St Vincent's Declaration 10 years on: outcomes of diabetic pregnancies

AIMS

To monitor pregnancies in women with pregestational Type 1 diabetes for pregnancy loss, congenital malformations and fetal growth parameters, in a geographically defined area in the north west of England.

METHODS

Population cohort study of 547 pregnancies in women with Type 1 diabetes from maternity clinics in 10 centres over a 5-year period (1995-1999 inclusive). Main outcome measures were numbers and rates of miscarriages, stillbirths, neonatal and post-neonatal deaths; prevalence of congenital malformations; birth weight in relation to gestational age.

RESULTS

Among 547 pregnancies, there were six (1.1%) pairs of liveborn twins, 439 (80.3%) liveborn singletons; 72 (13.2%) spontaneous abortions, 14 (2.6%) stillbirths and 16 (2.9%) terminations. Four of the terminations were performed because of congenital malformations. Both the stillbirth rate (30.1/1000 total births (95% confidence interval (CI) 16.6-50.0)), and prevalence of congenital malformations (84.3/1000 live births (95% CI 60.3-113.8)) were significantly higher than the local population (P < 0.001). When corrected for gestational age, mean birth weight in the sample was 1.3 sd greater than that of infants of non-diabetic mothers (P = 0.12). Infants with congenital malformations weighed less than those without.

CONCLUSION

In an unselected population, the infants of women with pregestational Type 1 diabetes mellitus have 6.4 times the reported risk of a congenital malformation and 5.1 times the reported risk of perinatal mortality than infants in the general population. Further improvements in the management of diabetes and pregnancy in these women are needed if the St Vincent's Declaration target is to be met.

Outcomes of pregnancy in insulin dependent diabetic women: results of a five year population cohort study

OBJECTIVE

To monitor pregnancies in women with pre-existent insulin dependent diabetes for pregnancy loss, congenital malformations, and fetal growth in a geographically defined area of north west England.

DESIGN

Population cohort study.

SETTING

10 maternity units in Cheshire, Lancashire, and Merseyside which had no regional guidelines for the management of pregnancy in diabetic women.

SUBJECTS

462 pregnancies in 355 women with insulin dependent diabetes from the 10 centres over five years (1990-4 inclusive).

MAIN OUTCOME MEASURES

Numbers and rates of miscarriages, stillbirths, and neonatal and postneonatal deaths; prevalence of congenital malformations; birth weight in relation to gestational age.

RESULTS

Among 462 pregnancies, 351 (76%) resulted in a liveborn infant, 78 (17%) aborted spontaneously, nine (2%) resulted in stillbirth, and 24 (5%) were terminated. Of the terminations, nine were for congenital malformation. The stillbirth rate was 25.0/1000 total births (95% confidence interval 8.9 to 41.1) compared with a population rate of 5.0/1000, and infant mortality was 19.9/1000 live births (5.3 to 34.6) compared with 6.8/1000. The prevalence of congenital malformations was 94.0/1000 live births (63.5 to 124.5) compared with 9.7/1000 in the general population. When corrected for gestational age, mean birth weight in the sample was 1.3 standard deviations greater than that of infants of non-diabetic mothers. Infants with congenital malformations weighed less than those without.

CONCLUSION

In an unselected population the infants of women with pre-existent insulin dependent diabetes mellitus have a 10-fold greater risk of a congenital malformation and a fivefold greater risk of being stillborn than infants in the general population. Further improvements in the management of pregnancy in diabetic women are needed if target of the St Vincent declaration of 1989 is to be met.

Adolescents' ideas about the health of the fetus

OBJECTIVE

To determine the preponderance of ideas in adolescents about the relationship between maternal habits and the health of the fetus.

DESIGN

Quantitative survey using a precoded questionnaire, the content of which was derived from the transcripts of interviews and the responses to open-form questionnaires.

SETTING

North West Region Health Authority area, UK.

PARTICIPANTS

674 adolescents in British National Curriculum Year 10 (age 14/15) from 6 Community Comprehensive Schools.

FINDINGS

Most of the adolescents were aware of the dangers to the fetus of alcohol and smoking, including passive smoking. However, they were less aware of the potential hazards during pregnancy of eggs (Salmonella), soft cheeses (Listeria), liver (Vitamin A excess) or handling cats (Toxoplasmosis). Most of the respondents thought that the optimum time to initiate actions for a healthy pregnancy was when pregnancy had been confirmed, suggesting that the benefits of preconceptual care are not well known.

KEY CONCLUSIONS

Adolescents lack knowledge about some of the specific hazards to the fetus of maternal diet and behaviour during pregnancy and are unaware of the importance of the early stages of pregnancy in this context.

IMPLICATIONS

There is a need for the provision of education about the importance of a healthy maternal lifestyle before conception and during early pregnancy for adolescents. Midwives may have a proactive role in such education, but should be aware that young people may have specific areas of ignorance and misconceptions which will need addressing.

Effect of propylthiouracil treatment during prenatal and early postnatal development on the neocortex of rat pups

The effects of a pre- and postnatal hypothyroid environment on the development of the neocortex have been determined. Rats were treated with propylthiouracil (PTU) with or without thyroid hormone supplementation during pregnancy and throughout the early development of the pups. The Cavalieri method was used to provide an estimate of the volume of the neocortex, and a combination of the Cavalieri method and the 'disector' particle-counting method provided an unbiased estimate of the numbers of glia and neurons in the neocortex. In pups from non-treated rats the mean volume of the neocortex increased from 31.3 mm3 at 5 days postnatally to 191.5 mm3 at 20 days and then remained constant to day 48. Similarly, the mean number of glial cells increased from 5.2 x 10(6) at day 5 to 12.0 x 10(6) on day 20 and then remained constant to day 48. The mean number of neurons in the neocortex in the control condition was constant at about 14.6 x 10(6) from day 5 to day 48. PTU treatment during pregnancy and postnatal development significantly decreased the mean volume of the neocortex at all of the stages studied, for example from 31.3 to 23.3 mm3 (p less than 0.001) on day 5 and from 191.5 to 155.0 mm3 (p less than 0.001) on day 20. Supplementation with thyroxine (T4) or tri-iodothyronine partially reversed this at certain stages. For example, the mean volume of the neocortex at 48 days was 197.5 mm3 in control rats, 118.1 mm3 in PTU-treated rats and 169.3 mm3 in PTU-treated rats supplemented with T4. Within the neocortex, the volume of the neuropile was more severely affected than was the volume of the neuron cell bodies.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer modelling of neural tube defects

Neurulation, the curling of the neuroepithelium to form the neural tube, is an essential component of the development of animal embryos. Defects of neural tube formation, which occur with an overall frequency of one in 500 human births, are the cause of severe and distressing congenital abnormalities. However, despite the fact that there is increasing information from animal experiments about the mechanisms which effect neural tube formation, much less is known about the fundamental causes of neural tube defects (NTD). The use of computer models provides one way of gaining clues about the ways in which neurulation may be compromised. Here we employ one computer model to examine the robustness of different cellular mechanisms which are thought to contribute to neurulation. The model, modified from that of Odell et al (Odell, G.M., Oster, G., Alberch, P. and Burnside, B., (1981)) mimics neurulation by laterally propagating a wave of apical contraction along an active zone within a ring of cells. We link the results to experimental evidence gained from studies of embryos in which neurulation has been perturbed. The results indicate that alteration of one of the properties of non-neural tissue can delay or inhibit neurulation, supporting the idea, gained from observation of embryos bearing genes which predispose to NTD, that the tissue underlying the neuroepithelium may contribute to the elevation of the neural folds. The results also show that reduction of the contractile properties of a small proportion of the neuroepithelial cell population may have a profound effect on overall tissue profiling. The results suggest that the elevation of the neural folds, and hence successful neurulation, may be vulnerable to relatively minor deficiencies in cell properties.

Effects of thyroid antagonists on rat embryos cultured in vitro

A literature review of individual pregnancies and recent surveys involving large cohorts reveal an association between congenital malformation and maternal hyperthyroidism, suggesting that some aspect of hyperthyroidism or its treatment might compromise the development of the fetus. Experiments have shown that the thyroid antagonist, ethylenethiourea (ETU), causes fetal malformations when administered to pregnant rats, but it is not known whether it is ETU or the imbalance in maternal thyroid hormone which it causes which is the teratogenic agent. Here we employ in vitro culture to determine the possible direct effects on rat embryos of two thyroid antagonists, ETU and methimazole (MMI), the latter being one which is used for treatment of thyrotoxicosis in humans. It was found that ETU can compromise the development of rat embryos in vitro, confirming that ETU has a direct effect on the rat embryo. It was also found that MMI can cause abnormal development of rat embryos in vitro, although the concentration at which MMI disturbs rat embryogenesis is higher than that which is reached in hyperthyroid patients treated with clinical doses of MMI or carbimazole.

Morphological and physiological effects of beta-hydroxybutyrate on rat embryos grown in vitro at different stages

Diabetic women are more likely to give birth to infants with congenital malformations than are nondiabetic women. Rodent embryos have been used as a model for the study of abnormal fetal development associated with maternal diabetes, and some of the metabolic factors which are altered in diabetes, such as raised glucose and ketones, have been shown to cause abnormal development of rodent embryos in vitro. The present work explores further the teratogenicity of beta-hydroxybutyrate to rat embryos. To determine the sensitivities of rat embryos at different stages of their development, rat embryos at 9.5 days of gestation have been cultured in vitro for 24 or 48 h, with or without 4 x 10(-2) M beta-hydroxybutyrate for all or part of the culture period. The embryos have been examined by scanning electron microscopy, and a detailed morphometric analysis of one tissue, the neuroepithelium, has been undertaken. The results confirm that beta-hydroxybutyrate causes abnormal development of rat embryos. The results of experiments in which embryos were exposed to beta-hydroxybutyrate for only part of a 48 h culture show that embryos exposed to beta-hydroxybutyrate for a complete 48 h culture are more severely affected than embryos exposed to beta-hydroxybutyrate for only part of the culture and that embryos are more vulnerable to beta-hydroxybutyrate during the first half of a 48 h culture (equivalent to 9.5 to 10.5 days of gestation) than during the second half of a 48 h culture (10.5 to 11.5 days of gestation). The results of experiments in which embryos were cultured with beta-hydroxybutyrate from 9.5 days of gestation for 24 h (equivalent to 9.5 to 10.5 days of gestation) showed that some effects of beta-hydroxybutyrate are already apparent after 24 hours in culture. Many of the abnormalities produced by beta-hydroxybutyrate can be classified as embryonic retardations rather than malformations--that is, embryos show features characteristic of normal, but younger, embryos. Embryos exposed to beta-hydroxybutyrate for the complete 48 h culture period consume less glucose and produce less lactate than control embryos on a per embryo basis, but not on a per microgram protein basis, suggesting that the reduced metabolism is an effect of beta-hydroxybutyrate-induced developmental delay rather than a cause of it.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphometric analyses of changes in cell shape in the neuroepithelium of mammalian embryos

During neurulation the elevation of the neural folds is accompanied by, and thought to be partly driven by, changes in the shapes of the neuroepithelial cells. This paper explores the use of form factors for the measurement of changes in cell shape during normal and perturbed neural fold elevation in rat embryos; it is the first attempt to quantify changes in the shapes of cells during neurulation in mammalian embryos. Rat embryos at 9.9 days of gestation, when the neural epithelium is a biconvex plate, and at 10.4 days of gestation, when the cervical neural epithelium has formed the neural tube and when the cephalic neural folds have elevated but not fused, were used. In addition, embryos in which the cephalic neural folds had been caused to re-open by culture in saline with low calcium were examined. Embryos were fixed and then fractured across the neural axis. A montage of the fractured edge of the neuroepithelium was prepared from a series of scanning electron micrographs. Cells of the neuroepithelium were classified according to the shapes of their profiles as rectangular, round, apically tapered, basally tapered or spindle-shaped, the last three categories being considered as 'tapered'. The outlines of the cells were digitised using a computer-linked graphics tablet to provide estimations of the perimeters (p) and areas (a) of the cell profiles, and the form factors, f. of the cell profiles were calculated by f = 4 pi a/p2. This factor is a unitless ratio which is unity for a circle and less than unity for any other shape. It provides a measure of the efficiency with which a perimeter encloses an area, and thus indicates the degree of deformation of a shape from circular. From 9.9 to 10.4 days the cervical neuroepithelium shows a decrease in the percentage of rectangular cells and an increase in the percentage of spindle-shaped cells. The mean form factors of cells in the apically tapered and spindle-shaped categories decrease, showing that these cells are more elongated and tapered in later embryos. When embryos at 10.4 days are cultured in saline with low calcium the elevated cephalic neural folds collapse. Concomitantly the percentage of round cells in the cephalic neural folds increases and the percentage of apically tapered and spindle-shaped cells decrease.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of mannose on rat embryos grown in vitro

Rat embryos have been cultured in vitro from 9.5 days of gestation for different times in serum containing mannose, and the embryos have been observed by scanning electron microscopy. Embryos cultured in 3 mg/ml (1.7 X 10(-2) M) or 6 mg/ml (3.3 X 10(-2) M) mannose for 48 h showed inhibition of the expansion of the yolk sac and were smaller than the control embryos. Mannose-treated embryos also showed delayed development according to morphological criteria, and a range of abnormalities including abnormalities of the neural tube. Embryos cultured in 6 mg/ml mannose for 24 h also showed significant inhibition of yolk-sac expansion and were smaller and less advanced than the control embryos. Abnormalities were seen, including a delay in the closure of the neural folds. Abnormalities were also observed in embryos cultured in mannose for 10 h; embryos at the neural groove stage showed irregularities in the neural groove. Mannose did not inhibit the re-elevation of neural folds which had been caused to collapse by exposure to medium containing low calcium. These results are compatible with the idea that mannose retards development and thereby perturbs the morphogenesis of the neural tube.

Effect on rat embryos of in vitro culture in sera from human diabetic patients

Recently conditions have been established whereby rat embryos can be cultured in vitro in human serum over the period of their major morphogenesis. By standardizing the amount of glucose in sera from diabetic subjects prior to culture, it has been possible to investigate factors other than hyperglycemia which might account for the increased incidence of congenital defects seen in infants of diabetic mothers. The incidence of abnormalities in rat embryos cultured in sera from chlorpropamide-treated diabetics was not significantly different from that using control sera from normal subjects. On the other hand, sera from insulin-dependent diabetics produced more defects in rat embryos than sera from either normal subjects or diabetics on oral agents. The incidence of abnormal rat embryos does not appear to be correlated with patient age, with the original blood glucose concentration or with the concentration of hemoglobin A1 or, in the insulin group, with the total daily insulin dosage.

Calcium and neurulation in mammalian embryos. II. Effects of cytoskeletal inhibitors and calcium antagonists on the neural folds of rat embryos

The role of calcium in neurulation in mammalian embryos has been studied by culturing rat embryos at 10.4 days of gestation, when the cephalic neural folds have elevated but not fused, in serum containing cytoskeletal inhibitors or calcium antagonists. The effects of these antagonists on the morphology of the cephalic neural folds have been examined by scanning electron microscopy. The different agents caused the cephalic neural folds to part to varying degrees. The neural folds were classified as intact (normal), open (folds parted up to 90 degrees with each other), flattened (folds parted from 90 degrees to 180 degrees) or collapsed (folds parted more than 180 degrees). The microtubule inhibitors colchicine and nocodazole at 10(-4) M respectively cause the cephalic neural folds of 10.4-day embryos to collapse after 60 min. At 5.2 X 10(-6)M the microfilament inhibitor cytochalasin B causes the folds to open after 60 min. Longer term culture of 9.5-day embryos for 24 h in diazepam, which is reported to inhibit myosin synthesis, causes general developmental retardation including a delay in the closure of the neural tube. Culture of 10.4-day rat embryos for 60 min in papaverine at 2.4 X 10(-4) M or gallopamil (D-600) at 5.0 X 10(-4) M, agents which reduce the entry of calcium into cells, causes opening of the elevated cephalic neural folds. In contrast TMB-8, which is purported to perturb some intracellular calcium-dependent functions, does not cause opening of the elevated cephalic neural folds, even at high concentrations. The results suggest that both microtubules and microfilaments are essential to the maintenance of the elevated cephalic neural folds in rat embryos. The results are also compatible with the idea that calcium ion flux across the membranes of the neuroepithelial cells might be important for the elevation of the neural folds, and thus for successful neurulation.

Calcium and neurulation in mammalian embryos

The role of calcium in neurulation in rat embryos has been studied. Rat embryos at 10 X 4 days of gestation, when the cephalic neural folds have elevated but not fused, have been cultured in various media, and the effects of these media on the morphology of the cephalic neural folds have been observed by scanning and transmission electron microscopy. Embryos cultured in serum containing EDTA or EGTA, or in saline without divalent cations exhibit opening, then folding back ('collapse') of the cephalic neural folds. The neural cells lose their elongated shape and become rounded. Older embryos in which the cephalic neural folds have already fused do not show collapse of the neural tube. Culture of 10 X 4-day rat embryos with elevated but unfused cephalic neural folds in calcium- and magnesium-free saline to which either calcium or magnesium has been restored shows that calcium is the divalent cation which is essential for the maintenance of the elevated neural folds. In the presence of calcium, lanthanum, which competes for calcium sites, causes opening but not collapse of the elevated cephalic neural folds. Embryos treated with trypsin show dissociation of the lateral (non-neural) ectoderm but the neural folds remain elevated. If embryos in which the cephalic neural folds have been caused to collapse are further cultured in serum the folds re-elevate, although normal neural tube morphology is not completely regained. The possible implications of these observations to the understanding of the cellular mechanisms of normal neurulation, and of neural tube malformations are discussed.

Effects of beta-hydroxybutyrate on rat embryos grown in culture

In order to investigate further the relationship between maternal diabetes and fetal malformation, rat embryos were grown in vitro in the presence of beta-hydroxybutyrate, one of the ketone bodies produced by diabetics. At 10 mM, beta-hydroxybutyrate produced minor abnormalities and at 20 mM it produced major abnormalities in rat embryos.

Scanning electron microscopy of wound healing in rat embryos

Wound healing in rat early embryos has been studied by scanning electron microscopy. Initially the wound gapes slightly and cells peripheral to the wound assume a cobble-stone appearance. Wound closure is quite rapid; some small wounds are almost closed within 10 min of incision. Wound closure is accompanied by the appearance of some elongated cells at the wound edge. These features are similar to, although less pronounced than, those which have been observed to accompany wound closure in amphibian and avian embryos. Healing of wounds made in the amnion is also accompanied by changes in the shapes of cells at the wound margins. Wound healing in embryos cultured in Hank's saline is similar to wound healing in embryos cultured in serum, suggesting that the macromolecular components of serum are not essential to wound healing. Cytochalasin B, which inhibits wound closure in amphibian embryos, does not inhibit wound healing in rat early embryos unless used at a concentration high enough to cause cell dissociation. Similarly chelation of the free calcium in the medium, which also prevents wound closure in amphibian embryos, does not inhibit wound closure unless the embryo is dissociating. Removal of free calcium does however cause collapse of the elevated neural folds. These observations suggest that the cellular mechanisms involved in wound healing are different in mammalian and amphibian embryos.

Effect of the calmodulin inhibitor R24571 (calmidazolium) on rat embryos cultured in vitro

The possible effects of inhibition of the calcium-binding protein, calmodulin, on mammalian morphogenesis have been investigated by culturing rat embryos in vitro from 9 1/2 to 11 1/2 days of development in the presence of R24571 (calmidazolium), a specific inhibitor of calmodulin. Embryos cultured in 10(-2) mM R24571 for 48 h show inhibited development and exhibit a range of morphogenetic abnormalities including assymetry and neural tube defects. Embryos exposed to R24571 for the first 24 h of a 48 h culture are more severely affected than embryos exposed to R24571 for the last 24 h.

Calcium, microfilaments and morphogenesis

Morphogenesis, the generation of tissue form, is important not only in the embryogenesis of a new individual, but also because a change in morphogenesis may be involved in the establishment of differences between individuals during evolution. Morphogenetic movements are effected in part by coordinated changes in the shapes of individual cells and over the past decade the cellular organelles responsible for cell shape have been identified as microfilaments and microtubules. In non-embryonic systems the contraction of microfilaments is controlled by the level of intracellular free calcium, and so calcium is implicated as an intermediate control mechanism in morphogenisis. Through techniques which perturb the calcium balance of cells, or which measure calcium ion concentration directly, evidence is accumulating that calcium is involved in morphogenetic movements such as gastrulation and neurulation, and related phenomena such as wound healing. Thus fundamental questions about the control of morphogenesis in embryogenesis and evolution may now be couched in more precise terms of the control of intracellular calcium ion balance.

Effects of glucose on rat embryos in culture

To elucidate the role of hyperglycaemia in causing fetal malformation, rat embryos have been grown in vitro from the head-fold stage for 48 h in the presence of excess glucose during different parts of the culture period. Culture of rat embryos for 10 or 21 h in 55 mmol/l exogenous glucose produced abnormalities observable after 48 h in culture. When embryos cultured for 10 or 21 h in excess glucose were observed by scanning electron microscopy at the end of the glucose treatment, abnormalities could be observed which may indicate how later malformations are formed. Thus it is possible that a relatively brief hyperglycaemic episode at a critical stage of embryogenesis may endanger the fetus of a diabetic mother.

Effects of puromycin and cycloheximide on properties of cells from Xenopus laevis early embryos

The effects have been studied of puromycin and cycloheximide on the reaggregation of ectoderm cells dissociated from Xenopus laevis blastulae. Puromycin or cycloheximide can inhibit reaggregation, suggesting that cell reassociation is dependent upon protein synthesis. If the cells are allowed a 3 h 'recovery' period in culture medium following dissociation, before being exposed to either puromycin or cycloheximide, higher concentrations of the inhibitors are required to prevent cell aggregation, suggesting that significant synthesis of the proteins required for reaggregation occurs in the 3 h immediately following dissociation. Lower concentrations of puromycin permit cell reaggregation but reduce the normal formation of cilia. The effects have also been observed of puromycin on the scanning electron microscopical appearance of Xenopus blastula ectoderm cells cultured singly in vitro. Puromycin reduces the normal formation of pseudopodia, suggesting that puromycin might inhibit reaggregation partly by inhibiting cell movement. Puromycin also produces some elongated cells, possibly by inhibition of cytokinesis.

Calcium and wound healing in Xenopus early embryos

The role of calcium in the healing of wounds made in the ectoderm of Xenopus neurulae has been studied. Embryos have been wounded in the presence of calcium inhibitors, and the effects on wound healing observed by scanning electron microscopy. In addition, unwounded embryos have been exposed to a local application of ionophore A23187 to simulate the possible calcium fluxes following wounding. Lanthanum, which competes for calcium channels, inhibits wound healing. EDTA, which binds divalent cations, also inhibits wound healing, but its effect can be reversed by the addition of excess calcium. Local application of ionophore A23187, which promotes transport of calcium across biological membranes, results in a local change in cell shapes. These observations lend support to the hypothesis that wound healing in amphibian early embryos, which is effected by changes in cell shapes similar to those seen in certain examples of normal morphogenesis, is initiated by a local influx of calcium into cells.

Scanning electron microscopy of wound healing in Xenopus and chicken embryos

Wound closure in the ectoderm of Xenopus early neurulae and chick primitive-streak embryos has been studied by scanning electron microscopy (SEM). Initial gaping of the wound and a cobble-stone appearance of cells peripheral to the wound in both Xenopus and chick confirm that the ectoderm is under lateral tension at these stages. Healing is rapid: in Xenopus embryos wound closure has started within 5 min of wounding; in chick healing is almost complete within 30 min in some cases. The SEM observations suggest that in Xenopus embryos changes in cell shape are the major mechanism for wound closure. In chick embryos wound healing is also accompanied by changes in the shape of the marginal cells, but evidence is presented that in this system cell proliferation is important. The mechanisms of wound healing in Xenopus and chick embryonic ectoderm are compared with those of wound healing in other tissues.

Effects of colchicine, cytochalasin-B and papaverine on wound healing in Xenopus early embryos

The effects of colchicine, cytochalasin-B and papaverine on wound healing in Xenopus early embryos have been studied. Colchicine does not prevent wound healing, whereas cytochalasin-B does. Papaverine, under conditions which prevent the completion of neurulation, does not prevent wound healing. A model is given which might explain these observations.

Scanning electron microscopy of cells from hydroxyurea-arrested blastulae of Xenopus laevis

Cells from Xenopus embryos blocked at the blastula stage by treatment with hydroxyurea have been isolated and cultured in vitro. The morphology of these cells has been compared with that of cells from normal embryos using scanning electron microscopy. Cells from such hydroxyurea-blocked embryos do not show the features, or changes in features, in culture shown by cells from normal embryos.

Scanning electron microscopy of cells isolated from amphibian early embryos

Cells have been dissociated from Xenopus and Ambystoma late blastulae, allowed to adhere to glass coverslips, and studied by scanning electron microscopy. Xenopus ectoderm cells initially show filopodia; later larger single pseudopodia are formed. Ambystoma ectoderm cells show fewer filopodia than Xenopus ectoderm, but later form pseudopodia. Ectoderm cells of both Xenopus and Ambystoma show links between adjacent cells. Xenopus endoderm cells do not show filopodia initially, but later show large pseudopodia.

The effect of concanavalin-A on the reaggregation of cells dissociated from Xenopus laevis early embryos

The effects of concanavalin-A on the reaggregation and sorting of cells from Xenopus laevis early embryos have been studied. The results suggest that at high concentrations, concanavalin-A can prevent reaggregation.

Scanning electron microscopy of lithium-induced exogastrulae of Xenopus laevis

Lithium-induced exogastrulae are abnormal embryos which fail to complete gastrulation and do not form normal neural structures. Scanning electron microscopy has been used to compare the surface structure of the ectoderm cells of exogastrulae with that of the ectoderm cells of normal embryos and has shown that the appearance of ciliated cells is delayed in exogastrulae. In addition, the structure of endoderm cells, which remain exposed in these embryos, has been studied.

Scanning electron microscopy of lithium-induced exogastrulae of Xenopus laevis

Lithium-induced exogastrulae are abnormal embryos which fail to complete gastrulation and do not form normal neural structures. Scanning electron microscopy has been used to compare the surface structure of the ectoderm cells of exogastrulae with that of the ectodermcells of normal embryos and has shown that the appearance of ciliated cells is delayed in exogastrulae. In addition, the surface structure of endoderm cells, which remain exposed in these embryos, has been studied.