Oxytocin neurones in the supraoptic nucleus (SON) are inhibited by endogenous opioids in late pregnant rats.
Late pregnant rats exhibit endogenous opioid restraint of oxytocin cells since i.v. naloxone (NLX opioid antagonist) increases oxytocin (OXT) secretion but OXT nerve terminals become desensitised to opioids. We have studied central opioid inhibition of OXT neurones in late pregnancy by measuring SON OXT neurones firing rate, immediate early gene (Fos) expression and dendritic OXT release under the influence of NLX On day 21 of pregnancy NLX strongly potentiated cholecystokinin (CCK) excitation of OXT neurones increased Fos protein expression and increased intranuclear release of OXT in the SON; NLX was ineffective in virgin rats. The data indicate central endogenous opioid inhibition of OXT neurone activity in late pregnancy which may restrain premature OXT release.
Dept. of Physiology, University Medical School, Edinburgh.
A J
AJ
Douglas
L E
LE
Johnstone
I
I
Neumann
G
G
Leng
J A
JA
Russell
D000818:Animals; D005260:Female; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009474:Neurons / Q000502:physiology*; D018847:Opioid Peptides / Q000037:antagonists & inhibitors / Q000502:physiology*; D010121:Oxytocin / Q000502:physiology*; D011247:Pregnancy; D051381:Rats; D013495:Supraoptic Nucleus / Q000166:cytology / Q000502:physiology*
D009292:Narcotic Antagonists; D018847:Opioid Peptides; D009270:Naloxone; D010121:Oxytocin