Research Department of Neuroscience, Wolfson Institute for Biomedical Research, University College London, London WC1E 6BT, United Kingdom.
Proc Natl Acad Sci U S A. 2010 Dec 21;107(51):22284-9. doi: 10.1073/pnas.1008605107. Epub 2010 Dec 3.
Dendritic spikes appear to be a ubiquitous feature of dendritic excitability. In cortical pyramidal neurons, dendritic spikes increase the efficacy of distal synapses, providing additional inward current to enhance axonal action potential (AP) output, thus increasing synaptic gain. In cerebellar Purkinje cells, dendritic spikes can trigger synaptic plasticity, but their influence on axonal output is not well understood. We have used simultaneous somatic and dendritic patch-clamp recordings to directly assess the impact of dendritic calcium spikes on axonal AP output of Purkinje cells. Dendritic spikes evoked by parallel fiber input triggered brief bursts of somatic APs, followed by pauses in spiking, which cancelled out the extra spikes in the burst. As a result, average output firing rates during trains of input remained independent of the input strength, thus flattening synaptic gain. We demonstrate that this "clamping" of AP output by the pause following dendritic spikes is due to activation of high conductance calcium-dependent potassium channels by dendritic spikes. Dendritic spikes in Purkinje cells, in contrast to pyramidal cells, thus have differential effects on temporally coded and rate coded information: increasing the impact of transient parallel fiber input, while depressing synaptic gain for sustained parallel fiber inputs.
树突棘似乎是树突兴奋性的普遍特征。在皮质锥体神经元中，树突棘增加了远端突触的效能，提供额外的内向电流以增强轴突动作电位 (AP) 的输出，从而增加突触增益。在小脑浦肯野细胞中，树突棘可以引发突触可塑性，但它们对轴突输出的影响尚不清楚。我们使用体和树突贴附式膜片钳记录的同步记录来直接评估树突钙峰对浦肯野细胞轴突 AP 输出的影响。平行纤维输入引发的树突棘会触发短暂的体 AP 爆发，随后是尖峰暂停，这会抵消爆发中的额外尖峰。结果，在输入的串中，平均输出发射率与输入强度无关，从而使突触增益变平。我们证明，树突棘后尖峰暂停对 AP 输出的“钳位”是由于树突棘激活了高电导钙依赖性钾通道。与锥体细胞相比，浦肯野细胞中的树突棘对时间编码和率编码信息具有不同的影响：增加了短暂平行纤维输入的影响，同时降低了持续平行纤维输入的突触增益。
