title: Activation of the TrkB neurotrophin receptor is induced by antidepressant drugs and is required for antidepressant-induced behavioral effects.
abstract: Recent studies have indicated that exogenously administered neurotrophins produce antidepressant-like behavioral effects. We have here investigated the role of endogenous brain-derived neurotrophic factor (BDNF) and its receptor trkB in the mechanism of action of antidepressant drugs. We found that trkB.T1-overexpressing transgenic mice, which show reduced trkB activation in brain, as well as heterozygous BDNF null (BDNF(+/)-) mice, were resistant to the effects of antidepressants in the forced swim test, indicating that normal trkB signaling is required for the behavioral effects typically produced by antidepressants. In contrast, neurotrophin-3(+/)- mice showed a normal behavioral response to antidepressants. Furthermore, acute as well as chronic antidepressant treatment induced autophosphorylation and activation of trkB in cerebral cortex, particularly in the prefrontal and anterior cingulate cortex and hippocampus. Tyrosines in the trkB autophosphorylation site were phosphorylated in response to antidepressants, but phosphorylation of the shc binding site was not observed. Nevertheless, phosphorylation of cAMP response element-binding protein was increased by antidepressants in the prefrontal cortex concomitantly with trkB phosphorylation and this response was reduced in trkB.T1-overexpressing mice. Our data suggest that antidepressants acutely increase trkB signaling in a BDNF-dependent manner in cerebral cortex and that this signaling is required for the behavioral effects typical of antidepressant drugs. Neurotrophin signaling increased by antidepressants may induce formation and stabilization of synaptic connectivity, which gradually leads to the clinical antidepressive effects and mood recovery.
authors.affiliation: Department of Neurobiology, A. I. Virtanen Institute, University of Kuopio, 70211 Kuopio, Finland.
authors.forename: Tommi
authors.initials: T
authors.lastname: Saarelainen
authors.forename: Panu
authors.initials: P
authors.lastname: Hendolin
authors.forename: Guilherme
authors.initials: G
authors.lastname: Lucas
authors.forename: Eija
authors.initials: E
authors.lastname: Koponen
authors.forename: Mikko
authors.initials: M
authors.lastname: Sairanen
authors.forename: Ewen
authors.initials: E
authors.lastname: MacDonald
authors.forename: Karin
authors.initials: K
authors.lastname: Agerman
authors.forename: Annakaisa
authors.initials: A
authors.lastname: Haapasalo
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Nawa
authors.forename: Raquel
authors.initials: R
authors.lastname: Aloyz
authors.forename: Patrik
authors.initials: P
authors.lastname: Ernfors
authors.forename: Eero
authors.initials: E
authors.lastname: Castrén
mesh_terms: D000818:Animals; D000928:Antidepressive Agents / Q000494:pharmacology*; D001522:Behavior, Animal / Q000187:drug effects*; D019208:Brain-Derived Neurotrophic Factor / Q000235:genetics / Q000502:physiology; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D005260:Female; D005473:Fluoxetine / Q000494:pharmacology*; D007099:Imipramine / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D020933:Neurotrophin 3 / Q000235:genetics; D010766:Phosphorylation; D017397:Prefrontal Cortex / Q000378:metabolism; D020813:Receptor, trkB / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D000928:Antidepressive Agents; D019208:Brain-Derived Neurotrophic Factor; D017362:Cyclic AMP Response Element-Binding Protein; D020933:Neurotrophin 3; D005473:Fluoxetine; D020813:Receptor, trkB; D007099:Imipramine