Sexual dimorphism in rat oxytocinergic hypothalamic regions.

Oxytocin (OT), a nonapeptide of the hypothalamo- neurohypophyseal system is known to be important for milk ejection and uterus contraction in females and for erection and seminal emissions in males. These sex-specific functional properties imply differential distribution of OT in the hypothalamus. In the present study, complete series of vibratome sections of male and female rat brains were stained for OT with either immunoperoxidase or immunofluorescence in order to evaluate such sex differences. While no significant differences were found in the classical magnocellular nuclei, females had more OT neurons in the zona incerta and the retrochiasmatic portion of the supraoptic nucleus. In males, the lateral subcommissural nucleus and the lateral preoptic area contained significantly more OT perikarya. These sexually dimorphic locations of O T - e x p ressing neuro ns may be th e n eu - roanatomical correlates of known gender-specific functions of O