title: Hypophysiotropic gonadotropin-releasing hormone projections are exposed to dense plexuses of kisspeptin, neurokinin B and substance p immunoreactive fibers in the human: a study on tissues from postmenopausal women.
abstract: Neuronal populations that synthesize kisspeptin (KP), neurokinin B (NKB) and substance P (SP) in the hypothalamic infundibular nucleus of humans are partly overlapping. These cells are important upstream regulators of gonadotropin-releasing hormone (GnRH) neurosecretion. Homologous neurons in laboratory animals are thought to modulate episodic GnRH secretion primarily via influencing KP receptors on the hypophysiotropic fiber projections of GnRH neurons. To explore the structural basis of this putative axo-axonal communication in humans, we analyzed the anatomical relationship of KP-immunoreactive (IR), NKB-IR and SP-IR axon plexuses with hypophysiotropic GnRH fiber projections. Immunohistochemical studies were carried out on histological samples from postmenopausal women. The neuropeptide-IR axons innervated densely the portal capillary network in the postinfundibular eminence. Subsets of the fibers formed descending tracts in the infundibular stalk, some reaching the neurohypophysis. KP-IR, NKB-IR and SP-IR plexuses intermingled, and established occasional contacts, with hypophysiotropic GnRH fibers in the postinfundibular eminence and through their lengthy course while descending within the infundibular stalk. Triple-immunofluorescent studies also revealed considerable overlap between the KP, NKB and SP signals in individual fibers, providing evidence that these peptidergic projections arise from neurons of the mediobasal hypothalamus. These neuroanatomical observations indicate that the hypophysiotropic projections of human GnRH neurons in the postinfundibular eminence and the descending GnRH tract coursing through the infundibular stalk to the neurohypophysis are exposed to neurotransmitters/neuropeptides released by dense KP-IR, NKB-IR and SP-IR fiber plexuses. Localization and characterization of axonal neuropeptide receptors will be required to clarify the putative autocrine and paracrine interactions in these anatomical regions.
authors.affiliation: Department of Forensic Medicine, Faculty of Medicine of the University of Debrecen, Debrecen, Hungary.
authors.forename: Beáta Á
authors.initials: BÁ
authors.lastname: Borsay
authors.forename: Katalin
authors.initials: K
authors.lastname: Skrapits
authors.forename: László
authors.initials: L
authors.lastname: Herczeg
authors.forename: Philippe
authors.initials: P
authors.lastname: Ciofi
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Bloom
authors.forename: Mohammad A
authors.initials: MA
authors.lastname: Ghatei
authors.forename: Waljit S
authors.initials: WS
authors.lastname: Dhillo
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Liposits
authors.forename: Erik
authors.initials: E
authors.lastname: Hrabovszky
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001369:Axons / Q000378:metabolism; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D006801:Humans; D007031:Hypothalamus / Q000166:cytology / Q000378:metabolism*; D007150:Immunohistochemistry; D059648:Kisspeptins / Q000378:metabolism*; D008875:Middle Aged; D015287:Neurokinin B / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism*; D017698:Postmenopause / Q000378:metabolism; D013373:Substance P / Q000378:metabolism*
chemical_list: D059648:Kisspeptins; D013373:Substance P; D007987:Gonadotropin-Releasing Hormone; D015287:Neurokinin B