Insular cortical descending projections facilitate neuronal responses to noxious but not innoxious stimulation in rat trigeminal spinal subnucleus caudalis
Insular cortical descending projections facilitate neuronal responses to noxious but not innoxious stimulation in rat trigeminal spinal subnucleus caudalis
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DOI：
10.1016/j.brainres.2023.148248
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发表时间：
2023-01
期刊：
影响因子：
2.9
通讯作者：
Y. Nakaya;K. Iwata;Masayuki Kobayashi
中科院分区：
文献类型：
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作者：
Y. Nakaya;K. Iwata;Masayuki Kobayashi
岛皮质(IC)接受口面部伤害性信息。IC V层锥体神经元将轴突投射到三叉神经脊束核尾侧亚核、臂旁核和中脑导水管周围灰质等不同脑区。然而，关于IC的这些下降投影的功能的信息很少。本研究旨在阐明IC、→和Sp5C对在人突触素启动子控制下注射编码修饰通道视紫红质-2(ChR2)的腺相关病毒融合到mCherry的大鼠面部伤害性和伤害性刺激反应的神经元放电的影响。我们将Sp5C神经元分为三组：低阈值(LT)、伤害性特异性(NS)和宽动态范围(WDR)神经元，分别对无害刺激(刷牙)、伤害性机械刺激(捏压)和伤害性和伤害性刺激都有反应。IC神经元的神经元活动通过对IC的光刺激(重复脉冲频率为20 GHz，频率为5 Hz)来激活，IC在IC的V层锥体神经元中持续地诱发动作电位。在光刺激诱导ChR2激活之前和期间，LT神经元对刷面皮肤表现出相似的尖峰放电频率。相反，在ChR2激活时，NS神经元表现出对收缩的放电频率增加。另一方面，在ChR2激活时，WDR神经元的Sp5C神经元放电增加到收缩，而对无害的机械刺激不改变其放电频率。这些结果表明，IC下行投射通过增加Sp5C神经元对伤害性机械刺激的反应而促进伤害性感觉。
The insular cortex (IC) receives orofacial nociceptive information. Pyramidal neurons in IC layer V send their axons to various brain regions, such as the trigeminal spinal subnucleus caudalis (Sp5C), parabrachial nucleus, and periaqueductal gray. However, little information has been available about the functions of these descending projections from the IC. This study aimed to elucidate the effect of IC → Sp5C on neuronal spike firings responding to noxious and innoxious stimuli to the face of the rat receiving an injection of adeno-associated virus encoding modified channelrhodopsin-2 (ChR2) fused to mCherry under the control of the human synapsin promotor. We classified Sp5C neurons responding to mechanical stimuli into three groups: low-threshold (LT), nociceptive specific (NS), and wide dynamic range (WDR) neurons, which respond to innoxious stimuli (brushing) only, noxious mechanical stimuli (pinching) only, and both noxious and innoxious stimuli, respectively. Neuronal activities of IC neurons were activated by photostimulation (repetitive pulses at 20 Hz for 5 Hz) to the IC that consistently induced action potentials in IC layer V pyramidal neurons. LT neurons showed comparable spike firing rates to brushing the facial skin before and during ChR2 activation induced by photostimulation. In contrast, NS neurons showed an increase in their firing frequency to pinching during ChR2 activation. On the other hand, WDR neurons increased their Sp5C neuronal firing to pinching during ChR2 activation without changing their firing rates to innoxious mechanical stimuli. These results suggest that the IC descending projections facilitate nociception by increasing Sp5C neuronal activities responding to noxious mechanical stimuli.