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Biomedical subjects

M G Murphy

Publications and source records attributed to M G Murphy.

At least 73 records · Page 4Linked to original sources
PubMed1986

Studies of the regulation of basal adenylate cyclase activity by membrane polyunsaturated fatty acids in cultured neuroblastoma.

The role of membrane polyunsaturated fatty acids (PUFAs) in the regulation of basal adenylate cyclase activity was examined in intact N1E-115 neuroblastoma cells. Addition of linoleic acid (50 microM) to the culture medium for 48 h resulted in a significant increase in phospholipid PUFA content and in a two- to fivefold increase in basal accumulation of cyclic AMP (cAMP). Both phenomena were reversed on removal of linoleate from the medium. PUFA enrichment stimulated cell proliferation by approximately 20% without altering the relative proportion of cellular protein. The supplemented cells synthesized significantly larger amounts of prostaglandin (PG) E and D than did the controls; however, blockade of PG synthesis by indomethacin or ibuprofen did not alter cAMP formation. Supplemented cells contained higher levels of malondialdehyde (MDA) than did controls, and MDA formation was reduced by coculture with alpha-tocopherol; however, its inclusion in the medium did not affect cAMP accumulation. Linoleate-supplemented cells responded to cyclase-activating agonists to the same extent as did control cells. Responses to inhibitory agonists (e.g., isoproterenol and carbamylcholine) were altered, but not to a sufficient extent to account for the PUFA-dependent increases in basal adenylate cyclase activity.

Adenylyl Cyclases↗
PubMed1985

Membrane fatty acids, lipid peroxidation and adenylate cyclase activity in cultured neural cells.

Lipid peroxidation and basal adenylate cyclase activity have been examined in neuroblastoma cultured with a variety of exogenous fatty acids. Formation of cyclic AMP depended upon fatty acid type, with supplementation affecting activities in the order: linoleate greater than cis-vaccenate = linolenate greater than control (132.7, 72.6, 71.9 and 36.0 pmol cAMP formed/mg protein, respectively). Lipid peroxidation, measured by formation of malondialdehyde (MDA), also varied with fatty acid; however, there was little correlation between MDA production and basal cyclase activity. Inclusion of alpha-tocopherol in culture-medium blocked MDA formation without affecting cAMP accumulation. Fe2+-dependent induction of peroxidation was accompanied by a time-dependent inhibition of cyclase activity.

Adenylyl Cyclases↗
PubMed1985

Oxygen dependent lactate utilization by Lactobacillus plantarum.

Lactobacillus plantarum P5 grew aerobically in rich media at the expense of lactate; no growth was observed in the absence of aeration. The oxygen-dependent growth was accompanied by the conversion of lactate to acetate which accumulated in the growth medium. Utilization of oxygen with lactate as substrate was observed in buffered suspensions of washed whole cells and in cell-free extracts. A pathway which accounts for the generation of adenosine triphosphate during aerobic metabolism of lactate to acetate via pyruvate and acetyl phosphate is proposed. Each of the enzyme activities involved, nicotinamide adenine dinucleotide independent lactic dehydrogenase, nicotinamide adenine dinucleotide dependent lactic dehydrogenase, pyruvate oxidase, acetate kinase and NADH oxidase were demonstrated in cell-free extracts. The production of pyruvate, acetyl phosphate and acetate was demonstrated using cell-free extracts and cofactors for the enzymes of the proposed pathway.

Energy Metabolism↗
PubMed1984

Correlation of oxygen utilization and hydrogen peroxide accumulation with oxygen induced enzymes in Lactobacillus plantarum cultures.

Two strains of Lactobacillus plantarum accumulated H2O2 when grown aerobically in a complex glucose based medium. The H2O2 accumulation did not occur immediately on exposure of the culture to O2 but was delayed for a time which, in the case of one strain, was dependent on the amount of inoculum used to seed the culture. The accumulation was always preceded by an increase in the rate of O2 utilization by the cultures. The latter coincided approximately with an increase in specific activity of NADH oxidase, pyruvate oxidase and NADH peroxidase. H2O2 was not a product of NADH oxidase in vitro but was formed in substantial quantities from O2 during oxidation of pyruvate. The three enzymes were induced by O2 and H2O2; the induction of NADH oxidase responded to lower levels of O2 (but not of H2O2) than the pyruvate oxidase or the NADH peroxidase.

Hydrogen Peroxide↗
PubMed1984

Increasing membrane polyunsaturated fatty-acid content augments cyclic AMP formation and prostaglandin production in NIE-115 neuroblastoma.

Addition of linoleic acid (50 microM) to culture medium significantly increases levels of polyunsaturated fatty acids (PUFA) in membrane phospholipids of NIE-115 neuroblastoma. Basal levels of cyclic AMP are elevated significantly in supplemented cells. Exogenous prostaglandins (PG) PGE1 and PGD2 stimulate cAMP formation in NIE-115 neuroblastoma. Supplemented cells produce higher levels of PGE and PGD than do control cultures. Inclusion of cyclooxygenase inhibitors in culture medium does not block elevation of cyclic nucleotide in supplemented cells. Endogenous PG production and receptor activation cannot account for increased cAMP in EFA-supplemented neuroblastoma.

Animals↗
PubMed1984

Opiate peptide receptors on intact NIE-115 neuroblastoma: radioligand binding properties, intracellular response, and effects of increasing membrane cholesterol.

Binding of [3H]methionine-enkephalin to intact N1E-115 neuroblastoma cells (competing ligand: naloxone) revealed a homogenous population of receptors with a density (Bmax) of 79.0 +/- 6.5 fmol/mg protein (mean SEM, N = 3) and an apparent Kd of 5.33 +/- 1.63 mM. The order of displacement of [3H]met-enkephalin was met-/leu-enkephalin greater than naloxone greater than morphine, suggesting that it is of the delta receptor class. Specific binding was heat-labile, stereospecific and sensitive to Na+. Adding met-enkephalin to intact neuroblastoma caused reductions of both basal and prostaglandin E1-stimulated levels of cyclic AMP (41.4 +/- 4.0% (N = 6) and 45.1 +/- 2.4% (N = 3) of control levels, respectively). Maximum inhibition (naloxone-reversible) was observed as low as 10(-7) M met-enkephalin. Preliminary results suggest that cells grown in cholesterol-supplemented medium show reduced binding of [3H]met-enkephalin.

Animals↗
PubMed1984

Bilateral ablation of the corticostriatal projection: behavioral, biochemical and electrophysiological correlates.

Striatal neuronal responses to dexamphetamine, 2.5 mg/kg i.p., were examined in normal and bilateral cortically ablated freely moving rats using multiunit recording. Striatal glutamate levels, D1 and D2 receptor binding, and haloperidal catalepsy were examined in both sham-operated and ablated animals. Bilateral ablation of the cortex, while not affecting dexamphetamine-induced behavioral activation, changed the striatal neuronal response from predominantly excitation to inhibition. Striatal glutamate levels were reduced 22% in ablated animals; and dopamine D-2 receptor binding sites were similarly decreased by 20%. In bilaterally ablated animals, haloperidol-induced catalepsy was greatly reduced.

Animals↗
PubMed1982

Collateral sprouting of somatosensory corticofugal axons into the cerebellar deafferented red nucleus.

Light microscopic-autoradiographic findings indicate that, following chronic lesions of cerebellorubral projections in the adult cat, somatosensory corticofugal axons in the cerebral crus give rise to collateral sprouts which reinnervate the deafferented red nucleus. These data strongly suggest that these new axons reinnervate the deafferented soma and proximal dendrites of the rubral neurons. This reactive synaptogenesis may complete with terminal sprouting from motor corticorubral synapses already present on the distal dendrites of the rubral neurons.

Animals↗
PubMed1982

Acid:coenzyme A ligase in brain: fatty acid specificity in cellular and subcellular fractions.

We measured long-chain fatty acid: coenzyme A (CoA) ligase (EC 6.2.1.3) activity with four fatty acids in brain homogenates, and cellular and subcellular fractions to determine whether there are differences in activity that could be correlated with differences in fatty acid composition and metabolism. In rat brain homogenates, ligase activity varied appreciably with the four acids, with 18:2 greater than 18:1 greater than 16:0 greater than 22:1 (nmol acyl-CoA formed/min/mg protein: 1.46, 1.20, 0.96, and 0.57, respectively). This order was similar under all incubation conditions tested, including variable pH and fatty acid concentrations. The relative specific activities (RSA, 16:0 = 1.0) with the four substrates were similar in rat brain homogenate, mitochondria, and microsomes, with the highest specific activities in the latter fraction. The RSA were also similar in ox brain homogenates, in rabbit brain microsomes prepared from gray and white matter, in neurons isolated from rat brain, and in cultured neuroblastoma cells. Rat liver homogenates had a significantly different pattern of RSA. These results indicate that the ligase(s) has a preference for certain fatty acids, but suggest that the major control of fatty acid composition and metabolism is a function of subsequent metabolic steps.

Animals↗
PubMed1981

Lipoprotein lipase and monoacylglycerol lipase activities during maturation of ob17 preadipocytes.

Lipoprotein lipase and monoacylglycerol lipase activities of developing ob17 preadipocytes were assayed through the selective inhibition of the former activity by 0.4% Triton X-100. After confluence both enzymes rose tao a peak activity around 13--15 days which was enhanced in insulin-treated cells. Inclusion of differentiation-blocking agents (bromodeoxyuridine, prostaglandin F2 alpha and bovine retinal extract) in the culture medium led in both enzymes to levels similar to those obtained in exponentially growing cells, in contrast to unspecific monoester hydrolase. Marked changes in the relative proportion of released to intracellular lipoprotein lipase activities were observed during adipose conversion. Our studies indicate that lipoprotein lipase and monoacylglycerol lipase are integral part of the program of differentiation of adipose cells.

Adipose Tissue↗
PubMed1980

Pontine gaze paresis due to traumatic craniocervical hyperextension. Report of two cases.

Pontine gaze paresis is frequently due to tumor of the brain stem. Occasionally it may be caused by inflammation or ischemia. Two cases are reported, each with pontine gaze paresis and other signs of lower brain-stem injury, basal skull fractures, and second cervical vertebra fractures. This pattern of injuries is believed to be the result of craniocervical hyperextension with stretch injury to the brain stem at the junction of the medulla and pons.

Accidents, Traffic↗
PubMed1976

The anatomical organization of the cerebello-olivary projection in the cat.

The cerebello-olivary pathway in the cat has been examined using orthograde and retrograde neuroanatomical tracing techniques. The orthograde transport of 3H-leucine from injection sites in the deep cerebellar nuclei labeled dentate and interpositus projections to the rostral two-thirds of the contralateral inferior olivary complex. These projections are topographically organized, with the dentate nucleus projecting to the principal olivary nucleus and the posterior and anterior interpositus nuclei projecting to the medial and dorsal accessory olives respectively. Fibers from the ventral half of the dentate nucleus terminate in the lateral bend and ventral lamina of the principal olive, whereas the medial and lateral parts of the dorsal half of the nucleus project to the medial and lateral regions of the dorsal lamina respectively. It is apparent that the more caudal parts of the interpositus nuclei project to areas of the medial and dorsal accessory olives near the caudal end of the principal olivary nucleus, whereas neurons in the more rostral parts of the interpositus nuclei project to the more rostral areas of the accessory olivary nuclei. A connection between the fastigial ncleus and the inferior olive could not be demonstrated. The retrograde transport of horseradish peroxidase (HRP) from injections sites in the inferior olive labeled cells throughout the contralateral dentate and interpositus nuclei. The labeled cells were especially numerous in the ventral parts of the dentate and posterior interpositus nlclei. These HRP-positive neurons were consistently small (10--15 mu) ovoid or spindle-shaped cells, with relatively large nuclei and light-staining Nissl substance. This evidence strongly suggests that the cerebello-olivary pathway originates from a population of small neurons in the dentate and interpositus nuclei and projects to specific, topographically defined areas in the contralateral inferior olive.

Animals↗