Sexually dimorphic expressio in the anteroventral perivenl rat preoptic area: Implicatior hormone surge

Striking sex difference was detected in the expression of estrogen In receptor (ER) P mRNA and protein by nonisotopic in situ hybridA ization and immunohistochemistry in the anteroventral periventricular nucleus (AVPV) of the rat preoptic area. In females more El than in males, a significantly larger number of ERP mRNA-positive st( cells were visualized in the medial-most portion of the AVPV within cc 50 ,tm from the ependymal lining of the third ventricle. Rats of 7, dc 14, 21, 35, and 60 days of age (d 1 = day of birth) showed the sex ot difference. Orchidectomy of male neonates or estrogen treatment re of female pups reversed the brain phenotype when examined on d 14. In the AVPV of adult females, ERa immunoreactivity colocalized in 83% of ERp mRNA-positive cells. Tyrosine hydroxylase Su immunoreactivity colocalized in 18% of ERp immunoreactive cells Pi in d 21 females. Infusion of an ERPJ antisense oligonucleotide into 7, the third ventricle in the vicinity of the AVPV resulted in signifiet cantly longer days of successive estrus and a 50% reduction in the wi number of ER3-immunoreactive cells in the AVPV. These findings w' provide support for the hypothesis that activation of ERp in the w; AVPV is an important regulatory event in the female-typical iner duction of luteinizing hormone surge by estrogen. s.i