School of Psychology, Cardiff University, Wales, UK.
Department of Veterinary and Animal Sciences, University of Copenhagen, Frederiksberg, Denmark.
Eur J Neurosci. 2022 Nov;56(10):5869-5887. doi: 10.1111/ejn.15819. Epub 2022 Sep 23.
As the functional properties of a cortical area partly reflect its thalamic inputs, the present study compared collateral projections arising from various rostral thalamic nuclei that terminate across prefrontal (including anterior cingulate) and retrosplenial areas in the rat brain. Two retrograde tracers, fast blue and cholera toxin B, were injected in pairs to different combinations of cortical areas. The research focused on the individual anterior thalamic nuclei, including the interanteromedial nucleus, nucleus reuniens and the laterodorsal nucleus. Of the principal anterior thalamic nuclei, only the anteromedial nucleus contained neurons reaching both the anterior cingulate cortex and adjacent cortical areas (prefrontal or retrosplenial), though the numbers were modest. For these same cortical pairings (medial prefrontal/anterior cingulate and anterior cingulate/retrosplenial), the interanteromedial nucleus and nucleus reuniens contained slightly higher proportions of bifurcating neurons (up to 11% of labelled cells). A contrasting picture was seen for collaterals reaching different areas within retrosplenial cortex. Here, the anterodorsal nucleus, typically provided the greatest proportion of bifurcating neurons (up to 15% of labelled cells). While individual neurons that terminate in different retrosplenial areas were also found in the other thalamic nuclei, they were infrequent. Consequently, these thalamo-cortical projections predominantly arise from separate populations of neurons with discrete cortical termination zones, consistent with the transmission of segregated information and influence. Overall, two contrasting medial-lateral patterns of collateral projections emerged, with more midline nuclei, for example, nucleus reuniens and the interoanteromedial nucleus innervating prefrontal areas, while more dorsal and lateral anterior thalamic collaterals innervated retrosplenial cortex.
由于皮质区域的功能特性部分反映了其丘脑输入，因此本研究比较了源自各种前丘脑核的侧支投射，这些投射终止于大鼠大脑的前额叶（包括前扣带回）和后扣带回区域。将两种逆行示踪剂，快蓝和霍乱毒素 B，成对注入到皮质区域的不同组合中。研究重点是个别前丘脑核，包括中间前联合核、联合核和外侧背核。在前丘脑核中，只有前内侧核包含到达前扣带回皮质和相邻皮质区域（前额叶或后扣带回）的神经元，尽管数量不大。对于这些相同的皮质配对（内侧前额叶/前扣带回和前扣带回/后扣带回），中间前联合核和联合核包含稍高比例的分叉神经元（多达 11%的标记细胞）。对于到达后扣带回皮质不同区域的侧支，情况则相反。在这里，通常是前背核提供最多比例的分叉神经元（多达 15%的标记细胞）。虽然也在前丘脑核中发现了终止于不同后扣带回区域的单个神经元，但它们很少见。因此，这些丘脑皮质投射主要来自具有离散皮质终止区的不同神经元群体，与分离信息和影响的传递一致。总体而言，出现了两种对比鲜明的内侧-外侧侧支投射模式，例如，更多的中线核，如联合核和中间前联合核，投射到前额叶区域，而更多的背侧和外侧前丘脑侧支投射到后扣带回皮质。
