Research ReportPre- and postnatal bisphenol A treatment does not alter the number of tyrosine hydroxylase-positive cells in the anteroventral periventricular nucleus (AVPV) of weanling male and female rats

- Pregnant rats treated orally with 2.5 or 25 µg BPA or 5 or 10 µg EE2/kg on GDs 6-21.
- All offspring/litter treated orally with same dose as dam on postnatal days 1-21.
- Tyrosine hydroxylase ir (TH-ir) quantified in AVPV on postnatal day 21.
- More TH-ir cells in females, but no significant effects of BPA or EE2 treatment.
- AVPV volume in separate cohort of PND 21 rats was not sexually dimorphic.

Exposure to Bisphenol A (BPA) may interfere with brain sexual differentiation. Altered numbers of tyrosine hydroxylase (TH) cells in the rodent anteroventral periventricular nucleus (AVPV) after developmental BPA treatment have been reported; however, definitive conclusions are lacking. The current study incorporated many of the guidelines suggested for endocrine disrupter research. Specifically, ethinyl estradiol (EE2) served as a reference estrogen, exogenous environmental estrogen exposure was controlled, BPA was administered orally, and subjects consumed a low phytoestrogen diet. Here, on gestational days 6-21, Sprague-Dawley rats (10-15/group) were gavaged with 2.5 or 25.0 µg BPA/kg/day or 5.0 or 10.0 µg EE2/kg/day or the vehicle (5 ml of 0.3% aqueous carboxymethylcellulose/kg/day). A naïve control group was weighed and restrained, but not gavaged. Beginning on postnatal day (PND) 1 and continuing until PND 21, the 4 pups/sex/litter were orally treated with the same dose their dam had received. On PND 21, 1/sex/litter was perfused and the brain removed. TH immunoreactivity (TH-ir) was counted in 8 images/pup by a technician blind to treatment status. ANOVA results indicated significantly higher TH-ir cells/mm2 in females (main effect of sex: p<0.01); however, there was no significant effect of treatment or a significant interaction of treatment with sex. In a separate untreated group of PND 21 Sprague-Dawley pups, AVPV volume was quantified and no significant sexual dimorphism was apparent. Similar to our reported results of behavioral assessments, the BPA treatment paradigm used here (2.5 or 25.0 µg BPA/kg/day administered orally) does not appear to cause significant alterations in AVPV TH-ir.

Average number of TH-ir cells in postnatal day 21 males (top) and females (bottom) treated with 2.5 or 25.0 µg BPA/kg/day or 5.0 or 10.0 µg EE2/kg/day or vehicle. The naïve control was treated similarly but was not gavaged. The box shows the 25th and the 75th percentiles and the “whiskers” (bars) show the 10th and 90th percentiles. The solid and dashed lines inside the box show the median and mean, respectively. Solid points are those data points falling outside the 10th and 90th percentiles. There were no significant effects of BPA or EE2 treatment; however, there was a significant overall effect of sex (p<0.01), indicating higher TH-ir cell numbers in females. Group sizes were: naïve control (12/sex), vehicle control (15/sex), BPA 2.5 (11 males, 14 females), BPA 25.0 (13/sex), EE2 5.0 (10 males, 12 females), EE2 10.0 (15 males, 13 females).62