Effect of maternal exposure to dioxin on the pituitary and hypothalamic expression of genes in PND70 male pups

Our previous studies have revealed that treatment of pregnant rats with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, 1 μg/kg) at gestational day (GD) 15 reduces the pituitary synthesis of luteinizing hormone (LH) during late fetal and early postnatal period, leading to imprinting of defects in sexual behaviors at adulthood. However, it remains obscure how the attenuation of pituitary LH links to sexual immaturity. To address this issue, we firstly performed a DNA microarray analysis to identify the gene(s) responsible for dioxin-induced sexual immaturity, using the pituitary and hypothalamus of male pups, at the age of postnatal day (PND)70, born from TCDD-treated dams. Among the reduced genes, we focused on gonadotropin-releasing hormone (GnRH) in the hypothalamus, because of its role in sexual behaviors suggested so far. The present study strongly suggests that maternal exposure to TCDD fixes the status of the lowered expression of GnRH in the offspring by reducing steroidogenesis at perinatal stage, and this is the mechanism for the imprinting of defects in sexual behaviors at adulthood. Total RNA was isolated from the pituitary and hypothalamus of PND70 male pups born from the dams treated with TCDD (1 μg/kg) or vehicle at GD15, using an RNeasy Mini Kit (QIAGEN). To identify the gene(s) the altered expression of which is fixed and linked to defects in sexual behaviors, the profile of gene expression was analyzed using the Illumina RatRef-12 Expression BeadChip. This series includes two dataset; hypothalamic and pituitary samples (each case; N=3x2). The normalization applied each dataset.