Sexually dimorphic expression of estrogen receptor β in the anteroventral periventricular nucleus of the rat preoptic area:: Implication in luteinizing hormone surge

Striking sex difference was detected in the expression of estrogen receptor (ER) 0 mRNA and protein by nonisotopic in situ hybridization and immunohistochemistry in the anteroventral periventricular nucleus (AVPV) of the rat preoptic area. In females more than in males, a significantly larger number of ERbeta mRNA-positive cells were visualized in the medial-most portion of the AVPV within 50 mum from the ependymal lining of the third ventricle. Rats of 7, 14, 21, 35, and 60 days of age (d 1 = day of birth) showed the sex difference. Orchidectomy of male neonates or estrogen treatment of female pups reversed the brain phenotype when examined on d 14. In the AVPV of adult females, ERalpha immunoreactivity colocalized in 83% of ER mRNA-positive cells. Tyrosine hydroxylase immunoreactivity colocalized in 18% of ERbeta immunoreactive cells in d 21 females. infusion of an ERbeta antisense oligonucleotide into the third ventricle in the vicinity of the AVPV resulted in significantly longer days of successive estrus and a 50% reduction in the number of ERbeta-immunoreactive cells in the AVPV. These findings provide support for the hypothesis that activation of ERbeta in the AVPV is an important regulatory event in the female-typical induction of luteinizing hormone surge by estrogen.