Ovarian steroids and sexual interaction alter oxytocinergic content and distribution in the basal forebrain

The immunoreactive levels of oxytocin (OXY) were assessed by radioimmunoassay (RIA) and immunohistology after treatments with estradiol or estradiol and progesterone in ovariectomized rats that were mounted or not mounted by males. In micropunches from the medial preoptic area (MPOA) OXY immunoreactive levels increased significantly in estrogen-progesterone-treated receptive animals (mean lordosis quotient (LQ) = 82.9 +/- 4.4) that were mounted by males over levels in estrogen-treated unreceptive animals (mean LQ = 2.3 +/- 1.3). No other areas demonstrated significant changes in OXY levels across these treatments, although the paraventricular nucleus also had elevated OXY levels in receptive mounted females. In other animals, immunocytochemistry revealed that the number of oxytocinergic perikarya in the MPOA decreased in receptive animals (LQ = 86.7 +/- 4.9) that were mounted. The number of oxytocinergic perikarya per 50 microns vibratome section in the lateral subcommissural nucleus was lower in all estrogen-treated groups than in oil vehicle-treated controls. We suggest that the combination of increasing immunoreactive levels of OXY in the MPOA with decreasing numbers of oxytocinergic perikarya indicates that preoptic OXY is moved out of cell bodies, in receptive rats that are mounted by males, to a state that is more accessible to the RIA.