Immunocytochemical and physiological evidence of a synapse between dopamine- and luteinizing hormone releasing hormone-containing neurons in the ewe median eminence.
Immunocytochemical labeling revealed that the arcuate nucleus (ARN) of the ewe's hypothalamus contains numerous tyrosine hydroxylase (TH)-positive neurons, that appear to lack dopamine-beta-hydroxylase (DBH)-like immunoreactivity. Axons of these presumed dopaminergic neurons converge in the median eminence (ME) with Luteinizing Hormone Releasing Hormone (LHRH)-containing axons originating mostly from neurons situated in the medial preoptic area. Electron microscopic double labeling revealed synaptic contacts between TH-positive presynaptic profiles and LHRH-containing postsynaptic elements. Samples of ME, ARN, paraarcuate and lateral hypothalamus were dissected and incubated to assess LHRH release and tissue content. Only ME-LHRH release was significantly reduced in the presence of dopamine (DA). All other regions released equal amounts with and without DA. Thus, a presynaptic dopaminergic inhibition of LHRH-containing axons at the level of the ME might contribute to the regulation of LHRH release into the portal vessels.
Kuljis
R O
RO
Department of Neurology, Yale University School of Medicine, New Haven, CT 06510.
Advis
J P
JP
D000818:Animals; D001369:Axons / Q000502:physiology / Q000648:ultrastructure; D004298:Dopamine / Q000032:analysis / Q000494:pharmacology / Q000502:physiology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000032:analysis / Q000378:metabolism*; D007124:Immunoenzyme Techniques; D008473:Median Eminence / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure*; D008854:Microscopy, Electron; D009474:Neurons / Q000502:physiology / Q000648:ultrastructure*; D012756:Sheep; D013569:Synapses / Q000502:physiology*; D014446:Tyrosine 3-Monooxygenase / Q000032:analysis
D007987:Gonadotropin-Releasing Hormone; D014446:Tyrosine 3-Monooxygenase; D004298:Dopamine