AN OXYTOCIN RECEPTOR ANTAGONIST INFUSED INTO THE SUPRAOPTIC NUCLEUS ATTENUATES INTRANUCLEAR AND PERIPHERAL RELEASE OF OXYTOCIN DURING SUCKLING IN CONSCIOUS RATS
I. Neumann et al., AN OXYTOCIN RECEPTOR ANTAGONIST INFUSED INTO THE SUPRAOPTIC NUCLEUS ATTENUATES INTRANUCLEAR AND PERIPHERAL RELEASE OF OXYTOCIN DURING SUCKLING IN CONSCIOUS RATS, Endocrinology, 134(1), 1994, pp. 141-148
We tested the hypothesis that oxytocin (OXT) released within the supra
optic nucleus (SON) during suckling in lactating rats facilitates its
own intranuclear release and thereby stimulates its secretion into blo
od during the milk ejection reflex. In the first study, to examine the
positive feedback action of OXT released within the SON, microdialysa
tes of the SON area were sampled before and during suckling. Either ve
hicle (1.0 mu l) or an OXT receptor antagonist (50 ng/mu l) was infuse
d adjacent to the microdialysis probe into the SON area before sucklin
g began. Compared to the corresponding presuckling values (100%), the
OXT content in microdialysates sampled during the suckling period incr
eased after vehicle treatment (to 501 +/- 174%; P < 0.01), whereas inf
usion of the OXT antagonist significantly (P < 0.05) attenuated the ri
se in the release of OXT during suckling (130 +/- 22.0%). In the secon
d study, the influence of intranuclear OXT on release of OXT into the
blood during suckling was examined. Compared to those in rats infused
with vehicle into both SON before suckling started (100%), injection o
f the OXT antagonist decreased the concentration of OXT in plasma (to
32.1 +/- 5.50%; P < 0.05) and the milk transfer to the pups during the
suckling period (to 30.2 +/- 13.3%; P < 0.01). Although the neuroendo
crine response to suckling was attenuated in rats receiving the OXT an
tagonist, maternal behavior, assessed as the time at which six to eigh
t pups began suckling and the time from the onset until the occurrence
of the third milk ejection reflex, was unaffected. These findings pro
vide evidence for a receptor-mediated positive feedback action of OXT
on its own release within the SON during suckling. The amplification o
f intranuclear release of OXT is needed for the release of appropriate
amounts of OXT into the bloodstream to stimulate milk transfer to the
suckling pups.