Institute of Neurobiology, University of Tübingen, Tübingen 72076, Germany.
Werner-Reichardt Centre for Integrative Neuroscience, Tübingen 72076, Germany.
J Neurosci. 2020 Jul 22;40(30):5797-5806. doi: 10.1523/JNEUROSCI.0099-20.2020. Epub 2020 Jun 18.
Plasticity within hippocampal circuits is essential for memory functions. The hippocampal CA2/CA3 region is thought to be able to rapidly store incoming information by plastic modifications of synaptic weights within its recurrent network. High-frequency spike-bursts are believed to be essential for this process, by serving as triggers for synaptic plasticity. Given the diversity of CA2/CA3 pyramidal neurons, it is currently unknown whether and how burst activity, assessed during natural behavior, relates to principal cell heterogeneity. To explore this issue, we juxtacellularly recorded the activity of single CA2/CA3 neurons from freely-moving male mice, exploring a familiar environment. In line with previous work, we found that spatial and temporal activity patterns of pyramidal neurons correlated with their topographical position. Morphometric analysis revealed that neurons with a higher proportion of distal dendritic length displayed a higher tendency to fire spike-bursts. We propose that the dendritic architecture of pyramidal neurons might determine burst-firing by setting the relative amount of distal excitatory inputs from the entorhinal cortex. High-frequency spike-bursts are thought to serve fundamental computational roles within neural circuits. Within hippocampal circuits, spike-bursts are believed to serve as potent instructive signals, which increase the efficiency of information transfer and induce rapid modifications of synaptic efficacies. In the present study, by juxtacellularly recording and labeling single CA2/CA3 neurons in freely-moving mice, we explored whether and how burst propensity relates to pyramidal cell heterogeneity. We provide evidence that, within the CA2/CA3 region, neurons with higher proportion of distal dendritic length display a higher tendency to fire spike-bursts. Thus, the relative amount of entorhinal inputs, arriving onto the distal dendrites, might determine the burst propensity of individual CA2/CA3 neurons during natural behavior.
海马电路中的可塑性对于记忆功能至关重要。海马 CA2/CA3 区域被认为能够通过其自身的递归网络中的突触权重的塑性变化来快速存储传入信息。高频尖峰爆发被认为是此过程的关键，因为它们充当突触可塑性的触发因素。鉴于 CA2/CA3 锥体神经元的多样性，目前尚不清楚在自然行为期间评估的爆发活动是否以及如何与主细胞异质性相关。为了探索这个问题，我们在自由移动的雄性小鼠中使用细胞外记录单个 CA2/CA3 神经元的活动，探索熟悉的环境。与之前的工作一致，我们发现锥体神经元的时空活动模式与它们的拓扑位置相关。形态测量分析显示，具有更高比例的远端树突长度的神经元表现出更高的尖峰爆发倾向。我们提出，锥体神经元的树突结构可能通过设定来自内嗅皮层的远端兴奋性输入的相对量来决定爆发放电。高频尖峰爆发被认为在神经回路中发挥基本的计算作用。在海马回路中，尖峰爆发被认为是作为有力的指导信号，增加信息传递的效率，并诱导突触效能的快速变化。在本研究中，通过在自由移动的小鼠中进行细胞外记录和标记单个 CA2/CA3 神经元，我们探讨了爆发倾向与锥体细胞异质性之间的关系。我们提供的证据表明，在 CA2/CA3 区域内，具有更高比例的远端树突长度的神经元表现出更高的尖峰爆发倾向。因此，到达远端树突的内嗅皮层输入的相对量可能决定了个体 CA2/CA3 神经元在自然行为期间的爆发倾向。
