title: A subset of estrogen receptor-containing neurons project to the median eminence in the ewe.
abstract: The neural pathways responsible for conveying the steroid feedback signals that ultimately affect reproductive neuroendocrine function remain largely undefined. One possibility involves a direct projection from estrogen receptor (ER)-containing neurons to the median eminence (ME), a site of neuroendocrine peptide release. To examine this possibility, 8 ewes received stereotaxic injections of the retrograde neuronal tract-tracing compound cholera toxin-beta subunit (CT beta) into the ME. Neurons sending projections to the ME and containing ER were identified using a dual-label immunoperoxidase method. Double-labeled cells were found in distinct regions: (1) the ER-rich arcuate nucleus (ARC) that contained the greatest number of double-labeled cells, and (2) the organum vasculosum of the lamina terminalis (OVLT) which contained a very consistent, but low, number of double-labeled cells. While a fairly large number of retrogradely-labeled ARC neurons containing ER were identified, the majority of ER-containing ARC neurons were unlabeled and thus send projections elsewhere. Other regions containing high concentrations of ER-positive cells such as the medial preoptic area (MPOA), anterior hypothalamic area, and ventrolateral portion of the ventromedial hypothalamic nucleus, were devoid of double-labeled cells. Similarly, regions rich in neuroendocrine neurons such as the periventricular hypothalamus and paraventricular and supraoptic hypothalamic nuclei contained no double-labeled cells. These results suggest that modulation of neuroendocrine secretory activity may occur directly at the level of the ME by ER-containing neurons located within restricted regions of the hypothalamus and forebrain. However, the relatively low proportion of ER-containing neurons projecting to the ME suggests that the influence of estradiol upon neuroendocrine function also may include target sites other than the ME.
authors.affiliation: Department of Cell Biology, Neurobiology, and Anatomy, University of Cincinnati College of Medicine, Ohio 45267, USA.
authors.forename: H T
authors.initials: HT
authors.lastname: Jansen
authors.forename: S M
authors.initials: SM
authors.lastname: Hileman
authors.forename: L S
authors.initials: LS
authors.lastname: Lubbers
authors.forename: G L
authors.initials: GL
authors.lastname: Jackson
authors.forename: M N
authors.initials: MN
authors.lastname: Lehman
mesh_terms: D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000166:cytology*; D005260:Female; D007150:Immunohistochemistry; D008473:Median Eminence / Q000166:cytology*; D009434:Neural Pathways; D009474:Neurons / Q000737:chemistry*; D011960:Receptors, Estrogen / Q000032:analysis*; D012756:Sheep; D014697:Ventromedial Hypothalamic Nucleus / Q000166:cytology*
chemical_list: D011960:Receptors, Estrogen