Department of Oral Anatomy and Neurobiology, Graduate School of Dentistry, Osaka University, Suita, Osaka 565-0871, Japan.
Department of Oral Anatomy and Neurobiology, Graduate School of Dentistry, Osaka University, Suita, Osaka 565-0871, Japan; Department of Orthodontics and Dentofacial Orthopedics, Graduate School of Dentistry, Osaka University, Suita, Osaka 565-0871, Japan.
Neuroscience. 2017 Dec 4;365:158-178. doi: 10.1016/j.neuroscience.2017.09.050. Epub 2017 Oct 6.
Little is known about how proprioceptive signals arising from muscles reach to higher brain regions such as the cerebral cortex. We have recently shown that a particular thalamic region, the caudo-ventromedial edge (VPMcvm) of ventral posteromedial thalamic nucleus (VPM), receives the proprioceptive signals from jaw-closing muscle spindles (JCMSs) in rats. In this study, we further addressed how the orofacial thalamic inputs from the JCMSs were transmitted from the thalamus (VPMcvm) to the cerebral cortex in rats. Injections of a retrograde and anterograde neuronal tracer, wheat-germ agglutinin-conjugated horseradish peroxidase (WGA-HRP), into the VPMcvm demonstrated that the thalamic pathway terminated mainly in a rostrocaudally narrow area in the dorsal part of granular insular cortex rostroventrally adjacent to the rostralmost part of the secondary somatosensory cortex (dGIrvs2). We also electrophysiologically confirmed that the dGIrvs2 received the proprioceptive inputs from JCMSs. To support the anatomical evidence of the VPMcvm-dGIrvs2 pathway, injections of a retrograde neuronal tracer Fluorogold into the dGIrvs2 demonstrated that the thalamic neurons projecting to the dGIrvs2 were confined in the VPMcvm and the parvicellular part of ventral posterior nucleus. In contrast, WGA-HRP injections into the lingual nerve area of core VPM demonstrated that axon terminals were mainly labeled in the core regions of the primary and secondary somatosensory cortices, which were far from the dGIrvs2. These results suggest that the dGIrvs2 is a specialized cortical region receiving the orofacial proprioceptive inputs. Functional contribution of the revealed JCMSs-VPMcvm-dGIrvs2 pathway to Tourette syndrome is also discussed.
对于来自肌肉的本体感觉信号如何到达大脑皮层等高级脑区，人们知之甚少。我们最近的研究表明，丘脑腹后内侧核（VPM）的一个特定丘脑区域，即尾-腹侧缘（VPMcvm），接收来自大鼠闭口肌梭（JCMS）的本体感觉信号。在这项研究中，我们进一步探讨了 JCMS 对口腔面部的丘脑传入信息如何从丘脑（VPMcvm）传递到大鼠的大脑皮层。将逆行和顺行神经元示踪剂，麦胚凝集素结合辣根过氧化物酶（WGA-HRP）注入 VPMcvm 后，证明丘脑通路主要终止于颗粒岛皮质背侧部一个头尾部较窄的区域，该区域与第二躯体感觉皮质的最头端部分相邻（dGIrvs2）。我们还用电生理学方法证实 dGIrvs2 接收来自 JCMS 的本体感觉输入。为了支持 VPMcvm-dGIrvs2 通路的解剖学证据，将逆行神经元示踪剂 Fluorogold 注入 dGIrvs2 后，证明投射到 dGIrvs2 的丘脑神经元局限于 VPMcvm 和腹后核的小细胞部。相比之下，将 WGA-HRP 注入 VPM 的舌神经区域后，轴突末梢主要标记在初级和次级躯体感觉皮质的核心区域，而这些区域远离 dGIrvs2。这些结果表明，dGIrvs2 是接收口腔本体感觉输入的专门皮质区域。还讨论了所揭示的 JCMS-VPMcvm-dGIrvs2 通路对妥瑞氏综合征的功能贡献。
