To evaluate developmental exposure effects of two brominated flame retardants, tetrabromobisphenol
A (TBBPA) and 1,2,5,6,9,10-hexabromocyclododecane (HBCD), pregnant Sprague-Dawley
rats were administered either chemical at doses of 100, 1000 or 10,000 ppm in a soy-free
diet from gestation day 10 until the day 20 after delivery. Offspring exposed to TBBPA
showed dose-unrelated slight decreases of serum triiodothyronine (T(3)) concentration
at postnatal day 20, and there was no evidence of hypothyroidism-related neuronal
mismigration and impaired oligodendroglial development as judged by morphometric analyses
of NeuN-immunoreactive neuronal distribution in the hippocampal CA1, and area of corpus
callosum as well as density of 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase)-immunoreactive
oligodendrocytes in the cingulate deep cortex at the adult stage. On the other hand,
HBCD exerted a weak hypothyroidism evident with increases in thyroid weight, thyroid
follicular cell hypertrophy and serum concentrations of thyroid-stimulating hormone
as well as decreases of serum T(3) concentrations in offspring at 10,000 ppm at weaning.
Increased thyroid weights and decreased serum T(3) concentrations were also observed
in the adult stage from 1000 ppm. With regard to the effect on brain development,
HBCD reduced density of CNPase-positive oligodendrocytes at 10,000 ppm, suggesting
an impaired oligodendroglial development. Results thus suggest that TBBPA did not
exert developmental brain effects, while HBCD did, and 100 ppm was determined to be
the no-observed-adverse-effect level of HBCD from changes in thyroid parameters at
the adult stage by maternal exposure, translating into 8.1-21.3mg/kg-d.