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Departments of Physiology and Pharmacology, University of Tennessee, Memphis, Tennessee 38163
Noradrenergic systems regulate the systemic
release of oxytocin (OT) in lactating rats. However, a role for
norepinephrine (NE) in release of OT within the magnocellular nuclei
during suckling has not been established. These studies were designed
to determine 1) if suckling induces
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
days
8-12.
The following day, the pups were isolated from the dams for 4 h.
Microdialysis probes were perfused with artificial cerebrospinal fluid
(ACSF) or with ACSF containing an 
- or a 
-adrenergic receptor
antagonist. Dialysate was collected before, during, and after suckling
and analyzed for NE or OT. In an additional experiment, an - or
-adrenergic agonist was administered via the microdialysis probes
into the PVN in nonsuckled, lactating rats. Extracellular NE increased in the PVN during suckling but was not detectable in the SON. OT
concentrations in dialysates from the PVN and SON significantly increased during suckling. Blockade of either - (in both PVN and
SON) or - (PVN) adrenergic receptors prevented the suckling-induced increase in central OT release. OT release was increased in nonsuckled, lactating rats by central application of either an - or
-adrenergic agonist. These data demonstrate that intranuclear NE
release is increased in the PVN by suckling and that subsequent
stimulation of both - and -noradrenergic receptors mediates
intranuclear OT release.
oxytocin; paraventricular nucleus; supraoptic nucleus
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