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Neuroscience. 2014 Oct 10;278:194-210. doi: 10.1016/j.neuroscience.2014.07.069. Epub 2014 Aug 15.

Frequency-dependent signal processing in apical dendrites of hippocampal CA1 pyramidal cells.

Author information

  • 1Department of Developmental Physiology, Division of Behavioral Development, National Institute for Physiological Sciences, Okazaki, Aichi, Japan. Electronic address: watanabe@nips.ac.jp.
  • 2Faculty of Health Science, Tohoku Fukushi University, Sendai, Japan.
  • 3Brain Science Institute, Tamagawa University, Tokyo, Japan.
  • 4Department of Engineering, Tamagawa University, Tokyo, Japan.

Abstract

Depending on an animal's behavioral state, hippocampal CA1 pyramidal cells receive distinct patterns of excitatory and inhibitory synaptic inputs. The time-dependent changes in the frequencies of these inputs and the nonuniform distribution of voltage-gated channels lead to dynamic fluctuations in membrane conductance. In this study, using a whole-cell patch-clamp method, we attempted to record and analyze the frequency dependencies of membrane responsiveness in Wistar rat hippocampal CA1 pyramidal cells following noise current injection directly into dendrites and somata under pharmacological blockade of all synaptic inputs. To estimate the frequency-dependent properties of membrane potential, membrane impedance was determined from the voltage response divided by the input current in the frequency domain. The cell membrane of most neurons showed low-pass filtering properties in all regions. In particular, the properties were strongly expressed in the somata or proximal dendrites. Moreover, the data revealed nonuniform distribution of dendritic impedance, which was high in the intermediate segment of the apical dendritic shaft (∼220-260μm from the soma). The low-pass filtering properties in the apical dendrites were more enhanced by membrane depolarization than those in the somata. Coherence spectral analysis revealed high coherence between the input signal and the output voltage response in the theta-gamma frequency range, and large lags emerged in the distal dendrites in the gamma frequency range. Our results suggest that apical dendrites of hippocampal CA1 pyramidal cells integrate synaptic inputs according to the frequency components of the input signal along the dendritic segments receiving the inputs.

KEYWORDS:

apical dendrite; frequency-dependent property; hippocampal CA1 pyramidal cell; membrane impedance; noise current injection

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