Biomedical subjects

Michel Denis

Publications and source records attributed to Michel Denis.

24 records · Page 2Linked to original sources

PubMed2004

Preserved visuo-spatial transformations in representational neglect.

Patients with representational unilateral neglect were impaired in immediate recall of novel material on the neglected side as presented (viewed and removed or verbally described) or following mental rotation. Transforming material from the neglected (left) side to the non-neglected (right) side resulted in no additional loss; patients were unimpaired in directing attention to the neglected side of their representation in order to perform the mental rotation. These findings cannot be explained by the widely adopted attention deficit hypothesis for representational neglect. It is suggested that the disorder arises from damage to temporary storage functions of visuo-spatial working memory.

Adult↗

PubMed2004

The boron-organic carbon correlation in water.

A linear correlation between boron and organic carbon has been identified for groundwater and surface water. The boron to organic carbon ratio is found to be higher for groundwaters than for surface waters, since surface waters are more heavily loaded with natural organic matter. This correlation in water might result from the complexation of boron with polar organic compounds, not adsorbed on activated carbon, or from independent species. Any deviation from the boron/organic carbon ratio is used to identify pollution events for both boron or organic compounds, and to characterise the origin of unusual water chemistries. Moreover, such a correlation could be used to define natural water pristine conditions in order to restore good quality of water resources.

Adsorption↗

PubMed2004

The metrics of spatial distance traversed during mental imagery.

The authors conducted 2 experiments to study the metrics of spatial distance in a mental imagery task. In both experiments, participants first memorized the layout of a building containing 10 rooms with 24 objects. Participants then received mental imagery instructions and imagined how they walked through the building from one room to another. The authors manipulated Euclidean distance involved in these imaginary motions: Spatial distance measured in centimeters on the layout was either short or long. Independently, they varied categorical distance: The motions led through one room or two rooms. The time needed to imagine motions and response times to test probes indicated that both Euclidean distance and categorical distance affected mental imagery. The authors discuss the new finding of categorical distance effects in mental imagery and relate the results to earlier failures to find Euclidean distance effects in formally equivalent studies of narrative comprehension.

Humans↗

PubMed2004

Temperature and growth-phase effects on Aeromonas hydrophila survival in natural seawater microcosms: role of protein synthesis and nucleic acid content on viable but temporarily nonculturable response.

The behaviour of Aeromonas hydrophila in nutrient-poor filter-sterilized seawater was investigated at 23 and 5 degrees C with respect to its growth phase. At both temperatures, the culturable A. hydrophila population declined below the detection level (0.1 c.f.u. ml(-1)) after 3-5 weeks, depending on the initial physiological state of the cells. During the first week, starved A. hydrophila cells appeared more resistant to the seawater stress at 5 degrees C than cells initially in the exponential growth phase. This difference was not observed at 23 degrees C, where de novo protein synthesis seemed to be required for long-term adaptation of cells from the exponential growth phase. Over the duration of the experiments, intact and total cell concentrations were not significantly affected, indicating that bacteria had entered a so-called viable but nonculturable state (VBNC). However, the incubated bacteria rapidly became heterogeneous with respect to their nucleic acid content, and their cell size decreased faster at 23 than at 5 degrees C. Resuscitation of VBNC cells was attempted by a temperature shift from 5 to 23 degrees C without exogenous nutrient addition. Comparison of the growth rates of the stressed population and of the untreated bacteria growing in the same autoclaved initial cell suspension showed significantly faster growth for the stressed cells, suggesting that in addition to growth of the few culturable stressed cells, a proportion of injured cells became culturable.

Aeromonas hydrophila↗

PubMed2003

[Viability of heterotrophic bacteria in the Bay of Marseilles].

Marine microorganism activities are commonly assessed by bulk methods and assigned to the total cell count. The presence in significant amounts of ghost, dead, and damaged cells makes such as assignment a non-correct one. A Nucleic Acid Double Staining protocol (NADS) of fresh water bacteria (Barbesti et al., Cytometry 40 (2000) 214-218) has been adapted to resolve viable, damaged and dead cells in marine environments (Grégori et al., Appl. Environ. Microbiol. 67 (2001) 4662-4670). The present reports the first in situ application of this approach, conducted in the Bay of Marseilles in winter and spring periods at two sites with contrasted features.

Bacteria↗

PubMed2002

A flow cytometric approach to assess phytoplankton respiration.

Microbial respiration in the ocean is considered as the major process representative of the organic matter biological oxidation. The corresponding metabolic CO2 production was estimated to be about 22 Pg C y(-1). However, the in situ respiration rate is generally too low (by several orders of magnitude) to be accessible to the available direct measurement methods. Some fluorescent probes, such as DiOC6(3) (Molecular Probes, USA) have been shown to be very sensitive to changes in the proton electrochemical potential difference (DeltamuH+), characterising mitochondrial and plasmic membranes bearing the cell respiratory system in eukaryotic and prokaryotic cells respectively. In mitochondria, DeltamuH+ is linked to the flux of oxygen uptake by a linear relationship. To our knowledge, no such relationship has been established in the case of whole marine cells. In the present work, we addressed the dark respiration rate of the Chlorophyceae Dunaliella tertiolecta (Butcher) in axenic cultures, both directly by using a highly sensitive oxygraph (Oroboros) and by staining cells with DiOC6(3). We found and standardized a linear relationship between oxygen uptake by D. tertiolecta and its green fluorescence induced by DiOC6(3), enabling the determination by flow cytometry of the respiration rate of D. tertiolecta.

Animals↗