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Biomedical subjects

J M Vincent

Publications and source records attributed to J M Vincent.

At least 55 records · Page 3Linked to original sources
PubMed1979

Ultrastructure of neurons in the auditory cortex of ageing rats: a morphometric study.

The cell bodies of pyramidal cells in layers II and V of rat auditory cortex were quantitatively examined in groups of rats 3, 6, 15, 23, 27 and 34-36 months of age. The mean diameters of cell bodies of both layer II and layer V neurons, as measured in 1 micron plastic sections, increased between 3 and 15 months of age, then decreased to a diameter that was less in the 36-month-old than in the 3-month-old rats. Morphometry of the nuclei of the cells was done by measuring nuclear area and nuclear envelope length directly on electron micrographs. In the layer II cells, neither parameter changed with advancing age. In the layer V cells, the mean nuclear area decreased significantly in the old animals and the mean envelope length increased. Point-counting techniques were applied to electron micrographs of cell bodies to determine the relative volume of selected organelles, inclusions and ground substance in the perikaryal cytoplasm. In this part of the study the chronological pattern of change in layer II and layer V pyramidal cells was similar. The relative volume of dense bodies increased linearly with advancing age, with a slightly more accelerated rate in layer II cells. The relative volume of ground substance remained essentially constant through 27 months, and then at 34-36 months decreased to 83% and 89% of the three-month level in layer V and layer II, respectively. The relative volume of the rough endoplasmic reticulum (RER) did not change significantly until after 15 months, at which time it began to occupy increasingly a larger fraction of the perikaryal cytoplasm. Finally, the relative volumes of mitochondria, multivesicular bodies and Golgi apparatus did not show clear trends of change during the 33-month period.

Aging↗
PubMed1979

Effect of a bacteriophage on the colonisation and nodulation of clover roots by a strain of Rhizobium trifolii.

The presence of a virulent bacteriophage in the root zone of clover growing in seedling agar under controlled environments (14--17 and 19--23 degrees C) produced changes in the persistence and symbiotic effectiveness of a susceptible strain of Rhizobium trifolii. The phage reduced the rhizoplane population of rhizobia and led to the appearance of variant substrains which were less susceptible to the bacteriophage and mostly ineffective in symbiotic nitrogen fixation. Some were also changed in colonial morphology and nutritional requirements. At the higher temperature, the frequency of bacterial variants increased and the number of nodules due to the parent strain decreased. A large initial population of bacteriophage was able to reduce, but generally did not completely suppress, nodulation.

Bacteriophages↗
PubMed1979

Effect of a bacteriophage on colonisation and nodulation of clover roots by paired strains of Rhizobium trifolii.

The effect of a virulent bacteriophage on the competitive behaviour of paired strains of Rhizobium trifolii in the root zone of clover plants was examined. The presence of bacteriophage reduced the population density of susceptible strains on the root surface and, in nodulation, favoured resistant or even partially resistant strains which were otherwise less able to form nodules. These effects occurred with different growth temperatures, host species, and ratios of strains in the inoculum.

Antibiosis↗
PubMed1975

Loss of agglutinating specificity in stock cultures of Rhizobium meliloti.

Several strains of Rhizobium meliloti which have been subcultured for 23-33 years have changed from being markedly specific in their somatic agglutination reactions to become widely cross-reactive. On the other hand a fresh collection of the same species obtained from naturally nodulated, field-grown plants revealed the high degree of agglutinating specificity which had previously characterised the old cultures. Attempts to reselect a specific substrain from old cross-agglutinating cultures by six plant passages, or to detect change to cross reactivity by ten successive subcultures of recent isolates were unsuccessful. However, one strain, isolated in 1939, was recently found to contain both specific and cross-reactive substrains. Practically all the cultures, both old and recent, showed considerable mutability in colony characteristics but none of these was consistently correlated with cross agglutinability. Instability in 6.4% (w/v) NaCl was characteristic of the cross-agglutinating cultures. Cross reactivity was associated with a shared lipopolysaccharide antigen (LPS) which appeared to be obscured by an outer antigen in most strains still showing specific agglutinability. In the exceptional case of strain SU27, agglutination could be attributed to its specific LPS.

Agglutination↗