May P J, Sun W, Hall W C
Department of Anatomy, University of Mississippi Medical Center, Jackson 39216, USA.
Neuroscience. 1997 Apr;77(4):1091-114. doi: 10.1016/s0306-4522(96)00535-0.
The goal of the present experiments was to examine the relationships of the zona incerta with two structures associated with visuomotor behavior, the superior colliculus and pretectum. The experiments were carried out in the cat, a species commonly used in studies of visuomotor integration, and utilized wheat germ agglutinin horseradish peroxidase and biocytin as retrograde and anterograde neuronal tracers. Retrograde axonal transport demonstrated that most cells in the ventral subdivision of the zona incerta project to the superior colliculus. Anterograde tracers demonstrated that the incertotectal terminal field is most dense in the intermediate gray layer, which is the primary source of the descending pathway from the superior colliculus to brainstem gaze centers. Further experiments showed that scattered cells within the intermediate gray layer give rise to a reciprocal pathway that terminates in both the dorsal and ventral subdivisions of the zona incerta. The distribution of both labeled incertotectal cells and tectoincertal terminals extends dorsolateral to the zona incerta proper, between the reticular thalamic nucleus and the external medullary lamina. Electron microscopic examination of labeled tectoincertal terminals demonstrated that they contain mainly spherical vesicles and have slightly asymmetric to symmetric synaptic densities. Labeled terminals were observed contacting labeled cells in the zona incerta, suggesting that the reciprocal pathway may be monosynaptic. The zona incerta is also reciprocally interconnected with the pretectum. The anterior pretectal nucleus provides a dense projection to the ventral part of the zona incerta and receives a sparse reciprocal projection. The posterior pretectal nucleus and nucleus of the optic tract may also project to the zona incerta. The pretectoincertal fibers form terminals that contain primarily spherical vesicles and make distinctly asymmetric synaptic contacts. In summary, these results indicate that the deep layers of the superior colliculus, which are important for controlling saccades, are the target of a projection from the ventral subdivision of the zona incerta. Like the substantia nigra, the zona incerta may play a permissive role in the tectal initiation of saccadic eye movements. The incertotectal terminal field in the cat is less dense than that observed previously in the rat, suggesting species differences in the development of this pathway. An additional finding of this study is that one of the main sources of input to these incertotectal cells is the anterior pretectal nucleus. This pretectal incertal tectal pathway is likely to play a role in the guidance of tectally initiated saccades by somatosensory stimuli.
本实验的目的是研究未定带与两个和视觉运动行为相关的结构，即上丘和顶盖前区之间的关系。实验在猫身上进行，猫是视觉运动整合研究中常用的物种，并使用了小麦胚凝集素辣根过氧化物酶和生物胞素作为逆行和顺行神经元示踪剂。逆行轴突运输显示，未定带腹侧亚区的大多数细胞投射到上丘。顺行示踪剂显示，未定带到上丘的终末场在中间灰质层最为密集，而中间灰质层是从上丘到脑干凝视中枢的下行通路的主要来源。进一步的实验表明，中间灰质层内的散在细胞产生一条双向通路，该通路终止于未定带的背侧和腹侧亚区。标记的未定带到上丘的细胞和上丘到未定带的终末的分布向未定带本身的背外侧延伸，位于丘脑网状核和外髓板之间。对标记的上丘到未定带的终末进行电子显微镜检查发现，它们主要含有球形囊泡，突触密度略不对称至对称。观察到标记的终末与未定带中的标记细胞接触，表明双向通路可能是单突触的。未定带也与顶盖前区相互连接。顶盖前核向前未定带的腹侧部分发出密集投射，并接受稀疏的反向投射。顶盖后核和视束核也可能投射到未定带。顶盖前区到未定带的纤维形成主要含有球形囊泡的终末，并形成明显不对称的突触联系。总之，这些结果表明，对控制扫视运动很重要的上丘深层是未定带腹侧亚区投射的靶区。与黑质一样，未定带可能在由上丘引发的扫视眼运动中起允许作用。猫的未定带到上丘的终末场比先前在大鼠中观察到的要稀疏，表明该通路的发育存在物种差异。本研究的另一个发现是，这些未定带到上丘的细胞的主要输入来源之一是顶盖前核。这条顶盖前区到未定带到上丘的通路可能在体感刺激对上丘引发的扫视运动的引导中起作用。
