Oxytocin neurone autoexcitation during morphine withdrawal in anaesthetized rats.
We investigated whether release of oxytocin into the supraoptic nucleus is involved in morphine-withdrawal excitation of oxytocin neurones. Retrodialysis of naloxone into the supraoptic nucleus of morphine-dependent rats increased intranuclear oxytocin release by 56.5p +/- 12.7% whereas no change was seen in vehicle-treated dependent rats. In another experiment, in morphine-dependent rats given intravenous (i.v.) naloxone, intracerebroventricular (i.c.v.) oxytocin receptor antagonist injection reduced the increase of plasma oxytocin concentration (to 28-fold) compared with i.c.v. vehicle (62-fold increase). Finally, the increase in oxytocin neurone firing rate following morphine-withdrawal in the presence of i.c.v. oxytocin antagonist infusion was 28% of the steady state firing rate (15-20 min later) and this was lower (p < 0.05) than the percentage increase in i.c.v. vehicle-infused rats (89%). Thus, central endogenous oxytocin may be involved in withdrawal excitation of oxytocin neurones.
Brown
C H
CH
Department of Physiology, University Medical School, Edinburgh, UK.
Munro
G
G
Johnstone
L E
LE
Robson
A C
AC
Landgraf
R
R
Russell
J A
JA
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000704:Analysis of Variance; D000818:Animals; D002552:Cerebral Ventricles / Q000187:drug effects / Q000503:physiopathology*; D005260:Female; D007275:Injections, Intravenous; D007276:Injections, Intraventricular; D017551:Microdialysis; D009021:Morphine Dependence / Q000503:physiopathology*; D009270:Naloxone / Q000008:administration & dosage / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D010121:Oxytocin / Q000097:blood / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013375:Substance Withdrawal Syndrome / Q000503:physiopathology*; D013495:Supraoptic Nucleus / Q000187:drug effects / Q000503:physiopathology*
D009270:Naloxone; D010121:Oxytocin