A posteroventral approach for access to separate branches of the cat vestibular nerve is presented which permits simultaneous surgical access to the ampullary and otolithic nerves. Surgical procedures are discussed

Ayzikov, G. S.

Radkevich, L. A.

English

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NASA TECHNICAL MEMORANDUM	 NASA TM-76478
(NASA-Tli-76478) SURGICAL ACCESS TO SEPARATE	 N81-20715
BRANCHES OF THE CAT VESTIBULAR NERVE
(National Aeronautics an%: Space
Administration) 8 p dC A02/8F AU1 CSCL 06C	 Unclas
G5/52 197-04
SURGICAL ACCESS TO SEPARATE BRANCHES OF
THE CAT VESTIBULAR NERVE
L.A. Radkevich and G.S. Ayzikov
Translation of "Operativnyy dostup k
otdel'nym vetvyam vestibulyarnogo nerva
koshki", Fiziologicheskiy Zhurnal SSSR
im I.M. Sechenova, Vol. 63, No. 12,
1977, pp 1748-1751
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON D.C. 20546 	 JANUARY 1981
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Translation of"Operativnyy dostup k otdel'nym vetvyam
vestibulyarnogo nerva koshki", Fiziologicheskiy zhurnal SSSR
im.	 I.M.	 Sechenova, Vol.	 63,	 No.	 12,	 1977,	 pp.	 1748-1751.
16. A►ssroas'
This article presents a new posteroventral approach for
access to separate branches of the cat vestibular nerve.
This procedure permits simultaneous surgical access to
the ampullary and otolithic nerves.
Details of the surgery are discussed.
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I
SURGICAL ACCESS TO SEPARATE BRANCHES OF THE CAT
VESTIBULAR NERVE
L. A. Radkevich and G. S. Ayzikov*
There are currently several published methods for access to separ- /1748 *4
ate branches of the cat vestibular nerve for purposes of electrical
stimulation [3-51. Their difference consists of the features of the
surgical approach to the middle and inner ear of the animal, as well
as the method of applying electrodes on that section of the vestibular
nerve that is exposed to electrical stimulation. The outlet to the
canalis and otolithic nerves at the level of receptor formations of the
vestibule is fairly complicated. It requires definite experience in
working with microobjects.
The method that some authors [3,51 use in experimental practice
is convenient for an outlet to the ampullae of the anterior and lateral
canals and is less suitable for separating the nerve from the posterior
semicircular canal and utriculus. These authors use the ventrolateral
access to the cat middle ear. The posterior ear approach used by other
researchers [4,61 facilitates the separation of small branches from
the posterior semicircular canal and the otolithic nerve, however, the
outlet to the nerves of the anterior and lateral canals is complicated,
The posteroventral approach that we developed permits simultaneous
surgical access to the ampullary and otolithic nerves. It is best to
conduct surgery under 	 general anesthesia.
The anesthesized animal is fastened into a stereotaxic instrument
in a horizontal position with rigid fixing of the head and torso.
Laboratory of Cellular Biophysics and Intercellular Interactions (headed
by A. G. Malenkov) of the Scientific Research Institute of Biological.
Testing of Chemical Compounds, Moscow (Staraya Kupavna).
**
Numbers in margin indicate pagination in original foreign text.
1
Standard head-holders with ear clamps are not suitable for holding the
head since they interfere with manipulation in the region of the
middle and inner ears. We used screw clamps with pointed needles on
the ends. They held the posterior section of the head in a horizontal
position by fixing the skull in the mediolateral section of the
parietal-occipital suture. The anterior part of the head was secured
normally with zygomatic and palatal clamps. Rotation of the frame
around the longitudinal body axis put the animal in a position that
provided convenient access to the meatus acusticus externus from the
side and somewhat from below. This corresponds to an 80° rotation of
the cranium. The skin incision was made by circular movements at the
base of the concha auriculae. The muscles and underlying tissues
were separated. The fibrocartilaginous section of the meatus acusticus
externus was detached at the bone. A raspatory cleaned the root of the
zygomatic process of the temporal bone and the bulla mastoidea 	 At
the site of emergence from the temporal bone the facial nerve was cut.
The middle ear was approached from the posteroventral side. For this
purpose the thin osseous plates of the bulla mastoidea that comprise
the external lower and posterior walls of it were cut. Then part of
the inner wall of the bulla mastoidea that is adjacent from the bottom
and the rear to the osseousmeatus acusticus was carefully removed
through the opened cavity. The middle ear kasthus entered. After
expanding the opening on the perimeter, the base of the cochlea and the
round window were revealed. They became the landmarks for further
surgical actions (see the figure, A). The roof of the bulls mastoidea
was removed in pieces from the posterior and lower section of the osseous
meatus. The tympanic membrane was removed and free access was obtained
to the structural components of the middle ear, The osseous nerve and
luscle-tendinous formations that are located in the middle ear (mm.
tensor tympard.,stapedius, n. facialis, malleus, incus)interfere with
the manipulations to open up the vestibule. They need to be removed.
The auditory ossicles were disarticulated in the joints. The malleus
and incus were completely disjointed. The stapes was left intact. The
run tensor tympani and stapedius were cut and removed. Consequently,
the medial and posterior walls of the cavum tympani became accessible.
The promontorium was clearly isolated in this region. The lateral knee
2
of the osseous canal of the facial nerve is located above the round
window. It was opened up by accurate cutting of the osseous tissue
until the facial nerve appeared. Then its anterior wall was removed
along the course of the canal in a proximal direction up to the oval
window (the canal passes somewhat higher than it, and 1-2 mm to the
front and to the medial of the oval window). The separated part of
the nerve was resected.
/1749
Separation of the ampullary nerves of the anterior and horizontal
semicircular canals. The ampullae of these canals are located in a row,
while the nerves coming off of them initially travel separately, and then.
are joined into a common column at a certain angle. The utricular
branch ( see figure, B) approaches this column. The ampullary thicken-
ings were visible on the posterior wall of the osseous canal of the facial
nerve after the latter was removed. With illumination th^-y were isolated
as two dark spots at the supermedial edge of the oval window. For an
outlet to the nerve branches in this region, thin openings were drilled,
or a sharply pointed lance was used to carefully chip off the thin
osseousplate that covered the nerve branches ( the nerve of the anterior
canal lies somewhat in a medial direction and towards the front). If
one has experience there is no need to remove the stapes. This would
inevitably lead to damage to the membrane that covers the oval window,
and to discharge of the perilymph.
Separation of the utricular. nerve. The utricular nerve was 	 /1750
separated during removal of the stapes since the access to it lies
through the oval window. After removing the stapes and enlarging
the oval window by chipping off the medial edge, it was possible to
enter the nerve of the utriculus directly. 11ith. sufficient magnifica-
tion the utriculus could be seen well under eirected illumination in the
form of an elongated oval of grayish-rosy color. In the selected
projection the utriculus was visible from the macula. The nerve fibers
exit from the entire visible surface of the utriculus and are directed
forward to the osseousseptum, connecting with a short column of light
gray color. Here the nerves join from the ampullae of the anterior
and horizontal canals. To the lateral of the utriculi:s) a sacculus is
3
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t
Osseous-Nerve Elements in Middle and Inner Cat Ear
a--middle ear of cat with open bulla (left labyrinth, view from
posteroventral side); b--plan of receptor formations of vestibule in
course of individual branches of vestibular nerve; 1--facial nerve;
2--ampulla of lateral canal; 3--ampulla of anterior canal; 4--ampulla
of vosterior canal; 5--utriculus; 6--sacculus; 7--utricular nerve; 8--
ampullary nerves of lateral and anterior canals; 9--oval window; 10--
round window; 11--vestibular ganglion; 12--chorda tympani; 13--stapes;
14--cochlea.
is visible. It is turned with the otolithic part to the oval window.
The sacculus lookedsignificantly lighter due to the reflection of light
from the surface of the otoliths. The saccular nervewas not visible
since it immediately enters t.t,e osseous septum. On the free space it
was covered by the mass of Liie sacculus itself. When the stapes was
removed and the oval window was expanded the outflowing perilymph was not
4
removed since it promotes the preservation of the visible nerve. This
method for separating the utriculur nerve was used by the authors in
and experimental work and the results have been published [1,2).
Separation of the ampullary nerve of the posterior semicircular
canal. The ampulla of the posterior semicircular canal approaches the
basal loop of the cochlea that projects to the rear from the round window.
Due to the fact that the preliminary access was made using the postero-
ventral approach to the vestibule, there was no difficulty in exposing
the ampulla and the nerve of its canal. On the side of the medial edge
of the round window and somewhat to the rear the bone was chipped off
(or drilled), as if enlarging the size of the window. The ampulla was
then accessible for visual examination. The nerve lies somewhat below
the ampulla and is directed forward and medially to the utriculo-
ampullary branches. If it is necessary to make an isolated approach
to the posterior ampullary nerve, then the posterior access to the
vestibule is used. Here the posterior part of the bulla mastoidea is
first cut, then part of its inner wall at the lower posterior edge of
the osseous meatus acusticus for outlet to the promontorium and round
window. After taking these points as the landmarks, the ampulla is
separated from the nerve as already described, by chipping the bone
to the rear from the round window.
In order to reveal the osseous iepta, one can use small and medium-
sized tooth drills. However, the drilling process produces chi-ps
that are hard to renove and forms heat during rotation of the drill
in the bone. This requires thermometric control and constant washing
of the surgical field with Ringer's solution to cool the tissues. In
addition, the rotating drill, through careless movement, can cause
damage to the structural elements of the vestibule. It is more con-
venient to use instruments from the standard eye and ear surgical sets,
to sharpen several thin duplicates made of hardened steel, and to
use small Luer's cutters.
During surgery, good hemostasis of the osseous hemorrhages is
desirable. They are not abundant, however, they make surgery difficult.
It is usually sufficient to apply a wax-paraffin paste with a thin
5
spatula, or paraffin paste that can be heated at the hemorrhage source
by a thermocoagulation loop.
The electrodes to be inserted into the nerve fibers are made of
thin platinum or tungsten wire with electrolytic sharpening of the end.
They are covered with electrical-insulating lacquer. It is best to
use a micromanipulator to insert the electrodes that has sufficient
mobility to direct it into the surgical field. The electrodes are
fixed by rapidly-hardening cement.
References
1. Ayzikov, G. S.; and Radkevich, L. A. "Induced Activity of Neurons
in the Respiratory Center during Stimulation of the Utricular
Nerve and Dorsal Roots of the Spinal Cord," Kosmichesk. biol. i
Med., 7, 5, 1973, pp. 55-60.
2. Radkevich, L. A.; and Ayzikov, G. S. "Change in Impulse Activity
of Neurons in Res p iratory Center during Electrical Stimulation of
the Vestibular Nerve and Dorsal Roots of the S pinal Cord," Kos-
michesk. biol. i med., 7, 4, 1973, pp. 6-13.
3. Anderson, S.; and Gernandt, B. "Cortical Projection of Vestibular
Nerve in Cat," Acta otolarynAol., (Stockh.), Suppl. ;16, 1954,
pp. 10-18.
4. Cohen, B.; Suzuki, J. "Eye Movements Induced by Ampullary Nerve
Stimulation," Amer. J. Physiol_ , 204, 1963, pp. 347-351.
5. Fluur, E. "Influences of Semicircular Ductus on Extraocular MusclEs,"
Acta Otolaryagol. (Stockh.), Suppl. 149, 1959, pp. 18-21.
6. Suzuki, J.; Goto, K.; and Tokumasu, K. "Implantation of Electrodes
near Individual Vestibular Nerve Branches in Mammals," Annals of
Oto-,Rhino-, Laryngology, 128, 4, 1969, pp. 815-826.
^
6


Surgical access to separate branches of the cat vestibular nerve

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