Reproductive state changes NADPH-diaphorase staining in the paraventricular and supraoptic nuclei of female rats

It has been demonstrated in guinea pigs that nitric oxide synthase (NOS) activity is increased in late pregnancy in some peripheral tissues and in the cerebellum. To determine whether similar changes would be observed in areas of the brain known to play a role in parturition, staining for NADPH-diaphorase, a histochemical marker of NOS synthase, in the paraventricular (PVN) and supraoptic nuclei (SON) was compared among ovariectomized, virgin and late pregnant rats. The number of cells showing dense staining for NADPH-diaphorase increased in both the SON and PVN in late pregnancy compared to that observed in virgin and ovariectomized females. Thus, changes in reproductive state are associated with changes in NADPH-diaphorase staining in areas of the brain that are intimately involved in the control of reproductive function.