A modification of tooth germ cultivation in vitro and in ovo

Mandibular molar anlages excised from 17-day mouse foetuses were cultured in vitro or in ovo (on the chorioallantoic membrane). In both cases, the explants were underlain either with a Millipore filter or with a piece of fibrin foam. Tooth germs were harvested after 7 days of cultivation and processed histologically. Spatial arrangement was highly preserved in the tooth germs cultured in vitro on fibrin foam. In vitro cultures on Millipore filters revealed significant flattening of tooth germs, caused especially by the collapse of enamel organ and the pulp. The cytodifferentiation of tooth germs cultured in vitro on both substrates (Millipore filter, fibrin foam) was characterized by the presence of odontoblasts, polarizing ameloblasts and predentine. The cytodifferentiation of tooth germs cultured in ovo on Millipore filters placed on chorioallantoic membrane was characterized by the presence of odontoblasts, ameloblasts, predentine, dentine and enamel. However, the flattening of these explants was identical with the changes of the explants cultured on Millipore filters in vitro. In ovo cultivation on the fibrin foam failed to bring satisfactory results.

[Sensitivity of the primordia of various organs to chemical substances]

In the experiments performed in chick embryos, using the chick embryo screening test (CEST)-1 and CEST-2 technique, 100 various classes of chemical substances have been tested for teratogenic activity. Estimation of three morphogenetic systems (caudal part of the body, facial skull and extremities) has demonstrated that some of the substances do not produce any damaging effect, other produce some lesions in selected germs, the third influence two or three germs simultaneously. Similar picture is also specific for the effect of the chemical substances to the rat intrauterine development. Owing to data obtained, we come to the conclusion that for screening of embryotoxicity of various xenobiotics under in vivo and in vitro experimental conditions one should not orient to one single germ.

Tooth size in children with cleft lip and palate

The mesiodistal and buccolingual dimensions of primary and permanent teeth were measured in 246 children with either isolated cleft palate or complete unilateral cleft lip and palate. The primary teeth of males with clefts were reduced in their buccolingual dimension compared to the control, while in females there were reductions in the mesio-distal dimension. There were no remarkable differences in the size of the permanent teeth in males with clefts. Females with clefts had reduced buccolingual dimensions of the permanent teeth, in both jaws.

Origin of hydrocortisone induced orofacial clefts in the chick embryo

The growth and fusion of facial processes were studied in White Leghorn chicken embryos treated with hydrocortisone. This treatment results in complete bilateral cleft beak in 80-100% of cases. The frontonasal complex of the experimental embryos exhibited marked hypoplasia prior to cleft manifestation. During the critical period for cleft beak formation, the maximum mitotic activity was concentrated in the medial nasal processes, which thus became vulnerable to the mitosis inhibiting effect of corticoids. Primary hypoplasia of the facial processes was documented as a causative factor of corticoid-induced cleft beak which is analogous to mammalian cleft lip/palate.

Glucocorticoid receptor-mediated teratogenesis in the chick embryo

The susceptibility of chick embryos to the teratogenic action of intraamniotically injected hydrocortisone increases by several orders during the first four days of incubation. An attempt was made to correlate this phenomenon with the appearance of specific intracellular binding proteins for glucocorticoids. The binding of [3H] corticosterone to the soluble cytoplasmic proteins of the chick embryo was investigated on days 1.5, 2, 3, and 4 of incubation using a gel filtration method. No evidence of high affinity binding was found in embryos on day 1.5. High affinity binding of [3H] corticosterone to the cytosol proteins was first observed in embryos on day 2, but the binding capacity was four times lower than that found in embryos on days 3 and 4. A correlation was obtained between the increasing sensitivity of the chick embryo to hydrocortisone and the appearance of the intracellular binding protein for glucocorticoids. The causal relationship between these two phenomena is further supported by the finding that administration of a nonteratogenic dose of cortexolone completely prevents the teratogenic "cleft beak" action of hydrocortisone, presumably on the basis of competition for binding sites to the glucocorticoid receptor. These findings are consistent with the hypothesis that the teratogenic action of glucocorticoids is mediated by specific cytoplasmic receptors in the chick embryo.

Cardiotoxicity of drugs detected on chicken embryos

Results of direct observation of the effects of 9 drugs with known cardiotoxic properties upon the embryonic chick heart after intraamniotic administration on days 4 and 3 respectively, revealed the possibility of rough detection of cardiotoxic properties of newly developed drugs using the rapid, simple and inexpensive technique on chicken embryos.

Differences in the size of the palatal processes in mouse embryos with cleft palate induced in two critical periods

Using planimetric measurements of projections of the space between the palatal processes of ICR-Velaz mouse embryos, we indirectly demonstrated that the pre-horizontalization size of the palatal processes after the i.m. administration of 7.5 mg cortsone acetate on the 12th day of gestation was smaller than in the controls. After horizontalization, the inadequate palatal processes were unable to meet in the midline as they do in the majority of normal embryos. The administration of 0.5 mg 6-amino-nicotinamide on the 14th day of gestation did not significantly affect the size of the palatal processes.

The role of the mandible in mouse palatal development revisited

Growth changes associated with formation of the secondary palate were studied in H-Velaz mouse embryos by morphometric measurement of medial sagittal sections of the heads between days 13 and 15 of embryonic development. Horizontalization of the palatine processes depends primarily on the length of the mandible and is effected by a shift of palatine process material into the supralingual space. The administration of 7.5 mg cortisone acetate im to the female on day 12, of 0.5 mg 6-aminonicotinamide im on day 14, or amniocentesis on day 14 significantly retards growth of the embryo in general and of the mandible in particular without significantly affecting deflexion of the skull base. The different spatial conditions created by disproportion between deflexion of the base and the length of the mandible cause irregularities in the course of horizontalization which lead, as a rule, to cleft palate.

Influence of cleft palate on growth of the maxilla in mouse embryos

Cortisone acetate (7.5 mg on day 12, or 4 X 2.5 mg on days 12-15) and single dose of 6-aminonicotinamide (0.5 mg on day 14) were administered to pregnant females of random bred strain H-Velaz mice. The width of the alveolar arch of the developing maxilla was measured in drawings of the roof of the mouth of 600 fixed embryos taken between days 16 and 19. The width of the maxilla of experimental embryos with a closed secondary palate was the same as in the control embryos throughout the observation period, whereas the maxilla of all embryos with cleft palates was wider than in the controls. Final expansion of the maxilla was the same in all experimental groups.