Hu Hang, Agmon Ariel
Department of Neurobiology and Anatomy and the Sensory Neuroscience Research Center, West Virginia University School of Medicine, Morgantown, West Virginia 26506.
Department of Neurobiology and Anatomy and the Sensory Neuroscience Research Center, West Virginia University School of Medicine, Morgantown, West Virginia 26506
J Neurosci. 2016 Jun 29;36(26):6906-16. doi: 10.1523/JNEUROSCI.0739-16.2016.
Thalamocortical neurons relay sensory and motor information to the neocortex using both single spikes and bursts; bursts prevail during low-vigilance states but also occur during awake behavior. Bursts are suggested to provide an alerting signal to the cortex and enhance stimulus detection, but the synaptic mechanisms underlying these effects are not clear, because the postsynaptic responses of different subtypes of cortical neurons to unitary thalamocortical bursts are mostly unknown. Using optogenetically guided recordings in mouse thalamocortical slices, we achieved the first reported paired intracellular recordings from nine monosynaptically connected thalamic and cortical neurons, including principal cells and two subtypes of inhibitory interneurons, and compared between cortical responses to single thalamocortical spikes and bursts. In 18 additional cortical neurons, we elicited unitary burst responses optogenetically. Short-term dynamics and temporal summation of burst-evoked EPSPs were cell-type dependent: in principal cells and somatostatin-containing (SOM), but not fast-spiking (FS), interneurons, peak response during a burst was on average more than twofold larger than the response to the first spike. Thus, firing a burst instead of a single spike would more than double the probability of firing in postsynaptic excitatory neurons and in SOM, but not FS, interneurons. Consistent with this prediction, FS interneurons held near firing threshold fired most often on the first burst component, whereas SOM interneurons fired only on the second or later components. By increasing excitation of principal cells together with SOM-mediated, distally directed inhibition, thalamocortical bursts could momentarily enhance the saliency of the ascending sensory stimulus over less urgent, top-down inputs.
Thalamocortical neurons relay sensory and motor information to the cerebral cortex using both single spikes and high-frequency bursts, but the function of bursts is not fully understood. Using brain slices from mouse somatosensory thalamus and cortex, we achieved the first dual recordings of directly connected thalamic and cortical neurons and compared between cortical responses to single thalamic spikes and to bursts. We report that bursts enhanced the responses of excitatory neurons and of inhibitory interneurons that preferentially target dendrites. A potential consequence is that bursts will enhance the response to the immediate sensory event over responses to less urgent, modulatory inputs.
丘脑皮质神经元通过单个动作电位和爆发式放电将感觉和运动信息传递至新皮质；爆发式放电在低警觉状态下占主导，但在清醒行为期间也会出现。爆发式放电被认为可向皮质提供警觉信号并增强刺激检测，但这些效应背后的突触机制尚不清楚，因为不同亚型的皮质神经元对单个丘脑皮质爆发式放电的突触后反应大多未知。利用小鼠丘脑皮质切片中的光遗传学引导记录，我们首次报告了对9对单突触连接的丘脑和皮质神经元进行的细胞内配对记录，包括主细胞和两种抑制性中间神经元亚型，并比较了皮质对单个丘脑皮质动作电位和爆发式放电的反应。在另外18个皮质神经元中，我们通过光遗传学方法诱发了单个爆发式放电反应。爆发式放电诱发的兴奋性突触后电位（EPSP）的短期动力学和时间总和具有细胞类型依赖性：在主细胞和含生长抑素（SOM）的中间神经元中，但在快速放电（FS）中间神经元中并非如此，爆发式放电期间的峰值反应平均比第一个动作电位的反应大两倍以上。因此，发放爆发式放电而非单个动作电位会使突触后兴奋性神经元和SOM中间神经元（而非FS中间神经元）的发放概率增加一倍以上。与这一预测一致，接近发放阈值的FS中间神经元最常在爆发式放电的第一个成分时发放，而SOM中间神经元仅在第二个或更晚的成分时发放。通过增加主细胞与SOM介导的、向远端的抑制作用的共同兴奋，丘脑皮质爆发式放电可暂时增强上行感觉刺激相对于不那么紧急的自上而下输入的显著性。
丘脑皮质神经元通过单个动作电位和高频爆发式放电将感觉和运动信息传递至大脑皮质，但爆发式放电的功能尚未完全了解。利用小鼠体感丘脑和皮质的脑切片，我们首次对直接连接的丘脑和皮质神经元进行了双记录，并比较了皮质对单个丘脑动作电位和爆发式放电的反应。我们报告称，爆发式放电增强了兴奋性神经元和优先靶向树突的抑制性中间神经元的反应。一个潜在的结果是，爆发式放电将增强对即时感觉事件的反应，超过对不那么紧急的调制性输入的反应。
