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

t25
7. Dlscusst0N
1'/i th progressive control of infectious diseasesi congenitar defects
have become an inportant cause of ¡nfant mortal ity and morbidity. Open
defects of the central nervous system form a signifrcant proportion of
the major malformations. Anencephaly ls uniformly fatal, but the effect
of spina bifîda varles ¡¡îth the exrent and level of the cord lesion (Barson,
1970).
ln an êttempt to lnvestlgate the embryogenesis of anencephaly and
splna bifida, ên exper¡mental method has been developed for produclng
open defects of the brain and splnal cord in the chlck embryo, by a simple
physlcal procedure.
The dlscussion ls llmlted to cons¡deration of the malformations
obtained by thls technlc - open neural lesions, skeletal defects of the
vertebra¡ column, and a range of associated non-neural malformations.
Anterîor spina bifida and neuro-enteric connectlons, hydrocephalus and
the Arnotd-chlari nalformation, syringomyelia and myelocystocele were not
diagnosed in the experimental enbryos, and so êre not consîdered in this
d i scuss íon.
A wlde renge of neural malformatíons has been produced in domestic
and faboratgly animals by a plethora of agents - vitamin and míneral
deflciences, stêrvat¡on, hypervítaminosis A, ionizing radîations, infections,
hypoxla, hypothermia, hypertherrnía, and many drugs, dyes, hormones and
chemîcal nateriêls (Kalter, l!68; Shepard, 1976; persaud, 1977).
0pen neural defects have been produced in the chick embryo by x-rays,
ultraviolet light, ultrasound, víruses, hypoxla, hypercarbía, and a variety
of drugs, hornones and chemicals (see Section 2.3.2 for references).