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Biomedical subjects

D Samuel

Publications and source records attributed to D Samuel.

At least 253 records · Page 14Linked to original sources
PubMed1985

Altered characteristics of [3H]dopamine release from superfused slices of corpus striatum obtained from rats receiving ethanol in vivo.

Ethanol, 50 mM, in vitro inhibited the release of [3H]dopamine ([3H]DA) induced by depolarisation with 40 mM K+ from slices of corpus striatum of the rat. In contrast, the release of [3H]DA induced by the Ca2+ ionophore (A23187) was enhanced by the presence of ethanol in vitro. When similar preparations were obtained from brains of rats which had received ethanol in vivo chronically by inhalation for 5-7 days the characteristics of release of [3H]DA were altered. Thus, the inhibitory effect of ethanol in vitro on release induced by K+-depolarisation was lost, as was the enhancing effect of ethanol on the release induced by A23187. When release of [3H]DA was studied in the absence of added ethanol the fraction of stored 3H released either by K+-depolarisation or by A23187 was increased in the preparations from animals which had received ethanol in vivo. Similar changes in release induced by A23187, though of lesser magnitude, could be seen in rats which had received ethanol acutely (3 g kg-1 i.p.; 30 min). An even greater fraction of [3H]DA was released by A23187 in preparations from rats which had been made physically dependent on ethanol. These changes in the release characteristics of [3H]DA were still apparent in animals undergoing a physical syndrome of withdrawal from ethanol. The results are discussed in relation to the cellular basis for the development of tolerance to and dependence on ethanol.

Animals↗
PubMed1985

Improved sensitivity and specificity of sandwich, competitive and capture enzyme-linked immunosorbent assays for allergen-specific antibodies.

Indirect ELISA is widely used to detect specific antibodies but can suffer from high non-specific binding-particularly of IgG. The use of affinity-purified rabbit antibody-coated microtitre plates to bind antigen greatly increases sensitivity without a significant increase in non-specific binding of IgG. Capture, competitive and sandwich assay procedures gave comparable results for IgG antibodies; but only the sandwich assay was suitable for detection of IgE antibodies.

Allergens↗
PubMed1985

[Encephalopathy following portal shunting in nodular regenerative hyperplasia of the liver].

Two patients with nodular hyperplasia of the liver developed a chronic disabling encephalopathy after an interposition mesocaval shunt. Both had a low total hepatic blood flow-rate postoperatively. Encephalopathy disappeared following surgical occlusion of the shunt. These observations emphasize the risk of postshunt encephalopathy in patients with non-cirrhotic intrahepatic portal hypertension.

Adult↗
PubMed1984

The maturation response of stage IV, V, and VI Xenopus oocytes to progesterone stimulation in vitro.

Full-grown Xenopus oocytes, Stage VI (1200-1300 microns), undergo meiotic maturation when exposed to progesterone. Smaller stage IV (800 microns) and stage V (1000 microns) oocytes remain in prophase arrest when exposed to this steroid. The larger stage VI oocytes undergo an intracellular alkalization from 7.2 to 7.6, a six- to eightfold increase in the phosphorylation of the 40 S ribosomal protein S-6, and a two- to threefold increase in total protein synthesis when exposed to progesterone. It was found that 800- to 1000-microns oocytes do not undergo these physiological changes when exposed to progesterone. This lack of response could explain the failure of small oocytes to undergo germinal vesicle breakdown (GVBD). However, when stage IV and V oocytes were artificially alkalized to a pHi of 7.6 by the weak bases, trimethylamine, procaine, or methylamine, S-6 phosphorylation was stimulated four- to sixfold and protein synthesis was stimulated two- to threefold, but they still did not undergo GVBD. Stage IV and V oocytes are able to amplify MPF injected into their cytoplasm and undergo GVBD. Thus, 800- to 1000-microns oocytes appear to contain a store of inactive MPF in their cytoplasm. It seems that an additional physiological parameter(s), that is unique to steroid-treated stage VI oocytes, is responsible for activating this MPF which induces GVBD.

Animals↗
PubMed1983

Picrotoxin inhibits the effect of ethanol on the spontaneous efflux of [3H]-dopamine from superfused slices of rat corpus striatum.

The presence of ethanol, 100 microM, in the superfusate enhanced the spontaneous release of previously uptaken [3H]-dopamine from slices of rat corpus striatum, but produced a small inhibition of K+-stimulated release. The concomitant presence of picrotoxin, 10 microM, in the superfusate prevented the enhancement of spontaneous release of [3H]-dopamine by ethanol with equivocal effects on K+-stimulated release. When present in the superfusate alone picrotoxin had no effect on [3H]-dopamine release.

Animals↗
PubMed1983

Intractable diarrhea in children with VIP-secreting ganglioneuroblastomas.

This paper describes two children with diarrhea, hypokalemia, and VIP-secreting ganglioneuroblastomas, and includes further evidence that VIP is the cause of the loose stools among patients with such tumors. It suggests that the level of this peptide should be measured in pediatric patients with intractable diarrhea of unknown etiology. Clinicians have long recognized intractable diarrhea as an occasional feature of neuroblastoma, ganglioneuroblastoma or ganglioneuroma. Until recently catecholamine was thought to cause the frequent stools in some patients with these tumors. New radioimmunoassay methods, the identification of new hormones and hormone-like substances, and the discovery that some of the tumors which cause diarrhea secrete Vasoactive Intestinal Peptide (VIP), make it probable that this substance is responsible for the diarrhea in such patients.

Child, Preschool↗
PubMed1982

Alleviation of drug withdrawal symptoms by treatment with a potent mixture of natural lipids.

Acute treatment with morphine, as well as with other addictives, causes an initial decrease in brain membrane lipid microviscosity. Upon chronic exposure to the addictive drug, the original fluidity of brain membranes is restored, mostly due to an increase in the cholesterol content. Withdrawal of the drug leaves the membranes hyperviscous and the central nervous system supersensitive, as manifested in the abstinence syndrome. Based on this scheme of events, we have designed treatments of addicted mice with a special lipid mixture extracted from hen egg-yolk (Active-lipid, AL), which is a highly potent membrane fluidizer. In vivo treatment of morphine-addicted mice with AL, either by injection or as a diet supplement, reversed the brain membrane hyperviscosity and, concomitantly, markedly reduced, or even completely abolished the withdrawal symptoms precipitated by naloxone. Treatments with the fully saturated, rigidifying phospholipid dipalmitoyl-lecithin, exacerbated the withdrawal symptoms. These results could be the basis for a novel innocuous treatment which may facilitate the rehabilitation of drug and alcohol addicts.

Animals↗
PubMed1981

Lipid-induced modulation of opiate receptors in mouse brain membranes.

The binding of [3H] D-Ala-enkephalinamide (DAEA) to crude mitochondrial fractions (P2M) from mouse forebrain was determined after modulation of membrane lipid microviscosity. Lipid fluidization of P2M membranes, following treatment with egg lecithin, resulted in a 50% loss of specific binding of DAEA. Increasing the P2M lipid microviscosity, by incorporation of cholesteryl hemisuccinate (CHS), increased the accessibility of the opiate receptors up to a peak level of 170% which decreased sharply upon further increase in lipid microviscosity. The processes resulting from lipid rigidification may have important implications for aging and for drug addiction.

Animals↗
PubMed1981

The effect of anti-synaptosomal membrane antibodies of neurotransmitter uptake.

Antibodies raised against synaptosomal plasma membranes of rat hippocampus (anti-HPC IgG) caused inhibition of [3H]noradrenaline, [3H]5-hydroxytryptamine, [3H]GABA and [3H]aspartate uptake into S1 fractions and slices of hippocampus and cerebral cortex, but not those of caudate nucleus and hypothalamus. Similar inhibition was not observed on using antibodies against synaptosomal membranes of rat caudate nucleus. Anti-HPC IgG raised against synaptosomal membranes of hippocampus failed to alter both spontaneous and K+-evoked release of [3H]noradrenaline. They did not interfere with the binding of [3H]desipramine (the potent noradrenaline-uptake inhibitor) and with the binding of [3H]dihydroalprenolol, thus excluding any interaction of the antibodies with drug receptors which are located on either the pre- or postsynaptic membrane. The anti-HPC IgG inhibit the enzymatic activity of [Na+-K+-]ATPase by 30% upon incubation of the antibodies with crude membrane preparations. A comparison of their inhibitory effects with those of the neurotoxin 6-hydroxydopamine suggests that the corresponding hippocampal specific antigens are located at a presynaptic site.

Animals↗
PubMed1980

The characterization and phosphorylation of an actin-like protein in synaptosomal membranes.

A protein of 43,000 daltons, named protein 'C', is a component of synaptosomal plasma membranes, vesicular and microsomal membranes, as well as synaptosomal and cellular cytoplasm. Protein 'C' undergoes endogeneous phosphorylation in synaptosomal plasma membranes but not in other subcellular fractions. This phosphorylation is stimulated by papaverine and calcium, inhibited by magnesium and not affected by cyclic nucleotides. Protein 'C' and muscle actin were shown to be very similar by isoelectric focusing, two dimensional gel electrophoresis, and by peptide mapping. This suggests that protein 'C' is an actin-like protein which undergoes endogenous phosphorylation specifically in synaptosomal plasma membranes. Phosphorylation of protein 'C' may be involved in neurotransmitter release.

Actins↗