Christie J M, Westbrook G L
Vollum Institute, Oregon Health and Science University, Portland 97201, USA.
J Neurophysiol. 2003 May;89(5):2466-72. doi: 10.1152/jn.00997.2002.
Dendrodendritic synapses, distributed along mitral cell lateral dendrites, provide powerful and extensive inhibition in the olfactory bulb. Activation of inhibition depends on effective penetration of action potentials into dendrites. Although action potentials backpropagate with remarkable fidelity in apical dendrites, this issue is controversial for lateral dendrites. We used paired somatic and dendritic recordings to measure action potentials in proximal dendritic segments (0-200 microm from soma) and action potential-generated calcium transients to monitor activity in distal dendritic segments (200-600 microm from soma). Somatically elicited action potentials were attenuated in proximal lateral dendrites. The attenuation was not due to impaired access resistance in dendrites or to basal synaptic activity. However, a single somatically elicited action potential was sufficient to evoke a calcium transient throughout the lateral dendrite, suggesting that action potentials reach distal dendritic compartments. Block of A-type potassium channels (I(A)) with 4-aminopyridine (10 mM) prevented action potential attenuation in direct recordings and significantly increased dendritic calcium transients, particularly in distal dendritic compartments. Our results suggest that I(A) may regulate inhibition in the olfactory bulb by controlling action potential amplitudes in lateral dendrites.
树突-树突突触分布于二尖瓣细胞的外侧树突，在嗅球中提供强大而广泛的抑制作用。抑制作用的激活取决于动作电位有效侵入树突。尽管动作电位在顶端树突中能以极高的保真度进行反向传播，但在外侧树突中这一问题仍存在争议。我们采用体细胞和树突配对记录法，测量近端树突段（距胞体0 - 200微米）的动作电位，并通过动作电位引发的钙瞬变来监测远端树突段（距胞体200 - 600微米）的活动。体细胞诱发的动作电位在近端外侧树突中衰减。这种衰减并非由于树突中输入电阻受损或基础突触活动所致。然而，单个体细胞诱发的动作电位足以在整个外侧树突引发钙瞬变，这表明动作电位能够到达远端树突区室。用4 - 氨基吡啶（10 mM）阻断A 型钾通道（I(A)）可防止直接记录中的动作电位衰减，并显著增加树突钙瞬变，尤其是在远端树突区室。我们的结果表明，I(A)可能通过控制外侧树突中的动作电位幅度来调节嗅球中的抑制作用。
