The effects of knife cuts in the sub-paraventricular zone of the female rat hypothalamus on oestrogen-induced diurnal surges of plasma prolactin and LH, and circadian wheel-running activity.
To investigate the role of suprachiasmatic efferent connections in the expression of diurnal hormone rhythms, the efferent pathway from the suprachiasmatic nucleus (the putative circadian generator in the rat) to the subparaventricular zone (the main terminal area of suprachiasmatic efferents) was disrupted using bilateral horizontal knife cuts in ovariectomized oestrogen-treated rats. The position of the knife cut was assessed by observing its effect on vasoactive intestinal polypeptide immunoreactivity (a marker for suprachiasmatic efferents into the sub-paraventricular zone). The size of both the diurnal plasma LH and prolactin surges was markedly and consistently reduced over the 3-week period following the lesion in animals with a total deafferentation of the subparaventricular zone, compared with sham-operated animals or lesioned animals with an intact subparaventricular zone. When lesioned animals were grouped according to the presence or absence of damage to the preoptic area, no significant differences were found in the sizes of the plasma hormone surges. When similar knife cuts were given to animals whose activity cycles were observed, no significant effects were noted in the ability of the animals to synchronize to a light/dark regime or to free-run in constant light conditions. These results suggest that the suprachiasmatic nucleus influences the diurnal surges of plasma LH and prolactin in oestrogen-treated ovariectomized rats, initially by an interaction with the subparaventricular zone and not by a direct influence on gonadotrophin-releasing hormone neurones or other more rostral structures.
MRC Brain Metabolism Unit, University Department of Pharmacology, Edinburgh.
A G
AG
Watts
W J
WJ
Sheward
D
D
Whale
G
G
Fink
D000818:Animals; D002940:Circadian Rhythm; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D007031:Hypothalamus / Q000502:physiology*; D007986:Luteinizing Hormone / Q000097:blood*; D009043:Motor Activity; D010286:Paraventricular Hypothalamic Nucleus / Q000502:physiology; D011301:Preoptic Area / Q000502:physiology; D011388:Prolactin / Q000097:blood*; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism
D014660:Vasoactive Intestinal Peptide; D004958:Estradiol; D011388:Prolactin; D007986:Luteinizing Hormone