Maternal caffeine consumption during pregnancy does not affect preimplantation development but delays early postimplantation growth in rat embryos

Models for studying prenatal drug-induced intrauterine growth retardation (IUGR) have, without exception, measured growth-related factors in the postimplantation embryo, fetus or neonate. Therefore, it is not known whether effects of drug exposure on growth and metabolism begin early in the preimplantation embryo, or whether IUGR is exclusively a postimplantation phenomenon. The present study investigates whether caffeine, a drug known to induce a dose-dependent fetal IUGR, affects embryo development before and/or after implantation or is exclusively a fetal phenomenon. Preimplantation embryo assessment (with treatment from Days 2 to 4 of pregnancy) included glucose utilization, cell number evaluation and stage of development (morula to hatched blastocyst); whereas, postimplantation embryo assessment (treatment from Days 2 to 10, 10.5 or 11 of pregnancy) included somite number evaluation and extent of neural tube closure, as seen using scanning electron microscopy. Comparing control preimplantation embryos with those exposed to 30 and 60 mg kg –1 caffeine did not reveal any effects of caffeine exposure, as assessed on Day 5 of gestation. However, postimplantation embryo development assessed on Day 12 of gestation revealed that caffeine exposure of 15 and 30 mg kg –1 significantly reduced, at both dosage levels, somite number and the extent of neural tube closure. In addition, comparisons of control and experimental groups revealed that in the high-dose caffeine group the forebrain cavity was significantly enlarged and bounded by a reduced, irregularly aligned neuroepithelium. The findings suggest that IUGR is a phenomenon first identifiable during late postimplantation embryogenesis and continues in fetal life.

Somite number and vertebrate evolution

Variation in segment number is an important but neglected feature of vertebrate evolution. Some vertebrates have as few as six trunk vertebrae, while others have hundreds. We examine this phenomenon in relation to recent models of evolution and development. Surprisingly, differences in vertebral number are foreshadowed by different somite counts at the tailbud stage, thought to be a highly conserved (phylotypic) stage. Somite number therefore violates the ‘developmental hourglass’ model. We argue that this is because somitogenesis shows uncoupling or dissociation from the conserved positional field encoded by genes of the zootype. Several other systems show this kind of dissociation, including limbs and feathers. Bmp-7 expression patterns demonstrate dissociation in the chick pharyngeal arches. This makes it difficult to recognise a common stage of pharyngeal development or ‘pharyngula’ in all species. Rhombomere number is more stable during evolution than somite number, possibly because segmentation and positional specification in the hindbrain are relatively interdependent. Although developmental mechanisms are strongly conserved, dissociation allows at least some major evolutionary changes to be generated in phylotypic stages.

Control of somite number in normal and amputated mutant mouse embryos: an experimental and a theoretical analysis

A regulation is shown for size and number of serially repeated axial structures, the somites, in a mammalian embryo. The mammalian embryo is normally inaccessible to operation at post-implantation stages. This problem is resolved by the quantitative analysis of somite size, number and development in a recessive mutant of the mouse, amputated, whose axial length is greatly reduced. The effect of the gene simulates an experiment ablating part of the embryonic tissue available for somitic segmentation. Regulation occurs at the time when the somite is first formed, by control of the quantity of cells included in each new somite. A model is devised for the control of somitic segmentation which explains most of the features observed and which can be simulated on a computer.

Development in culture of rat foetuses explanted at 12·5 and 13·5 days of gestation

1. As a result of the relatively simple operation of opening the yolk sac and thus exposing the foetal capillary circulation to flowing medium, it has proved possible to grow 12·5- and 13·5-day rat foetuses for a period of 42 h in culture. 2. 25% rat serum, 75% Tyrode has been found to be a satisfactory and economic culture medium, and has the added attraction that foetal survival is improved compared with that obtained in whole rat serum. 3. For both 12·5- and 13·5-day foetuses grown with open yolk sacs, a gas mixture of 95% O2, 5% CO2 in equilibrium at 1 atm with culture medium flowing at about 15 ml/min has been found to give the best results. 4. Under these conditions, foetuses explanted at 12·5 days increased their protein content from 1·0–1·3 mg to 2·3–2·7 mg during culture. Their somite number was 40–44 at explantation and reached 50–55 during culture. 5. Foetuses explanted at 13·5 days increased their protein content from 3·2–4·0 mg to 6·1–7·5 mg during culture. Their somite number was 51–55 at explantation and reached 60–63 during culture.

The effect of trypan blue on the growth of the rat embryo in vivo

In a previous paper (Berry, 1968) it has been demonstrated, by comparison of in vivo and in vitro growth of the rat foetus, that it is possible to dissociate growth and differentiation in the rat. In a series now exceeding 1000 embryos it is evident that for a given somite number the protein content of an animal developing in vitro might be less than half that of the normal control, suggesting that a considerable reduction in growth rate might be found without necessarily inducing death or malformation. The rate of somite formation is not reduced in vitro in the rat; it has been shown by Herrman & Schultz (1958) that the rate of somite formation is not interfered with by different expiant conditions in the chick embryo. These findings suggest that the increase in somite number is more rigidly determined than the increase in growth rate.

Study on the Formation of Somites in Chick Embryo

Context: The chick embryo is used as a research model in developmental biology. The present study was designed to see the difference in the somite number evolution during the early embryogenesis in two hen breeds i.e. Local (deshi) hen and Plymouth Rock hen and to achieve a more profound knowledge of avian embryology as well as correlate with human early development. Study design: Descriptive type of study. Place and period of study: Histology and Embryology Laboratory, Department of Anatomy, Dhaka Medical College, Dhaka, from July to December 2004. Materials & Methods: The experiment was carried out on embryos groups at the age of 24, 36, 48, and 72 hours of incubation for two individual hen breeds. For each incubation period, 10 samples were prepared in the laboratory and studied in each breed. The number of somite was observed under the light microscope with low power objective and recorded for individual sample. Obtained data was statistically processed in order to quantify the influence of the genetic variation. Results: The number of somite found in Local (deshi) hen and Plymouth Rock (broiler) hen after 24 hours of incubation were 1.02±0.34 and 0.86±0.65, after 36 hours 12.26±2.14 and 10.24±2.58, after 48 hours 21.34±2.57and 18.62±0.84, after 60 hours 32.14±2.31and 29.82±2.72 and after 72 hours 41.66±2.24 and 39.89±2.95 respectively. Key words: Chick embryo; somite; early development; avian embryology. DOI: 10.3329/jdmc.v19i2.7083J Dhaka Med Coll. 2010; 19(2) : 122-125