Krieger Patrik, de Kock Christiaan P J, Frick Andreas
Department of Cell Physiology, Max Planck Institute for Medical ResearchHeidelberg, Germany.
Department of Systems Neuroscience, Medical Faculty, Ruhr University BochumBochum, Germany.
Front Cell Neurosci. 2017 Jul 11;11:194. doi: 10.3389/fncel.2017.00194. eCollection 2017.
Layer 5 (L5) is a major neocortical output layer containing L5A slender-tufted (L5A-st) and L5B thick-tufted (L5B-tt) pyramidal neurons. These neuron types differ in their firing patterns, connectivity and dendritic morphology amongst other features, reflecting their specific functional role within the neocortical circuits. Here, we asked whether the active properties of the basal dendrites that receive the great majority of synaptic inputs within L5 differ between these two pyramidal neuron classes. To quantify their active properties, we measured the efficacy with which action potential (AP) firing patterns backpropagate along the basal dendrites by measuring the accompanying calcium transients using two-photon laser scanning microscopy in rat somatosensory cortex slices. For these measurements we used both "artificial" three-AP patterns and more complex physiological AP patterns that were previously recorded in anesthetized rats in L5A-st and L5B-tt neurons in response to whisker stimulation. We show that AP patterns with relatively few APs (3APs) evoke a calcium response in L5B-tt, but not L5A-st, that is dependent on the temporal pattern of the three APs. With more complex recorded AP patterns, the average calcium response was similar in the proximal dendrites but with a decay along dendrites (measured up to 100 μm) of L5B-tt but not L5A-st neurons. Interestingly however, the whisker evoked AP patterns-although very different for the two cell types-evoke similar calcium responses. In conclusion, although the effectiveness with which different AP patterns evoke calcium transients vary between L5A-st and L5B-tt cell, the calcium influx appears to be tuned such that whisker-evoked calcium transients are within the same dynamic range for both cell types.
第5层（L5）是新皮层的主要输出层，包含L5A细簇状（L5A-st）和L5B粗簇状（L5B-tt）锥体神经元。这些神经元类型在放电模式、连接性和树突形态等其他特征方面存在差异，反映了它们在新皮层回路中的特定功能作用。在这里，我们询问在这两类锥体神经元中，接收L5内绝大多数突触输入的基底树突的活性特性是否不同。为了量化它们的活性特性，我们通过使用双光子激光扫描显微镜测量伴随的钙瞬变，来测量动作电位（AP）放电模式沿基底树突反向传播的效率，该实验在大鼠体感皮层切片中进行。对于这些测量，我们使用了“人工”的三个AP模式以及更复杂的生理AP模式，这些模式先前是在麻醉大鼠的L5A-st和L5B-tt神经元中记录的，用于响应触须刺激。我们发现，相对较少AP的AP模式（3APs）在L5B-tt中引发钙反应，但在L5A-st中不会，这种反应取决于三个AP的时间模式。对于更复杂的记录AP模式，近端树突中的平均钙反应相似，但L5B-tt神经元的树突（测量长度达100μm）上有衰减，而L5A-st神经元则没有。然而，有趣的是，触须诱发的AP模式——尽管这两种细胞类型非常不同——却引发相似的钙反应。总之，尽管不同的AP模式诱发钙瞬变的有效性在L5A-st和L5B-tt细胞之间有所不同，但钙内流似乎经过调节，使得触须诱发的钙瞬变在两种细胞类型中都处于相同的动态范围内。
