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

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neural tissue ât the later stages of closure ¡n most control and normal
experlmental embryos. Hany embryos wÌth myeloschisis, however, show
some loss of con.tact between neural tissue and protosomìtes (stages 13-16)
or somìtes (Stages 17-20'). Embryos with myelodysplasia general ly retain
contact between somite mesoderm and neural t¡ssue, but the mesoderm often
shows cystic changes and reduced volume.
Even though the distrlbution of Stages is not perfectly mêtched,
there ls no major difference ín the number of accessory canals between
experimental and control groups, though embryos wîth myeloschisis and
myelodysplasla show some delay in the disappearance of accessory canals
at Stages I 3- 16.
When the development of neural defects is followed, myeloschisis
appeårs ât an eêrlier Stage ênd at a slightly higher level than the myelodysplaslas
(see Tables 37 è 3B). Thus myeloschisis is first detectable as
a wide eversìon of the neural folds, in smooth cont¡nu¡ty wíth ectoderm at
Stage 10 (6E 45), leading to non-closure and separation of the two sources
of neural material by Stage 13 (18E 61). ln Stage 1/-20 embryos the lesíons
lie in regions B, C and D, gíving way to a normal cord developed from
tail-bud material in region E.
tlyelodysplasía fîrst appears âs a narrow eversion of the neural folds
at Sta.ge 16 (3OE 35, 30E 76) wittr no separatîon into rwo sorr".s of neural
materlal and partial ectoderm cover. At Stages 17-20 the lesions occupy
regions B, C, D and E, gîving way to a rather small cord or to diplomyel ia
or amyel ia in region E.
0n the basls of these findings several aspects of neurulatîon were
analysed quantltatlvely to determine the significance of differences
between experimentat and control embryos (see Sections 6.7, 6.8 and 6.9).