Lechnical Papers

The Electron Microscopy | of
Sectioned Nerve

George Rozsa, Councilman Morgan,
Albert Szent-Gyérgyi,! and Ralph W. G. Wyckoff

Laboratory of Physical Biology,
Experimental Biology and Medicine Institute,
National Institutes of Health,

Bethesda, Maryland -

Nerve is one of the most important tissues for study

under the electron microscope both because knowledge
of its macromolecular structure is needed for an under-
standing of the mechanism of impulse propagation and
because this knowledge is essential for any study of the
neurotropic virus diseases. Until recently little prog-
ress in such a study has been possible on account of the
large size and fragility of moat nerve fibers, They can,
however, now be examined to great advantage in thin
section,

Fie, 1,
through a single fiber of myelinated nerve.
tents of the central axon are clearly seen, as are the denser

An electron micrograph of a longitudinal section
The fibrous con-

lamellae of the surrounding myelin. The thin neurilemma

enveloping the whole is visible at the very top and bottom of
the photograph. Magnification, 5,000 x.

i Special fellows, Experimental Biology and Medicine, Na-
tional Institutes of Health, U. 8. Public Health Service.

42

 

 

Fic. 2.

A nearly transverse section through part of a
nerve bundle. One fiber showing the same structures as Fig.
1 fills most of the picture. Small parts of two other fibers
are in the lower right corner and the top, left of center. A
band of connective tissue and the embedded sectioned tip of
another fiber separate the lower fiber from the one in the
eenter. Magnification, 5,000 x.

Very recently preliminary electron micrographs have
been published of sectioned nerve (1) but these phote-
graphs were of fibers that were so seriously damaged
during preparation that their fine structures and the
relation of these structures to one another were not evi-—
dent. We have found that excellent sections can be
obtained of nerve prepared and eut according to the
techniques outlined by Newman, Borysko and Swerdlow
(2). What is seen in such sections under the high reso-
lution of the electron microscope depends in marked

_ degree on the kind of fixation and dehydration used, and

it will require much experimentation with many reagents
to establish beyond doubt all aspects of the macromolecu-
lar texture of native nerve. Nevertheless, nerve can now
be sectioned without disturbing its various componenta
and consequently a detailed study can now be begun of
its structure and of the changes caused by various pre-
parative reagents.

Results of a first set of such experiments are being
published elsewhere (%) but the accompanying photo-
graphs illustrate the kind of electron micrographs of
sectioned nerve that can readily be prepared. These

Screnon, Vol. 112
show a longitudinal (Fig. 1) and nearly transverse (Fig.
2) section through the nervus tschiadicus of the adult
rabbit fixed in 4%. formalin and dehydrated in one case
in ethyl aleohol and in the other with pyridine. In the
longitudinal section one can see the filamentous fine struc-
ture of the central axon and the more ‘‘opaque’’ lamellar
texture of the nonlipid portion of the enveloping myelin
sheath. The neurilemma outside this and the absence of
an axilemma of similar structure between axon and
myelin are apparent. The same structures are visible in
Fig. 2; which also gives an idea of the relation of a nerve
fiber to the connective tissue elements with which it is
associated in a complete nerve bundle. This photograph
likewise brings out the fact that in many parts of nerve
fibers the texture of the lamellae of the myelin is less
coarse in the region immediately enveloping the axon.
Other photographs wehave made both at these and at
higher magnifications show the fine details of the struc-
tures, the kinds of alteration in these details that result
from the use of other fixatives, and the nature of such
other optically recognized structures as the clefts of
Schmidt-Lantermann and the nodes of Ranvier. .

; References
1. FeRNANDEz-MoraN, H. ‘Hap. cell. Res., 1950, 1, 142.
2. NewMaN, §. B., BORYSKO, B., and SWERDLOW, M. Science,
1949, 110, 66.
83. Rozsa, G, et al. Biochim. Biophys. Acta, in press.