To identify the central innervating the mammary nerve, viral retrograde transneuronal labelling methods were employed. Pseudorabies virus 6 microliter was injected into the mammary nerve of adult female Sprague-Dawley rats. After 4 days of survival, the animals were perfused with 4% paraformaldehyde-lysine periodate and their brains were processed for immunohistochemistry and double immunofluorescent staining of Pseudorabies virus or oxytocin using polyclonal antibodies. Several nuclei in brain were retrogradely labelled with Pesudorabies virus.Only a few magnocellular neurons of the paraventricular nucleus throughout whole brain showed double immunoreactivity to Pseudorabies virus and oxytocin. Approximately 11 percent of the oxytocinergic cells of the paraventricular nucleus,especially in three subnuclei[dorsomedial cap, lateral magnocelluar part and ventral part] showed double positive reaction to both Pseudorabies virus and oxytocin. These data demonstrate that some CNS cells projecting to the mammary nerve contained oxytocin and it may acts as a neurotransmitter in this pathway and a hormone targeting milk production and secretion.