Neurochemical regulation of hypothalamic oxytocin messenger ribonucleic acid levels during early lactation in rats.
The objective of the present studies was to investigate whether the stimulatory influence of the suckling offspring on the level of hypothalamic oxytocin (OT) messenger RNA (mRNA) in early lactation in rats is mediated by activation of the central noradrenergic and/or oxytocinergic systems, both of which have been strongly implicated in suckling-induced OT release. Experiments tested whether the effect of litter separation immediately postpartum to reduce hypothalamic OT mRNA could be mimicked by pharmacological disruption of either noradrenergic or oxytocinergic signals. Bilateral microinjections of the catecholamine neurotoxin 6-hydroxydopamine into either the supraoptic nucleus (SON) or paraventricular nucleus/anterior commissural nucleus regions significantly reduced the concentrations of norepinephrine in these areas, but did not alter the relative levels of OT mRNA in these regions, suggesting that the stimulatory inputs provided by the suckling offspring are not transmitted through the noradrenergic system. However, 24-h infusion of the OT antagonist desGLY-NH2, d(CH2)5 [Tyr (Me)2 Thr4]OVT into the third ventricle of rats maintaining their litters immediately postpartum reduced the level of OT mRNA in the SON. Conversely, chronic infusion of OT into the third ventricle of rats separated from their litters immediately postpartum attenuated the decline in OT mRNA in the SON. OT mRNA levels in the paraventricular nucleus/anterior commissural nucleus region did not change in response to litter separation, or infusion of OT or OT antagonist, implying differential regulation of OT mRNA expression in the magnocellular nuclei. The present results suggest that in addition to promoting OT secretion, OT released centrally by suckling may facilitate OT gene expression, at least during the early postpartum period when OT mRNA is subject to some degree of afferent regulation.
Department of Pharmacology, University of Tennessee-Memphis College of Medicine, Memphis 38163.
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Spinolo
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Crowley
D000818:Animals; D000833:Animals, Suckling / Q000378:metabolism; D001921:Brain / Q000502:physiology*; D002395:Catecholamines / Q000037:antagonists & inhibitors; D005260:Female; D007031:Hypothalamus / Q000378:metabolism*; D007774:Lactation / Q000378:metabolism*; D009638:Norepinephrine / Q000037:antagonists & inhibitors / Q000502:physiology*; D016627:Oxidopamine / Q000494:pharmacology; D010121:Oxytocin / Q000235:genetics / Q000494:pharmacology / Q000502:physiology*; D010904:Pituitary Gland, Posterior / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D002395:Catecholamines; D012333:RNA, Messenger; D010121:Oxytocin; D016627:Oxidopamine; D009638:Norepinephrine