昆虫の偏光コンパスの神経機構  [in Japanese] Neural basis of the polarization compass in insects  [in Japanese]

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Author(s)

    • 佐倉 緑 SAKURA Midori
    • 神戸大学大学院理学研究科生物学専攻 Department of Biology, Graduate School of Science, Kobe University

Abstract

多くの昆虫は天空の偏光パターンから方向を検出する。偏光のe-ベクトル方向の情報は,複眼の偏光受容に特化した領域[dorsal rim area(DRA)]で検出される。DRAで検出されたe-ベクトル情報は,その後,視葉の視髄(medulla)で3種類の情報に収斂されることから,人間の3色型色覚のように3種類の異なるニューロンの応答比率によって符号化される(即時型検出;instantaneous method)と考えられる。Medullaの3種類の情報から任意のe-ベクトル方向を符号化するニューラルネットワークを構築し,その動作を検証した結果,様々な自然条件の刺激に対して高い精度で体軸方向を検出できることが明らかとなった。また,コオロギ脳内神経細胞からの細胞内記録により,ネットワーク構築の際に想定したものと同じ応答特性を持つニューロン群が見つかった。これらのニューロンは特定のe-ベクトル方向に対して強い興奮性の応答を示し,脳内でコンパスの働きをすることが示唆される。さらに,ミツバチの吻伸展反射を利用して偏光刺激のe-ベクトル方向を弁別させる学習実験を行った結果,彼らが偏光刺激をスキャンすることなく90°異なるe-ベクトル方向を弁別することが明らかとなった。これらの一連の結果は,昆虫がinstantaneous methodに基づく偏光視システムを持つことを強く示唆している。

Many animals show sophisticated navigational behavior based on their spatial memory. Path integration is one of the common strategies for navigation, in which the travel distance and direction are separately monitored and then the locational relationship between the current position and the goal was calculated. It has been well known that many insects can deduce their heading direction using a polarization pattern of the sky and use it for path integration. Although there are intensive studies focusing on sensory mechanisms underlying insect polarization vision, relatively few efforts has been taken for understanding central brain mechanisms. Here, I summarize the neural basis underlying polarization vision in insect, especially focusing on our recent progresses about possible brain mechanisms for encoding e-vector orientations.In the cricket optic lobe, information of the e-vector orientation is converged into the three types of polarization-sensitive neurons (POL1-neurons), each of which is tuned to the different e-vector orientation, suggesting that each e-vector orientation is encoded as a triplet signal of POL1-neurons. This idea is termed 'instantaneous method' because, using this method, the animal can deduce orientations 'instantaneously', i.e. without any rotation of the body. To confirm whether the insects can use this method, we constructed a neural network model that received inputs from POL1-neurons and that encoded any particular e-vector orientations unequivocally. In this model, each e-vector orientation was represented as a response pattern of 'compass neurons'. For a reliable output of the model, a sufficient number of compass neuron types, each of which was narrowly tuned to a certain e-vector orientation, were required. Next, by intracellular recordings from the cricket brain, we found a group of central complex neurons exactly showing the response properties as we supposed for the compass neurons. We also examined the e-vector discriminative capability of honeybees by a classical conditioning paradigm using proboscis extension reflex and found that they could discriminate two 90° different e-vector orientations without any head movement. Taken these results together, we concluded that the insects could use 'instantaneous method' to detect e-vector orientation of the polarized light.

Journal

  • Hikaku seiri seikagaku(Comparative Physiology and Biochemistry)

    Hikaku seiri seikagaku(Comparative Physiology and Biochemistry) 32(4), 195-204, 2015

    THE JAPANESE SOCIETY FOR COMPARATIVE PHYSIOLOGY AND BIOCHEMISTRY

Codes

  • NII Article ID (NAID)
    130005116608
  • NII NACSIS-CAT ID (NCID)
    AN10391932
  • Text Lang
    JPN
  • ISSN
    0916-3786
  • NDL Article ID
    027031172
  • NDL Call No.
    Z18-1651
  • Data Source
    NDL  J-STAGE 
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