Bruce E. Walker

Radioautographic Study of Interkinetic Nuclear Migration in the Neural Tube.

Conclusion Radioautographs of early neural tube of chick embryos treated with thymidine-H3 for varying intervals of time give evidence substantiating the concept of inter-kinetic migration of nuclei. Synthesis of DNA occurs only in nuclei of peripheral part of wall, and does not take place in those of juxta-luminal zone. The period of DNA synthesis continues for at least 4 hours, but does not extend much beyond this time.

Induction of Cleft Palate in Rabbits by Several Glucocorticoids.

Summary Six glucocorticoids were administered separately to pregnant rabbits of one breed over a 4-day period preceding the time of normal palate closure. Triamcinolone, dexamethasone and prednisolone regularly produced cleft palates at several dose levels below that causing litter resorption. Cortisone and betamethasone induced cleft palate sporadically and methylprednisolone did not cause cleft palate formation at any of the dose levels tested. In a second breed of rabbit higher doses of triamcinolone were required to produce cleft palates than in the first breed.

Radiation Injury Resulting from Nuclear Labeling with Tritiated Thymidine in the Chick Embryo

Two- to three-day old chick embryos were treated with thymidine-H/sup 3/ (10 to 50 mu c per embryo; specific activity 1.6 or 1.9 curies per millimole) through a window in the shell, and incubation was continued for 12 to 55 hours longer. All embryos incubated after treatment for 12 hours or longer displayed cytological changes characteristic of radiation injury. Injury could be avoided and satisfactory radioautographs still obtained by diluting the thymidine-H/sup 3/ one hundred to five hundred times with unlabeled thymidine, thus reducing the specific activity to 4 to 20 mu c/ mu M. (auth)

Abnormal Palate Morphogenesis in Mouse Embryos Induced by Riboflavin Deficiency.

Summary Retardation of palatine shelf movement was found to be the morphogenetic basis for the cleft palates induced in DBA strain mouse embryos by a riboflavin-deficient, galactoflavin-containing diet.

Pineal Cell Proliferation in the Mouse.

Summary In mice killed 2 days after birth, pineal parenchymal cells had a high proliferative rate as indicated by the large number of labeled nuclei. At 21 days, DNA synthesis occurred in less than 1% of the cells and by one month it had essentially ceased. The rate of DNA synthesis was lower in pineal parenchymal cells than in any other tissue of the adult mouse studied except for neurons of the central nervous system. No DNA synthesis was seen after injections of estrogen and progesterone in ovariectomized mice.

Amniotic fluid measurement in cortisone treated and x-irradiated mice.

Summary The amount of amniotic fluid associated with mouse embryos at the normal time for palate closure was determined in cortisone treated, X-irradiated, and control embryos. Both of these cleft palate-inducing teratogens caused a significant reduction in amount of amniotic fluid. However, a few embryos destined to have cleft palate had as much amniotic fluid as most normal embryos, and a few normal embryos had as little amniotic fluid as most treated embryos. Therefore, the reduction in amniotic fluid caused by these teratogens is not the effect which is primarily responsible for development of the cleft palates.

Proliferation of Mast Cells in Normal and Dystrophic Mice.

Summary Using thymidine-H3 incorporation as a criterion of cell division, mast cells in adult mice show a very low rate of proliferation which may increase sporadically in dystrophic mice. No evidence was found for a precursor cell. A few mitotic figures were identified.

Effect of Thymectomy on Mast Cells in Mice.

Summary Neonatal thymectomy did not significantly reduce the size of the mast cell population in young and adult mice. Consequently, the thymus is not necessary for mast cell production during postnatal development.