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Discussion
Our results suggest that valproic acid exposure during
development causes noticeable developmental delay. This
implies that valproic acid has toxic effects on developing
embyos in addition to specifically affecting somite
organization. We were unable to observe any somite
malformation or cartilage malformation for two possible
reasons. Somite malforamation was unobservable presumably
because antibody staning was unsuccessful. Cartilage
malformation was unobservable because the concentrations of
valproic acid were too toxic and fish died before cartilage
formation began.
Previous research has shown that embryonic exposure to
valproic acid acts by down-regulating the expression of
pax-1 thereby causing several skeletal malformations
(Vorhees, 1987; Barnes, 1996). The study upon which this
research was based (Graye
and Mindel, 2001) found that exposing zebrafish embryos
to valproic acid led to somite malformations (including
somite fusion) that were consistant with the findings of
previous studies ( i.e. Barnes, 1996). Somite abnormalities
were found to increase proportionally with valproic acid
concentration. While Graye and Mindel (2001) did not test
for changes in Pax1 expression, previous studies in chick
embryos show that a down-regulation of Pax-1 expression
leads to somite abnormalities (Barnes, 1996).
In order to better test for abnormal bone development,
either lower concentrations of valproic acid should be used
or VA should be added at a later developmental stage.
Because fish are outbred, the reported range of effective
concentrations may vary between batches of fish. As such, it
would be advisable to perform a preliminary test to
determine a range of concentrations. Exposure to VA at a
later stage might also better affect bone formation, given
that VA affects Pax-1 expression and chondrocyte
differentiation, both of which do not occur until ~60 hrs
after fertilization (Kimmel, 1995). Also, in order to be
able to observe vertebrae malformation, it is advisable to
allow zebrafish larvae to develop to a stage that is later
than the 96 hr stage. This would necessitate the feeding of
the larvae, given that their endogenous food supply is fully
consumed by this point in development. (J. Cebra-Thomas,
personal communication, spring 2004)
© Cebra-Thomas, 2001
Last Modified: 14 July 2014
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