Control of the estradiol-induced prolactin surge by the suprachiasmatic nucleus.
In the present study we investigated how the suprachiasmatic nucleus (SCN) controls the E(2)-induced PRL surge in female rats. First, the role of vasopressin (VP), a SCN transmitter present in medial preoptic area (MPO) projections and rhythmically released by SCN neurons, as a circadian signal for the E(2)-induced PRL surge was investigated. Using a reverse microdialysis technique, VP was administered in the MPO during the PRL surge, resulting in a suppression of the surge. VP administration before the surge did not affect PRL secretion. Also, administration of a V1a receptor antagonist before the surge was ineffective. Second, lesions of the SCN were made that resulted in constant basal PRL levels, suggesting that with removal of the SCN a stimulatory factor for PRL secretion disappeared. Indeed, the PRL secretory response to blockade of pituitary dopamine receptors was significantly reduced in SCN-lesioned animals. These data suggest that the afternoon decrease of VP release in the MPO by SCN terminals enables the PRL surge to occur, and may thus be a circadian signal for the PRL surge. Simultaneously the SCN is involved in the regulation of the secretory capacity of the pituitary, possibly via specific PRL-releasing factors.
Palm
I F
IF
Netherlands Institute for Brain Research, 1105 AZ Amsterdam, The Netherlands. I.Palm@nih.knaw.nl
van der Beek
E M
EM
Swarts
H J
HJ
van der Vliet
J
J
Wiegant
V M
VM
Buijs
R M
RM
Kalsbeek
A
A
D000818:Animals; D002940:Circadian Rhythm; D004343:Drug Implants; D004958:Estradiol / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D017551:Microdialysis; D010052:Ovariectomy; D011301:Preoptic Area / Q000187:drug effects / Q000502:physiology; D011359:Proestrus; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013493:Suprachiasmatic Nucleus / Q000502:physiology* / Q000601:surgery; D014667:Vasopressins / Q000378:metabolism / Q000494:pharmacology
D004343:Drug Implants; D014667:Vasopressins; D004958:Estradiol; D011388:Prolactin