Frappé I, Roger M, Gaillard A
UMR 6558, Département des Neurosciences, Laboratoire de Neurophysiologie, Faculté des Sciences, Université de Poitiers, France.
Neuroscience. 1999 Mar;89(2):409-21. doi: 10.1016/s0306-4522(98)00379-0.
A number of molecular and hodological experiments have provided evidence that there is an early commitment of neocortical neurons to express features unique to a certain cortical area. However, the findings of several transplantation experiments have indicated that late embryonic cortical tissue heterotopically grafted into the neocortex of newborn rats receives a set of thalamic projections appropriate for the host cortical locus within which it develops. To provide further information on the extent to which neocortical neurons are predetermined to develop area-specific systems of connections, in this study we have compared the pattern of thalamic afferents to grafts of embryonic day 16 occipital or frontal neocortex transplanted into the occipital cortex of newborn rats. Two months after grafting, a retrograde neurotracer (cholera toxin, subunit b) was injected into the grafts to precisely assess the number of cells in the visual- and/or motor-related nuclei of the host thalamus projecting to each category of transplants (occipital-to-occipital or frontal-to-occipital). Transplants of embryonic occipital cortex received significant input from several visual-related thalamic nuclei, i.e. the lateral posterior and lateral dorsal nuclei, and no input from motor-related thalamic nuclei. However, only few labeled cells were found in the dorsal lateral geniculate nucleus, which was systematically affected by a severe atrophy, probably in response to the lesion of the occipital cortex performed prior to the transplantation. By comparison, transplants of frontal origin received a substantial input from the ventrolateral and ventromedial thalamic nuclei, which normally project to the frontal cortex, but received a weak input from the lateral posterior and lateral dorsal nuclei. Neocortical neurons grafted heterotopically into the neocortex of newborn hosts are not only able to contact cortical and subcortical targets appropriate for their embryonic site of origin, but are also susceptible to derive thalamic inputs closely related to their embryonic origin.
大量分子和组织学实验已提供证据表明，新皮质神经元在早期就倾向于表达特定皮质区域特有的特征。然而，一些移植实验的结果表明，将胚胎晚期皮质组织异位移植到新生大鼠的新皮质中，它会在其发育所在的宿主皮质位点接受一组适合该位点的丘脑投射。为了进一步了解新皮质神经元在多大程度上预先注定会发育出区域特异性的连接系统，在本研究中，我们比较了移植到新生大鼠枕叶皮质的胚胎第16天枕叶或额叶新皮质移植体的丘脑传入模式。移植两个月后，将逆行神经示踪剂（霍乱毒素B亚基）注入移植体，以精确评估宿主丘脑视觉和/或运动相关核中投射到每种移植类型（枕叶到枕叶或额叶到枕叶）的细胞数量。胚胎枕叶皮质移植体从几个视觉相关的丘脑核，即外侧后核和外侧背核，接受了大量输入，而没有从运动相关的丘脑核接受输入。然而，在外侧膝状体背核中仅发现少量标记细胞，该核受到严重萎缩的系统性影响，这可能是对移植前进行的枕叶皮质损伤的反应。相比之下，额叶来源的移植体从腹外侧和腹内侧丘脑核接受了大量输入，这些核通常投射到额叶皮质，但从外侧后核和外侧背核接受的输入较弱。异位移植到新生宿主新皮质中的新皮质神经元不仅能够与适合其胚胎起源部位的皮质和皮质下靶点建立联系，而且还容易获得与其胚胎起源密切相关的丘脑输入。
