The adrenal medullae of hamsters of both sexes progressing in ages from birth to 200 days were studied from the histogenetic point of view, and the functional structure was considered with special emphasis.
The medullary cells differentiate from sympathogonia after passing through the stage of pheochromoblasts. The sympathogonia are the most primitive forms with very characteristic featuies. In postnatal life they are present only in the newborn medulla. The pheochromoblasts are PAS-positive, undifferentiated medullary cells, and, consequently, the immature medulla composed mainly of these cells in early life is stained positively with the PAS method. The medulla becomes stronger in PAS-staining until the age of '12-13 days. With progress of the differentiation, the PAS-reaction of these cells rapidly declines in intensity, until finally the medullary cells show no or little staining ability for PAS when they have differentiated into the last developmental stage or pheochromocytes. Thus the medulla developmentally reaches an almost definitive state at approximately 30-50 days of age.
In the medulla of adult hamsters there are two types of parenchymal cells; namely, large polygonal lightly-staining cells arranged commonly in compact masses mainly in the periphery of the medulla and columnar finely granular cells arranged as follicles or in cords or masses. These two types of cells are transitional with one another, and considerable variation exists in regard to relative amounts of the respective cell types from gland to gland. Both types of medullary cells are essentially similar in process and mode of secretion. In any type the secretory materials appear to liquefy into vacuoles in the cytoplasm. The mode of secretion is regarded as an indirect one in both types; the medullary cells appear to pour their secretory products first intercellularly and not directly into the blood stream. In this connection, the follicles, characteristic of the medulla of this animal, are structures of particular interest.
The nuclei of the medullary cells with highly developed activity frequently present peculiar deformation of various appearances. The possible significance of such deformation may be understood in the light of the modern concept that the nucleus, especially nucleolus, plays a direct role in functional activity of the cell.

抄録全体を表示

The ultrastructure of the sheath components of the myelinated and non-myelinated peripheral nerve fibers of adult mice and frogs has been studied with the electron microscope using thin sections, macerated materials and replica preparations. The results obtained are summarized as follows:
1. The myelin sheath is an integral part of the Schwann cell.
2. The axolemma membrane and the surface membrane of the Schwann cell appear as thin, double-edged membranes.
3. The myelin sheath consists of a double-edged membrane which is wound helically about the axon. An inner, thin, double-edged membrane connects the axolemma membrane with the innermost lamella of the myelin sheath. The outermost lamella of the myelin sheath is connected with the surface membrane of the Schwann cell by a similar double-edged membrane, which lie in the cytoplasm of the Schwann cell.
4. These observations indicate that the axolemma membrane, the helical myelin lamella and the surface membrane of the Schwann cell compose, as a whole, a large continuous membrane system which is invaginated into the cytoplasm of the Schwann cell to envelop the axon.
5. The myelin sheath is completely interrupted at the node of Ranvier, in which the axon is constricted by the narrow ends of the myelin tubes. The cytoplasm and surface membrane of the Schwann cell and the axolemma membrane are continuous across the node. This indicates that the Schwann cells exhibit a large syncytium along the neve fiber.
6. Several non-myelinated axons are enclosed in the cytoplasm of a single Schwanncell. The axolemma membrane of the non-myelinated fiber is connected with the surface membrane of the Schwnn cell by a double-edged membrane, which lie in the cytoplasm of the Schwann cell.
7. The cytoplasm of the Schwann cell contains in its interior mitochondria and small vesicular endoplasmic reticula.
8. About and between the nerve fibers are observed many fibrils which present periodic cross striation that is typical of all collagen fibrils elsewhere in the body. The collagen fibrils in the endoneural connective sheath are closely attached to the outer surface of the Schwann cell membrane and are oriented parallel to the longitudinal axis of the nerve fiber in a close side, by side apposition. In the endoneurium, many of the collagen fibrils run parallel with one another, but some of them take oblique course.

抄録全体を表示