title: Fimbrial control of bidirectional synaptic plasticity of medial perforant path-dentate transmission.
abstract: Lesions of the fimbria-fornix (FF) tract cause profound impairments of cognitive ability in animals. Our previous study showed that spatial performance correlates with long-term potentiation (LTP) of the dentate gyrus (DG), but not of the CA1 region, in rats with bilateral FF lesions, suggesting that FF lesions selectively inhibited LTP in the DG. The cortical input to the DG is anatomically and physiologically divided into two types of afferents, i.e., the medial perforant path (MPP) and the lateral perforant path (LPP), which show distinct synaptic properties. To elucidate the difference in the FF modulation of these two inputs, field responses were recorded from MPP- or LPP-DG synapses in anesthetized rats. MPP-DG synapses of rats with FF lesions displayed neither LTP in response to theta-burst stimulation nor long-term depression (LTD) in response to low-frequency burst stimulation. In contrast to the MPP, LPP-DG synapses showed normal LTP in rats with FF lesions. The low-frequency burst stimulation could not induce LTD at LPP-DG synapses in either intact or FF-lesioned rats. These results suggest that the FF pathway selectively supports the mechanisms of bidirectional synaptic plasticity at MPP-DG synapses. This study provides new insights into external control of information processing in the hippocampus.
authors.affiliation: Laboratory of Chemical Pharmacology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan.
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Nakao
authors.forename: Yuji
authors.initials: Y
authors.lastname: Ikegaya
authors.forename: Maki K
authors.initials: MK
authors.lastname: Yamada
authors.forename: Nobuyoshi
authors.initials: N
authors.lastname: Nishiyama
authors.forename: Norio
authors.initials: N
authors.lastname: Matsuki
mesh_terms: D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D018891:Dentate Gyrus / Q000502:physiology*; D004558:Electric Stimulation / Q000379:methods; D004567:Electrodes, Implanted; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D020712:Fornix, Brain / Q000502:physiology*; D017774:Long-Term Potentiation / Q000502:physiology; D036881:Long-Term Synaptic Depression / Q000502:physiology; D008297:Male; D009473:Neuronal Plasticity / Q000502:physiology*; D019580:Perforant Pathway / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D009435:Synaptic Transmission / Q000502:physiology*; D013826:Theta Rhythm