title: Prolactin regulation of oxytocin neurone activity in pregnancy and lactation.
abstract: During lactation, prolactin promotes milk synthesis and oxytocin stimulates milk ejection. In virgin rats, prolactin inhibits the activity of oxytocin-secreting neurones. We found that prolactin inhibition of oxytocin neurone activity is lost in lactation, and that some oxytocin neurones were excited by prolactin in lactating rats. The change in prolactin regulation of oxytocin neurone activity was not associated with a change in activation of intracellular signalling pathways known to couple to prolactin receptors. The change in prolactin regulation of oxytocin neurone activity in lactation might allow coordinated activation of both populations of neurones when required for successful lactation.
  
  
  
  Secretion of prolactin for milk synthesis and oxytocin for milk secretion is required for successful lactation. In virgin rats, prolactin inhibits oxytocin neurones but this effect would be counterproductive during lactation when secretion of both hormones is required for synthesis and delivery of milk to the newborn. Hence, we determined the effects of intracerebroventricular (i.c.v.) prolactin on oxytocin neurones in urethane-anaesthetised virgin, pregnant and lactating rats. Prolactin (2 μg) consistently inhibited oxytocin neurones in virgin and pregnant rats (by 1.9 ± 0.4 and 1.8 ± 0.5 spikes s-1, respectively), but not in lactating rats; indeed, prolactin excited six of 27 oxytocin neurones by >1 spike s-1in lactating rats but excited none in virgin or pregnant rats (χ22= 7.2, P = 0.03). Vasopressin neurones were unaffected by prolactin (2 μg) in virgin rats but were inhibited by 1.1 ± 0.2 spikes s-1in lactating rats. Immunohistochemistry showed that i.c.v. prolactin increased oxytocin expression in virgin and lactating rats and increased signal transducer and activator of transcription 5 phosphorylation to a similar extent in oxytocin neurones of virgin and lactating rats. Western blotting showed that i.c.v. prolactin did not affect phosphorylation of extracellular regulated kinase 1 or 2, or of Akt in the supraoptic or paraventricular nuclei of virgin or lactating rats. Hence, prolactin inhibition of oxytocin neurones is lost in lactation, which might allow concurrent elevation of prolactin secretion from the pituitary gland and activation of oxytocin neurones for synthesis and delivery of milk to the newborn.
authors.affiliation: Brain Health Research Centre, University of Otago, Dunedin, New Zealand.|Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.|Department of Physiology, University of Otago, Dunedin, New Zealand.
authors.forename: Rachael A
authors.initials: RA
authors.lastname: Augustine
authors.affiliation: Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.|Department of Anatomy, University of Otago, Dunedin, New Zealand.
authors.forename: Sharon R
authors.initials: SR
authors.lastname: Ladyman
authors.affiliation: Brain Health Research Centre, University of Otago, Dunedin, New Zealand.|Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.|Department of Physiology, University of Otago, Dunedin, New Zealand.
authors.forename: Gregory T
authors.initials: GT
authors.lastname: Bouwer
authors.affiliation: Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.|Department of Physiology, University of Otago, Dunedin, New Zealand.
authors.forename: Yousif
authors.initials: Y
authors.lastname: Alyousif
authors.affiliation: Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.|Department of Anatomy, University of Otago, Dunedin, New Zealand.
authors.forename: Tony J
authors.initials: TJ
authors.lastname: Sapsford
authors.affiliation: Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.|Department of Physiology, University of Otago, Dunedin, New Zealand.
authors.forename: Victoria
authors.initials: V
authors.lastname: Scott
authors.affiliation: Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.|Department of Anatomy, University of Otago, Dunedin, New Zealand.
authors.forename: Ilona C
authors.initials: IC
authors.lastname: Kokay
authors.affiliation: Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.|Department of Anatomy, University of Otago, Dunedin, New Zealand.
authors.forename: David R
authors.identifier: 0000-0001-5606-2559
authors.initials: DR
authors.lastname: Grattan
authors.affiliation: Brain Health Research Centre, University of Otago, Dunedin, New Zealand.|Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.|Department of Physiology, University of Otago, Dunedin, New Zealand.
authors.forename: Colin H
authors.identifier: 0000-0003-2305-846X
authors.initials: CH
authors.lastname: Brown
mesh_terms: D000200:Action Potentials; D000818:Animals; D005260:Female; D007774:Lactation / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism* / Q000502:physiology; D010121:Oxytocin / Q000378:metabolism*; D011247:Pregnancy / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism*; D051381:Rats
chemical_list: D010121:Oxytocin; D011388:Prolactin
keywords: erk; lactation; oxytocin; pregnancy; stat5; vasopressin