[Folates and the neural tube. Review of the literature]. / Folates et tube neural. Revue de la littérature.

There are two types of neural tube fusion abnormality (NTFA)--craniorachischisis and rachischisis--with a prevalence of 11.2/10,000 in continental Europe. Their prevalence varies widely and is influenced by many factors, including geographical, racial and seasonal components. The transmission of NTFAs is usually polygenic and affected by many factors, and far more rarely of the mendelian monogenic type. The occurrence of NTFAs has been shown to be due to folic acid (FA) deficiency. First suspected in 1965, FA deficiency was proved to be a cause of NTFAs both occurring and recurring in the 1980s. FA deficiency might act by preventing the remethylation of homocysteine to methionine, the latter is known to play an essential role in fusion of the neural tube in animals. Primary prevention of NTFAs therefore requires that FA supplementation be given to women planning a pregnancy and after conception. Two possible ways of preventing FA deficiency can be envisaged, ie. via folic acid supplementation or systemic enrichment of the basic diet. Neither of the two alternatives is sufficient by itself and probably a combination of the two would provide the best means of preventing neural tube defects.

[The cervix uteri in pregnancy]. / Le col de l'utérus en cours de grossesse.

It is during labor that the most dramatic changes to the cervix are apparent, yet the cervix begins its process of adapting early on in pregnancy. From an anatomic perspective, the gravid cervix is changed little in the beginning of pregnancy. It is strikingly less muscular than the rest of the uterus and its connective tissue is comprised essentially of collagen fibers and a matrix rich in proteoglycans. Cervical maturation begins imperceptibly during pregnancy but does not become noticeable until shortly before labor. These changes result from biochemical modifications of the cervical constituents with dissolving of collagen fibers and changes in the respective levels of different proteoglycans. The regulation of this maturation is still poorly understood; steroid hormones, prostaglandins, and collagenases have all been implicated. The effacement and dilatation of the cervix occur with labor. Effacement corresponds with thinning and opening of the internal os and dilatation corresponds with opening of the external os. These phenomena are passive, resulting from physical pressure from fetal engagement under the effects of uterine contractions. Our material understanding of cervical maturation and dilatation are still insufficient, for although we are better and better able to guide the induction and course of labor, it still is impossible for us to arrest premature cervical maturation in the setting of a threatened abortion or premature delivery.

The expression of neuropeptide Y immunoreactivity in the avian sympathoadrenal system conforms with two models of coexpression development for neurons and chromaffin cells.

We have studied the expression and development of neuropeptide Y-like immunoreactivity (NPY-LI) in the sympathoadrenal system of the chicken using single and double immunocytochemical techniques and radioimmunoassay. NPY-LI is expressed by neurons of the paravertebral sympathetic ganglia and by chromaffin cells of the adrenal gland in embryonic and adult chickens. The peptide is coexpressed with catecholaminergic properties in neurons. In chromaffin cells, it is also expressed with immunoreactivity to somatostatin and serotonin. We have used the expression of NPY-LI to analyze how cells that coexpress two or more neuroactive substances arrive at their final phenotype. Our results suggest that the ontogeny of coexpression in neurons of the avian paravertebral sympathetic ganglia occurs in a sequential pattern, where the expression of the peptide follows the initial expression of the "classical neurotransmitter". In contrast, in chromaffin cells, expression of the peptides occurs concomitantly with expression of catecholaminergic properties or soon after. Initially, coexpression of several neuroactive substances occurs, but this is followed by further specialization where the expression of one peptide prevails over the other. We believe that the two models of coexpression shown by our results can be used to describe the ontogeny of coexpression in other cells of the nervous system.