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Visual System

開催日 2014/9/11
時間 16:00 - 17:00
会場 Poster / Exhibition(Event Hall B)

Two-photon imaging of lateral interaction in the superficial layer of the superior colliculus

  • P1-172
  • 笠井 昌俊 / Masatoshi Kasai:1 伊佐 正 / Tadashi Isa:1,2 
  • 1:生理研発達生理認知行動発達 / Dept Develop Physiol, National Institute for Physiological Sciences, Aichi, Japan 2:総研大院生命科学生理 / Dept Life Sci, The Grad Univ for Advanced Studies, Kanagawa, Japan 

The superior colliculus (SC) is a brainstem center which plays a key role in sensory-motor translation and attention. The superficial layer of the SC (sSC) is directly innervated by the optic tract and visual space is represented in the retinotopic coordinates. In the early stage of visual processing, firing activity of neuronal population in response to the stimuli presented in their response field is often inhibited by stimuli presented outside of their receptive field. This effect is known as "lateral inhibition" or "surround suppression". To date, neural implementation of the "lateral inhibition" remains unclear, especially at the neuronal population level. In this study, we applied in vivo two-photon calcium imaging to reveal visually evoked neuronal population activities. We tested two-point stimulus, in which spatially separated two stimuli were presented simultaneously. When the two stimuli were close as respective excitatory response fields were overlapped, neuronal responses were increased. On the other hand, when the two stimuli were presented with larger separation, resulted neuronal responses were significantly decreased. These results indicated there was inhibitory interconnection from the outside of their excitatory response filed. More than half of neurons in the sSC are GABAergic inhibitory neurons and it has been debated whether horizontal inhibitory connection is responsible for such lateral inhibition. To understand the relationship between the inhibitory interconnection and underlying neural circuits, we used GAD67-GFP knock-in mice, in which GABAergic neurons are specifically labelled with GFP and examined differences between stimulus size tuning properties, another form of lateral inhibition, of the excitatory and inhibitory neurons. We found both non-GABAergic and GABAergic neurons showed similar center-suppression profiles when a large stimulus was presented. These results suggested that long-range GABAergic neurons mediate the lateral inhibition in the sSC.

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