Concentrations of estradiol in ewe cerebrospinal fluid are modulated by photoperiod through pineal-dependent mechanisms.
In the ewe, seasonal anestrus results from an increased responsiveness of the hypothalamus to the negative feedback of estradiol (E2) on the gonadotropic axis under long-day conditions. However, this seasonal effect could also depend upon variable uptake of steroids by the brain. The aim of the present experiment was to compare the concentration of E2 in the blood plasma and in the cerebrospinal fluid (CSF) from the third ventricle in groups of ovariectomized, estradiol treated ewes maintained under short day (SD) or long day (LD) conditions and to study the involvement of the pineal gland in this photoperiodic regulation. Pinealectomized and sham-operated ewes were equipped with an intracerebral cannula to sample the CSF. The plasma E2 concentrations showed no difference between LD and SD in sham-operated and pinealectomized animals. In contrast, in the CSF, E2 concentration was higher in the LD than the SD group, and pinealectomy suppressed this effect of photoperiod. Concomitantly, the stimulatory effect of SD on luteinizing hormone levels observed in sham-operated ewes was abolished by pinealectomy. The results demonstrate that LD increases the E2 concentration in the CSF by a mechanism involving the pineal gland.
Thiery
Jean-Claude
JC
UMR INRA-CNRS-Université de Tours, Physiologie de la Reproduction et des Comportements, Nouzilly, France. thiery@tours.inra.fr
Lomet
Didier
D
Schumacher
Michael
M
Liere
Philippe
P
Tricoire
Helene
H
Locatelli
Alain
A
Delagrange
Philippe
P
Malpaux
Benoit
B
D000818:Animals; D004958:Estradiol / Q000097:blood / Q000134:cerebrospinal fluid* / Q000528:radiation effects*; D005260:Female; D007986:Luteinizing Hormone / Q000097:blood / Q000134:cerebrospinal fluid; D008550:Melatonin / Q000097:blood / Q000134:cerebrospinal fluid; D010052:Ovariectomy; D017440:Photoperiod; D010870:Pineal Gland / Q000502:physiology* / Q000528:radiation effects* / Q000601:surgery; D012756:Sheep
D004958:Estradiol; D007986:Luteinizing Hormone; D008550:Melatonin