Barbaresi P, Bernardi S, Manzoni T
Institute of Human Physiology, University of Ancona, Italy.
J Comp Neurol. 1989 May 15;283(3):355-73. doi: 10.1002/cne.902830305.
The homotopic and heterotopic callosal connections in the forelimb representations of the second (SII) and fourth (SIV) somatic sensory areas of cats were investigated by means of the axonal transport of horseradish peroxidase (HRP) in conjunction with microelectrode recording. The tracer was injected in the electrophysiologically identified hand and/or digit zone of SII (six cats) or SIV (four cats). The homotopic area in the contralateral hemisphere was explored with microelectrodes in five animals (three injected in SII and two in SIV) to map neuronal receptive fields. The aim was to correlate in the same experimental case the topography of labelled callosal neurons with the physiological map of the forelimb. Labelled cells and recording sites were plotted on planar maps reconstructed with the aid of a computer from serial coronal sections from the anterior ectosylvian gyrus. After SII injections, labelled callosal neurons were observed throughout the forelimb representation in the contralateral area, but in the tangential plane their distribution was uneven. Each somatotopic zone composing the forelimb map, that is, the arm, hand, and digit zones, contained several subzones in which callosal neurons were either dense or rare. Microelectrode explorations showed that receptive fields mapped from callosal and relatively acallosal subzones representing the same body part were similar in extent and location. After SIV injections, labelled callosal neurons were observed throughout the forelimb and proximal body representation of the contralateral area. Although slight regional variations in the density of labelled cells were apparent, no subzones bare of callosal labelling were observed in SIV. In both SII and SIV, callosal neurons were concentrated mainly in layer III, but a significant number was also evident in the infragranular layers. After HRP injections in the digit zone of SII or SIV, labelled cell bodies were also observed in heterotopic areas of the contralateral hemisphere. Most of these neurons were clustered in the medial bank of the coronal sulcus and in two other heterotopic cortical regions lying, respectively, in the anterior suprasylvian sulcus and in the lateral branch of the ansate sulcus. Some callosal cells interconnecting SII and SIV were also labelled. The results show that the distal forelimb zones in SII and SIV are callosally connected with the respective homotopic zones and with several somatosensory fields located heterotopically in the contralateral hemisphere.
采用辣根过氧化物酶（HRP）轴突运输结合微电极记录的方法，研究了猫的第二躯体感觉区（SII）和第四躯体感觉区（SIV）前肢代表区的同侧和异侧胼胝体连接。将示踪剂注入电生理确定的SII（6只猫）或SIV（4只猫）的手部和/或手指区。在5只动物中用微电极探索对侧半球的同侧区域（3只注射于SII，2只注射于SIV），以绘制神经元感受野。目的是在同一实验病例中将标记的胼胝体神经元的地形图与前肢的生理图谱相关联。将标记细胞和记录位点绘制在借助计算机从外侧前回的系列冠状切片重建的平面图谱上。在SII注射后，在对侧区域的整个前肢代表区观察到标记的胼胝体神经元，但在切线平面上它们的分布不均匀。构成前肢图谱的每个体素区，即臂区、手区和手指区，都包含几个亚区，其中胼胝体神经元要么密集要么稀少。微电极探索表明，从代表同一身体部位的胼胝体和相对无胼胝体的亚区绘制的感受野在范围和位置上相似。在SIV注射后，在对侧区域的整个前肢和近端身体代表区观察到标记的胼胝体神经元。尽管标记细胞密度存在轻微的区域差异，但在SIV中未观察到无胼胝体标记的亚区。在SII和SIV中，胼胝体神经元主要集中在III层，但在颗粒下层也有相当数量的神经元。在SII或SIV的手指区注射HRP后，在对侧半球的异位区域也观察到标记的细胞体。这些神经元大多聚集在冠状沟的内侧壁以及分别位于前上薛氏沟和袢状沟外侧支的另外两个异位皮质区域。一些连接SII和SIV的胼胝体细胞也被标记。结果表明，SII和SIV中的前肢远端区与各自的同侧区以及对侧半球中异位定位的几个躯体感觉区胼胝体相连。
