NORADRENERGIC CONTROL OF CENTRAL OXYTOCIN RELEASE DURING LACTATION INRATS

Noradrenergic systems regulate the systemic release of oxytocin (OT) i n lactating rats. However, a role for norepinephrine (NE) in release o f OT within the magnocellular nuclei during suckling has not been esta blished. These studies were designed to determine 1) if suckling induc es NE release in the supraoptic (SON) and paraventricular (PVN) nuclei of conscious rats and 2) the role of NE in the central, intranuclear release of OT within these nuclei. Female Holtzman rats were implanted with microdialysis probes adjacent to the PVN or SON on lactation day s 8-12. The following day, the pups were isolated from the dams for 4 h. Microdialysis probes were perfused with artificial cerebrospinal fl uid (ACSF) or with ACSF containing an alpha- or a beta-adrenergic rece ptor antagonist. Dialysate was collected before, during, and after suc kling and analyzed for NE or OT. In an additional experiment, an alpha - or beta-adrenergic agonist was administered via the microdialysis pr obes into the PVN in nonsuckled, lactating rats. Extracellular NE incr eased in the PVN during suckling but was not detectable in the SON. OT concentrations in dialysates from the PVN and SON significantly incre ased during suckling. Blockade of either alpha- (in both PVN and SON) or beta-(PVN) adrenergic receptors prevented the suckling-induced incr ease in central OT release. OT release was increased in nonsuckled, la ctating rats by central application of either an alpha- or beta-adrene rgic agonist. These data demonstrate that intranuclear NE release is i ncreased in the PVN by suckling and that subsequent stimulation of bot h alpha- and beta-noradrenergic receptors mediates intranuclear OT rel ease.