By the cytological study on the neurosecretory cell of supraoptic and paraventricular nuclei in the normal dog with special reference to the relation of the secretory material to cytorganelles and NISSL substance, and following findings were obtained.
1. The most frequently observed form of the neurosecretory cell is a multipolar one, while the bipolar and unipolar cells are rather rare.
2. A few binucleate cells and several cells which show a colloidal inclosed body in the cell nucleus, which are suggestive of an amitosis and of a nuclear secretion respectively, were observed, but their significances could not be confirmed.
3. The most frequently observed form of mitochondria of the neurosecretory cell is rod-like, next, granular, and the filamentous form is exceptional. These mitochondria are often gathered near the nucleus, and in the other areas of the cytoplasm they are scattered evenly, exclusive of the NISSLarea.
4. The GOLGI-apparatus makes a complete or an incomplete network around the nucleus. The network is relatively well developed in the area of the cytoplasm opposite to the nucleus, which usually takes a more or less excentric situation.
5. In the dog too, the neurosecretory material is divided, according to its forms and the affinities to dyes, into three types-irregularly formed fine granules, spherical granules and irregularly formed larger masses.
6. By double- or re-staining methods, the relation of the neurosecretion findings to the forms, amounts, and situations of mitochondria and of GOLGI-apparatus has been studied, but no definite result could be obtained. But, as the fine granules are most frequently observed in the cytoplasmic area near the nucleus where usually many mitochondria and a well-developed GOLGI-apparatus are found, it is presumed that mitochondria, with their enzym system, and GOLGI-apparatus, with its chemical components, might have intimate relations to the production of the secretory material.
7. Near infundibulum in pars ventromedialis of supraoptic nucleus, several cells which have a deeply stained, pycnotic nucleus are frequently observed. Such a cell is considered to be degenerating, also by the form of nucleus and the findings of mitochondria. As, on the other hand, such a cell is stained by CHP method as a mass of gomoriphil substance, the occurrence of holocrine secretion as a mode of neurosecretion is presumable.
8. The NISSL substance of a neurosecretory cell differs in form, distribution and amount according to the cell size. Two types are observed on the amount of the NISSL substance in smaller cells-in some cases they are rich in NISSL substance and in other cases poor. But, in both cases the neurosecretory material is scanty. In moderate-sized cells, it is typical that massive NISSL-substance is located in the perihery of the cytoplasm and powdery formed lie in the central area, and the cell becomes larger as the secretory material increases in it. Larger cells are generally filled with neurosecretory material with a little amount of NISSL-substance scattered in the cytoplasm. By the production and accumulation of the secretory material a moderate-sized cell becomes larger, which returns to a smaller cell by the intraaxonal or extracellular discharge of the granules. And a smaller cell, storing the NISSL substance, becomes larger as the production of the secretory material again takes place in it. Such a functional cycle can be presumed showing interrelationships among the secretory material, NISSL substance and the cell size.
9. In this functional cycle it is presumable that the production of the neurosecretory material occurs at the cost of the NISSL-substance, but not presumable that it takes place by a direct transformation of it, considering above-mentioned findings.