title: Dendritic branching of olfactory bulb mitral and tufted cells: regulation by TrkB.
abstract: BACKGROUND
  Projection neurons of mammalian olfactory bulb (OB), mitral and tufted cells, have dendrites whose morphologies are specifically differentiated for efficient odor information processing. The apical dendrite extends radially and arborizes in single glomerulus where it receives primary input from olfactory sensory neurons that express the same odor receptor. The lateral dendrites extend horizontally in the external plexiform layer and make reciprocal dendrodendritic synapses with granule cells, which moderate mitral/tufted cell activity. The molecular mechanisms regulating dendritic development of mitral/tufted cells is one of the unsolved important problems in the olfactory system. Here, we focused on TrkB receptors to test the hypothesis that neurotrophin-mediate mechanisms contributed to dendritic differentiation of OB mitral/tufted cells.
  
  
  RESULTS
  With immunohistochemical analysis, we found that the TrkB neurotrophin receptor is expressed by both apical and lateral dendrites of mitral/tufted cells and that expression is evident during the early postnatal days when these dendrites exhibit their most robust growth and differentiation. To examine the effect of TrkB activation on mitral/tufted cell dendritic development, we cultured OB neurons. When BDNF or NT4 were introduced into the cultures, there was a significant increase in the number of primary neurites and branching points among the mitral/tufted cells. Moreover, BDNF facilitated filopodial extension along the neurites of mitral/tufted cells.
  
  
  CONCLUSIONS
  In this report, we show for the first time that TrkB activation stimulates the dendritic branching of mitral/tufted cells in developing OB. This suggests that arborization of the apical dendrite in a glomerulus is under the tight regulation of TrkB activation.
authors.affiliation: Department of Neurosurgery, Yale University School of Medicine, New Haven, Connecticut, USA.
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Imamura
authors.forename: Charles A
authors.initials: CA
authors.lastname: Greer
mesh_terms: D000818:Animals; D003712:Dendrites; D007150:Immunohistochemistry; D051379:Mice; D009830:Olfactory Bulb / Q000166:cytology / Q000254:growth & development*; D020813:Receptor, trkB / Q000502:physiology*
chemical_list: D020813:Receptor, trkB
references.citation: J Comp Neurol. 1968 Nov;134(3):305-22
references.pmid: 5721257
references.citation: BMC Neurosci. 2005 Jun 21;6:42
references.pmid: 15969745
references.citation: J Comp Neurol. 2001 Nov 19;440(3):219-35
references.pmid: 11745619
references.citation: Neuron. 2000 Apr;26(1):233-45
references.pmid: 10798407
references.citation: Nature. 2007 Nov 22;450(7169):503-8
references.pmid: 17989651
references.citation: J Cell Sci. 1970 Nov;7(3):631-51
references.pmid: 5492279
references.citation: Annu Rev Biochem. 2003;72:609-42
references.pmid: 12676795
references.citation: Chem Senses. 2008 Jul;33(6):531-9
references.pmid: 18495654
references.citation: Neuron. 2000 Apr;26(1):69-80
references.pmid: 10798393
references.citation: J Neurosci. 2005 Oct 26;25(43):9989-99
references.pmid: 16251447
references.citation: Nat Neurosci. 2003 Nov;6(11):1201-7
references.pmid: 14528309
references.citation: Annu Rev Neurosci. 2001;24:677-736
references.pmid: 11520916
references.citation: J Comp Neurol. 1976 Sep 1;169(1):15-40
references.pmid: 956463
references.citation: Neuron. 1996 Jul;17(1):91-102
references.pmid: 8755481
references.citation: Neurosci Lett. 2008 Dec 5;447(1):42-7
references.pmid: 18834927
references.citation: J Comp Neurol. 2006 Apr 20;495(6):754-68
references.pmid: 16506198
references.citation: Prog Neurobiol. 2003 Apr;69(5):341-74
references.pmid: 12787574
references.citation: Nat Neurosci. 2002 Mar;5(3):225-33
references.pmid: 11836532
references.citation: Exp Brain Res. 1983;50(2-3):329-40
references.pmid: 6641865
references.citation: J Comp Neurol. 2003 Dec 1;467(1):60-79
references.pmid: 14574680
references.citation: J Comp Neurol. 1983 Sep 20;219(3):339-55
references.pmid: 6619342
references.citation: J Comp Neurol. 1994 Jun 15;344(3):336-48
references.pmid: 8063958
references.citation: Brain Res. 2008 Feb 27;1196:13-21
references.pmid: 18234155
references.citation: Eur J Neurosci. 2007 Mar;25(5):1373-83
references.pmid: 17425564
references.citation: Cell. 1990 May 18;61(4):647-56
references.pmid: 2160854
references.citation: Dev Neurobiol. 2007 Jul;67(8):1079-93
references.pmid: 17565001
references.citation: Neuron. 1995 Oct;15(4):791-803
references.pmid: 7576629
references.citation: J Neurosci. 1997 Sep 15;17(18):7007-16
references.pmid: 9278536
references.citation: Learn Mem. 2004 Jul-Aug;11(4):406-11
references.pmid: 15286182
references.citation: J Neurosci. 2007 Jul 4;27(27):7256-67
references.pmid: 17611278
references.citation: J Comp Neurol. 1996 Apr 22;368(1):1-16
references.pmid: 8725290
references.citation: J Comp Neurol. 1984 Jul 1;226(3):346-56
references.pmid: 6747027
references.citation: J Comp Neurol. 1968 Nov;134(3):287-304
references.pmid: 5721256
references.citation: Brain Res Dev Brain Res. 2003 Feb 16;140(2):277-86
references.pmid: 12586433
references.citation: J Neurobiol. 2005 Feb 5;62(2):278-88
references.pmid: 15514998
references.citation: Dev Biol. 2001 Jun 1;234(1):80-92
references.pmid: 11356021
references.citation: J Neurosci Res. 1993 Aug 1;35(5):468-79
references.pmid: 8377221
references.citation: J Comp Neurol. 2006 Jun 1;496(4):529-43
references.pmid: 16572431
references.citation: Mol Cell Biol. 1991 Jan;11(1):143-53
references.pmid: 1846020
references.citation: J Physiol. 2007 Jul 15;582(Pt 2):629-46
references.pmid: 17463037
references.citation: Dev Dyn. 2005 Feb;232(2):325-35
references.pmid: 15614760
references.citation: J Comp Neurol. 1999 Oct 18;413(2):289-304
references.pmid: 10524340
references.citation: PLoS One. 2008;3(11):e3816
references.pmid: 19043569
references.citation: Neuron. 2000 Oct;28(1):41-51
references.pmid: 11086982
references.citation: Curr Biol. 2007 Jun 5;17(11):911-21
references.pmid: 17493809
references.citation: Nat Neurosci. 2004 Mar;7(3):254-60
references.pmid: 14758365
references.citation: J Comp Neurol. 2000 Mar 20;418(4):402-10
references.pmid: 10713569
references.citation: J Comp Neurol. 1996 Oct 07;374(1):21-40
references.pmid: 8891944