Axis of Cellular and Molecular Neuroscience, CRULRG, Department of Biochemistry, Microbiology and Bioinformatics, Université Laval, Québec, PQ, Canada.
J Physiol. 2011 Apr 15;589(Pt 8):1957-77. doi: 10.1113/jphysiol.2010.204255. Epub 2011 Feb 28.
In most central neurons, action potentials (APs), generated in the initial axon segment, propagate back into dendrites and trigger considerable Ca(2+) entry via activation of voltage-sensitive calcium channels (VSCCs). Despite the similarity in its underlying mechanisms, however, AP-evoked dendritic Ca(2+) signalling often demonstrates a cell type-specific profile that is determined by the neuron dendritic properties. Using two-photon Ca(2+) imaging in combination with patch-clamp whole-cell recordings,we found that in distinct types of hippocampal inhibitory interneurons Ca(2+) transients evoked by backpropagating APs not only were shaped by the interneuron-specific properties of dendritic Ca(2+) handling but also involved specific Ca(2+) mechanisms that were regulated dynamically by distinct activity patterns. In dendrites of regularly spiking basket cells, AP-evoked Ca(2+) rises were of large amplitude and fast kinetics; however, they decreased with membrane hyperpolarization or following high-frequency firing episodes. In contrast, AP-evoked Ca(2+) elevations in dendrites of Schaffer collateral-associated cells exhibited significantly smaller amplitude and slower kinetics, but increased with membrane hyperpolarization. These cell type-specific properties of AP-evoked dendritic Ca(2+) signalling were determined by distinct endogenous buffer capacities of the interneurons examined and by specific types of VSCCs recruited by APs during different patterns of activity. Furthermore, AP-evoked Ca(2+) transients summated efficiently during theta-like bursting and were associated with the induction of long-term potentiation at inhibitory synapses onto both types of interneurons. Therefore, the cell type-specific profile of AP-evoked dendritic Ca(2+) signalling is shaped in an activity-dependent manner, such that the same pattern of hippocampal activity can be differentially translated into dendritic Ca(2+) signals in different cell types. However, Cell type-specific differences in Ca(2+) signals can be 'smoothed out' by changes in neuronal activity, providing a means for common, cell-type-independent forms of synaptic plasticity.
在大多数中枢神经元中，动作电位（APs）在初始轴突段产生，然后反向传播到树突并通过激活电压敏感钙通道（VSCCs）引发可观的 Ca（2+）内流。然而，尽管其潜在机制相似，但 AP 诱发的树突 Ca（2+）信号通常表现出特定于细胞类型的特征，这由神经元树突特性决定。我们使用双光子 Ca（2+）成像结合膜片钳全细胞记录，发现在不同类型的海马抑制性中间神经元中，反向传播的 APs 诱发的 Ca（2+）瞬变不仅受到树突 Ca（2+）处理的中间神经元特异性特性的影响，还涉及特定的 Ca（2+）机制，这些机制受不同的活动模式动态调节。在规则放电篮状细胞的树突中，AP 诱发的 Ca（2+）上升幅度大、动力学快；然而，它们会随着膜超极化或高频放电事件而降低。相比之下，在 Schaffer 侧枝相关细胞的树突中，AP 诱发的 Ca（2+）升高幅度较小、动力学较慢，但随着膜超极化而增加。这些特定于细胞类型的 AP 诱发树突 Ca（2+）信号特征是由所研究的中间神经元的不同内源性缓冲能力以及在不同活动模式下由 APs 募集的特定类型的 VSCC 决定的。此外，AP 诱发的 Ca（2+）瞬变在类似 theta 的爆发期间有效地叠加，并与两种类型的中间神经元上抑制性突触的长时程增强诱导相关。因此，AP 诱发的树突 Ca（2+）信号的特定于细胞类型的特征以依赖于活动的方式形成，使得相同的海马活动模式可以在不同的细胞类型中以不同的树突 Ca（2+）信号形式被转化。然而，神经元活动的变化可以“平滑”细胞类型特异性差异的 Ca（2+）信号，为共同的、与细胞类型无关的突触可塑性形式提供了一种手段。
