Electron Microscope Studies on the Spinal Ganglion Cells

Abstract

Normal spinal ganglia of the rabbit and the dog were observed with the electron microscope. Nerve cells and satellite cells and their mutual relationship were especially studied.
1. The nucleus of the spinal ganglion nerve cell is extremely large and less in electron density. The nuclear envelope shows a double structure, whose outer membrane is smooth but not attached with granules. This fact is of great interest comparing with the fact that the membrane in NISSL substance is also smooth.
2. The karyoplasm consists of filaments (chromonemata) composed of small Particles arranged in a row like a stringe of beads. In the nerve cell, helical structure of chromonemata is generally loosened and indistinct, but it is evident at the portion of densely aggregated chromatin.
3. Well developed nucleoli have no limiting membrane, and made up of tangled skein, the nucleolonema, which consists of more than ten filaments (primary nucleolonemata) twisted helically. Node-like portions of nucleolonema may be manifested by an extremely strong twisting of such a helical bundle.
4. The NISSL substance is a mixture of clusters of small dense granules and vacuoles belonging to the endoplasmic reticulum. The surface of the membrane of such vacuoles is smooth. The granules are not generally attached to the membrane surface. Rarely clusters of granules may attach, but even in this case each granule does not attach solitarily. Therefore, the NISSL substance may be called as an intermediate between the rough and smooth types of the endoplasmic reticulum and not as a typical rough surfaced variety.
Clusters of granules is thought to be three-dimensionally of a globular arrangement, whose center may be lacking in granules. The disposition of granules in the NISSL substance quite differs from that in the nucleolus.
5. The GOLGI apparatus can be distinguished from the NISSL substance by the absence of clustered granules. The fundamental structure of the GOLGI apparatus may be vesicles. Large vacuoles may be formed by the expansion of vesicles, and the lamellae from the fusion of neighboured vesicles arranged in rows like strings of beads.
6. Mitochondria of the spinal ganglion cell are spherical and rod-shaped, and contain tubular cristae mitochondriales. Transformation from mitochondria into pigment granules is suggested. Decrease of mitochondria in number due to their conversion into pigment may be supplied by fission of mitochondria themselves.
7. In the cytoplasm of the perikaryon, neurofilaments run in all directions, but in the axon they are arranged in general longitudinally, and consist of bundles which are twisted with one another.
8. The intercellular margin between the nerve cell and the satellite cell is seen as a double membrane, each of them belongs to one of the neighbouring cells. Plasma membrane of satellite cell side frequently invades into the cytoplasm of the latter, forming double membraned folds. Small vesicles are often associated to such infoldings. These features may be related to the fluid-transport for mainteining the nutrition of nerve cells.