Zarzecki P
Department of Physiology, Queen's University, Kingston, Ontario, Canada.
Somatosens Mot Res. 1991;8(4):313-25. doi: 10.3109/08990229109144755.
Motor cortex neurons were identified antidromically in anesthetized cats by their axonal projections to one of six targets: (1) somatosensory cortex, (2) opposite motor cortex, (3) red nucleus, (4) lateral reticular nucleus, (5) spinal cord, and (6) ventrolateral thalamus. Three inputs to motor cortex were tested for their influences on the identified cortical efferent neurons. The tested inputs originated from ipsilateral somatosensory cortex, opposite motor cortex, and ventral thalamus. Subthreshold effects of input pathways were detected by monitoring latency variations of antidromic responses. The three afferent sources, when activated by electrical stimulation, were not equally effective on motor cortex neurons. Ipsilateral corticocortical and thalamocortical excitation were found for the majority of neurons; the influenced proportions ranged from 55% to 100%, according to the target of the output neurons. Effects from the opposite hemisphere were found for only 5% to 30% of the neurons in the same projection classes. Many neurons (36 of 81, or 44%) were excited from more than one source, but few (5 of 37, or 14%) were influenced by all three possible sources of input, even in small regions of cortex innervated by all three of the inputs. Among 19 electrode tracks where all three inputs were present, there were only 2 tracks where all the neurons shared the same combination of inputs. Even for neurons in closest anatomical proximity ("clusters"), it was unusual (only 7 of 25 clusters) for all the neurons to have the same input pattern. Among the seven clusters where all the neurons shared the same input pattern, five of the clusters projected to the same target. These variable combinations of inputs to motor cortex neurons support the conclusion that efferent neurons could be recruited selectively from separate cortical layers or from within clusters of nearby neurons, according to the target of their axonal projection.
在麻醉猫中，通过轴突投射至六个目标之一来逆向鉴定运动皮层神经元：(1) 躯体感觉皮层，(2) 对侧运动皮层，(3) 红核，(4) 外侧网状核，(5) 脊髓，以及(6) 腹外侧丘脑。测试了运动皮层的三种输入对鉴定出的皮层传出神经元的影响。测试的输入源自同侧躯体感觉皮层、对侧运动皮层和腹侧丘脑。通过监测逆向反应的潜伏期变化来检测输入通路的阈下效应。当通过电刺激激活时，这三种传入源对运动皮层神经元的作用并不相同。发现大多数神经元存在同侧皮质 - 皮质和丘脑 - 皮质兴奋；根据输出神经元的目标，受影响的比例在55%至100%之间。在相同投射类别的神经元中，仅5%至30%的神经元发现有来自对侧半球的效应。许多神经元（81个中的36个，即44%）受到不止一个源的兴奋，但很少有神经元（37个中的5个，即14%）受到所有三种可能输入源的影响，即使在由所有三种输入支配的小皮层区域也是如此。在所有三种输入都存在的19条电极轨迹中，只有2条轨迹上所有神经元共享相同的输入组合。即使对于解剖位置最接近的神经元（“簇”），所有神经元具有相同输入模式的情况也不常见（25个簇中只有7个）。在所有神经元共享相同输入模式的七个簇中，有五个簇投射至相同目标。运动皮层神经元输入的这些可变组合支持这样的结论，即传出神经元可根据其轴突投射的目标，从不同的皮层层或附近神经元簇中被选择性地募集。
