Land P W, Buffer S A, Yaskosky J D
Department of Neurobiology, University of Pittsburgh School of Medicine, Pennsylvania 15261, USA.
J Comp Neurol. 1995 May 15;355(4):573-88. doi: 10.1002/cne.903550407.
Histochemical staining for cytochrome oxidase (CO) and axonal transport of horseradish peroxidase (HRP) were used to investigate thalamocortical connections in the vibrissa-barrel system of adult rats. CO staining revealed that the medial division of the ventrobasal thalamic nucleus (VBm) consists of intensely stained rod-like configurations, containing thalamocortical projection neurons and intervening neuropil, separated by lighter-stained septa. CO-dark rods span the thickness of VBm, are arranged in a pattern of rows and arcs that resembles the distribution of vibrissae on the mystacial pad, and are similar to the cytoarchitectonic structures termed "barreloids" in the mouse thalamus. Based upon the dimensions of CO-dark structures and the numerical density of neurons in VBm we estimated that a barreloid in the rat may contain 250-300 neurons. HRP injections into lamina IV of the somatosensory cortex led to retrograde labeling of neurons within one or more barreloids. When injections were centered within the CO-dark hollows of cortical barrels about 95% of retrogradely labeled neurons were located in the barreloid that is isomorphic to the injected barrel; up to 5% of labeled neurons were located within a single adjacent barreloid. Barrel hollow injections that also included a barrel side yielded a larger proportion of labeled neurons in non-isomorphic barreloids. Interestingly, such extra-barreloid labeling was topologically consistent in that HRP-labeled neurons were distributed among barreloids that corresponded to cortical barrels nearest the injected barrel side. Injections into the septa between barrels similarly resulted in labeling within barreloids that corresponded to cortical barrels flanking the septal injection site. Following lamina IV injections the density of labeled neurons tended to be highest in the ventrolateral one-half to two-thirds of VBm. Retrograde labeling of neurons in the dorsomedial one-third to one-half of VBm was more often observed after HRP injections at the lamina V/VI border. Thus, barreloid neurons may be heterogeneous with respect to their laminar pattern of terminations within the somatosensory cortex. Some HRP injections in the cortex resulted in orthograde labeling of corticothalamic axons in the barreloids. When observed, labeled corticothalamic axons arborized principally within the barreloid isomorphic to the injected barrel column. Indeed, terminal labeling was densest in the vicinity of neurons retrogradely labeled by the same injection.
采用细胞色素氧化酶（CO）组织化学染色和辣根过氧化物酶（HRP）轴突运输法，研究成年大鼠触须 - 桶状系统中的丘脑皮质连接。CO染色显示，腹基底丘脑核内侧部（VBm）由染色强烈的杆状结构组成，包含丘脑皮质投射神经元和其间的神经毡，被染色较浅的间隔分隔。CO阴性杆贯穿VBm的厚度，呈行和弧的模式排列，类似于触须垫上触须的分布，并且与小鼠丘脑中称为“桶状小体”的细胞构筑结构相似。根据CO阴性结构的尺寸和VBm中神经元的数量密度，我们估计大鼠中的一个桶状小体可能包含250 - 300个神经元。将HRP注射到体感皮层IV层导致一个或多个桶状小体内的神经元逆行标记。当注射集中在皮质桶的CO阴性凹陷内时，约95%的逆行标记神经元位于与注射桶同构的桶状小体内；高达5%的标记神经元位于单个相邻的桶状小体内。包括桶侧的桶状凹陷注射在非同构桶状小体中产生了更大比例的标记神经元。有趣的是，这种桶状小体之外的标记在拓扑上是一致的，因为HRP标记的神经元分布在与最靠近注射桶侧的皮质桶相对应的桶状小体之间。向桶间间隔注射同样导致与间隔注射部位两侧的皮质桶相对应的桶状小体内的标记。在IV层注射后，标记神经元的密度在VBm的腹外侧二分之一至三分之二处往往最高。在V/VI层边界注射HRP后，更常观察到VBm背内侧三分之一至二分之一处的神经元逆行标记。因此，桶状小体神经元在体感皮层内的终末层模式可能是异质性的。皮层中的一些HRP注射导致桶状小体内皮质丘脑轴突的顺行标记。当观察到时，标记的皮质丘脑轴突主要在与注射桶柱同构的桶状小体内分支。实际上，终末标记在由同一注射逆行标记的神经元附近最密集。
