title: Noradrenaline concentrations in the hypothalamus of anoestrus ewes following the ram-induced luteinizing hormone release.
abstract: Sheep are seasonal breeders, but exposure of anoestrus ewes to rams results in a rapid increase in luteinizing hormone (LH) secretion, eventually leading to surge in LH. Although LH secretion is known to be under the control of many neurotransmitters, noradrenaline (NA) is of particular importance for the LH surge in induced ovulators, although little is known about its role in LH secretion induced by males in spontaneous ovulators. To address this question, anoestrus ewes fitted with guide-tubes in the medial preoptic area (MPOA) or the ventromedial hypothalamus were subjected to microdialysis and blood sampling every 15 min for an hour before and 2 h after exposure to rams, and the concentrations of LH, monoamine and amino acid transmitters were measured. In ewes implanted in the posterior MPOA that responded to the ram by an increase in LH pulses, NA concentrations changed after exposure to the ram (P<0.018) and were higher at 15 (P<0.054) and 45 min (P<0.03) after male introduction than before. By contrast, no change in NA could be detected in ewes implanted in the same region, but not responding to the ram, or in those showing increased LH pulsatility, but implanted in the anterior MPOA or in the ventromedial hypothalamus. No changes were observed in other neurotransmitters or when the ewes were exposed to male odour alone. These results suggest that NA release in the posterior MPOA is selectively involved in the triggering of LH secretion by rams in anoestrus ewes.
authors.affiliation: aUMR 7247 Physiology of Reproduction and Behaviour, CNRS, INRA, Tours University, French Institute for Horses, Department Animal Physiology and Livestock Systems, Nouzilly, France bKey Laboratory for Neuroinformation, School of Life Science and Technology, Center for Information in Medicine, University of Electronic Science and Technology of China, Chengdu, China.
authors.forename: Claude
authors.initials: C
authors.lastname: Fabre-Nys
authors.forename: Keith M
authors.initials: KM
authors.lastname: Kendrick
mesh_terms: D000780:Anestrus / Q000378:metabolism*; D000818:Animals; D002408:Catheters, Indwelling; D004298:Dopamine / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D007986:Luteinizing Hormone / Q000378:metabolism*; D008297:Male; D017551:Microdialysis; D009638:Norepinephrine / Q000378:metabolism*; D009812:Odorants; D055696:Olfactory Perception; D010812:Physical Stimulation; D011301:Preoptic Area / Q000378:metabolism*; D012756:Sheep / Q000378:metabolism*; D012919:Social Behavior; D014697:Ventromedial Hypothalamic Nucleus / Q000378:metabolism*
chemical_list: D007986:Luteinizing Hormone; D004298:Dopamine; D009638:Norepinephrine