Miller B, Windrem M S, Finlay B L
Department of Psychology, Cornell University, Ithaca, New York 14853.
Cereb Cortex. 1991 May-Jun;1(3):241-61. doi: 10.1093/cercor/1.3.241.
Corticofugal pathways (callosal, intracortical, and subcortical) have initial axon outgrowth to many areas where no adult connections will persist. Corticofugal projections also demonstrate considerable reorganization after early damage. At the level of gross projections from specific thalamic nuclei to cortical cytoarchitectonic areas, early thalamocortical projections appear to show greater specificity for their targets than do corticofugal projections, and their potential for reorganization after early damage is not known. In this article, we explore the nature of the reorganization shown by the thalamocortical system after early thalamic lesions, and contrast it with reorganization of the origin of contralateral visual callosal projections in the same animals. Hamster pups were given electrolytic lesions in the posterior thalamus on the day of birth, damaging principally either the ventrobasal (somatosensory) or the dorsal lateral geniculate (visual) nucleus. After 30 d of age, HRP was implanted in either the somatosensory or the visual cortex, matching the area of implant with the intended thalamic lesion. The thalamus was reconstructed to determine the remaining nuclei, and the distribution of retrogradely labeled cells was plotted. For animals with HRP implants in visual cortex, the location of callosally projecting cells from the contralateral cortex was charted. These animals were compared to a group of normal adult animals with HRP implants approximately matched for size and location. In seven of eight adult animals with neonatal thalamic lesions, the remaining thalamus did not reorganize to innervate the thalamically denervated cortex. In contrast, the callosal projections from the contralateral visual cortex showed a wider tangential origin in the experimental animals compared to the controls. This expanded callosal projection included cells from temporal cortex, a projection not seen in normal animals. Thus, thalamocortical and callosal projection systems differ in both the magnitude and the nature of their reorganization after early damage.
皮质传出通路（胼胝体通路、皮质内通路和皮质下通路）最初轴突向许多区域生长，而这些区域在成年后不会保留连接。早期损伤后，皮质传出投射也会出现相当程度的重组。在从特定丘脑核到皮质细胞构筑区域的大体投射水平上，早期丘脑皮质投射对其靶标的特异性似乎比皮质传出投射更高，且早期损伤后其重组潜力尚不清楚。在本文中，我们探究了早期丘脑损伤后丘脑皮质系统所表现出的重组性质，并将其与同一动物中对侧视觉胼胝体投射起源的重组进行对比。出生当天给仓鼠幼崽在后丘脑进行电解损伤，主要损伤腹侧基底（躯体感觉）核或背外侧膝状体（视觉）核。30日龄后，将辣根过氧化物酶（HRP）植入躯体感觉或视觉皮质，使植入区域与预期的丘脑损伤区域相匹配。对丘脑进行重建以确定剩余核团，并绘制逆行标记细胞的分布。对于HRP植入视觉皮质的动物，绘制对侧皮质胼胝体投射细胞的位置。将这些动物与一组大小和位置大致匹配的正常成年HRP植入动物进行比较。在8只患有新生儿期丘脑损伤的成年动物中，有7只剩余丘脑未重组以支配丘脑去神经支配的皮质。相比之下，与对照组相比，实验动物中来自对侧视觉皮质的胼胝体投射显示出更广泛的切线起源。这种扩大的胼胝体投射包括来自颞叶皮质的细胞，这是正常动物中未见到的投射。因此，早期损伤后丘脑皮质和胼胝体投射系统在重组的程度和性质上均有所不同。
