Hikosaka O
Rinsho Shinkeigaku. 1989 Dec;29(12):1515-8.
Saccadic eye movement is controlled by a midbrain structure, superior colliculus (SC). Cells in its intermediate layer show a burst of spikes before saccades to the contralateral disc. A major input to the SC comes from the substantia nigra pars reticulata (SNr). SNr cells are characterized by their high frequency tonic discharge. Many of them stop discharging before a contralateral saccade only when the saccade is made intentionally. The mirror image-like relationship between the SNr and the SC suggests that the nigro-collicular connection is inhibitory. To determine whether the nigro-collicular inhibition is necessary for normal eye movements, we injected a small amount of GABA-related substances into the SC or the SNr. Following injection of muscimol (GABA agonist) into the SC, contralateral saccades became delayed, hypometric and slower; the monkey finally became unable to make saccades. This result indicated that the SC is crucial for normal saccades and that SC cells have ample GABA receptors. Following injection of bicuculline (GABA antagonist), irrepressible saccades occurred repeatedly to the contralateral side, suggesting that SC cells are under tonic inhibition which is mediated by GABA. Similar involuntary saccades were induced by injection of muscimol into the SNr. This suggested that the SNr is the origin of the GABAergic tonic inhibition. These results suggested that the basal ganglia control the initiation of saccadic eye movement by changing the level of the nigro-collicular inhibition.
扫视眼动由中脑结构上丘（SC）控制。其中间层的细胞在向对侧视野区进行扫视之前会出现一阵动作电位发放。上丘的一个主要输入来自黑质网状部（SNr）。SNr细胞的特征是高频紧张性放电。其中许多细胞仅在有意进行对侧扫视时，才会在对侧扫视之前停止放电。SNr与SC之间镜像般的关系表明黑质-上丘连接是抑制性的。为了确定黑质-上丘抑制对于正常眼动是否必要，我们将少量GABA相关物质注入上丘或SNr。向SC注射蝇蕈醇（GABA激动剂）后，对侧扫视变得延迟、幅度减小且速度减慢；猴子最终无法进行扫视。这一结果表明上丘对于正常扫视至关重要，且上丘细胞有丰富的GABA受体。注射荷包牡丹碱（GABA拮抗剂）后，对侧反复出现无法抑制的扫视动作，提示上丘细胞受到由GABA介导的紧张性抑制。向SNr注射蝇蕈醇也诱导出类似的不自主扫视。这表明SNr是GABA能紧张性抑制的起源。这些结果提示基底神经节通过改变黑质-上丘抑制水平来控制扫视眼动的起始。
