Veinante Pierre, Deschênes Martin
UMR 7519 CNRS/ULP, Neurophysiologie Cellulaire et intégrée, 67084 Strasbourg Cedex, France.
J Comp Neurol. 2003 Sep 8;464(1):98-103. doi: 10.1002/cne.10769.
In freely moving rats, whisking is associated with a slow modulation of neuronal excitability in the primary somatosensory cortex. Because it persists after the blockade of vibrissa input, it was suggested that the slow modulation might be mediated by motor-sensory corticocortical connections and perhaps result from the corollary discharges of corticofugal cells. In the present study, we identified motor cortical cells that project to the barrel field and reconstructed their axonal projections after juxtacellularly staining single cells with a biotinylated tracer. On the basis of the final destination of main axons, two groups of neurons contribute to motor-sensory projections: callosal cells (87.5%) and corticofugal cells (12.5%). Axon collaterals of callosal cells arborize in layers five to six of the granular and dysgranular zones and give off several branches that ascend between the barrels to ramify in the molecular layer. In contrast, the axon collaterals of corticofugal cells do not ramify in the infragranular layers but in layer 1. The origin of the majority of motor sensory projections from callosally projecting cells does not support the notion that the slow modulation results from the corollary discharges of corticofugal axons. It would rather originate from a separate population of cells, which could output the slow signal to the barrel field in parallel with the corticofugal commands to a brainstem pattern generator. As free whisking is characterized by bilateral concerted movements of the vibrissae, the transcallosal contribution of motor-sensory axons represents a substrate for synchronizing the slow modulation across both hemispheres.
在自由活动的大鼠中，胡须运动与初级躯体感觉皮层中神经元兴奋性的缓慢调节有关。由于在阻断触须输入后这种调节仍持续存在，有人提出这种缓慢调节可能是由运动-感觉皮质-皮质连接介导的，并且可能源于皮质离心细胞的伴随放电。在本研究中，我们识别出投射到桶状区的运动皮层细胞，并用生物素化示踪剂对单个细胞进行细胞旁染色后重建了它们的轴突投射。根据主要轴突的最终目的地，有两组神经元参与运动-感觉投射：胼胝体细胞（87.5%）和皮质离心细胞（12.5%）。胼胝体细胞的轴突侧支在颗粒状和颗粒减少区的第五至六层形成分支，并发出几条分支，这些分支在桶间上升并在分子层分支。相比之下，皮质离心细胞的轴突侧支不在颗粒下层分支，而是在第一层分支。大多数来自胼胝体投射细胞的运动感觉投射的起源并不支持缓慢调节是由皮质离心轴突伴发放电导致的这一观点。它更可能起源于一个单独的细胞群，该细胞群可以在向脑干模式发生器发出皮质离心指令的同时，将缓慢信号输出到桶状区。由于自由胡须运动的特征是触须的双侧协同运动，运动-感觉轴突的胼胝体投射为跨半球同步缓慢调节提供了一个基础。
