Rat Whole Embryo Culture.

The direct effects of chemical exposures, environmental extremes, and nutrient quality/quantity have been very difficult to study in mammalian embryos due to their anatomical inaccessibility, paucity of tissue, and other factors that make human studies unethical. Many acute and chronic developmental anomalies can trace their origins to postimplantation phases of gestation, where the organs are first being established and growth and differentiation are in highly active states of flux. Most chemical insults and conditions that produce birth defects are believed to act during this period of organogenesis. The evolution of rodent whole embryo culture (WEC) techniques has provided a valuable experimental model where physiological conditions and exposures can be carefully controlled and manipulated to test hypotheses and explore biochemical and molecular mechanisms of action that would otherwise be extremely difficult. Exposure to chemicals can be controlled through their direct addition to the culture medium. Optimal in vitro culture conditions support the growth of intact, viable conceptuses (embryo and associated extraembryonic membranes) from early egg cylinder stages through the establishment of the neural plate, gastrulation, neural tube closure, onset of active heartbeat and circulation, and the initial formation of all major organ systems that occur prior to the establishment of a functional placenta. Detailed comparisons of in vivo and in vitro growth show that conceptuses grown in WEC are nearly identical, structurally and functionally, to conceptuses of the same developmental stage that are allowed to develop normally in utero during a comparable developmental period. Culture conditions and mechanical apparatuses can be modified to suit a large number of different experimental approaches and paradigms.