第13回神経科学学術集会(新潟)1989.10.

藤田一郎、Masakazu Konishi 「両耳間時差検出における抑制の役割」 

メンフクロウは、両耳間の継時的時差(ITD)ミを用いて、音の水平位置を知る。ITD情報は脳幹に存する神経経路によって処理され、最終的には下丘外側核に伝えられる。その過程で、神経細胞はITDに対してより鋭い選択性を持つようになり、また、phase ambiguity (等しい両耳間位相差を生ずる全てのITDに神経細胞が応じてしまう現象)を解決して真のITDをコードするようになる。GABAを介する抑制がこのITD選択性の鋭敏化とphase ambiguityの除去に寄与している。





Gabaergic inhibition shapes neuronal selectivity to interaural time difference.

ICHIRO FUJITA1,2, AND MASAKAZU KONISHI2
l: Frontier Research Program, RIKEN Institute. Hirosawa 2-1. Wako. Saitama 351-01, Japan
2; Division of Biology 216-76. California Institute of Technology, Pasadena. California 91126, U.S.A.

Interaural time difference (ITD) is the principal cue for the barn owl to locate the horizontal position of sound. Neuronal selectivity to ITD first appears in the nucleus laminaris which projects to a lemniscal nucleus and the central nucleus "core" of the inferior coliiculus (ICc). The ICc in turn projects to the lateral shell of the central nucleus (ICl) and to the external nucleus of the inferior colliculus (ICx). Sharpness of ITD tuning improves in the ICc and ICx. ICx neuronsresolve phase ambiguity when they are stimulated with noise bursts (Takahashi and Konishi, J. Neurosci., 6: 3413-3422, 1986). All these nuclei contain GABAergic cell bodies, terminals or both (Can, Fujita and Konishi, J. Comp. Neuroi., 286: 190-207, 1989). Iontophoretic application ofbicuculline methiodide {BMI, a selective GABA antagonist) decreased ITD selectivity in ICc, ICl and ICx neurons. ICx neurons became phase ambiguous in the presence of BMI. These actions of BMI were cancelled by simultaneous application of GABA. The results suggest that GABAergic inhibition contributes to the sharpening of ITD tuning and the elimination of phase ambiguity.