Since the beginning of the last century, fertilised chicken eggs have been an established model system and are nowadays often used as an alternative to animal experiments. The test model involves the use of the outer, strongly vascularised amnion (the so-called chorioallantoic membrane, CAM) which surrounds the embryo and is used for gas exchange during embryonic development.
This membrane forms an excellent substrate for the seeding of cultured cells or the transplantation of xenogeneic tissue. As a test system, the early development stages of an incubated chicken egg have an intermediary position between in vitro and in vivo systems.
In the first half of the incubation time, i.e. up until the 10th day of incubation, the membrane is a living test system that is insensitive to pain. In analogy to immunoincompetent mice, chicken embryos do not have a fully functional immune system up until shortly before hatching. This is the prerequisite for transplanting xenogeneic material. The extraembryonic vascular system of the chorioallantoic membrane (CAM) constitutes an excellent substrate both for the seeding of cells from cell cultures as well as for the transplantation of solid tissue segments.
Vascularised organotypical tissue complexes develop a few days after cell suspensions are applied to the membrane. Solid tissue segments such as human biopsy material are connected to and supplied by the chicken embryo's vascular system 48 to 72 hours after transplantation. This means that test substances can not only be applied locally but also systemically. Recent research has shown that this model is also suitable for pharmacokinetic investigations, where it correlates with investigations involving mice. In addition, this model has also increased in global importance as a test system for neoangiogenesis in tumour research.
Many investigations have shown that the results obtained with the CAM model correlated both with in vitro and in vivo results (from cell cultures and animal experiments). As it meets these necessary prerequisites, the CAM model is excellently suited as an intermediary model between cell culture experiments and animal experiments.
Since the model is inexpensive and can be handled relatively easily, it is well suited for screening procedures. The preselection of suitable candidates or experimental approaches in a living, complex system can make an important contribution to the more systematic carrying out of animal experiments and thus to the reduction in the number of experimental animals.