ABSTRACT Reports of malformations are already documented in the writings of Assyrian and Babylonian astrologists dating back 1800 before our chronology. Historically, a significant source of informations are pamphlets. These publications started in Germany in the 15th century to disseminate news. For most congenital anomalies the causes are unknown. The majority of developmental defects have a multifactorial etiology and are induced interactions of environmental and genetic factors. In order to examine the effect of noxae the development of mammals is subdivided into several segments. On the base of guidelines which were issued by the Food and Drug Administration (FDA) in 1966 the principles of in-vivo teratogenicity testing procedures are discussed. As a rule reproduction toxicological investigations are carried out on mice, rats and rabbits. Special attention is to be payed on dose limits, mode of application, toxicokinetics of the test agents, morphological criteria and specific disorders of developmental rhythm. Stimulating factors for the use of in-vitro tests are the increasing number of chemical substances. Advantages and disadvantages of in-vitro technique are discussed. Some of the actual in-vitro models are presented, such as monolayer culture, organoid culture, organ cultures, “whole embryo” culture. It is concluded that in-vivo experiments can- not be replaced by in-vitro systems, but its usefulness in teratological research has been proven.
ABSTRACT Methods for assessing animal neurobehavior following prenatal/perinatal exposures have been in use for almost 20 years and screening tests incorporating them are regulated in three settings: in Japanese Segment I1 and I11 studies on drugs, Europe- an (EEC/UK) Segment I studies on drugs, and American neurotoxicity studies on chemicals. The methods used in the West for assessing behavior in these contexts at present are described in detail. The evolution of the methods over time, the concepts of apical tests and functional domains, the use of positive control agents, what the U.S. Collaborative Study has shown us, and justification for assessing animal behavior in predicting out- come from human exposures are discussed.
ABSTRACT Mouse embryo culture has been established and applied in the study of the causal mechanisms of abnormal development. Mouse embryo culture can be used as an experimental system to examine the influence of teratogen on early development, together with investigations using developmental engineering such as chimera, transgenic mice and nuclear transfer. We combined mouse embryo culture with embryo transfer and chromosome analysis, and studied the relationship between environmental factors (including maternal factors) and genetic predisposition in developmental abnormalities in the embryos of diabetic mice. In mouse embryo culture from one-cell to the blastocyst stage, fertilized eggs were incubated in modified Whitten’s medium and mixed gas (5% 02, 5% C02 and 90% N2) at 37°C for three days. 0-Mercaptoethanol 20 pM and EDTA-2Na 100 pM were added in order to overcome “two-cell block” in which two-cell stage embryos could not develop further. Under theses conditions, from 55 to 100% of the cultured one-cell stage embryos developed into blastocysts depending on the strain. For chromosome preparation, Mikamo and Hamaguchi’s method (1975) was modified. This method can be applied from one-cell to pre-implantation stage embryos, and allows a higher rate of success (63% of prepared embryos) in preparing chromosome slides than that reported in the literature. Using improved methods of embryo culture, embryo transfer and chromosome analysis, we have obtained evidence that both environ- mental and genetic factors are the causes of malformation during diabetic pregnancy in mice. Mouse embryo culture associated with chromosome analysis is a useful procedure, and offers important data for the clarification of the causal mechanisms in developmental abnormalities.
ABSTRACT Neuropathological and electrophysiological studies were designed to clarify the pathomechanism of motor disturbance in the hind limbs of rats with sacral agenesis. The model animals were obtained from mother rats which had been treated with trypan blue on day 8 of gestation. Mirror movements in the hind limbs were observed in 7 out of 56 rats with lumbosacral agenesis. The conus medullaris in rats with lumbosacral agenesis ended at the level between Thl3-Ll vertebra, whereas that in normal cases terminated between L3-4. The spinal cord of the lumbosacral region was hypoplastic and dysplastic particularly in the ventral half. Anterior horn cells were sporadic and there were no apparent median fissure in the spinal cord of the lumbosacral region. On the other hand, any abnormality was not found in the brain, the brain stem, and the spinal cord of the cervicothoracic region. Horseradish peroxidase (HRP) was injected into the unilateral hind limbs. In segments of the anomalous spinal cord, HRP-labeled neurons in the anterior horn were found not only on the injected side but also on the other side. In electrophysiological examination, F’ wave was recorded on the non- stimulated side with longer latency and duration compared with that of the stimulated side. These morphological and physiological findings indicated that the mirror movements in the hind limbs of the model animals may arise from developmental errors of motor nervous pathway, with some deficient inhibitory mechanism in the upper neural system.
ABSTRACT Maternal hyperthermia of short duration had significant short and long term effects on the developing guinea-pig eye at embryonic days 19, 21 and 23. A marked regionalisation of the heat-induced effects was observed in the developing retinae, but the lens defects were most obvious following heat at E21 and E23. Bilateral anterior pole cataracts, bipolar zonular cataracts and microphthalmia have been produced fol- lowing maternal heat stress. It is suggested that these are determined by the cellular events initiated in the developing eye following the teratogenic insult.
ABSTRACT We employed the chick embryo in a comparative study of the effect of Tedral and theophylline on anatomical development. Tedral, which contains theophyl- line in combination with ephedrine and phenobarbital in the relative dose ratio of the- ophylline 33: ephedrine 6: phenobarbital 2, or saline for control was dropped onto the surface of the chorioallantoic membrane of 2, 3,4 and 5-day-old chick embryos. In groups A (theophylline 0.015 M, ephedrine 0.0027 M, phenobarbital 0.0009 M) and B (theophyl- line 0.01 1 M, ephedrine 0.0020 M, phenobarbital 0.0007 M), 100% of embryos treated on the 5th day of incubation developed aortic aneurysms with associated cardiovascular malformations. In group C (theophylline 0.005 M, ephedrine 0.0009 M, phenobarbital 0.0003 M), 36.8% of embryos treated on the 5th day of incubation developed aortic aneurysms, and 73.7% of embryos had cardiovascular malformations. These data were compared with those obtained by using theophylline, ephedrine or phenobarbital alone. The commonest cardiovascular anomalies induced by Tedral were double-outlet right ventricle with ventricular septal defect. Aneurysms were larger in size and cardiovascular malformations were more complex in embryos exposed to Tedral than in those treated with theophylline alone. Complex cardiac defects produced by Tedral included transposition of the great arteries, double-outlet right ventricle with double-inlet left ventricle, and truncus arteriosus communis. A slit-like small ventricular septal defect was found in 9.5% of the ephedrine-treated (0.51 mg) chick embryo group and 9.1% in the control embryos. These data show: (1) theophylline, a major component of Tedral, produces cardiovascular anomalies in embryonic chick hearts; (2) there is synergy of all three drugs in Tedral; (3) the specific type of conotruncal defect depends on the timing of administration, e.g., truncus arteriosus communis was produced on day 4 of Tedral administration in chick embryos.