Jaeger D, Bower J M
Department of Biology, Emory University, Atlanta, Georgia 30322, USA.
J Neurosci. 1999 Jul 15;19(14):6090-101. doi: 10.1523/JNEUROSCI.19-14-06090.1999.
Previous simulations using a realistic model of a cerebellar Purkinje cell suggested that synaptic control of somatic spiking in this cell type is mediated by voltage-gated intrinsic conductances and that inhibitory rather than excitatory synaptic inputs are more influential in controlling spike timing. In this paper, we have tested these predictions physiologically using dynamic current clamping to apply model-derived synaptic conductances to Purkinje cells in vitro. As predicted by the model, this input transformed the in vitro pattern of spiking into a different spike pattern typically observed in vivo. A net inhibitory synaptic current was required to achieve such spiking, indicating the presence of strong intrinsic depolarizing currents. Spike-triggered averaging confirmed that the length of individual intervals between spikes was correlated to the amplitude of the inhibitory conductance but was not influenced by excitatory inputs. Through repeated presentation of identical stimuli, we determined that the output spike rate was very sensitive to the relative balance of excitation and inhibition in the input conductances. In contrast, the accuracy of spike timing was dependent on input amplitude and was independent of spike rate. Thus, information could be encoded in Purkinje cell spiking in a precise spike time code and a rate code at the same time. We conclude that Purkinje cell responses to synaptic input are strongly dependent on active somatic and dendritic properties and that theories of cerebellar function likely need to incorporate single-cell dynamics to a greater degree than is customary.
先前使用小脑浦肯野细胞的真实模型进行的模拟表明，这种细胞类型中体细胞放电的突触控制是由电压门控的内在电导介导的，并且抑制性而非兴奋性突触输入在控制放电时间方面更具影响力。在本文中，我们使用动态电流钳制在体外将模型推导的突触电导应用于浦肯野细胞，从生理学角度测试了这些预测。正如模型所预测的那样，这种输入将体外放电模式转变为通常在体内观察到的不同放电模式。需要净抑制性突触电流来实现这种放电，这表明存在强大的内在去极化电流。触发尖峰平均法证实，单个尖峰之间的间隔长度与抑制性电导的幅度相关，但不受兴奋性输入影响。通过重复呈现相同的刺激，我们确定输出尖峰频率对输入电导中兴奋和抑制之间的相对平衡非常敏感。相比之下，尖峰时间的准确性取决于输入幅度，并且与尖峰频率无关。因此，信息可以同时以精确的尖峰时间编码和频率编码的形式编码在浦肯野细胞放电中。我们得出结论，浦肯野细胞对突触输入的反应强烈依赖于活跃的体细胞和树突特性，并且小脑功能理论可能需要比通常情况更大程度地纳入单细胞动力学。
