Institute of Neuroscience, Technische Universität München, 80802 Munich, Germany.
Proc Natl Acad Sci U S A. 2014 May 6;111(18):6798-803. doi: 10.1073/pnas.1318665111. Epub 2014 Apr 18.
A major synaptic input to the thalamus originates from neurons in cortical layer 6 (L6); however, the function of this cortico-thalamic pathway during sensory processing is not well understood. In the mouse whisker system, we found that optogenetic stimulation of L6 in vivo results in a mixture of hyperpolarization and depolarization in the thalamic target neurons. The hyperpolarization was transient, and for longer L6 activation (>200 ms), thalamic neurons reached a depolarized resting membrane potential which affected key features of thalamic sensory processing. Most importantly, L6 stimulation reduced the adaptation of thalamic responses to repetitive whisker stimulation, thereby allowing thalamic neurons to relay higher frequencies of sensory input. Furthermore, L6 controlled the thalamic response mode by shifting thalamo-cortical transmission from bursting to single spiking. Analysis of intracellular sensory responses suggests that L6 impacts these thalamic properties by controlling the resting membrane potential and the availability of the transient calcium current IT, a hallmark of thalamic excitability. In summary, L6 input to the thalamus can shape both the overall gain and the temporal dynamics of sensory responses that reach the cortex.
皮质 6 层（L6）的神经元向丘脑发出主要的突触传入；然而，这种皮质-丘脑通路在感觉处理过程中的功能尚不清楚。在小鼠胡须系统中，我们发现体内 L6 的光遗传学刺激导致丘脑靶神经元发生混合超极化和去极化。超极化是短暂的，对于较长时间的 L6 激活（>200ms），丘脑神经元达到去极化的静息膜电位，这影响了丘脑感觉处理的关键特征。最重要的是，L6 刺激减少了丘脑对重复胡须刺激的适应，从而允许丘脑神经元传递更高频率的感觉输入。此外，L6 通过将丘脑中的爆发式传递转变为单个尖峰传递来控制丘脑的反应模式。对细胞内感觉反应的分析表明，L6 通过控制静息膜电位和瞬时钙电流 IT 的可用性来影响这些丘脑特性，这是丘脑兴奋性的标志。总之，丘脑的 L6 输入可以塑造到达皮层的感觉反应的整体增益和时间动态。
