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Biomedical subjects

M Bernard

Publications and source records attributed to M Bernard.

249 records · Page 14Linked to original sources
PubMedDate not supplied

Cellular and molecular regulation of serotonin N-acetyltransferase activity in chicken retinal photoreceptors.

Serotonin N-acetyltransferase (AA-NAT; arylalkylamine N-acetyltransferase; EC 2.3.1.87) is the penultimate enzyme in melatonin synthesis and large changes in the activity of this enzyme appear to regulate the rhythm in melatonin synthesis. Recent advances have made it possible to study the mRNA encoding chicken AA-NAT, which has only been detected in the retina and pineal gland. Within the retina, AA-NAT mRNA is expressed primarily in photoreceptors. The levels of chicken retinal AA-NAT mRNA and activity exhibit 24-hour rhythms with peaks at night. These rhythms appear to reflect circadian clock control of AA-NAT mRNA abundance and independent effects of light and darkness on both mRNA levels and enzyme activity. The effects of darkness and light may occur through alterations in cAMP-dependent protein phosphorylation, which increases AA-NAT activity in photoreceptor cell cultures. The cAMP-dependent increase of AA-NAT enzyme activity reflects, at least in part, increased mRNA levels and inhibition of enzyme inactivation by a posttranslational mechanism. This review discusses a hypothetical model for the cellular and molecular regulation of AA-NAT activity by circadian oscillators and light in chicken retinal photoreceptor cells.

Animals↗
PubMedDate not supplied

[Maternal serum screening for Down's syndrome: a user's club experience].

Screening of Down syndrome using maternal serum markers requires specific quality management. We report here a user's club experience (Down's Club Abbott) in surveying performances of AxSYM total beta hCG and AFP reagents combined to Maciel software. Regular analysis was carried out during three years (1998 to 2000). Values from five laboratories were collected to achieve calculation of medians for each parameter, multiple of the medians and initial positive rate (cut-off of 1/250 established in France). The large size of the observed population (3,1020 women during the studied period) increased the performances of statistical evaluations. In July 1999, five months after a change in reagents leading to new medians, these latter were recalculated in agreement with the manufacturer. Our experience exhibits that only the concomitant analysis of all parameters (medians, multiple of medians and initial positive rate) can allow the monitoring of a potential drift (bound or not to reagents). Moreover, such user's clubs enhance the individual quality management of the laboratories and allow a good follow-up of the performances of the testing in time.

Adult↗
PubMedDate not supplied

On some glycosidases (beta-D-mannosidase, alpha-L-fucosidase, N-acetyl-beta-D-glucosaminidase) of human seminal plasma.

The glycosidase activities (beta-D-mannosidase, alpha-L-fucosidase and N-acetyl-beta-D-glucosaminidase) have been compared in whole and split ejaculate samples from men whose couple suffers from infertility. The site of secretion of enzymatic activities is either prostatic or epididymal. The three enzymatic activities have possibly different origin and should constitute new biochemical markers of male genital tract.

Acetylglucosaminidase↗