Functional anatomy of motor control system of the cortico-basal ganglial-thalamo loop without passing through the cerebral cortex

本研究的主要目的是确定组成顶盖网状脊髓束的SC深层神经元的上行投射模式的特征。用生物素葡聚糖胺(BDA)标记一小群神经元，研究猫上丘(SC)深层单个神经元的上行轴突轨迹。构成背前束的所有SC轴突在交叉前发出1~3支上行支。同侧升支沿吻侧走行，在进入丘脑前，向中央灰质和中脑网状结构发出多条侧支。在中间脑交界处，这些分支开始向背侧和/或腹侧向丘脑投射。根据轴突侧支和终末在丘脑的分布，在连续切片上重建的28个SC神经元被分为3种类型：1)投射到丘脑腹侧(Forel和Incerta区)的神经元(n=10)，2)投射到丘脑背侧(主要是板内核)的神经元(n=4)，3)投射到丘脑腹侧和背侧的神经元(n=14)。我们的数据表明，SC神经元向脊髓、脑干和丘脑传递同样的信息。这些结果表明，单个SC神经元同时控制眼睛、头部和身体的运动，并将它们的信息通过丘脑作为色觉放电发送到大脑皮层和基底节。解剖学研究表明，背前束神经元可能受到广泛的黑质顶盖投射的影响。本研究发现背前束细胞投射到CM-PF复合体，该复合体是丘脑纹状体投射的主要来源。因此，黑质基底节的输出可以通过黑质-顶盖-丘脑-纹状体的投射回传至纹状体。

The main purpose of the present study was to determine the characteristics of ascending projection pattern of neurons in the deep layers of the SC constituting the tecto-reticulospinal tract. We studied ascending axonal trajectories of single neurons in the deep layers of the cat superior colliculus(SC) by labeling a small pool of neurons with biotinylated dextran amine(BDA). All of the SC axons forming the predorsal bundle emitted 1-3 ascending branches before decussation. Ipsilateral ascending branches ran rostrally and gave rise to several collaterals to the central gray and mesencephalic reticular formation before entering the thalamus. At the meso-diencephalic junction, these branches began to run dorsally and/or ventrally towards the thalamus. Based on the distribution of axon collaterals and terminals in the thalamus, 28 SC neurons reconstructed on serial sections were classified into 3 types : 1) neurons projecting to the ventral thalamus (the fields of Forel and zona incerta)(n=10), 2)neurons projecting to the dorsal thalamus (mainly to the intralaminar nuclei) (n=4), and 3)neurons projecting to both the ventral and dorsal thalamus (n=14). Our data indicate that SC neurons convey the same information to the spinal cord, brainstem, and the thalamus. These results suggest that single SC neurons simultaneously control eyes, head and body movements, and also send their information to the cerebral cortex and the basal ganglia via the thalamus as a collorary discharge. Anatomical studies have indicated that predorsal bundle neurons could be influenced by extensive nigrotectal projections. The present study has revealed that predorsal bundle cells projected to the CM-pf complex, which is known as a major source of thalamostriatal projection. Therefore, outputs of the basal ganglia from the substantia nigra could be transmitted by way of the nigrotectal-tectothalamic-thalamostriatal projection back to the striatum.