Seasonal regulation of reproductive activity in sheep: modulation of access of sex steroids to the brain.
Sheep in temperate latitudes are seasonal breeders. In female sheep, ovarian activity decreases during the anestrous period due to modification of secretion of luteinizing hormone (LH). The seasonal changes in the hormonal LH pattern mainly reflect an increase in the brain responsiveness to the negative feedback exerted by estradiol during long days (LD) on the frequency of pulsatile LH secretion, under neurohormonal GnRH control. The resulting seasonal inhibition of LH secretion mainly involves the activation of dopaminergic systems by E2, which in turn inhibits the GnRH cells from the preoptico-hypothalamic structures. The increased responsiveness of the brain during LD could lead to increased expression of central E2 receptors. In addition, our study shows that steroid access to the brain could be modulated by photoperiodism, thus increasing the availability of steroids to the nervous structures during LD.
Neurobiologie et Maîtrise des Fonctions Saisonnières, UMR 6073 INRA/CNRS/Université de Tours, 37380 Nouzilly, France. thiery@tours.inra.fr
Jean-Claude
JC
Thiery
Benoit
B
Malpaux
D000818:Animals; D001812:Blood-Brain Barrier / Q000502:physiology; D001921:Brain / Q000502:physiology*; D004958:Estradiol / Q000502:physiology; D005260:Female; D012739:Gonadal Steroid Hormones / Q000502:physiology*; D007986:Luteinizing Hormone / Q000502:physiology; D008297:Male; D017440:Photoperiod; D011374:Progesterone / Q000502:physiology; D012098:Reproduction / Q000502:physiology*; D012621:Seasons; D012756:Sheep / Q000502:physiology*
D012739:Gonadal Steroid Hormones; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone