Négyessy L, Hámori J, Bentivoglio M
Department of Anatomy, Semmelweis University Medical School, Budapest, Hungary.
Neuroscience. 1998 Jun;84(3):741-53. doi: 10.1016/s0306-4522(97)00559-9.
The origin of the corticothalamic projections to the contralateral mediodorsal nucleus, the collateralization of cortical fibers and their synaptic organization in the ipsi- and contralateral mediodorsal nuclei were investigated in adult rats with double retrograde fluorescent and anterograde tracing. After tracer injections in the mediodorsal nuclei on either side, neurons were retrogradely labeled in all the areas of the contralateral prefrontal cortex in which ipsilateral labeling was also observed. Contralateral corticothalamic cells accounted for 15% of the labeled neurons in the orbital and agranular insular areas, while their proportion was lower (3%) in the anterior cingulate cortex. Up to 70% of the contralateral cortical neurons were double labeled by bilateral injections in the mediodorsal nuclei. At the electron microscopic level, unilateral injections of biotinylated dextran-amine in the orbitofrontal cortex resulted in anterograde labeling of small terminals and a few large boutons in the ipsilateral mediodorsal nucleus, while only small boutons were identified contralaterally. The diameter of postsynaptic dendritic profiles contacted by labeled small cortical endings was significantly larger in the ipsilateral mediodorsal nucleus than contralaterally. These findings demonstrate that dense contralateral cortical projections to the mediodorsal nucleus derive from the orbital and agranular insular areas, and that crossed corticothalamic afferents are mostly formed by collaterals of the ipsilateral connections. Our observations also point out the heterogeneity of corticothalamic boutons in the rat mediodorsal nucleus and morphological differences in the synaptic organization of prefrontal fibers innervating the two sides, indicating that ipsilateral cortical afferents may be more proximally distributed than crossed cortical fibers on dendrites of mediodorsal neurons.
采用双逆行荧光和顺行追踪技术，在成年大鼠中研究了投射至对侧背内侧核的皮质丘脑投射的起源、皮质纤维的侧支化及其在同侧和对侧背内侧核中的突触组织。在双侧背内侧核注射示踪剂后，在对侧前额叶皮质的所有区域均观察到逆行标记的神经元，同时也观察到同侧标记。对侧皮质丘脑细胞在眶额和无颗粒岛叶区域的标记神经元中占15%，而在前扣带回皮质中其比例较低（3%）。高达70%的对侧皮质神经元通过双侧注射背内侧核而被双重标记。在电子显微镜水平上，在眶额叶皮质单侧注射生物素化葡聚糖胺，导致同侧背内侧核中小终末和少数大终扣的顺行标记，而对侧仅识别出小终扣。与标记的小皮质终末接触的突触后树突轮廓的直径在同侧背内侧核中明显大于对侧。这些发现表明，投射至背内侧核的密集对侧皮质投射源自眶额和无颗粒岛叶区域，并且交叉的皮质丘脑传入纤维主要由同侧连接的侧支形成。我们的观察结果还指出了大鼠背内侧核中皮质丘脑终扣的异质性以及支配两侧的前额叶纤维突触组织的形态学差异，表明同侧皮质传入纤维在背内侧神经元树突上的分布可能比交叉的皮质纤维更靠近近端。
