Studies of normal development of the New Zealand white strain of rabbit. I. Oogenesis. II. External morphology of the embryo

Refinement of a morphological scoring system for postimplantation rabbit conceptuses

“…This report provides what we believe to be the most detailed description of normal postimplantation rabbit embryo available to date, thus building on the work of Pitt and Carney (1999a) and earlier investigators (Minot and Taylor, 1905;Waterman, 1943;Edwards, 1968) providing much needed basic embryological data to underpin the widespread use of rabbits in regulatory testing. The scoring system applies specifically to the GD 8.0-12.0 developmental window, which was chosen based on the extensive and rapid events in organogenesis that occur during this period, the ability to conduct whole embryo cultures within this window, and because of the often heightened susceptibility to teratogenic insult at these stages of development (Schardein et al, 1985).…”

“…Until recently, anatomical descriptions of normal embryo development were limited to a 1905 study of the hare (Lepus cuniculus) by Minot and Taylor, and two studies in rabbits (genus Orytolagus) of unspecified species or strain (Waterman, 1943;Edwards, 1968). Also, these reports generally were not very detailed with respect to the period of early to mid organogenesis, and in particular provided little information on the extraembryonic structures of the rabbit conceptus, such as the allantois, yolk sacs, and chorioallantoic placenta.…”

Neurulation in the rabbit embryo

“…When such embryos were dissected free from the decidua, they inevitably deformed. This is what probably happened in previous studies, when embryos were stretched before fixation (e.g., Waterman 1943). In order to prevent unwanted disturbances of morphology as much as possible, embryos were briefly fixed in situ, and the subsequent dissection and transport to a Petri dish were performed in excess PBS.…”

“…Multiple closure sites can be seen, in fact, in photographs (Waterman 1943;Gottschewsky 1967) and a drawing (Evans and Sack 1973), but are not further explained. An intermittent initial closure with the RNP present was described previously by Minot and Taylor (1905) in two embryos (8 and 9 somites), but a MNP was not mentioned.…”

“…In a more extensive study (Minot and Taylor 1905), eight embryos were described during the whole process of neurulation, and although the descriptions are rather detailed, the small number of embryos do not elucidate neurulation as a continuous process. In another study (Waterman 1943), six embryos between 4 and 12 somites were shown in photographs and described in rather general terms; progress of closure was seen from the stage of 4 somites onward, and at the stage of 10 somites large anterior and posterior neuropores were seen. In an immunohistochemical study the expression of cytokeratin 8 and 18 appeared to be gradually lost from the neural plate cells, which was mirrored by a gradual increase of vimentin expression in a highly ordered manner.…”