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G Guyot

Publications and source records attributed to G Guyot.

11 recordsLinked to original sources
PubMed2004

Key role of the low molecular size fraction of soil humic acids for fluorescence and photoinductive activity.

The IHSS soil humic acid (HA) standard and two HAs from soils of very different origin (Chernozem and Ranker) were fractionated by tandem size-exclusion chromatography-polyacrylamide gel electrophoresis. From each HA, three fractions with different molecular sizes (MSs) and electrophoretic mobilities were obtained and investigated for their fluorescence properties and abilityto photoinduce the transformation of 2,4,6-trimethylphenol and herbicide fenuron. Regardless of the source of the HA, the two high MS fractions were found to be very weakly fluorescent. They photoinduced the degradations of fenuron and 2,4,6-trimethylphenol less efficiently than the bulk HA (10-50-fold and 1.4-5.3-fold, respectively). In contrast, the low MS fraction was proved to be fluorescent and to photoinduce the transformation of probes as least as efficiently than the bulk HA. These results show that (i) most of fluorophores and a great part of photoinductive chromophores are located in the low MS fractions of soil HAs and (ii) this distribution of photochemically active constituents may be characteristic across broad soil types.

Chromatography, Gel↗
PubMed1983

[Adapto-electroretinographic study of regeneration of the visual pigments in the fauve de Bourgogne and albino rabbit after photobleaching with monochromatic light].

Kinetics of rod pigment regeneration were studied in vivo in Fauve de Bourgogne and Albino rabbits by adapto-electroretinography (AERG). Electroretinography in the rabbit using polychromatic flashes affords the means to dissociate the response of the cones (a-wave, b1-wave: photopic function), from that of the rods (b2-wave scotopic function). After photobeachting, electroretinograms were recorded at two minutes' intervals during dark adaptation of one hour duration. Variations of b2/b1 with time of dark adaptation provide an adapto-electroretinogram giving relative measurements of rod pigment concentration at various stages of regeneration. In the present study, photobleaching was provoked by monochromatic light (at 405, 436 and 546 nm) actinometrically controlled. Studies were conducted in two Fauve de Bourgogne and two Albino rabbits. The effect of four doses, varying from 4.10(17) photon.cm-2 to 1.10(19) photon.cm-2, was measured at each wavelength on the AERG in the four rabbits. First order kinetics for rod pigment regeneration were observed, mainly at 546 nm and at high dose levels: overall regeneration rate is apparently controlled by the isomerization step. For Fauve de Bourgogne and Albino rabbits, the regeneration rate depends on the bleaching wavelength and on the dose. At high dose levels and for long wavelengths, delayed recoveries are observed in the Fauve de Bourgogne animals. However, durations of delays are shorter with monochromatic light experiments than with polychromatic light bleaching, at the same dose. Differences of ocular media transmission may be responsible for a faster regeneration process at shorter than at longer wavelengths.

Adaptation, Physiological↗
PubMedDate not supplied

Field dependence in the institutionalized elderly.

The institutional-inducement hypothesis of field dependence regression in the elderly was assessed by administering the Children's Embedded Figures Test (CEFT) to a group of elderly upon admission to a nursing home and to a group of community-living elderly. Both groups were retested four months later. The institutionalized group exhibited significantly lower CEFT scores on initial testing than the community-living group. In addition, the CEFT scores for the institutionalized group declined significantly from pretest to posttest. The results suggested that greater field dependence in the institutionalized elderly may be due to pre-institutional dependence regression that continues after institutionalization. Additional measures of mental status and activity levels were also lower in the institutionalized group upon admission supporting a pre-institutional generalized regression effect.

Aged↗