title: Nitric oxide-containing pyramidal neurons of the subiculum innervate the CA1 area.
abstract: Neurons and axon terminals containing neuron-specific nitric oxide synthase (nNOS) were examined in the rat subiculum and CA1 area of Ammon's horn. In the subiculum, a large subpopulation of the pyramidal neurons and non-pyramidal cells are immunoreactive for nNOS, whereas in the neighbouring CA1 area of Ammon's horn only non-pyramidal neurons are labelled with the antibody against nNOS. In the pyramidal layer of the subiculum, nNOS-positive axon terminals form both asymmetric and symmetric synapses. In the adjacent CA1 area the nNOS-positive terminals that form symmetric synapses are found in all layers, whereas those terminals that form asymmetric synapses are only in strata radiatum and oriens, but not in stratum lacunosum-moleculare. In both the subiculum and CA1 area, labelled terminals make symmetric synapses only on dendritic shafts, whereas asymmetric synapses are exclusively on dendritic spines. Previous observations demonstrated that all nNOS-positive non-pyramidal cells are GABAergic local circuit neurons, which form exclusively symmetric synapses. We suggest that nNOS-immunoreactive pyramidal cells of the subiculum may innervate neighbouring subicular pyramidal cells and, to a smaller extent, pyramidal cells of the adjacent CA1 area, forming a backward projection between the subicular and hippocampal principal neurons.
authors.affiliation: Central Electron Microscopic Laboratory, Faculty of Medicine, University of Pécs, 7643 Pécs, Szigeti u. 12, Hungary. seress@main.pote.hu
authors.forename: László
authors.initials: L
authors.lastname: Seress
authors.forename: Hajnalka
authors.initials: H
authors.lastname: Abrahám
authors.forename: Hong
authors.initials: H
authors.lastname: Lin
authors.forename: Susan
authors.initials: S
authors.lastname: Totterdell
mesh_terms: D000818:Animals; D003712:Dendrites / Q000201:enzymology / Q000648:ultrastructure; D006624:Hippocampus / Q000166:cytology / Q000201:enzymology / Q000502:physiology*; D008297:Male; D008854:Microscopy, Electron; D009569:Nitric Oxide / Q000378:metabolism / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052248:Nitric Oxide Synthase Type I; D017966:Pyramidal Cells / Q000201:enzymology / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013569:Synapses / Q000201:enzymology / Q000648:ultrastructure; D005680:gamma-Aminobutyric Acid / Q000502:physiology
chemical_list: D009569:Nitric Oxide; D005680:gamma-Aminobutyric Acid; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; C496322:Nos1 protein, rat