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Biomedical subjects

M T Silva

Publications and source records attributed to M T Silva.

At least 91 records · Page 5Linked to original sources
PubMed1976

Bacterial mesosomes. Real structures or artifacts?

The ultrastructural study of membrane organization in gram-positive bacteria related to the OSO4 fixation conditions revealed that large, complex mesosomes are observed only when the bacteria are subjected to an initial fixation with 0.1%OSO4 in the culture broth, as in the prefixation step of the Ryter-Kellenberger procedure. Evidence was obtained suggesting that the large mesosomes are produced by this prefization. The kinetic study of the membrane morphological alterations occurring during the prefixation of Bacillus cereus with 0.1%OSO4 in the culture broth showed that the amount of mesosome material increases linearly from zero to a maximum observed at 1.7 min of prefixation and that at about this time a maximum is reached for the number of mesosomes per unity of cell area and for the average individual mesosome area. The large mesosomes observed in gram-positives fixed by the complete Ryter-Kellenberger procedure would be the result of the membrane-damaging action of 0.1%OSO4. Such damaging action was deduced from the observation thay 0.1%OSO4 quickly lyses protoplasts and induces a quick and extensive leakage of intracellular K+ from B. cereus and Streptococcus faecalis. In support of that interpretation is the observation that in bacteria subjected to several membrane-damaging treatments, mesosome-like structures are seen after three different fixation procedures. In bacteria initially fixed with 1% OSO4, 4% OSO4 or 2.5% glutaraldehyde, no large complex mesosomes are observed, small and simple invaginations of the cytoplasmic membrane being present. The size of these minute mesosomes is inversely proportional that causes of fixation. Uranyl acetate was found among the studied fixatives the one to the rate the least damage to bacterial membranes. This fixative satisfactorily preserves protoplasts. In bacteria initially fixed with uranyl acetate no mesosomes were found. The results of the present work throw serious doubts on the existence of mesosomes, both large and small, as real structures of bacterial cells. It is proposed that a continuous cytoplasmic membrane without infoldings (mesosomes) would be the real pattern of membrane organization in gram-positives.

Bacillus cereus↗
PubMed1976

The fine structure of Micrococcus radiophilus and Micrococcus radioproteolyticus.

The radiation resistant bacteria Micrococcus radiophilus and M. radioproteolyticus were studied by thin sectioning and freez-etching techniques and the two species were found to be similar in the fine structure. The only significant difference was in the appearance of the surfaces of the cell walls in freeze-etched preparations. Since the two species, together with M. radiodurans, possess a unique cell wall structure and a cell wall peptidoglycan, which is different from that of other micrococci and Gram-positive cocci, it is recommended that they be reclassified into a new genus.

Cell Division↗
PubMed1976

Effects of phenethyl alcohol on Bacillus and Streptococcus.

The activity of phenethyl alcohol (PEA) on Bacillus cereus, B. megaterium, and Streptococcus faecalis was studied by electron microscopy of thin sections and by the assay of intracellular K+ leakage. S. faecalis was unaffected by PEA at concentrations up to 0.5%, B. cereus was severely damaged by 0.5% PEA, and B. megaterium behaved intermediately. Important membrane ultrastructural alterations were observed in B. cereus cells treated with 0.5% PEA, namely the change in the geometry of the membrane profile from asymmetric to symmetric, the occurrence of prominent, complex mesosome-like structures, and membrane fracturing and solubilization. Protoplasts from B. megaterium were found to be quickly lysed by 0.5% PEA due to the disruption of the cytoplasmic membrane. The electron microscopic observations, together with the results of the study of the K+ efflux from B. cereus and B. megaterium, indicate that PEA primarily and directly damages the cytoplasmic membrane of sensitive bacteria. The breakdown of the permeability barrier probably is responsible for the observed bactericidal action of 0.5% PEA on B. cereus.

Bacillus cereus↗
PubMed1975

Screening hallucinogenic drugs: systematic study of three behavioral tests.

The effects of several hallucinogenic and non-hallucinogenic drugs have been studied on three behavioral tests proposed as useful indexes of hallucinogenic activity: "head-twitching" in mice, defecation in an open-field, and suppression of responding on a differential reinforcement of low rates (DRL) schedule of reinforcement. According to the original propositions, after administration of hallucinogenic agents the frequency of head-twitches would increase in mice, the defecation of rats in an open field would decrease without consistent change in ambulation, rearing and grooming, and the responding of rats on a DRL schedule would yield a typical cumulative record pattern. It was found that the head-twitch test was sensitive to mescaline and LSD-25, but not to delta9-THC or to myristicin and elemicin. Besides, the data on interobserver agreement suggested there is a high degree of subjectivity involved in assessing this response. In the open-field test, non-hallucinogenic drugs such as chlorpromazine and apomorphine fell into the hallucinogenic pattern proposed. In addition, the post-injection interval selected seemed to critically affect defecation scores. The DRL "hallucinogenic" pattern occurred nonspecifically after administration of hallucinogenic and non-hallucinogenic drugs. It was concluded that the three tests have limited value for screening purposes.

5-Hydroxytryptophan↗
PubMed1973

Ultrastructure of the cell wall and cytoplasmic membrane of gram-negative bacteria with different fixation techniques.

The ultrastructure of the cytoplasmic membrane and cell wall of two strains of Escherichia coli, Proteus morganii, P. vulgaris, Acinetobacter anitratum, Moraxella lacunata, Erwinia amylovora, Acinetobacter sp., and of a plant pathogen, unclassified gram-negative, fixed by the Ryter-Kellenberger procedure, was found to be significantly affected by the use or omission of the uranyl postfixation included in that procedure, and by the presence or absence of calcium in the OsO(4) fixative. The omission of the uranyl treatment results in a less clear profile of both the outer membrane of the cell wall and of the cytoplasmic membrane. The observation of these two membranes is further limited when both uranyl and calcium are omitted. The R-layer and the material covering the surface of the cell wall appear more distinct when the uranyl postfixation is not used. Evidence is given suggesting that the influence of uranyl and calcium ions on the appearance of the outer and cytoplasmic membranes would be primarily due to their action as fixatives, whereas the influence of uranyl on the appearance of the R-layer would be due to a direct action on the peptidoglycan component of this layer. When uranyl acetate is used as a section stain after the embedding in plastic, it improves the observation of the R-layer. In this case, a well contrasted R-layer is consistently observed in all strains studied, provided that the postfixation has been omitted. The frequent difficulty in clearly observing the R-layer in many published micrographs probably results from the common use of uranyl postfixation.

Alcaligenes↗
PubMed1972

Ultrastructural alterations induced by moist heat in Bacillus cereus.

The ultrastructural alterations induced in vegetative, exponentially growing Bacillus cereus cells suspended in broth, by heating at 65 C for 2 and 15 min and 100 C for 5 min, were studied by electron microscopy of thin sections. The following alterations were observed: (i) change in the triple-layered profile of the membranes from the normal asymmetric to a symmetric geometry, appearance of fractures in the membranes, occurrence of prominent myelin-like systems of concentric membranes; (ii) disappearance of the ribosomes in most cells heated at 65 C and in all cells heated at 100 C; (iii) cytoplasmic precipitation resulting in the appearance of dense blocks of Pronase-sensitive material. The cell wall appears unaffected in most preparations. No signs of deoxyribonucleic acid damage are observed. These ultrastructural data are discussed in relation to the alterations in the chemistry and physiology of heated bacteria described in the literature.

Bacillus cereus↗
PubMed1971

Telemetered recording of hormone effects on hippocampal neurons.

Frequency-modulated telemetry was used to record the effects of hormones on single-unit activity in the brains of freely moving rats. Corticosterone decreased unit activity in the dorsal hippocampus. Adrenocorticotrophic hormone had the opposite effect.

Adrenocorticotropic Hormone↗
PubMed1969

Pituitary-adrenal influences on fear responding.

In a passive avoidance situation, hypophysectomized male rats show less fear than normal rats, whereas adrenalectomized rats show greater fear than normals. These results probably occur because hypophysectomized rats lack adrenocorticotrophic hormone, which increases arousal or emotionality, whereas adrenalectomized animals lack certain adrenal steroids, which inhibit excitatory effects. The results indicate that adrenocorticotrophic hormone and certain adrenal steroids have opposite effects in regulating fear-motivated behavior.

Adrenal Cortex Hormones↗