Enduring consequences of neonatal treatment with antisense oligodeoxynucleotides to estrogen receptor messenger ribonucleic acid on sexual differentiation of rat brain.

Sexual differentiation of the mammalian brain is regulated by steroids during a critical developmental period, particularly by estradiol, which is believed to be aromatized in brain from gonadally derived testosterone. To ascertain the importance of neuronal estrogen receptor expression during sexual differentiation, we infused a 15-mer oligodeoxynucleotide antisense to the region of the translation start codon of estrogen receptor messenger RNA (mRNA), into the hypothalamus of 3-day-old rat pups. Two separate control treatments consisted of either a scrambled nucleotide sequence oligodeoxynucleotide, which had little homology to known mRNAs, or vehicle. Female pups either received a lightly androgenizing dose of testosterone 6 h after oligo infusion or were not hormone treated. Infusion of antisense oligo to estrogen receptor mRNA protected against many of the androgenizing effects of testosterone. Androgenized females infused with antisense oligo were significantly more likely to exhibit female sexual behavior in adulthood after treatment with estrogen plus progesterone and remained sensitive to the induction of wheel-running behavior by estrogen treatment seen in normal females, whereas the control androgenized females did not. Normal females did not exhibit any effects of antisense oligo treatment on sexual or locomotor behavior, but antisense oligo-treated normal females showed a trend (P = 0.09) toward disrupted estrous cyclicity and behaved differently in tests of open field behavior compared to controls. After killing, brains were processed for histology. Morphometric analysis of the sexually dimorphic nucleus of the preoptic area demonstrated a significantly smaller volume in antisense oligo-infused androgenized females compared with vehicle and scrambled oligo-infused controls. The sexually dimorphic nucleus volume was smaller still in normal females infused with antisense oligo, consistent with estrogen receptor activation playing an active role in sexual differentiation of the female brain. These results demonstrate the effectiveness of antisense oligodeoxynucleotides in permanently altering a developmental process if administered during a critical period.