Rouiller E M, Moret V, Liang F
Institute of Physiology, University of Fribourg, Switzerland.
Somatosens Mot Res. 1993;10(3):269-89. doi: 10.3109/08990229309028837.
The existence of multiple motor cortical areas that differ in some of their properties is well known in primates, but is less clear in the rat. The present study addressed this question from the point of view of connectional properties by comparing the afferent and efferent projections of the caudal forelimb area (CFA), considered to be the equivalent of the forelimb area of the primary motor cortex (MI), and a second forelimb motor representation, the rostral forelimb area (RFA). As a result of various tracing experiments (including double labeling), it was observed that CFA and RFA had reciprocal corticocortical connections characterized by preferential, asymmetrical, laminar distribution, indicating that RFA may occupy a different hierarchical level than CFA, according to criteria previously discussed in the visual cortex of primates. Furthermore, it was found that RFA, but not CFA, exhibited dense reciprocal connections with the insular cortex. With respect to their efferent projection to the basal ganglia, it was observed that CFA projected very densely to the lateral portion of the ipsilateral caudate putamen, whereas the contralateral projection was sparse and more restricted. The ipsilateral projection originating from RFA was slightly less dense than that from CFA, but it covered a larger portion of the caudate putamen (in the medial direction); the contralateral projection from RFA to the caudate putamen was of the same density and extent as the ipsilateral projection. The reciprocal thalamocortical and corticothalamic connections of RFA and CFA differed from each other in the sense that CFA was mainly interconnected with the ventrolateral thalamic nucleus, while RFA was mainly connected with the ventromedial thalamic nucleus. Altogether, these connectional differences, compared with the pattern of organization of the motor cortical areas in primates, suggest that RFA in the rat may well be an equivalent of the premotor or supplementary motor area. In contrast to the corticocortical, corticostriatal, and thalamocortical connections, RFA and CFA showed similar efferent projections to the subthalamic nucleus, substantia nigra, red nucleus, tectum, pontine nuclei, inferior olive, and spinal cord.
在灵长类动物中，多个运动皮层区域在某些特性上存在差异，这是众所周知的，但在大鼠中情况不太清楚。本研究从连接特性的角度探讨了这个问题，通过比较被认为相当于初级运动皮层（MI）前肢区域的尾侧前肢区（CFA）和第二个前肢运动代表区——嘴侧前肢区（RFA）的传入和传出投射。通过各种示踪实验（包括双重标记），观察到CFA和RFA具有相互的皮质皮质连接，其特征是优先、不对称、分层分布，这表明根据先前在灵长类动物视觉皮层中讨论的标准，RFA可能占据与CFA不同的层级水平。此外，发现RFA与岛叶皮层表现出密集的相互连接，而CFA则没有。关于它们向基底神经节的传出投射，观察到CFA非常密集地投射到同侧尾状壳核的外侧部分，而对侧投射稀疏且范围更受限。源自RFA的同侧投射比来自CFA的同侧投射密度略低，但它覆盖了尾状壳核更大的部分（在内侧方向）；RFA到尾状壳核的对侧投射与同侧投射具有相同的密度和范围。RFA和CFA的相互丘脑皮质和皮质丘脑连接彼此不同，因为CFA主要与腹外侧丘脑核相互连接，而RFA主要与腹内侧丘脑核连接。总的来说，与灵长类动物运动皮层区域的组织模式相比，这些连接差异表明大鼠中的RFA很可能相当于运动前区或辅助运动区。与皮质皮质、皮质纹状体和丘脑皮质连接不同，RFA和CFA向丘脑底核、黑质、红核、顶盖、脑桥核、下橄榄核和脊髓显示出相似的传出投射。
