Effect of suckling on NADPH-diaphorase (nitric oxide synthase, NOS) reactivity and NOS gene expression in the paraventricular and supraoptic nuclei of lactating rats

This study examined the effect of suckling on nicotinamide adenine dinucleo tide phosphate diaphorase (NADPH-d, a histochemical marker for nitric oxide synthase, NOS) reactivity and neuronal NOS mRNA expression in the paravent ricular (PVN) and supraoptic (SON) nuclei of lactating rats. Freely nursing (non-separated) dams and those separated from pups for 12 h and then reuni ted for 0, 15, 30, 60, 90, 120 and 180 min were used for the study. Dams se parated from pups and sacrificed at time zero (without reunion) showed a si gnificant decrease in NADPH-d staining and NADPH-d positive cells as well a s in the NOS mRNA expression in the PVN and SON compared to that observed i n non-separated dams. Reunion with pups and restoration of suckling signifi cantly increased NADPH-d reactivity after 15, 30, 60 min, but not after 90, 120 and 180 min compared to non-reunited pups-deprived dams. A pattern of NADPH-d reactivity and neuronal NOS mRNA expression indistinguishable from that observed during free lactation was reinstated shortly (15 min) after t he restoration of suckling stimulus, suggesting that the NADPH-d reactivity in lactation depends on the presence of the suckling stimulus. These resul ts show that suckling stimulus may play a modulatory role in the regulation of NOS reactivity in the magnocellular neurones of the hypothalamic PVN an d SON during lactation.