神経移動中のNMDA受容体チャネル活性の発達開始

in vitroで維持された発達中のラット小脳の薄いスライスにおける顆粒細胞のパッチクランプ記録は、N-メチル-D-アスパラギン酸（NMDA）受容体の活性化を介して媒介される自発的な単一チャネル活性を示しました。The frequency of tonic single-channel activity was reversibly inhibited by the NMDA receptor/channel antagonists D-2-amino-5-phosphonovalerate (D-AP5), 7-chloro-kynurenate (7-Cl-Kynu) and MgCl2, potentiated by glycine, and unaffected by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX)またはテトロドトキシン（TTX）。顆粒細胞のNMDA感受性に影響を与えなかった、グルタミン酸ピルビン酸トランスアミナーゼによる内因性グルタミン酸の酵素分解により、強壮剤チャネル活性はまた、可逆的に阻害されました。自発的チャネル活性の頻度とNMDA感度の両方は、外胚層（EGL）の前序細胞では低く、分子層（ML）の移動細胞と内顆粒細胞層（GCL）内の単純細胞で大幅に増加しました。トニックチャネル活性は、グルタミン酸塩摂取阻害剤L-α-アミノアジペート（L-alpha-AA）によって強化されました。結果は、顆粒細胞の分化、移動、シナプス形成の段階で強壮剤NMDA受容体チャネル活性の劇的な増加が起こることを示しています。これは、内因性グルタミン酸の放出によって駆動され、NMDA受容体密度と局所グルタミン酸摂取によって調節されます。

Patch-clamp recordings of granule cells in thin slices of developing rat cerebellum maintained in vitro displayed spontaneous single-channel activity mediated via activation of N-methyl-D-aspartate (NMDA) receptors. The frequency of tonic single-channel activity was reversibly inhibited by the NMDA receptor/channel antagonists D-2-amino-5-phosphonovalerate (D-AP5), 7-chloro-kynurenate (7-Cl-Kynu) and MgCl2, potentiated by glycine, and unaffected by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) or tetrodotoxin (TTX). Tonic channel activity was also reversibly inhibited by enzymatic degradation of endogenous glutamate by glutamate pyruvate transaminase, which did not affect the NMDA sensitivity of granule cells. Both the frequency of spontaneous channel activity and the NMDA sensitivity were low in premigratory cells of the external germinal layer (EGL), with large increases observed in migrating cells in the molecular layer (ML) and in postmigratory cells within the internal granule cell layer (GCL). Tonic channel activity was enhanced by the glutamate uptake inhibitor L-alpha-aminoadipate (L-alpha-AA), the degree of enhancement being greater in the EGL than the GCL. The results demonstrate that a dramatic increase in the tonic NMDA receptor-channel activity occurs during the stages of granule cell differentiation, migration and synaptogenesis, which is driven by endogenous glutamate release and regulated by NMDA receptor density and local glutamate uptake.