Universlty of Manitoba, ln Partîal Fulfiìlment - MSpace at the ...

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Congenital malformêtlons of the ðentral nervous system may be open
or closed. 0pen defects involve the braîn or the spinal cord, or both.
lnvestîgation of the etiology of these defects involves epìdemiological
stud¡es of their distribution in human populaiions and embryological
studies of their development in experimental animals and human abortuses.
For this investigation the chick embryo was ¡nìtíâl ly selected,
because of its accessibil ¡ty to treatment and observation through a
wíndow in the overìyìng shell; the use of an 4n o7)o system al lowed
culture of the embryos to 12 days of incubation. ln addition, early
neurogenesÌs in avian and human embryos is very similar, wÌth development
of the spÌnal cord from neural plate and tai l-bud materials, which
fuse in an overlap zone.
Prel iminary experiments, in which early chîcl< enrb ryos were exposed
to several known teratogenic agents through a window în the shell, revealed
that windowing alone was highly teratogenic. By using a standard
windowing technic at 26 - l0 hours of incubation a range of neurôl ånd
non-neural mal formations were obtained.
The morial ity and malformations produced by windowîng at l4 hours
of incubat¡on were greater than those at 26 hours, but by lB houis the
teratogenic effect was less pronounced. 0bl íterat¡on of the introduced
air space,by the addition of albumen or F 12 medîum or by reexpansion of
the air celì, almost abol ished the teratogenic effect of wíndowing if
performed immediately.
Skeletal staining of 11 - 12 day embryos showed that vertebral
lesions increased in severîty in a cranio-caudal sequence, spina bifida occuì ta