Functional Imaging Group, Deutsches Zentrum für Neurodegenerative Erkrankungen, and Special Laboratory for Noninvasive Brain Imaging, Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany
J Neurosci. 2014 Jun 18;34(25):8529-45. doi: 10.1523/JNEUROSCI.0472-14.2014.
Paired-pulse stimulation of the perforant pathway was used to study the relation between granular cell activity and the resultant fMRI response in the rat dentate gyrus. By varying the interpulse interval (IPI), paired-pulse stimulations caused: a depression (20 ms IPI), a facilitation (100 ms IPI), a mixture of depression and facilitation (30 ms IPI), or no change (500 ms IPS) in the second response. Eight identical paired pulses were applied during one stimulation train and the evoked field potentials and generated fMRI responses were measured simultaneously. Application of consecutive stimulation trains caused time-dependent variations in electrophysiological and fMRI responses, which were characteristic for each stimulus protocol. Depending on the IPI, the magnitude of the fMRI response either correlated strongly with or was apparently unrelated to the spiking or postsynaptic activity of the granular cells. A strong relation between spiking activity and resultant fMRI response was only found when the stimulation protocol caused an increase in the recorded population spike latency. If the latency was decreased, the fMRI response was more closely related to the applied input activity. Perforant pathway fibers monosynaptically activate granular cells, so variations in population spike latencies reflect changes in their intrinsic excitability. Therefore, during increased intrinsic excitability, signaling cascades upstream of the granular cells determine the fMRI response, whereas granular cell activity-related mechanisms control the fMRI response during decreased intrinsic excitability.
我们采用成对电刺激齿状回的穿通纤维来研究颗粒细胞的活动与功能磁共振成像(fMRI)反应之间的关系。通过改变两个刺激脉冲之间的间隔(interpulse interval, IPI)，我们发现成对刺激会引起以下不同的反应：第二个反应的抑制（20ms IPI）、易化（100ms IPI）、抑制与易化的混合（30ms IPI）或无变化（500ms IPI）。在一个刺激序列中施加 8 个相同的成对脉冲，同时测量诱发的场电位和生成的 fMRI 反应。连续刺激序列的应用引起了电生理和 fMRI 反应的时间依赖性变化，这些变化对每个刺激方案都是特征性的。根据 IPI 的不同，fMRI 反应的幅度与颗粒细胞的放电或突触后活动密切相关或明显无关。只有当刺激方案引起记录的群体锋电位潜伏期增加时，才会发现放电活动与产生的 fMRI 反应之间存在很强的关系。如果潜伏期缩短，则 fMRI 反应与施加的输入活动更为密切相关。穿通纤维单突触激活颗粒细胞，因此群体锋电位潜伏期的变化反映了其内在兴奋性的变化。因此，在内在兴奋性增加时，颗粒细胞上游的信号级联决定了 fMRI 反应，而在内在兴奋性降低时，颗粒细胞活动相关机制控制了 fMRI 反应。
