title: Structural basis for cholinergic regulation of neural circuits in the mouse olfactory bulb.
abstract: Odor information is regulated by olfactory inputs, bulbar interneurons, and centrifugal inputs in the olfactory bulb (OB). Cholinergic neurons projecting from the nucleus of the horizontal limb of the diagonal band of Broca and the magnocellular preoptic nucleus are one of the primary centrifugal inputs to the OB. In this study, we focused on cholinergic regulation of the OB and analyzed neural morphology with a particular emphasis on the projection pathways of cholinergic neurons. Single-cell imaging of a specific neuron within dense fibers is critical to evaluate the structure and function of the neural circuits. We labeled cholinergic neurons by infection with virus vector and then reconstructed them three-dimensionally. We also examined the ultramicrostructure of synapses by electron microscopy tomography. To further clarify the function of cholinergic neurons, we performed confocal laser scanning microscopy to investigate whether other neurotransmitters are present within cholinergic axons in the OB. Our results showed the first visualization of complete cholinergic neurons, including axons projecting to the OB, and also revealed frequent axonal branching within the OB where it innervated multiple glomeruli in different areas. Furthermore, electron tomography demonstrated that cholinergic axons formed asymmetrical synapses with a morphological variety of thicknesses of the postsynaptic density. Although we have not yet detected the presence of other neurotransmitters, the range of synaptic morphology suggests multiple modes of transmission. The present study elucidates the ways that cholinergic neurons could contribute to the elaborate mechanisms involved in olfactory processing in the OB. J. Comp. Neurol. 525:574-591, 2017. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Department of Anatomy, Kawasaki Medical School, Okayama, 701-0192, Japan.|Department of Otolaryngology, Kawasaki Medical School, Okayama, 701-0192, Japan.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Hamamoto
authors.affiliation: Department of Anatomy, Kawasaki Medical School, Okayama, 701-0192, Japan.
authors.forename: Emi
authors.initials: E
authors.lastname: Kiyokage
authors.affiliation: Department of Morphological Brain Science, Graduate School of Medicine, Kyoto University, Kyoto, 606-8501, Japan.|Division of Cerebral Circuitry, National Institute for Physiological Sciences, Aichi, 444-8787, Japan.
authors.forename: Jaerin
authors.initials: J
authors.lastname: Sohn
authors.affiliation: Department of Morphological Brain Science, Graduate School of Medicine, Kyoto University, Kyoto, 606-8501, Japan.
authors.forename: Hiroyuki
authors.identifier: 0000-0002-0152-7854
authors.initials: H
authors.lastname: Hioki
authors.affiliation: Department of Otolaryngology, Kawasaki Medical School, Okayama, 701-0192, Japan.
authors.forename: Tamotsu
authors.initials: T
authors.lastname: Harada
authors.affiliation: Department of Anatomy, Kawasaki Medical School, Okayama, 701-0192, Japan.|Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, Osaka, 567-0047, Japan.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Toida
mesh_terms: D000818:Animals; D002795:Choline O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D059329:Cholinergic Neurons / Q000166:cytology* / Q000378:metabolism; D000229:Dependovirus; D055032:Electron Microscope Tomography; D005822:Genetic Vectors; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D021621:Imaging, Three-Dimensional; D007150:Immunohistochemistry; D008297:Male; D008809:Mice, Inbred C3H; D008822:Mice, Transgenic; D056347:Neuroanatomical Tract-Tracing Techniques; D009830:Olfactory Bulb / Q000166:cytology* / Q000378:metabolism; D009833:Olfactory Pathways / Q000166:cytology / Q000378:metabolism; D012903:Smell / Q000502:physiology
chemical_list: D049452:Green Fluorescent Proteins; D002795:Choline O-Acetyltransferase
keywords: AB_11180610; AB_2079760; AB_2187708; AB_2301794; AB_2315522; AB_572263; AB_887872; AB_94952; IMSR_JAX:006410; RRIDs: SCR_001775; acetylcholine; centrifugal projection; cholinergic neuron; nif-0000-30467; olfactory bulb; synapse