Barbaresi P, Minelli A, Manzoni T
Institute of Human Physiology, University of Ancona, Italy.
Neuroscience. 1992;46(1):149-63. doi: 10.1016/0306-4522(92)90014-s.
The thalamic connections of the second somatosensory area in the anterior ectosylvian gyrus of cats have been investigated using the retrograde tracer horseradish peroxidase and the anterograde tracer Phaseolus vulgaris leucoagglutinin. Horseradish peroxidase was injected iontophoretically in several somatotopic zones of the second somatosensory area map of six cats. Sites of horseradish peroxidase delivery were identified preliminarily by recording with microelectrodes the responses of neurons to skin stimulation. Phaseolus vulgaris leucoagglutinin was iontophoretically injected within the ventrobasal complex (one cat) or in the posterior complex (one cat). Horseradish peroxidase injections into cytoarchitectonic area SII retrogradely labeled neurons in the ipsilateral ventrobasal complex and in the posterior complex. Counts of labeled neurons from the ipsilateral thalamus showed that the overwhelming majority of horseradish peroxidase-labeled neurons were in the ventrobasal complex (96.3-96.9%) and few were in the posterior complex (3.1-3.7%). Neurons labeled in the ventrobasal complex were observed throughout the anteroposterior extent of the nucleus, while their mediolateral distribution varied with the site of horseradish peroxidase delivery in the body map of the second somatosensory area, which indicates that the projections from the ventrobasal complex to the second somatosensory area are somatotopically organized. In the cat in which the horseradish peroxidase injection involved both the second somatosensory area proper and the second somatosensory area medial, which lies in the lower bank of suprasylvian sulcus, labeled neurons were almost as numerous in the ventrobasal complex as in the posterior complex. Phaseolus vulgaris leucoagglutinin injected in the ventrobasal complex anterogradely labeled thalamocortical fibers in the ipsilateral anterior ectosylvian gyrus. In this case, patches of labeled fibers and terminals were distributed exclusively within the cytoarchitectonic borders of the second somatosensory area proper. Labeled terminals were numerous in layer IV and lower layer III, but terminal boutons and fibers with axonal swellings, probably forming synapses en passant, were frequently observed also in layers VI and I. Injection of Phaseolus vulgaris leucoagglutinin in the posterior complex labeled thalamocortical fibers in two distinct regions in the ipsilateral anterior ectosylvian gyrus, one lying laterally and the other medially, which correspond, respectively, to the fourth somatosensory area and the second somatosensory area medial. In both areas the densest plexus of labeled fibers and axon terminals was in layer IV and lower layer III, but numerous labeled fibers and terminals were also observed in layer I. In this case, only rare fragments of labeled fibers were present in second somatosensory area proper, but no labeled terminals could be observed.
利用逆行示踪剂辣根过氧化物酶和顺行示踪剂菜豆凝集素，对猫前外侧薛氏回中第二体感区的丘脑连接进行了研究。在6只猫的第二体感区图谱的几个躯体定位区，通过离子电渗法注射辣根过氧化物酶。通过用微电极记录神经元对皮肤刺激的反应，初步确定了辣根过氧化物酶的注射部位。在腹侧基底复合体（1只猫）或后复合体（1只猫）内通过离子电渗法注射菜豆凝集素。向细胞构筑区SII注射辣根过氧化物酶，可逆行标记同侧腹侧基底复合体和后复合体内的神经元。对同侧丘脑标记神经元的计数表明，绝大多数辣根过氧化物酶标记的神经元位于腹侧基底复合体（96.3% - 96.9%），少数位于后复合体（3.1% - 3.7%）。在腹侧基底复合体整个前后范围内均观察到标记神经元，但其内外侧分布随第二体感区体表图谱中辣根过氧化物酶注射部位的不同而变化，这表明从腹侧基底复合体到第二体感区的投射是躯体定位组织的。在那只辣根过氧化物酶注射涉及第二体感区本身和位于上薛氏沟下壁的第二体感区内侧的猫中，腹侧基底复合体中的标记神经元数量几乎与后复合体中的一样多。向腹侧基底复合体注射菜豆凝集素，可顺行标记同侧前外侧薛氏回中的丘脑皮质纤维。在这种情况下，标记纤维和终末的斑块仅分布在第二体感区本身的细胞构筑边界内。标记终末在IV层和III层下部较多，但在VI层和I层也经常观察到可能形成旁突触的终末小体和有轴突膨大的纤维。向后复合体注射菜豆凝集素，可在同侧前外侧薛氏回的两个不同区域标记丘脑皮质纤维，一个位于外侧，另一个位于内侧，分别对应于第四体感区和第二体感区内侧。在这两个区域，标记纤维和轴突终末最密集的丛位于IV层和III层下部，但在I层也观察到大量标记纤维和终末。在这种情况下，在第二体感区本身仅存在罕见的标记纤维片段，但未观察到标记终末。
