Liang F Y, Moret V, Wiesendanger M, Rouiller E M
Institute of Physiology, University of Fribourg, Switzerland.
J Comp Neurol. 1991 Sep 15;311(3):356-66. doi: 10.1002/cne.903110306.
In order to investigate the possibility of direct corticomotoneuronal (CM) connections in the rat, an anterograde-retrograde double-labeling method was developed. Phaseolus vulgaris-leucoagglutinin (PHA-L) anterograde tracing of corticospinal axons was combined with retrograde labeling of spinal motoneurons either by a conjugate of choleragen subunit B with horseradish peroxidase (CB-HRP) or by wheat germ agglutinin (WGA). The location of PHA-L injection unilaterally in the forelimb area of sensorimotor cortex and the CB-HRP or WGA injections in corresponding contralateral wrist or digit extensors or flexors were determined and matched on the basis of movement responses elicited by intracortical microstimulation. Light microscopic observation showed, in addition to the main contralateral dorsal corticospinal tract (CST), the presence of four other CST minor components in the contralateral lateral, ipsilateral ventral, and ipsilateral dorsal funiculi of the cervical spinal white matter and at the base of contralateral dorsal horn of the gray matter, respectively. PHA-L-labeled CST axonal arbors were observed from Rexed's lamina I through lamina X of contralateral spinal gray matter, most extensively in laminae VI and VII; some CST axons reached the zone of motoneuronal somata in lamina IX and a few of them also entered the lateral and occasionally the ventral funiculi, ramifying in the white matter. Between the zones of PHA-L-labeled CST axonal arbors on the one hand and CB-HRP/WGA labeled spinal motoneuronal somata with their extensive dendritic trees on the other, there was a large overlap, covering partly both the gray and the white matter. PHA-L-labeled axonal boutons (en passant or terminaux) were seen to contact the dendrites or even the somata of motoneurons in the gray matter, according to light-microscopic criteria for identification of synaptic contacts. Axodendritic CM contacts were occasionally observed in the lateral funiculus of the white matter as well. In general, only a single contact was observed between an individual PHA-L-labeled CST axon and a given retrogradely labeled motoneuron. In contrast to the common notion that direct CM connections are a specialty of primates, the present morphological data support the presence of direct CM connections also in some other mammals, such as the rat.
为了研究大鼠中皮质脊髓运动神经元（CM）直接连接的可能性，开发了一种顺行 - 逆行双重标记方法。将菜豆白细胞凝集素（PHA-L）对皮质脊髓轴突的顺行示踪与通过霍乱毒素B亚基与辣根过氧化物酶（CB-HRP）的共轭物或小麦胚凝集素（WGA）对脊髓运动神经元的逆行标记相结合。根据皮质内微刺激引发的运动反应，确定并匹配PHA-L单侧注射在感觉运动皮质前肢区域的位置以及CB-HRP或WGA在相应对侧腕部或手指伸肌或屈肌中的注射位置。光镜观察显示，除了主要的对侧背侧皮质脊髓束（CST）外，在颈髓白质的对侧外侧、同侧腹侧和同侧背侧索以及灰质对侧背角底部还分别存在其他四个CST次要成分。在对侧脊髓灰质从雷克斯德板层I到板层X观察到PHA-L标记的CST轴突分支，在板层VI和VII中最为广泛；一些CST轴突到达板层IX中运动神经元胞体区域，其中一些还进入外侧索，偶尔进入腹侧索，并在白质中分支。一方面是PHA-L标记的CST轴突分支区域，另一方面是CB-HRP/WGA标记的脊髓运动神经元胞体及其广泛的树突区域，两者之间有很大的重叠，部分覆盖了灰质和白质。根据用于识别突触接触的光镜标准，可见PHA-L标记的轴突终扣（过路或终末）与灰质中运动神经元的树突甚至胞体接触。在白质的外侧索中偶尔也观察到轴突 - 树突CM接触。一般来说，在单个PHA-L标记的CST轴突与给定的逆行标记运动神经元之间仅观察到单个接触。与直接CM连接是灵长类动物特有的这一普遍观念相反，目前的形态学数据支持在一些其他哺乳动物如大鼠中也存在直接CM连接。
