Abstract

Previous research has demonstrated that staining for NADPH-diaphorase (NADPH-d) a histochemical marker for nitric oxide synthase is increased in the supraoptic (SON) and paraventricular (PVN) nuclei in late pregnancy. This work was extended to investigate whether increases in staining were evident at other times during pregnancy and lactation. The number of cells in the SON and PVN that stained for NADPH-d in rats on Day 4, 12, 16, and 22 of pregnancy and on Day 4, 12, and 20 of lactation was compared to that in virgin females. In other studies, the influence of ovarian hormones and central oxytocin infusion on NADPH-d staining in these nuclei was examined. Staining in the SON and PVN was compared among ovariectomized (ovex) animals exposed to either a steroid hormone regimen that mimics late pregnancy (estrogen (E) + progesterone (P) treatment followed by P removal), E alone, E + P, or cholesterol alone. A second study compared NADPH-d staining in ovex animals exposed to either chronic E or cholesterol treatment and infused with oxytocin or vehicle into the third ventricle for 7 days. On the appropriate day, all animals were perfused and the brains were processed for NADPH-d histochemistry. In both the SON and PVN the number of densely stained cells present on Days 12 and 22 of pregnancy and 4 and 12 of lactation was greater than that seen in virgin females. Both the steroid treatment that mimicked late pregnancy and chronic i.c.v. oxytocin infusion in E-primed animals increased NADPH-d staining in ovex animals. These data suggest that, in general, NADPH-d staining in the SON and PVN is increased at times when oxytocin cells in these areas are activated and that the hormonal state associated with late pregnancy is sufficient to up-regulate NADPH-d in these regions