title: Contextual learning induces an increase in the number of hippocampal CA1 neurons expressing high levels of BDNF.
abstract: We examined behaviorally induced expression of brain-derived neurotrophic factor (BDNF) in area CA1 of the hippocampus. Sprague-Dawley rats were trained in a contextual fear conditioning (CFC) task, sacrificed 4h later, and their brains were processed for immunohistochemistry. We found distinctively high levels of BDNF immunoreactivity in a small number ( approximately 1%) of CA1 neurons in untrained animals. The number of these exceptional neurons, which are identified as BDNF(++) in this study, was increased by up to approximately 3% after CFC. This increase was blocked in the presence of a memory-impairing dose of a NMDA receptor antagonist (MK801 0.3 mg/kg, i.p.) given 30 min prior to training. The BDNF signal intensity in BDNF(++) neurons correlated with that of surrounding glutamic acid decarboxylase (GAD) 65. This correlation between GAD65 and BDNF signal intensities suggests that BDNF upregulation was associated with increased signaling via inhibitory GABAergic synapses that would lessen further intervening neuronal activity. Our observation that neurons which upregulate BDNF expression following a learning experience are rich in GAD65-enriched afferent synapses suggests that these neurons may have distinct roles in memory consolidation.
authors.affiliation: Laboratory of Chemical Pharmacology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Jenru
authors.initials: J
authors.lastname: Chen
authors.forename: Takuma
authors.initials: T
authors.lastname: Kitanishi
authors.forename: Takamitsu
authors.initials: T
authors.lastname: Ikeda
authors.forename: Norio
authors.initials: N
authors.lastname: Matsuki
authors.forename: Maki K
authors.initials: MK
authors.lastname: Yamada
mesh_terms: D000818:Animals; D001245:Association Learning / Q000502:physiology*; D019208:Brain-Derived Neurotrophic Factor / Q000378:metabolism*; D003214:Conditioning, Classical / Q000502:physiology*; D005239:Fear / Q000502:physiology; D005968:Glutamate Decarboxylase / Q000378:metabolism*; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism*; D008297:Male; D009475:Neurons, Afferent / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D009435:Synaptic Transmission; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D019208:Brain-Derived Neurotrophic Factor; D005680:gamma-Aminobutyric Acid; D005968:Glutamate Decarboxylase; C401141:glutamate decarboxylase 2