title: Regional- and age-dependent reduction in trkB receptor expression in the hippocampus is associated with altered spine morphologies.
abstract: BACKGROUND
  Changes in densities and in the morphology of dendritic spines in the hippocampus are linked to hippocampal long-term potentiation (LTP), spatial learning, and depression. Decreased brain-derived neurotrophic factor (BDNF) levels seem to contribute to depression. Through its receptor trkB, BDNF is also involved in hippocampal LTP and hippocampus-dependent learning. Conditionally gene-targeted mice in which the ablation of trkB is restricted to the forebrain and occurs only during postnatal development display impaired learning and LTP.
  
  
  METHODS
  To examine whether there is a link among impaired hippocampal synaptic plasticity, altered spines, and trkB receptors, we performed a quantitative analysis of spine densities and spine length in the hippocampal area CA1 and the dentate gyrus in conditional mutant mice (trkB(lox/lox)CaMKII-CRE mice). TrkB protein and mRNA levels were assayed using Western blot and in situ hybridization analysis.
  
  
  RESULTS
  Fifteen-week-old mutant mice exhibit specific reductions in spine densities and a significant increase in spine length of apical and basal dendrites in area CA1. These alterations correlate with a time- and region-specific reduction in full-length trkB mRNA in the hippocampus.
  
  
  CONCLUSIONS
  TrkB functions in structural remodeling of hippocampal dendritic spines, which in turn may affect synaptic transmission and plasticity.
authors.affiliation: Department of Neuroanatomy, Interdisciplinary Center for Neurosciences, University of Heidelberg, Heidelberg, Germany. O.von_Bohlen@web.de
authors.forename: Oliver
authors.initials: O
authors.lastname: von Bohlen und Halbach
authors.forename: Sonja
authors.initials: S
authors.lastname: Krause
authors.forename: Diego
authors.initials: D
authors.lastname: Medina
authors.forename: Carla
authors.initials: C
authors.lastname: Sciarretta
authors.forename: Liliana
authors.initials: L
authors.lastname: Minichiello
authors.forename: Klaus
authors.initials: K
authors.lastname: Unsicker
mesh_terms: D000367:Age Factors; D000818:Animals; D015153:Blotting, Western / Q000379:methods; D049229:Dendritic Spines / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D006624:Hippocampus / Q000166:cytology* / Q000254:growth & development / Q000378:metabolism; D047468:Immunoprecipitation / Q000379:methods; D017403:In Situ Hybridization / Q000379:methods; D051379:Mice; D018345:Mice, Knockout; D009474:Neurons / Q000378:metabolism / Q000648:ultrastructure*; D020813:Receptor, trkB / Q000172:deficiency / Q000378:metabolism*; D016622:Silver Staining / Q000379:methods
chemical_list: D020813:Receptor, trkB