黒質の樹状突起の分布について

THE DENDRITIC ARBORIZATION OF THE SUBSTANTIA NIGRA

I．はじめに

　人をふくむ哺乳類の黒質の細胞構築については古くより多くの研究があり，ことにBauer^2），Sano^24），Hassler^11）Olszewski^20）らは主としてニッスル法によつて精細な記載を行なっている。しかしニューロン間の興奮の授受にあたつて重要な役割をはたすと考えられている樹状突起についてはCajal^3），Foix et Nicolsco^9）などのごく少数の人々が言及しているに過ぎない。

　他方黒質の線維結合についてもFerraro^8），Ranson^21），Mettler^17），Ogawa^18），Carpenter^4），Rinvik^23），Faull^7）をはじめ多くの業績があるが，そのいずれにおいても樹状突起の存在はほとんど完全に黙過されてきた。黒質は錐体外路系の一中枢と目され，また，大脳脚と内側毛帯の間に介在し，その線維結合は当然多彩なことが予想される。したがつて，その解明については大きな考慮が払われなければならないと思う。

1. The caudal half of the red nucleus in man is surrounded by the " Formation grise cupuliforme peri-retrorublique de Foix et Nicolesco " which con-sists of the neuromelanin containing nerve cells concentrated especially in the ventro-medial and para-raphal area of the midbrain reticular formation (Fig. 1). According to the results of our cytoarchi-tectonic study showing that these cells are in close proximity to the substantia nigra and there is the similarity of the morphological characteristics be-tween them and those of the substantia nigra, they can be considered as a tegmental continuation of the substantia nigra. The topographical and cyto-logical relation of these cells to those of the substan-tia nigra is almost the same in the cat, though the cat cells do not contain apparently any neuromelanin granules. Therefore, the substantia nigra should be regarded as having a considerably greater extent than is usually described in man and in the cat (Fig. 2).

2. The dendritic arborization of the substantia nigra as so defined was studied by means of serial transverse or sagittal sections of numerous kittens stained in all cases by the Golgi-Cox method. Pano-ramic mantages of microphotographs were used to trace precisely the courses of the dendrites. At the point of the dendritic arborization. the substantia nigra belongs to the " open nucleus " (Mannen). Its dendrites which are 400 or 500 microns long on the average, interlace each other in the interior of the nucleus, and at the same time they enter the neigh-bouring structures, ventral part of the midbrain reticular formation, medial lemniscus, decussating fibers of the superior cerebellar peduncle and cereb-ral peduncle (Fig. 3). Reciprocally, the dorsal half of the substantia nigra is covered by the dendrites of the reticular formation core (Fig. 4). In regard to the disposition of the dendrites, the majority of the dendrites of nigra cells extend in a plane per- pendicular to the vertical axis of the brain stem and in the lemniscal area, they course from dorso-medial to ventrolateral through the medial lemniscus (Fig. 3).

3. Finally, it is important to establish that these extrafocal dendrites act as a receptive surface of the substantia nigra. Due to the results obtained by Golgi-stained materials that the dendrites found in the cerebral peduncle are exclusively of nigral origin, the cerebral peduncle of kittens was in-vestigated electromicroscopically to find the synaptic relation of such extrafocal dendrites. Our observa-tions revealed that the total surface of unknown origin (Fig. 5). This fact suggests that all extra-focal dendrites found in other parts are also effec-tive as a receptive surface of the substantia nigra.