Vaithiyalingam Chandra Sekaran Nathiya, Deshpande Meena S, Ibrahim Baher A, Xiao Gang, Shinagawa Yoshitaka, Llano Daniel A
Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Champaign, IL, United States.
Beckman Institute for Advanced Science and Technology, Urbana, IL, United States.
Front Syst Neurosci. 2021 Oct 21;15:674098. doi: 10.3389/fnsys.2021.674098. eCollection 2021.
The auditory cortex sends massive projections to the inferior colliculus, but the organization of this pathway is not yet well understood. Previous work has shown that the corticocollicular projection emanates from both layers 5 and 6 of the auditory cortex and that neurons in these layers have different morphological and physiological properties. It is not yet known in the mouse if both layer 5 and layer 6 project bilaterally, nor is it known if the projection patterns differ based on projection location. Using targeted injections of Fluorogold into either the lateral cortex or dorsal cortex of the inferior colliculus, we quantified retrogradely labeled neurons in both the left and right lemniscal regions of the auditory cortex, as delineated using parvalbumin immunostaining. After dorsal cortex injections, we observed that approximately 18-20% of labeled cells were in layer 6 and that this proportion was similar bilaterally. After lateral cortex injections, only ipsilateral cells were observed in the auditory cortex, and they were found in both layer 5 and layer 6. The ratio of layer 5:layer 6 cells after lateral cortex injection was similar to that seen after dorsal cortex injection. Finally, injections of different tracers were made into the two inferior colliculi, and an average of 15-17% of cells in the auditory cortex were double-labeled, and these proportions were similar in layers 5 and 6. These data suggest that (1) only the dorsal cortex of the inferior colliculus receives bilateral projections from the auditory cortex, (2) both the dorsal and lateral cortex of the inferior colliculus receive similar layer 5 and layer 6 auditory cortical input, and (3) a subpopulation of individual neurons in both layers 5 and 6 branch to innervate both dorsal cortices of the inferior colliculus.
听觉皮层向下丘发出大量投射，但该通路的组织情况尚未得到充分了解。先前的研究表明，皮质-下丘投射源自听觉皮层的第5层和第6层，且这些层中的神经元具有不同的形态和生理特性。在小鼠中，目前尚不清楚第5层和第6层是否都进行双侧投射，也不清楚投射模式是否因投射位置而异。我们通过向下丘的外侧皮层或背侧皮层靶向注射荧光金，使用小白蛋白免疫染色来勾勒听觉皮层的左右lemniscal区域，对逆行标记的神经元进行了定量分析。在背侧皮层注射后，我们观察到约18%-20%的标记细胞位于第6层，且双侧比例相似。在外侧皮层注射后，仅在听觉皮层中观察到同侧细胞，且它们在第5层和第6层均有发现。外侧皮层注射后第5层与第6层细胞的比例与背侧皮层注射后相似。最后，将不同的示踪剂注射到两个下丘中，听觉皮层中平均有15%-17%的细胞被双重标记，且这些比例在第5层和第6层中相似。这些数据表明：（1）只有下丘的背侧皮层接受来自听觉皮层的双侧投射；（2）下丘的背侧和外侧皮层都接受相似的第5层和第6层听觉皮层输入；（3）第5层和第6层中的单个神经元亚群分支支配下丘的两个背侧皮层。
