Cell proliferation in embryonic mouse neural tube following urethane exposure

Toxicological effects of the different substances in tobacco smoke on human embryonic development by a systems chemo-biology approach

The physiological and molecular effects of tobacco smoke in adult humans and the development of cancer have been well described. In contrast, how tobacco smoke affects embryonic development remains poorly understood. Morphological studies of the fetuses of smoking pregnant women have shown various physical deformities induced by constant fetal exposure to tobacco components, especially nicotine. In addition, nicotine exposure decreases fetal body weight and bone/cartilage growth in addition to decreasing cranial diameter and tibia length. Unfortunately, the molecular pathways leading to these morphological anomalies are not completely understood. In this study, we applied interactome data mining tools and small compound interaction networks to elucidate possible molecular pathways associated with the effects of tobacco smoke components during embryonic development in pregnant female smokers. Our analysis showed a relationship between nicotine and 50 additional harmful substances involved in a variety of biological process that can cause abnormal proliferation, impaired cell differentiation, and increased oxidative stress. We also describe how nicotine can negatively affect retinoic acid signaling and cell differentiation through inhibition of retinoic acid receptors. In addition, nicotine causes a stress reaction and/or a pro-inflammatory response that inhibits the agonistic action of retinoic acid. Moreover, we show that the effect of cigarette smoke on the developing fetus could represent systemic and aggressive impacts in the short term, causing malformations during certain stages of development. Our work provides the first approach describing how different tobacco constituents affect a broad range of biological process in human embryonic development.

Cell cycle analysis in the cardiac and neuroepithelial tissues of day 10 rat embryos and the effects of phosphoramide mustard, the major teratogenic metabolite of cyclophosphamide

Using the autoradiographic technique of percent labeled mitoses (PLM), total cell cycle length (Tc) and length of the cell cycle phases G1, S, G2, and M have been estimated for the neuroepithelium and heart of day 10 rat embryos. The Tc for the neuroepithelium was estimated to be 9.45 hr, consisting of G1 of 1.24 hr, S of 6.15 hr, G2 of 1.34 hr, and M of 0.72 hr. The Tc for the heart was estimated to be 13.37 hr, consisting of G1 of 4.30 hr, S of 7.01 hr, G2 of 1.81 hr, and M of 0.25 hr. Comparison of cell cycle parameters in these two tissues indicates that the longer cell cycle in heart tissue is related primarily to an increase in G1. If embryos are exposed to the major teratogenic metabolite of cyclophosphamide, phosphoramide mustard, cell cycle analysis reveals that the S phase of the neuroepithelial cell cycle is lengthened and cells are either slowed or arrested in G2.

Influence of cis-dichlorodiammineplatinum on the structure of the immature rat cerebellum

Groups of 6- to 7-day-old and 10- to 11-day-old rats received cis-dichlorodiammineplatinum (cis-DDP) or inactive trans-DDP subcutaneously and were killed after 1, 6, 10, 15, or 21 days. In both age groups the acute effect (postinjection day 1) was most obvious in the germinal external granular layer (EGL), where many cells underwent shrinkage necrosis (pyknosis, apoptosis); the latter were more frequent within the fissures than on the surface of the cerebellar folia. Cell debris were often seen to be engulfed by macrophages, Bergmann cell fibers, and meningocytes. Bergmann cell bodies were swollen and the nuclei of Purkinje cells as well as of surviving cells of the EGL were enlarged. No comparable effects were observed in animals that had received an injection of trans-DDP in the same dose. Toward postinjection (p.i.) day 6, pyknotic cells disappeared from the EGL or, after the larger doses of cis-DDP, substantially decreased in number. Small nests of pyknotic cells appeared, however, at some places of the internal granular layer (IGL). The EGL was discontinuous or thinner in both age groups. In the IGL and molecular layer (ML) multiple focal fresh hemorrhages appeared together with some macrophages. The packing cell density in the IGL was less than in the controls, especially at the top of the cerebellar folia, i.e., contrary to the distribution of the primary damage in the EGL. Later, at p.i. day 10, ectopic nests of the IGL occurred occasionally in animals injected when 10 to 11 days old and severe atrophy of the ML and Purkinje cell population was observed at some places. At p.i. days 15 to 21, invasion of microglia-like cells appeared in the IGL and in some regions of the ML. Occasionally, subpial hemorrhages occurred at this interval. The acute damage caused by cis-DDP is thus similar to the effect of X rays or some, but not all, drugs with a cytostatic action. In addition, a more profound influence on dividing cells of the EGL within the fissures and distinct capillary lesions, indicated by hemorrhages, were found after cis-DDP. As in other experimental models, the acute cis-DDP damage of the immature cerebellum was partly repaired within a few p.i. days. Spatial difference of the repair process was inferred from the packing cell density in the IGL measured at the top and bottom of the cerebellar folia.

A comparative analysis of [3H]thymidine labeling in the embryonic tectum of the rhesus monkey (Macaca mulatta) and C57BL mouse

The pattern of [3H]thymidine incorporation in the dorsolateral wall of the embryonic tectum was studied and compared one hour after injection of the label in the rhesus monkey (Macaca mulatta) at stages 11-20 (25-37 days of gestation) and in the C57BL mouse at stages 14-22 (9-14 days of gestation). During the early stages of development, the labeled nuclei were located peripherally in the ventricular zone in both the rhesus monkey and mouse embryo, although a number of labeled nuclei tended to occur closer to the ventricular border in the mouse, whereas there was little or no encroachment at the ventricular border in the rhesus monkey. The ventricular zone of the rhesus monkey and mouse embryos initially showed a high labeling index (LI) of about 59% which subsequently declined with increasing age. However, the decline occurred earlier and more precipitously in the rhesus monkey. At stage 17 of the rhesus monkey the LI had dropped to about 42%, whereas it still remained at 59% in the 12-day mouse, and by stage 20 of the monkey the LI was approximately 26%, in contrast to 41% in the stage 22 (14-day) mouse. At stage 20 of the mouse (12 days of gestation) the intermediate zone became much thicker than in the comparable stage (17) of the rhesus monkey, and this discrepancy continued at each successive stage observed in the current study. Also, whereas lamination became apparent in the intermediate zone of the mouse at stage 22, the monkey tectum at a comparable stage (20) was poorly differentiated.

A model of neocortical histogenesis based on Cajal's principles of homotropism and neurocladism

Generation and regeneration of the Nervous System are considered essentially similar processes since the pioneering studies of Cajal (15). The present paper is a hypothetical attempt to explain the puzzling internal-to-external histogenetic pattern of the mammalian neocortex(4), largely on the basis of various observations made by Cajal on the developing and regenerating Central and Peripheral Nervous System. Fundamental to our model are the principles of excitatory neurocladism and of reciprocal homotropism as described by Cajal. By assuming that both latter principles are valid for the early stages of neocortical development, an explanation can be given for most of the main events of neocortical histogenesis that is consistent with known facts. Our main conclusion is that neocortical neurogenesis differs from that of any other area of the neural tube due to the interposition of the corticipetal fiber system in between the cortical matrix layer and the cortical plate. The mechanical obstacle thus posed to neuroblast migration by this fiber system appears responsible - by activating the operation of the aforementioned principles of Cajal - for both the cellular and topographical neurogenetic sequences of neocortical development, as well as the growth predominantly in width, all features that are unique to the neocortex as compared to the rest of the neural tube.