title: Anatomic organization of the ascending branch of the milk-ejection reflex in sheep: primary afferent neurons.
abstract: The present study examines the anatomic characteristics of the primary afferent neurons that innervate the nipples and pseudonipples of ewes and the nipples of lambs. For this purpose, horseradish-peroxidase coupled to wheat germ agglutinin (WGA-HRP) was injected intradermally into the whole extent, the tip, or the base of the nipples and pseudonipples, as well as into a region of the posterior surface of the udder. After survival periods of 72-96 hours, dorsal root ganglia (DRG), segments of the spinal cord and medulla oblongata were sectioned and reacted histochemically with tetramethylbenzidine to reveal the transganglionically transported tracer. Injections of WGA-HRP in the nipples and pseudonipples of the ewe resulted in labeled cells in the second to fifth ipsilateral lumbar spinal ganglia (L(2)-L(5)) and third and fourth (L(3) and L(4)) lumbar spinal ganglia, respectively. Labeled cells after WGA-HRP injections in the nipples of the lamb were found in the ipsilateral L(3)-L(5) spinal ganglia. Central projections of the DRG-labeled cells were found in the medial part of laminae I-III of the ipsilateral L(3) and L(4) spinal segments (ewe and lamb) and in the ipsilateral dorsal column nuclei (ewe). Central projections of the DRG-labeled cells after injections in the pseudonipples of the ewe were located in the medial part of laminae I-III of the ipsilateral L(3) spinal segment. The results of this study demonstrate that, whereas the innervation of the nipples of the ewe originates from four successive lumbar spinal ganglia (L(2)-L(5)), the innervation of the nipples of the lamb and the pseudonipples of the ewe originates from three (L(3)-L(5)) and two (L(3) and L(4)) successive ganglia, respectively.
authors.affiliation: Department of Anatomy and Histology, School of Veterinary Medicine, University of Thessaloniki, 54006 Thessaloniki, Greece. astsing@ucla.edu
authors.forename: Anastasia S
authors.initials: AS
authors.lastname: Tsingotjidou
authors.forename: Georgios C
authors.initials: GC
authors.lastname: Papadopoulos
mesh_terms: D000344:Afferent Pathways / Q000033:anatomy & histology* / Q000166:cytology; D000367:Age Factors; D000818:Animals; D002452:Cell Count; D005260:Female; D005727:Ganglia, Spinal / Q000166:cytology; D008321:Mammary Glands, Animal / Q000166:cytology / Q000294:innervation / Q000502:physiology; D008526:Medulla Oblongata / Q000166:cytology; D008893:Milk Ejection / Q000502:physiology; D009475:Neurons, Afferent / Q000166:cytology*; D012018:Reflex / Q000502:physiology; D012756:Sheep; D013116:Spinal Cord / Q000166:cytology; D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate / Q000493:pharmacokinetics
chemical_list: D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate