Department Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York 10027, USA.
J Neurosci. 2011 Dec 7;31(49):17872-86. doi: 10.1523/JNEUROSCI.3894-11.2011.
Chandelier (axoaxonic) cells (ChCs) are a distinct group of GABAergic interneurons that innervate the axon initial segments of pyramidal cells. However, their circuit role and the function of their clearly defined anatomical specificity remain unclear. Recent work has demonstrated that chandelier cells can produce depolarizing GABAergic PSPs, occasionally driving postsynaptic targets to spike. On the other hand, other work suggests that ChCs are hyperpolarizing and may have an inhibitory role. These disparate functional effects may reflect heterogeneity among ChCs. Here, using brain slices from transgenic mouse strains, we first demonstrate that, across different neocortical areas and genetic backgrounds, upper Layer 2/3 ChCs belong to a single electrophysiologically and morphologically defined population, extensively sampling Layer 1 inputs with asymmetric dendrites. Consistent with being a single cell type, we find electrical coupling between ChCs. We then investigate the effect of chandelier cell activation on pyramidal neuron spiking in several conditions, ranging from the resting membrane potential to stimuli designed to approximate in vivo membrane potential dynamics. We find that under quiescent conditions, chandelier cells are capable of both promoting and inhibiting spike generation, depending on the postsynaptic membrane potential. However, during in vivo-like membrane potential fluctuations, the dominant postsynaptic effect was a strong inhibition. Thus, neocortical chandelier cells, even from within a homogeneous population, appear to play a dual role in the circuit, helping to activate quiescent pyramidal neurons, while at the same time inhibiting active ones.
烛台（轴突-轴突）细胞（ChCs）是一类独特的 GABA 能中间神经元，它们支配着锥体细胞的轴突起始段。然而，它们的回路作用和其明确的解剖特异性的功能仍然不清楚。最近的工作表明，烛台细胞可以产生去极化的 GABA 能 PSPs，偶尔会驱动突触后靶标产生尖峰。另一方面，其他工作表明 ChCs 是超极化的，可能具有抑制作用。这些不同的功能效应可能反映了 ChCs 的异质性。在这里，我们使用转基因小鼠品系的脑片首先证明，在不同的新皮层区域和遗传背景下，上 2/3 层 ChCs 属于一个单一的电生理和形态定义的群体，用不对称的树突广泛地采样 1 层的输入。与单一细胞类型一致，我们发现 ChCs 之间存在电耦合。然后，我们在几种条件下研究了烛台细胞激活对锥体神经元尖峰的影响，这些条件从静息膜电位到旨在近似体内膜电位动力学的刺激。我们发现，在静息状态下，ChCs 既能促进也能抑制尖峰的产生，这取决于突触后膜电位。然而，在类似于体内的膜电位波动期间，主要的突触后效应是强烈的抑制。因此，即使在同质群体中，新皮层的烛台细胞似乎在回路中发挥双重作用，有助于激活静息的锥体神经元，同时抑制活跃的神经元。
