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Sleep and Biological Rhythms

開催日 2014/9/11
時間 11:00 - 12:00
会場 Poster / Exhibition(Event Hall B)

The involvement of recurrent inhibitory network in the Diurnal variation of neuronal rhythm and synaptic plasticity in rat hippocampal slices

  • P1-211
  • 中司 弘樹 / Hiroki Nakatsuka:1 夏目 季代久 / Kiyohisa Natsume:1 
  • 1:九工大院生命体工学系脳情報 / Kyushu Institute of Technology 

Learning process of rodents has diurnal variation. The neuronal activities in hippocampus also show the variation. Cholinergic receptor agonist carbachol induces β oscillation intermittently in the hippocampal slices. In vitro condition, whether the oscillation has diurnal variation was not revealed. While, one of the synaptic potentiation, long-term potentiation (LTP) has diurnal variation in the light and dark cycle (LD cycle) condition in vivo, and the variation is kept in hippocampal slices. However, in the slices of nocturnal rodents, CA1 of a rat hippocampus has the exception. The mechanism of the modulation of LTP with LD cycle also remains unknown. In the present paper, we studied diurnal variation of carbachol-induced β oscillation and LTP in the LD cycle. First, carbachol-induced β oscillations were compared in both phases. The oscillations were recorded at CA3, had frequency at 12-18 Hz. The frequency of β oscillations were not significantly different in both phases, but the inter-burst interval (IBI) in dark-phase slices was significantly shorter than that in light-phase slices. A GABAA receptor antagonist gabazine significantly shortened IBI of the oscillation in the light-phase slices, while it did not change it in the dark-phase slices. Next, population spike (PS)-LTP were recorded at CA1. The stimulation induced more facilitated LTP at dark phase than at light phase. The magnitude of PS-LTP in dark-phase slices was significantly larger than that in light-phase ones. Paired-pulse stimulation and local gabazine-application to stratum pyramidale experiments found that disinhibition at the soma layer will occur at dark phase. The local gabazine-application experiment also found that the disinhibition induced facilitated LTP. Thus the obtained results suggest that the disinhibition of GABAA recurrent inhibitory network can be induced, and LTP can be facilitated at dark phase. Neuronal rhythms and synaptic plasticity show diurnal variation caused by the suppression of recurrent inhibitory network in hippocampus.

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