- Email: [email protected]
Electron micrographs of myelin figures and the problem of submicroscopic nerve fibers
477
BRIEF
NOTES
ELECTRON MICROGRAPHS OF MYELIN FIGURES AND THE PROBLEM OF SUBMICROSCOPIC NERVE FIBERS E. DE ROBERTIS Institute de Investigacirh
de Ciencias Biolbgicas, Dept. de Ultraestructura Montevideo, Uruguay
Celular,
Received October 28, 1952
IN
an electron microscope study of nerve tissue cultured in vitro we have recently described nerve fibers ranging in diameter from 0.1 p up to 1 p or more (1). A considerable number of nerve fibers, collaterals and terminal tips growing in tissue culture are thus of submicroscopic dimensions and could not be resolved with the optical microscope. In all cases these fibers and collaterals have a rather high electron density and show a compact parallel arrangement of structure within the fiber (see Figs. 8, 9, 10 in (1)). The terminal endings generally show an enlarged mass containing a tightly packed microvesicular material and thin finger-like processes in which a certain orientation and aggregation of this material is seen (see Figs. 11, 12). In a recent study FernBndez-Moran (2) describes fibers, obtained by dissociation of the white matter of the spinal cord, which range in diameter from 0.1 to 0.5 CL, and whose nervous nature is claimed. At variance with the dense submicroscopic nervous fibers grown in vitro, these fibers “merely consist of a single layered tube or sheath containing one filament” (2). Judging from the published electron micrographs this filament is frequently absent and the entire fiber is reduced to an apparently empty tubular membrane. Some hollow terminal club-like formations of these tubes having about 1 p in diameter, which according to the author resemble “nerve endings”, are also described. In 1950, in the course of observations of tissue culture material stained with methylene blue we have observed the development of myelin figures which after fixation in osmic acid show a strong resemblance with Fernandez-Moran’s “fine submicroscopic fibers” and “nerve endings”. Fig. 1 shows a nerve fiber of 170 rnp and a tubular myelin figure provided with several vesicular enlargements. The nerve fiber has a very high electron density and shows a compact parallel structure, while the myelin figure is only an empty tubular membrane with many folds. In Fig. 2 two tubular myelin figures are seen. One of them has some vesicular and tubular structures within it. A wide variety of sizes in the tubes ranging from 100 rnp or less to 1 or more microns can be observed (Figs. 1, 2, 3, 4). The terminal ending of some of these tubes present a club-shaped enlargement (Fig. 4). 28t - 633702
478
E. De Robertis
Electronmicrographs
of myelin figures
We want to stress the fact that in our tissue culture preparations these myelin formations could always be distinguished from true nerve fibers and nerve endings, and that they were considered as artefacts by us. In view of the similarity of these figures with some of Fernandez-Moran’s electron micrographs of “fine submicroscopic nerve fibers and nerve endings” the publication of electron micrographs of our artefacts seemed pertinent, since they will probably stimulate interest in the further study of the submicroscopic organization of nerve fibers. REFERENCES
1. DE ROBERTIS, E., and SOTELO J. R., Expll. Cell Research, 3, 433 (1952). 2. FERNANDEZ-MORAN, H., ibid, 3, 282 (1952).
Fig. 1. Electron micrograph of chick embryo nervous tissue cultured in vitro and stained with methylene blue. Below a submicroscopic nerve fiber (n.f.); Above a tubular and vesicular myelin figure. Osmic acid fixation. 20 000 x . Fig. 2. Electron micrograph showing two myelin figures. The lower one shows myelin vesicles and tubules within the larger tube. Osmic acid fixation. 20 000 x . Fig. 3. Tubular myelin figure of about 170 my provided of a vesicular enlargement. Osmic acid fixation. 20 000 x . Fig. 4. Electron micrograph showing a dense submicroscopic nerve fiber (n.f.) of 125 rnp and a tubular myelin figure ending in large club-like enlargement. Osmic acid fixation. 20 000 x . 29 - 533702
BRIEF
NOTES
ELECTRON MICROGRAPHS OF MYELIN FIGURES AND THE PROBLEM OF SUBMICROSCOPIC NERVE FIBERS E. DE ROBERTIS Institute de Investigacirh
de Ciencias Biolbgicas, Dept. de Ultraestructura Montevideo, Uruguay
Celular,
Received October 28, 1952
IN
an electron microscope study of nerve tissue cultured in vitro we have recently described nerve fibers ranging in diameter from 0.1 p up to 1 p or more (1). A considerable number of nerve fibers, collaterals and terminal tips growing in tissue culture are thus of submicroscopic dimensions and could not be resolved with the optical microscope. In all cases these fibers and collaterals have a rather high electron density and show a compact parallel arrangement of structure within the fiber (see Figs. 8, 9, 10 in (1)). The terminal endings generally show an enlarged mass containing a tightly packed microvesicular material and thin finger-like processes in which a certain orientation and aggregation of this material is seen (see Figs. 11, 12). In a recent study FernBndez-Moran (2) describes fibers, obtained by dissociation of the white matter of the spinal cord, which range in diameter from 0.1 to 0.5 CL, and whose nervous nature is claimed. At variance with the dense submicroscopic nervous fibers grown in vitro, these fibers “merely consist of a single layered tube or sheath containing one filament” (2). Judging from the published electron micrographs this filament is frequently absent and the entire fiber is reduced to an apparently empty tubular membrane. Some hollow terminal club-like formations of these tubes having about 1 p in diameter, which according to the author resemble “nerve endings”, are also described. In 1950, in the course of observations of tissue culture material stained with methylene blue we have observed the development of myelin figures which after fixation in osmic acid show a strong resemblance with Fernandez-Moran’s “fine submicroscopic fibers” and “nerve endings”. Fig. 1 shows a nerve fiber of 170 rnp and a tubular myelin figure provided with several vesicular enlargements. The nerve fiber has a very high electron density and shows a compact parallel structure, while the myelin figure is only an empty tubular membrane with many folds. In Fig. 2 two tubular myelin figures are seen. One of them has some vesicular and tubular structures within it. A wide variety of sizes in the tubes ranging from 100 rnp or less to 1 or more microns can be observed (Figs. 1, 2, 3, 4). The terminal ending of some of these tubes present a club-shaped enlargement (Fig. 4). 28t - 633702
478
E. De Robertis
Electronmicrographs
of myelin figures
We want to stress the fact that in our tissue culture preparations these myelin formations could always be distinguished from true nerve fibers and nerve endings, and that they were considered as artefacts by us. In view of the similarity of these figures with some of Fernandez-Moran’s electron micrographs of “fine submicroscopic nerve fibers and nerve endings” the publication of electron micrographs of our artefacts seemed pertinent, since they will probably stimulate interest in the further study of the submicroscopic organization of nerve fibers. REFERENCES
1. DE ROBERTIS, E., and SOTELO J. R., Expll. Cell Research, 3, 433 (1952). 2. FERNANDEZ-MORAN, H., ibid, 3, 282 (1952).
Fig. 1. Electron micrograph of chick embryo nervous tissue cultured in vitro and stained with methylene blue. Below a submicroscopic nerve fiber (n.f.); Above a tubular and vesicular myelin figure. Osmic acid fixation. 20 000 x . Fig. 2. Electron micrograph showing two myelin figures. The lower one shows myelin vesicles and tubules within the larger tube. Osmic acid fixation. 20 000 x . Fig. 3. Tubular myelin figure of about 170 my provided of a vesicular enlargement. Osmic acid fixation. 20 000 x . Fig. 4. Electron micrograph showing a dense submicroscopic nerve fiber (n.f.) of 125 rnp and a tubular myelin figure ending in large club-like enlargement. Osmic acid fixation. 20 000 x . 29 - 533702