Department of Biology, The University of Texas at San Antonio, San Antonio, Texas.
J Neurophysiol. 2019 Sep 1;122(3):1060-1072. doi: 10.1152/jn.00369.2019. Epub 2019 Jul 17.
Striatal fast-spiking interneurons (FSIs) fire in variable-length runs of action potentials at 20-200 spikes/s separated by pauses. In vivo, or with fluctuating applied current, both runs and pauses become briefer and more variable. During runs, spikes are entrained specifically to gamma-frequency components of the input fluctuations. We stimulated parvalbumin-expressing striatal FSIs in mouse brain slices with broadband noise currents added to direct current steps and measured spike entrainment across all frequencies. As the constant current level was increased, FSIs produced longer runs and showed sharper frequency tuning, with best entrainment at the stimulus frequency matching their intrarun firing rate. We separated the contributions of previous spikes from that of the fluctuating stimulus, revealing a strong contribution of previous action potentials to gamma-frequency entrainment. In contrast, after subtraction of the effect inherited from the previous spike, the remaining stimulus contribution to spike generation was less sharply tuned, showing a larger contribution of lower frequencies. The frequency specificity of entrainment within a run was reproduced with a phase resetting model based on experimentally measured phase resetting curves of the same FSIs. In the model, broadly tuned phase entrainment for the first spike in a run evolved into sharply tuned gamma entrainment over the next few spikes. The data and modeling results indicate that for FSIs firing in brief runs and pauses firing within runs is entrained by gamma-frequency components of the input, whereas the onset timing of runs may be sensitive to a wider range of stimulus frequency components. Specific types of neurons entrain their spikes to particular oscillation frequencies in their synaptic input. This entrainment is commonly understood in terms of the subthreshold voltage response, but how this translates to spiking is not clear. We show that in striatal fast-spiking interneurons, entrainment to gamma-frequency input depends on rhythmic spike runs and is explained by the phase resetting curve, whereas run initiation can be triggered by a broad range of input frequencies.
纹状体中快速放电中间神经元（FSI）以 20-200 个尖峰/秒的可变长度动作电位序列放电，序列之间有停顿。在体内或施加波动电流时，两者都会变得更短且更具可变性。在序列期间，尖峰被特定地与输入波动的伽马频率分量锁相。我们使用宽带噪声电流刺激表达 Parvalbumin 的纹状体 FSI，将其添加到直流阶跃中，并在所有频率下测量尖峰锁相。随着恒定电流水平的增加，FSI 产生更长的序列，并显示出更尖锐的频率调谐，最佳锁相在与它们的序列内放电率匹配的刺激频率处。我们将前一个尖峰的贡献与波动刺激的贡献分开，揭示了前一个动作电位对伽马频率锁相的强烈贡献。相比之下，在扣除前一个尖峰遗传的影响后，刺激对尖峰产生的剩余贡献的调谐不那么尖锐，显示出较低频率的较大贡献。基于相同 FSI 的实验测量的相位重置曲线的相重置模型，再现了序列内锁相的频率特异性。在模型中，对于序列中的第一个尖峰的广泛调谐的相位锁相演变为接下来的几个尖峰的尖锐的伽马锁相。数据和建模结果表明，对于在短暂的序列和序列内的停顿中放电的 FSI，输入的伽马频率分量会使尖峰锁相，而序列的起始时间可能对更广泛的刺激频率分量敏感。特定类型的神经元将其尖峰与突触输入中的特定振荡频率锁相。这种锁相通常根据亚阈值电压响应来理解，但这如何转化为尖峰尚不清楚。我们表明，在纹状体快速放电中间神经元中，对伽马频率输入的锁相取决于有节奏的尖峰序列，并通过相位重置曲线来解释，而序列的起始可以由广泛的输入频率触发。
