lipids on the rate of transfer of anthrylvinyl-labeled galactosylceramide (1 mol %) from a donor to acceptor vesicle population at neutral pH. Compared to neutral donor vesicle membranes, introduction of negatively charged lipid at 5 or 10 mol % into the donor vesicles significantly decreased the transfer rate. Introduction of the same amount of negative charge into the acceptor vesicle membrane did not impede the transfer rate as effectively. Also, positive charge in the donor vesicle membrane was not as effective at slowing the transfer rate as was negative charge in the donor vesicle. Increasing the ionic strength of the buffer with NaCl significantly reversed the charge effects. At neutral pH, the transfer protein (pI congruent with 9.0) is expected to be positively charged, which may promote association with the negatively charged donor membrane. Based on these and other experiments, we conclude that the transfer process follows first-order kinetics and that the off-rate of the transfer protein from the donor vesicle surface is the rate-limiting step in the transfer process.

Animals↗