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Biomedical subjects

M Costa

Publications and source records attributed to M Costa.

At least 541 records · Page 30Linked to original sources
PubMed1980

gamma-Aminobutyric acid stimulates intrinsic inhibitory and excitatory nerves in the guinea-pig intestine.

The sites of action of gamma-aminobutyric acid (GABA) were examined in preparations of the distal colon and ileum of guinea pigs. GABA caused transient relaxations of the longitudinal and circular muscle of the colon and transient contractions followed by relaxation of the muscle of the ileum. The responses of both parts of the intestine were antagonized by tetrodotoxin and by bicuculline. Nerve-free preparations of the longitudinal muscle of the ileum were not affected by GABA, even in concentrations up to 10(-4) g/ml. There was a marked tachyphylaxis of the responses to GABA. Relaxations in response to GABA were not affected by pentolinium or by a combination of phentolamine and propranolol. Contractions in response to GABA were blocked by hyoscine. Neither the ascending excitatory or descending inhibitory components of the peristaltic reflex in the distal colon were affected by bicuculline or by making the intestine tachyphylactic to GABA. The results indicate that GABA stimulates receptors mediating excitation of cholinergic excitatory and enteric inhibitory neurons whereas it has little or no direct effect on the muscle of the ileum or distal colon.

Amino Acids↗
PubMed1980

Regulation of ornithine decarboxylase activity by amino acids, cyclic AMP and luteinizing hormone in cultured mammalian cells.

Any one of five amino acis (alanine, asparagine, glutamine, glycine, and serine) is an essential requirement for the induction of ornithine decarboxylase (EC 4.1.1.17) in cultured chinese hamster ovary (CHO) cells maintained with a salts/glucose, medium. Each of these amino acids induced a striking activation of ornithine decarboxylase in the presence of dibutyryl cyclic AMP and luteinizing hormone. The effect of the other amino acids was considerably less or negligible. The active amino acids at optimal concentrations (10 mM) induced only a 10-20 fold enhancement of enzyme activity alone, while in the presence of dibutyryl cyclic AMP, ornithine decarboxylase activity was increased 40-50 fold within 7-8 h. Of the hormones and drugs tested, luteinizing hormone resulted in the highest (300-500 fold) induction of ornithine decarboxylase with optimal concentrations of dibutyryl cyclic AMP and asparagnine. Omission of dibutyryl cyclic AMP reduced this maximal activation to one half while optimal levels of luteinizing hormone alone caused no enhancement of ornithine decarboxylase activity. The induction of ornithine decarboxylase elicited by dibutyryl cyclic AMP, amino acid and luteinizing hormone was diminished about 50% with inhibitors of RNA and protein synthesis. The specific amino acid requirements for ornithine decarboxylase induction in chinese hamster ovary cells was similar to the requirements for induction in two other transformed cell lines. Understanding the mechanism of enzyme induction requires an identification of the essential components of the regulatory system. The essential requirement for enzyme induction is one of five amino acids. The induction of ornithine decarboxylase by dibutyryl cyclic AMP and luteinizing hormone was additive in the presence of an active amino acid.

Amino Acids↗
PubMed1980

Carcinogenic activity of particulate nickel compounds is proportional to their cellular uptake.

Particles (less than or equal to 5 micrometers) of the potent carcinogen crystalline nickel subsulfide were actively phagocytized by cultures of Syrian hamster embryo cells and Chinese hamster ovary cells. Cells did not take up significant quantities of similar-sized particles of the noncarcinogen amorphous nickel monosulfide. The carcinogenic activity of this and other metal compounds appears to be proportional to their cellular uptake.

Animals↗
PubMed1980

Cyanylation of rhodanese by 2-nitro-5-thiocyanobenzoic acid.

Cyanylation of rhodanese (thiosulfate:cyanide sulfurtransferase, EC 2.8.1.1) with a nearly stoichiometric amount of 2-nitro-5-thiocyanobenzoic acid produces a modification of the essential sulfhydryl group. Different S-cyano derivatives are obtained with the enzyme intermediate bearing transferable sulfur bound as a persulfide group (sulfur-rhodanese: E-S-SH) and with the sulfur-free rhodanese (E-SH). The interaction of a neighboring sulfhydryl group splits thiocyanate from the sulfur-rhodanese derivative and cyanide from the sulfur-free rhodanese derivative. In both cases an intramolecular disulfide bond is formed. Iodoacetate is effective on the modified enzyme only after cyanide addition which splits the disulfide so that the essential sulfhydryl group can be alkylated.

Animals↗
PubMed1980

Immunohistochemical localization of polypeptides in peripheral autonomic nerves using whole mount preparations.

A method is described for the immunohistochemical localization of peptides in whole-mount preparations. Tissue is fixed as laminae with a picric acid/formaldehyde mixture and then dehydrated, cleared and rehydrated before exposure to antibodies. This procedure ensures adequate penetration of the antibody molecules without the need to freeze and thaw the tissue or to use detergents, preserves antigenicity and lowers non-specific background staining. The laminae are incubated with the primary antisera for 16 h at room temperature and, after washing, with a second, fluorescent tagged, antiserum. This can be followed by a peroxidase-anti-peroxidase localization of the second antiserum, which acts as a bridge. The method gives a precise and reproducible localization of immunoreactive peptides, with good penetration and low background even in thick preparation. Large areas can be scanned and neuroeffector relationships studied more easily than in sections.

Animals↗
PubMed1980

Phagocytosis of nickel subsulfide particles during the early stages of neoplastic transformation in tissue culture.

Cellular uptake of crystalline Ni3S2 particles (a potent carcinogen) and amorphous NiS particles (a noncarcinogen) were studied using light and electron microscopy. Cultured Syrian hamster embryo cells and Chinese hamster ovary cells actively phagocytized Ni3S2 particles (less than or equal to 5 micrometer) but did not take up NiS particles (less than 5 micrometer). For example, within 30 min after addition of Ni3S2 (high dose) to cell cultures, 12.5% of the cells contained nickel particles in the cytoplasm. Within 6 hr, 75% of the cells had engulfed Ni3S2 particles. Cultures exposed to NiS under similar conditions had less than 1.0% of the cells containing particulate nickel within 6 hr. The uptake of Ni3S2 was related to the particle concentration and duration of exposure. Concentration-dependent morphological transformation was induced by Ni3S2 in Syrian hamster embryo cells, but similar treatment of cells with amorphous NiS resulted in no morphological transformation. Pretreatment of Syrian hamster embryo cells with benzopyrene enhanced the cellular uptake of Ni3S2 particles and also the incidence of Ni3S2-induced morphological transformation. Our results suggest that the carcinogenic activity of particulate Ni3S2 is related to its cellular uptake.

Animals↗
PubMed1979

Immune lesions of central noradrenergic neurons produced by antibodies to dopamine-beta-hydroxylase.

(1) Intraventricular injection of antibodies to dopamine-beta-hydroxylase (DBH) caused degeneration of central noradrenergic nerve terminals in rats and guinea-pigs. In rats it was necessary to infuse exogenous complement in the form of guinea-pig serum together with the anti-DBH, whereas in guinea-pigs the anti-DBH was effective on its own. Control animals were infused with equivalent amounts of non-immune serum and complement and showed no signs of degeneration other than in the region of the needle tract. (2) There was a loss of varicosities in most terminal fields of the noradrenergic projections and swollen distorted axons were seen in both ascending and descending noradrenergic pathways. Noradrenergic cell bodies in the locus coeruleus and subcoeruleus appeared unaffected. No histochemical changes were observed in dopaminergic neurons. (3) The ultrastructural changes in degenerating axons that were first identifided by fluorescence histochemistry included swelling, vacuolation, accumulation of dense cored vesicles, lysosome-like bodies and smooth membranous sacs. The surrounding neuropil appeared normal. (4) There was a significant depletion of noradrenaline in all regions of the rat brain ranging from 20% in the hypothalamus to 80% in the neocortex. Dopamine concentrations were unaffected. (5) These observations provide a new approach to the production of selective lesions in specific neurotransmitter pathways that could be extended to non-adrenergic neurones. They may also be useful as a model for the study of autoimmune diseases of the nervous system.

Animals↗