Changes in the 5-HT2A receptor system in the pre-mammillary hypothalamus of the ewe are related to regulation of LH pulsatile secretion by an endogenous circannual rhythm.
BACKGROUND
We wanted to determine if changes in the expression of serotonin 2A receptor (5HT2A receptor) gene in the premammillary hypothalamus are associated with changes in reproductive neuroendocrine status. Thus, we compared 2 groups of ovariectomized-estradiol-treated ewes that expressed high vs low LH pulsatility in two different paradigms (2 groups per paradigm): (a) refractoriness (low LH secretion) or not (high LH secretion) to short days in pineal-intact Ile-de-France ewes (RSD) and (b) endogenous circannual rhythm (ECR) in free-running pinealectomized Suffolk ewes in the active or inactive stage of their reproductive rhythm.


RESULTS
In RSD ewes, density of 5HT2A receptor mRNA (by in situ hybridization) was significantly higher in the high LH group (25.3 +/- 1.4 vs 21.4 +/- 1.5 grains/neuron, P < 0.05) and 3H-Ketanserin binding (a specific radioligand) of the median part of the premammillary hypothalamus tended to be higher in the high group (29.1 +/- 4.0 vs 24.6 +/- 4.2 fmol/mg tissu-equivalent; P < 0.10). In ECR ewes, density of 5HT2A receptor mRNA and 3H-Ketanserin binding were both significantly higher in the high LH group (20.8 +/- 1.6 vs 17.0 +/- 1.5 grains/neuron, P < 0.01, and 19.7 +/- 5.0 vs 7.4 +/- 3.4 fmol/mg tissu-equivalent; P < 0.05, respectively).


CONCLUSIONS
We conclude that these higher 5HT2A receptor gene expression and binding activity of 5HT2A receptor in the premammillary hypothalamus are associated with stimulation of LH pulsatility expressed before the development of refractoriness to short days and prior to the decline of reproductive neuroendocrine activity during expression of the endogenous circannual rhythm.
Chemineau
Philippe
P
Equipe de Neuroendocrinologie et Maîtrise des Fonctions Saisonnières, Unité de Physiologie de la Reproduction et des Comportements, UMR INRA-CNRS- Univ, F, Rabelais, 37380 Nouzilly, France. Philippe.Chemineau@tours.inra.fr
Daveau
Agnès
A
Pelletier
Jean
J
Malpaux
Benoît
B
Karsch
Fred J
FJ
Viguié
Catherine
C
D000818:Animals; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D007031:Hypothalamus / Q000166:cytology / Q000378:metabolism*; D017403:In Situ Hybridization; D007650:Ketanserin / Q000493:pharmacokinetics; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism; D010052:Ovariectomy; D010507:Periodicity; D017440:Photoperiod; D010870:Pineal Gland / Q000502:physiology / Q000601:surgery; D012333:RNA, Messenger; D044402:Receptor, Serotonin, 5-HT2A; D011985:Receptors, Serotonin / Q000235:genetics / Q000378:metabolism*; D012098:Reproduction / Q000502:physiology; D012621:Seasons; D012756:Sheep
D012333:RNA, Messenger; D044402:Receptor, Serotonin, 5-HT2A; D011985:Receptors, Serotonin; D004958:Estradiol; D007986:Luteinizing Hormone; D007650:Ketanserin