Explanation of fetal murine retinae to the chorioallantoic membrane of the chicken embryo

A technique is here described for the culture of mammalian retinal explants on the chorioallantoic membrane of the developing chicken embryo. As an integral part of the central nervous system, the mammalian retina is characterised by its highly organised laminar structure and developmental timetable. Study of its prenatal development is, however, difficult to undertake in utero. In an attempt to render the organ of vision more accessible experimentally, fetal mouse retinae were explanted across major species barriers to the live chorioallantoic membrane of the chick. From 26 experiments, 128 explants (70% of the total) were recovered and 27 possessed a cytomorphology apparently identical to that of age-matched controls. The surviving retinae were analysed using a specifically devised set of criteria and they had developed a normal laminar structure (ganglion cell, inner plexiform, inner nuclear, outer plexiform and outer nuclear layers) but increased numbers of pyknotic profiles were present and somal sizes in the ganglion cell layer were significantly smaller. Such patterns have been obtained in other studies, both in vivo and in vitro, in which retinae had no access to their major targets in the brain, the superior colliculus and lateral geniculate nucleus. Explantation to the chorioallantoic membrane is thus a viable alternative for experiments requiring tissue isolation from natural surroundings since the explants are accessible for manipulation and observation while interacting with the host chick embryo. Furthermore, the technique allows examination of retinal differentiation, offering the opportunity to answer a number of important questions regarding development in the central nervous system.