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

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Uindowîlg at ear¡y stages of avian development can be regarded
as another physícal teratogenÌc procedure. The standard windowíng technic
at 26-30 hours produced a high incldence of mortal ity and marformatíons.
This effect was almost abol ished by obliteration of the introduced air
space, if performed i mmed îa te I y.
The teratogenlc actlon of windowing at êarly stages of development
has been reported by Ancel (19\6-47 t '1956),Hinsch and Hami lton (1956),
l4cCalllon ånd Clarke (1gSÐ, ,"nn et ê1. (i973). ln many publ îcations
"nO
no attempt to obl iterate the a¡r space is reported, so thât any nalformations
recorded mlght be caused by windowing as well as by the agents
emp I oyed .
ln the presen, "rp.rlr"ntr,
embryos at the t¡me of treêtment ranged
from Stage 5 to Stage 10. The effect of wîndowing is not confined to
a short period like other physical agents, though formation of the amnîon
by Stage 1B protects the embryo after about 60 hours. Some defects (such
as neural dysraphism, eye defects, and trunk cysts) can be attrÍbuted to
an early effect; others (such as rumplessness, ectop¡a viscerum, and limb
defects) arise later. A¡though windowing exposes the dorsal surface of
the chick embryo, and neural defects originate dorsally, other defects
(such as ecto¡iía viscerum) involve ventral structures.
ln the neural tube, four degrees of involvement resulted from
windowing. l4any embryos developed quite normally. Embryos with early
myeloschisis showed necrosis ín the superflcial cells of the neural plate,
which later resolved. Hyelodysplasia, due to absence of neural plate
materîal,was comblned with mesodermal cysts and hemorrhages. The most
severely affected embryos (not examined histological ly),showed early death
associated wlth open neural defects, severe trunk dlstorsion, reduced