Acta Oto-Laryngologica
ISSN: 0001-6489 (Print) 1651-2251 (Online) Journal homepage: http://www.tandfonline.com/loi/ioto20
Neurophysiology of Ischemic Facial Nerve Paralysis in an Animal Model Hiroshi Iritani, Yoshihiko Nishimura & Toru Minatogawa To cite this article: Hiroshi Iritani, Yoshihiko Nishimura & Toru Minatogawa (1991) Neurophysiology of Ischemic Facial Nerve Paralysis in an Animal Model, Acta OtoLaryngologica, 111:5, 934-942, DOI: 10.3109/00016489109138433 To link to this article: http://dx.doi.org/10.3109/00016489109138433
Published online: 08 Jul 2009.
Submit your article to this journal
Article views: 5
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ioto20 Download by: [Purdue University Libraries]
Date: 23 March 2016, At: 19:47
Acta Otolaryngol (Stockh) 1991; 1 1 1: 934-942
Neurophysioiogy of Ischemic Facial Nerve Paralysis in an Animal Model HIROSHI IRITANI. YOSHIHIKO NlSHIMURA and TORU MINATOGAWA From the Dt.pattment of Otolann&ogy. Hyogo College of Medicine, Nishinomiya 663, Japan
Downloaded by [Purdue University Libraries] at 19:47 23 March 2016
iritani H, Nishimura Y. Minatogawa T. Neurophysiology of ischemic facial nerve paralysis in an animal model. Acta Otolaryngol (Stockh) 1991: I I I: 934-942. The establishment of an animal model for facial nerve paralysis is assuming increasing importance in clinical medicine and also in basic facial nerve research. We previously reported an animal model for ischemic facial nerve paralysis using selective vascular embolization through the internal maxillary and posterior auricular arteries in cats using Avitene which contains bovine microfibril collagen. In this paper, we determined the exact site of the lesion in established facial paralysis. A descending signal produced by direct stimulation to the contralatera1 motor cortex was able to elicit firing of the motor nucleus of the facial nerve, the extratemporal portion of the peripheral nerve. and the orbicularis oris muscle. After achieving complete facial nerve paralysis. this descending signal was completely abolished within the temporal bone area. whereas peripheral facial nerve stimulation elicited a normal evoked electromyogram of the orbicularis oris muscle. The present results suggest that the site of the lesion of ischemic facial nerve paralysis produced by ernbolization in an animal model is within the temporal portion of the seventh nerve, and this animal model may lead to the advancement of future facial nerve research which cannot be conducted in humans. Key words: cortieal stimulation. selective enibolization. motor eL.oked potentiab (MEPI.
INTRODUCTION In 1986, Balkany (1) demonstrated the precise intrinsic vasculature of the cat facial nerve, and reported that the main extrinsic vascular supply to the nerve was from the anterior inferior cerebellar artery which supplies the area from the pons to the geniculate ganglion. the petrosai artery. a branch of the middle meningeal artery, which supplies the area from the horizontal segment to the geniculate ganglion, and the stylomastoid artery, a branch of the posterior auricular artery, which supplies the inferior course of the facial nerve. One possible cause of peripheral idiopathic facial palsy is considered to be ischemia of the nerve in the Fallopian canal (2), and we have therefore focused our attention on obstruction of the vascular circulation to the nerve. In our previous report (3). we established an animal model for ischemic Facial nerve paralysis with selective vascular embolization in cats. Our animal model was a n atraumatic procedure and had a high rate of success in producing complete facial nerve paralysis with good reproducibility. Several other studies on experimental facial nerve palsy have been performed; however, most have employed some form of mechanical manipulation of the nerve, which makes interpretation of results difficult. Experimental studies (4, 5) on ligation of blood vessels to the peripheral nerve have been performed in order to produce nerve fiber degeneration. In 1990, experimental thrombosis of the intratympanic portion of the facial nerve using infusion of a suspension of ferrous carbonyl and cobalt magnet placed against the bony lining of the facial canal in the middle ear cavity was attempted on 10 rabbits with no clinical or electrophysiological signs of facial palsy, in order to elucidate the effects of impaired microcirculation on facial nerve function (6). The aim of the present study was to demonstrate neurophysiological evidence confirming the site of the lesion of ischemic facial nerve paralysis in our animal model.
Downloaded by [Purdue University Libraries] at 19:47 23 March 2016
Acla Ololaryngol (Slockh) 1 I I
Facial nerve paralysis in an animal model 935
Fig. 1. Ventral view of subtraction carotid angiogram of the head including the temporal bone (right), and its schematic illustration (left). There is a S-shaped curve in the internal maxillary artery proximal to the external rete. R.e.:external rete (carotid plexus), M.i.: internal maxillary artery, M.e.: external maxillary artery, L: lingual artery. A.p.: posterior auricular artery, T.s.:superficial temporal artery, C i . : internal carotid artery.
MATERIAL AND METHODS
Preparation Twenty-one healthy adult cats weighing more than 2.5 kg were used for this study. The animals were anesthetized with i.p. injection of ketamine hydrochloride (50 mg/kg) supplemented with one-third of the initial dose every 2 h during surgery. Xylocaine was used as a local anesthetic for the superficial tissues and for the pressure points of the restraints on the animal’s body. Atropine sulfate was given intravenously. All animals underwent tracheostomy and insertion of an intravenous cannula. Respiratory status was maintained with a Harvard ventilator, and body temperature was maintained using thermostatically controlled blankets with a rectal temperature probe set at 39°C. The skull covering the cerebellum was carefully removed by separating the temporal and occipital muscles. The cerebellum was removed to expose the rhomboid fossa, while performing meticulous haemostasis using a bipolar electrocoagulator and oxidized cellulose under a dissection microscope. Warm liquid paraffin was applied to the exposed areas to insulate them from the surrounding tissues and keep them moist. The left motor cortex was exposed via left frontal craniectomy, for placement of bipolar stimulating electrodes. The right extra-temporal portion of the facial nerve was prepared for the placement of recording and stimulating electrodes, and the nerve was insulated with warm liquid paraffin. After ligation of the right external carotid artery just distal to the external maxillary artery branch. a fine 1.0 mm diameter catheter was introduced into the right internal maxillary artery as schematically illustrated in Fig. 2, according to the angiogram of the cat’s head obtained in our previous report (3) (Fig. I). The experimental paradigm is shown in Fig. 3.
936 H. lririluni et al.
Acta Otolalyngol (Stockh) 1 1 1
rostra1 M.i.
Downloaded by [Purdue University Libraries] at 19:47 23 March 2016
M.i.
ri
-
caudal Type 1
embolization
Type 11
embolization
Fig 2. Schematic illustration of the two types of selective embolization used in this study. Abbreviations as in Fig. 1.
Coronal s.
1 . l .
Right motor nucleus of N.VU
-
Facial k n re In the right temporal bone
1
Facial n e w of
-a,
+
I
M. wbicuiaris oris
Fig.3. Neurophysiological experimental paradigm used in the present study.
Facial nerve paralysis in an animal model 937
Acta Otolalrngol (Stockh) I 1 1
:I\' :
:I\::: 5.0 msec.
-1o.vT
Downloaded by [Purdue University Libraries] at 19:47 23 March 2016
I
5.0 msec.
5.0 msec.
I
. 100 P
V
T
5.0 msec.
Fig. 4. Evoked responses of the motor nucleus of N. VII, the extra-temporal portion of the VIIth cranial nerve and the orbicular oris muscle elicited by contralateral motor cortex stimulation. Lefrr before embolization; Right: after embolization. (A) evoked response of motor nucleus of facial nerve; (B)evoked response of extra-temporal bone portion of facial nerve; (C) evoked response of orbicularis oris muscle.
After completion of a series of preparations, the head was fixed to a David Kopf stereotaxic frame for cats (David Kopf Instruments, California) with the animal in a prone position.
Stimulation The bipolar stimulating electrodes (tiny ball-shaped Ag-AgC1 electrodes) were placed over the left motor cortex for orthodromic activation of the right motor nucleus of the facial nerve, and a pair of U-shaped tungsten electrodes was applied to the extra-temporal portion of the right facial nerve, and connected for antidromic stimulation.
rnsec.
5.0 msec.
Fig. 5. The site of the recording electrode is confirmed to be in the motor nucleus of N. VII using antidromic stimulation of the VIIth nerve.
Downloaded by [Purdue University Libraries] at 19:47 23 March 2016
938 H.tritani et 01.
Acta Otolaryngol (Stockh) I1 I
Fig. 6. (A) Low magnification view showing the cat's brain stem thin section stained by Cresyl Violet. Scale bar = 1 mm; original magnification x 10. The area outlined in the box is shown at higher magnification in (B). (B) Detail of the area in (A) revealing the electrode (arrow) into the pool of motor nerve cell bodies (Nucleus of Vllth nerve motoneuron, arrouhmfs). Scale bar = 200 pm: original magnification ~ 4 0 .
Monophasic current (5-10 mA, 0.1-0.3 ms square wave pulses, frequency 0.2 Hz) was applied over the left facial representation of the motor cortex and to the right extra-temporal portion of the facial nerve. Recordings For recording of the facial nerve motoneurons, a monopolar tungsten electrode was placed in the center of the right facial nerve motoneuron pool in the facial nucleus, determined by recording orthodromic field potentials after direct stimulation to the left motor cortex. The evoked electromyogram (EMG)of the right orbicularis oris muscle was obtained using a standard bipolar concentric needle electrode for electromyography. To obtain action potentials of the extra-temporal portion of the facial nerve. a pair of Ushaped tungsten stimulation electrodes was used for recording. Recording positions in the right facial nucleus were marked by passing a 10 mA current through the recording electrode when each recording was completed. At the end of each experiment, the animal was injected with a lethal i.v. dose of pentobarbital sodium (NembutaP. Abbott) and perfused through the heart with saline followed by IOYo formaldehyde solution. The recording site was identified histologically with 10 pm serial frontal sections stained with Cresyl Violet. RESULTS As described in the methods section, the experimental procedures were so time-consuming and complicated that only half of the animals tolerated the entire procedure. We therefore only obtained data from 10 animals. For all cats, the first procedure was direct stimulation of the left motor cortex to record the evoked responses of the right orbicularis oris muscle. Supramaximal threshold stimulation elicited an evoked EMG response of the orbicularis oris muscle. Following EMG, a monopolar
Facial nerve paralysis in an animal model 939
Acta Otolaryngol (Stockh) I I 1
msec.
Fig. 7. Evoked response of orbicularis oris muscle
Downloaded by [Purdue University Libraries] at 19:47 23 March 2016
5.0 msec.
elicited by Vllth nerve stimulation (before embolization).
recording electrode was carefully inserted into the pons to identify the facial motor nucleus, in order to record the evoked potentials produced by direct orthodromic motor cortex stimulation. As shown in Fig. 4A, a large evoked response was obtained when the tip of the recording electrode entered the motor nucleus of the facial nerve. Evoked action potentials of the extratemporal portion of the right facial nerve and of the orbicularis oris muscle to direct stimulation of left motor cortex were also recorded, as shown in Fig. 4 B and 4C. The site of the recording electrode in the motor nucleus of the facial nerve was reconfirmed by antidromic stimulation of the extra-temporal portion of the facial nerve, as shown in Fig. 5. Histological confirmation of positioning of the recording electrode in the motor nucleus of the facial nerve is shown in Fig. 6. The evoked EMG response of the orbicularis oris muscle elicited by direct stimulation of the peripheral facial nerve was demonstrated (Fig. 7) prior to the embolization procedure. The motor nucleus of the facial motor nucleus was activated by stimulation of contralateral motor cortex with different latencies ranging from 6.0 to 7.9 ms with a mean of 7.1 50.7 ms depending on the depth of anesthesia in each of the 10 animals examined because of subtle differences in change of synaptic delay. The latencies of evoked responses obtained from the extra-temporal portion of the facial nerve ranged from 7.4 to 10.1 ms with a mean of 8.5 t0.8 ms, and from the orbicularis oris muscle ranged from 8.7 to 14.7 ms with a mean of 10.7?2.0 ms. However, when the motor nucleus of the facial nerve was identified and the experimental sequence commenced, these latencies remained unchanged in each animal throughout the course of the experiment. Therefore, in the present report only one set of representative data recorded from cat No. 11 are given. Representative data in the left hand traces of Fig. 4A-C, show the latencies of each evoked response of the motor nucleus of the facial nerve and peripheral facial nerve and the EMG ofthe orbicularis oris muscle to direct stimulation of the contralateral motor cortex: 7.8. 8.8 and 10.1 ms, respectively. When embolization of the right internal maxillary artery was performed through a fine catheter with 1.5 ml of 1.OYo Avitene@(microfibril bovine collagen, Avicone Inc, Texas) for 40 min, no immediate obvious changes were observed in the previously described evoked
Fig. 8. Evoked EMG of orbicularis oris muscle elicited by peripheral VIIth nerve stimulation after establishment of facial paralysis (60 min after embolization).
940
n. frirani et at.
Acta Otolaryngol (Stockh) 111
1 0 o p v ~
Downloaded by [Purdue University Libraries] at 19:47 23 March 2016
5.0 msec.
Fig. 9. Evoked response of orbicularis oris muscle elicited by stronger stimulation of N. VlI after establishment of complete facial paralysis (60 min after embolization).
responses to direct stirnulation of the contralateral motor cortex, and contractile movements of the right orbicularis oris muscle were observed. Forty-five minutes after embolization, however, there was abrupt cessation of the evoked responses of the extra-temporal portion of the peripheral facial nerve and the EMG of the orbicularis oris muscle. The evoked response of the motor nucleus of the facial nerve still showed an active recording, as shown in the right hand traces of Fig. 4A-C. At that time, no visible contractile movement of the orbicularis oris muscle was observed. The evoked EMG response of orbicularis oris muscle could still be elicited by peripheral facial nerve stimulation after establishing complete facial nerve paralysis (Fig. 8). To confirm the conduction block in the temporal bone area. a much stronger orthodromic stimulus to the motor nucleus of the facial nerve was applied t o record the evoked response of orbicularis oris muscie (Fig. 9). and this was also applied to the extra-temporal portion of the peripheral facial nerve to elicit an antidromically evoked response of the motor nucleus of the facial nerve (Fig. 10). As is shown in Figs. 9 and 10, only a slight response was recorded.
DISCUSSION
In our previous report (3), we stated that the establishment of an animal model for ischemic or viral facial nerve paralysis is crucial to future developments in facial nerve research. The present results show that direct stimulation of the facial representation of the motor cortex in the experimental animal can produce a descending evoked potential distally in the end organ (the orbicularis oris muscle) through the motor nucleus of the facial nerve. Many of the recent developments in clinical intraoperative monitoring of the motor system have been made by Levy et al. (7-9). who reported techniques for stimulating the motor system and recording from the spinal cord of animals and humans. A descending signal originating from pyramidal cells activated by motor cortex stimulation elicits the motor-evoked potential
6.05 msec.
50
P.TL 5.0 m s e c .
Fig. 10. Evoked response of motor nucleus of N. VIl elicited by antidromic stimulation of the peripheral seventh nerve (60 min after embolization).
Downloaded by [Purdue University Libraries] at 19:47 23 March 2016
Acta Otolaryngol (Stockh) I 1 1
Facial nerve paralysis in an animal model 94 1
(MEP), and this MEP has been recorded traveling down the spinal cord, and finally activating muscle action potentials. When the lesion is created within the course of the pathway, the signal is almost completely abolished. Thus, the techniques for recording of MEPs have been utilized for intraoperative diagnostic and prognostic testing of cranial nerves. Recently in 1988, Estrem et al. (10) documented their data on MEPs of the facial musculature in dogs, and stated that magnetic stimulation of the motor cortex allows noninvasive study of the entire course of the facial nerve. In a similar manner, our present results clearly demonstrated that the lesion of established ischemic facial nerve paralysis with selective vascular embolization in the experimental animal model is located in the segment of the facial nerve within the temporal bone. The pathogenesis of Bell’s palsy still remains controversial, but there is some histologic and clinical evidence to suggest that the injury to the facial nerve occurs within its intratemporal course (11). In Gantz, Gmuer & Fisch’s paper, the site of the block of nerve impulse conduction was identified in 16 of 18 patients undergoing decompression for Bell’s palsy, and in whom the lesions extended for only a few millimeters and were proximal to the geniculate ganglion in 15 (94%) of these patients. Fisch & Felix (12) in 1983 reviewed anatomical, electrophysiological and histopathological data obtained in the acute phase of Bell’s palsy, and their results supported the entrapment neuropathy concept of Bell’s palsy. They postulated that the meatal foramen is by far the narrowest point of the entire Fallopian canal, and confirmed that the conduction block was situated between the geniculate ganglion and the meatal foramen in 94%of the patients, confirming the critical role of the meatal foramen and proximal labyrinthine segment in the pathogenesis of Bell’s palsy. Although, in the present experimental series, we could not define the precise location of the lesion of ischemic facial paralysis in our animal model as Fisch & Felix did, it is a useful animal model for facial nerve palsy, because the site of the lesion is within the temporal bone area. The other important point which should be discussed in this paper is that the present results are not in agreement with those reported by Frankander et al. (6) as described in the Introduction. In their experiment, despite a total absence of “open” vessels on the treated side, no light or electron microscopic signs of nerve damage were observed, and they concluded that intraneural vascular insufficiency in itself was not sufficient to cause facial palsy. Parry & Brown ( I 3) injected arachidonic acid, a potent stimulus to platelet aggregation and vasoconstriction, into the femoral artery of normal rats, and this resulted in the rapid onset of focal infarction of the proximal posterior tibia1 nerve in all animals, with distal evidence of Wallerian degeneration. A possible reason for the discrepancy between our data and that of Frankander et al. is thought to be related to the rapidity of development of vascular thrombosis. Another possible explanation is the occlusion of different vessels in experimental animals. Calcaterra et al. (14) in 1976 described two patients who, following embolization of vascular tumors with occlusion of the middle meningeal artery, developed total peripheral facial nerve paralysis which persisted for at least 6 months. This paper demonstrates the important role of the petrosal artery, a branch of the middle meningeal artery, in the vascular supply to the facial nerve. If the cobalt magnet in the experiment of Frankander et al. was placed more rostrally in the middle ear. thrombosis of the petrosal artery, with resulting facial nerve palsy. would be expected to occur. Further histological studies clarifying the location of lesions in ischemic facial paralysis are in progress.
ACKNOWLEDGMENTS The authors wish to thank Professor Takeo Kumoi for his generous advice and help with this study.
942 H.iritani et at.
Ada Otolaryngol (Stockh) 1 I 1
Downloaded by [Purdue University Libraries] at 19:47 23 March 2016
REFERENCES I. Balkany TB. The intrinsic vasculature of the cat facial nerve. Laryngoscope 1986; 96: 70-7. 2. Blunt MJ. The Dossible role of vascular changes in the etiology of Bell's palsy. J Laryngol 1956; 70: 701-13. 3. Iritani H, Nishimura Y, Minatogawa T et al. An animal model for ischemic facial nerve paralysis with a selective embolization. Ear Res Jpn 1989; 20: 195-6. 4. Korthals JK. Wisniewski HM. Peripheral nerve ischemia: Part I. Experimental model. J Neurol Sci 197%24: 65-76. 5. Hess K. Eames RA, Darveniza P. Gilliatt RW. Acute ischemic neuropathy in the rabbit. J Neurol Sci 1979; 4 4 19-43. 6. Frankander L. Thomander L, Bagger-Sjobick D. Experimental thrombosis of the microcirculation in the intratympanic portion of the facial nerve. An experimental study in the rabbit. In: Castro D, ed. The facial nerve. Amstelveen, Netherlands: Kugler, 1990: 131-3. 7. Levy WJ. York DH. Evoked potentials from the motor tracts in humans. Neurosurgery 1983; 12: 422-9. 8. Levy WJ. York DH. McCaffrey M,Tanzer F. Motor evoked potentials from transcranial stimulation of the motor cortex in humans. Neurosurgery 1984; 15: 287-302. 9. Levy WJ, Mctaffrey M. York DH. Tanzer F. Motor evoked potentials from transcranial stimulation of the motor cortex in cats. Neurosurgery 1984; 15: 214-27. 10. Estrem SA. Haghighi S, Levy WJ. Wertheimer R, Kendall M. Motorevoked potentials of facial musculature in dogs. Laryngoscope 198% 98: 1012-5. 11. Gantz BJ, Gmuer A, Fisch U. lntraoperative evoked electromyography in Bell's palsy. Am J Otolaryngo1 1982; 3: 273-8. 12. Fisch U. Felix H. On the pathogenesis of Bell's palsy. Acta Otolaryngol (Stockh) 1983; 95: 532-8. 13. Parry GJ. Brown MJ. Arachidonate-induced experimental nerve infarction. J Neurol Sci 1981; 5 0 123-33. 14. Calcaterra TC. Rand RW,Bentson JR. ischemic paralysis ofthe facial nerve: A possible etiologic factor in Bell's palsy. Laryngoscope 1976; 86: 92-7. Manuscript received Nocrrnber 9. 1990: accrpied March 22. I991
Address for correspondence: H. Iritani, Department of Otolaryngology, Hyogo College of Medicine, 1-1, Mukogawa-cho, Nishinomiya 663, Japan
ISSN: 0001-6489 (Print) 1651-2251 (Online) Journal homepage: http://www.tandfonline.com/loi/ioto20
Neurophysiology of Ischemic Facial Nerve Paralysis in an Animal Model Hiroshi Iritani, Yoshihiko Nishimura & Toru Minatogawa To cite this article: Hiroshi Iritani, Yoshihiko Nishimura & Toru Minatogawa (1991) Neurophysiology of Ischemic Facial Nerve Paralysis in an Animal Model, Acta OtoLaryngologica, 111:5, 934-942, DOI: 10.3109/00016489109138433 To link to this article: http://dx.doi.org/10.3109/00016489109138433
Published online: 08 Jul 2009.
Submit your article to this journal
Article views: 5
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ioto20 Download by: [Purdue University Libraries]
Date: 23 March 2016, At: 19:47
Acta Otolaryngol (Stockh) 1991; 1 1 1: 934-942
Neurophysioiogy of Ischemic Facial Nerve Paralysis in an Animal Model HIROSHI IRITANI. YOSHIHIKO NlSHIMURA and TORU MINATOGAWA From the Dt.pattment of Otolann&ogy. Hyogo College of Medicine, Nishinomiya 663, Japan
Downloaded by [Purdue University Libraries] at 19:47 23 March 2016
iritani H, Nishimura Y. Minatogawa T. Neurophysiology of ischemic facial nerve paralysis in an animal model. Acta Otolaryngol (Stockh) 1991: I I I: 934-942. The establishment of an animal model for facial nerve paralysis is assuming increasing importance in clinical medicine and also in basic facial nerve research. We previously reported an animal model for ischemic facial nerve paralysis using selective vascular embolization through the internal maxillary and posterior auricular arteries in cats using Avitene which contains bovine microfibril collagen. In this paper, we determined the exact site of the lesion in established facial paralysis. A descending signal produced by direct stimulation to the contralatera1 motor cortex was able to elicit firing of the motor nucleus of the facial nerve, the extratemporal portion of the peripheral nerve. and the orbicularis oris muscle. After achieving complete facial nerve paralysis. this descending signal was completely abolished within the temporal bone area. whereas peripheral facial nerve stimulation elicited a normal evoked electromyogram of the orbicularis oris muscle. The present results suggest that the site of the lesion of ischemic facial nerve paralysis produced by ernbolization in an animal model is within the temporal portion of the seventh nerve, and this animal model may lead to the advancement of future facial nerve research which cannot be conducted in humans. Key words: cortieal stimulation. selective enibolization. motor eL.oked potentiab (MEPI.
INTRODUCTION In 1986, Balkany (1) demonstrated the precise intrinsic vasculature of the cat facial nerve, and reported that the main extrinsic vascular supply to the nerve was from the anterior inferior cerebellar artery which supplies the area from the pons to the geniculate ganglion. the petrosai artery. a branch of the middle meningeal artery, which supplies the area from the horizontal segment to the geniculate ganglion, and the stylomastoid artery, a branch of the posterior auricular artery, which supplies the inferior course of the facial nerve. One possible cause of peripheral idiopathic facial palsy is considered to be ischemia of the nerve in the Fallopian canal (2), and we have therefore focused our attention on obstruction of the vascular circulation to the nerve. In our previous report (3). we established an animal model for ischemic Facial nerve paralysis with selective vascular embolization in cats. Our animal model was a n atraumatic procedure and had a high rate of success in producing complete facial nerve paralysis with good reproducibility. Several other studies on experimental facial nerve palsy have been performed; however, most have employed some form of mechanical manipulation of the nerve, which makes interpretation of results difficult. Experimental studies (4, 5) on ligation of blood vessels to the peripheral nerve have been performed in order to produce nerve fiber degeneration. In 1990, experimental thrombosis of the intratympanic portion of the facial nerve using infusion of a suspension of ferrous carbonyl and cobalt magnet placed against the bony lining of the facial canal in the middle ear cavity was attempted on 10 rabbits with no clinical or electrophysiological signs of facial palsy, in order to elucidate the effects of impaired microcirculation on facial nerve function (6). The aim of the present study was to demonstrate neurophysiological evidence confirming the site of the lesion of ischemic facial nerve paralysis in our animal model.
Downloaded by [Purdue University Libraries] at 19:47 23 March 2016
Acla Ololaryngol (Slockh) 1 I I
Facial nerve paralysis in an animal model 935
Fig. 1. Ventral view of subtraction carotid angiogram of the head including the temporal bone (right), and its schematic illustration (left). There is a S-shaped curve in the internal maxillary artery proximal to the external rete. R.e.:external rete (carotid plexus), M.i.: internal maxillary artery, M.e.: external maxillary artery, L: lingual artery. A.p.: posterior auricular artery, T.s.:superficial temporal artery, C i . : internal carotid artery.
MATERIAL AND METHODS
Preparation Twenty-one healthy adult cats weighing more than 2.5 kg were used for this study. The animals were anesthetized with i.p. injection of ketamine hydrochloride (50 mg/kg) supplemented with one-third of the initial dose every 2 h during surgery. Xylocaine was used as a local anesthetic for the superficial tissues and for the pressure points of the restraints on the animal’s body. Atropine sulfate was given intravenously. All animals underwent tracheostomy and insertion of an intravenous cannula. Respiratory status was maintained with a Harvard ventilator, and body temperature was maintained using thermostatically controlled blankets with a rectal temperature probe set at 39°C. The skull covering the cerebellum was carefully removed by separating the temporal and occipital muscles. The cerebellum was removed to expose the rhomboid fossa, while performing meticulous haemostasis using a bipolar electrocoagulator and oxidized cellulose under a dissection microscope. Warm liquid paraffin was applied to the exposed areas to insulate them from the surrounding tissues and keep them moist. The left motor cortex was exposed via left frontal craniectomy, for placement of bipolar stimulating electrodes. The right extra-temporal portion of the facial nerve was prepared for the placement of recording and stimulating electrodes, and the nerve was insulated with warm liquid paraffin. After ligation of the right external carotid artery just distal to the external maxillary artery branch. a fine 1.0 mm diameter catheter was introduced into the right internal maxillary artery as schematically illustrated in Fig. 2, according to the angiogram of the cat’s head obtained in our previous report (3) (Fig. I). The experimental paradigm is shown in Fig. 3.
936 H. lririluni et al.
Acta Otolalyngol (Stockh) 1 1 1
rostra1 M.i.
Downloaded by [Purdue University Libraries] at 19:47 23 March 2016
M.i.
ri
-
caudal Type 1
embolization
Type 11
embolization
Fig 2. Schematic illustration of the two types of selective embolization used in this study. Abbreviations as in Fig. 1.
Coronal s.
1 . l .
Right motor nucleus of N.VU
-
Facial k n re In the right temporal bone
1
Facial n e w of
-a,
+
I
M. wbicuiaris oris
Fig.3. Neurophysiological experimental paradigm used in the present study.
Facial nerve paralysis in an animal model 937
Acta Otolalrngol (Stockh) I 1 1
:I\' :
:I\::: 5.0 msec.
-1o.vT
Downloaded by [Purdue University Libraries] at 19:47 23 March 2016
I
5.0 msec.
5.0 msec.
I
. 100 P
V
T
5.0 msec.
Fig. 4. Evoked responses of the motor nucleus of N. VII, the extra-temporal portion of the VIIth cranial nerve and the orbicular oris muscle elicited by contralateral motor cortex stimulation. Lefrr before embolization; Right: after embolization. (A) evoked response of motor nucleus of facial nerve; (B)evoked response of extra-temporal bone portion of facial nerve; (C) evoked response of orbicularis oris muscle.
After completion of a series of preparations, the head was fixed to a David Kopf stereotaxic frame for cats (David Kopf Instruments, California) with the animal in a prone position.
Stimulation The bipolar stimulating electrodes (tiny ball-shaped Ag-AgC1 electrodes) were placed over the left motor cortex for orthodromic activation of the right motor nucleus of the facial nerve, and a pair of U-shaped tungsten electrodes was applied to the extra-temporal portion of the right facial nerve, and connected for antidromic stimulation.
rnsec.
5.0 msec.
Fig. 5. The site of the recording electrode is confirmed to be in the motor nucleus of N. VII using antidromic stimulation of the VIIth nerve.
Downloaded by [Purdue University Libraries] at 19:47 23 March 2016
938 H.tritani et 01.
Acta Otolaryngol (Stockh) I1 I
Fig. 6. (A) Low magnification view showing the cat's brain stem thin section stained by Cresyl Violet. Scale bar = 1 mm; original magnification x 10. The area outlined in the box is shown at higher magnification in (B). (B) Detail of the area in (A) revealing the electrode (arrow) into the pool of motor nerve cell bodies (Nucleus of Vllth nerve motoneuron, arrouhmfs). Scale bar = 200 pm: original magnification ~ 4 0 .
Monophasic current (5-10 mA, 0.1-0.3 ms square wave pulses, frequency 0.2 Hz) was applied over the left facial representation of the motor cortex and to the right extra-temporal portion of the facial nerve. Recordings For recording of the facial nerve motoneurons, a monopolar tungsten electrode was placed in the center of the right facial nerve motoneuron pool in the facial nucleus, determined by recording orthodromic field potentials after direct stimulation to the left motor cortex. The evoked electromyogram (EMG)of the right orbicularis oris muscle was obtained using a standard bipolar concentric needle electrode for electromyography. To obtain action potentials of the extra-temporal portion of the facial nerve. a pair of Ushaped tungsten stimulation electrodes was used for recording. Recording positions in the right facial nucleus were marked by passing a 10 mA current through the recording electrode when each recording was completed. At the end of each experiment, the animal was injected with a lethal i.v. dose of pentobarbital sodium (NembutaP. Abbott) and perfused through the heart with saline followed by IOYo formaldehyde solution. The recording site was identified histologically with 10 pm serial frontal sections stained with Cresyl Violet. RESULTS As described in the methods section, the experimental procedures were so time-consuming and complicated that only half of the animals tolerated the entire procedure. We therefore only obtained data from 10 animals. For all cats, the first procedure was direct stimulation of the left motor cortex to record the evoked responses of the right orbicularis oris muscle. Supramaximal threshold stimulation elicited an evoked EMG response of the orbicularis oris muscle. Following EMG, a monopolar
Facial nerve paralysis in an animal model 939
Acta Otolaryngol (Stockh) I I 1
msec.
Fig. 7. Evoked response of orbicularis oris muscle
Downloaded by [Purdue University Libraries] at 19:47 23 March 2016
5.0 msec.
elicited by Vllth nerve stimulation (before embolization).
recording electrode was carefully inserted into the pons to identify the facial motor nucleus, in order to record the evoked potentials produced by direct orthodromic motor cortex stimulation. As shown in Fig. 4A, a large evoked response was obtained when the tip of the recording electrode entered the motor nucleus of the facial nerve. Evoked action potentials of the extratemporal portion of the right facial nerve and of the orbicularis oris muscle to direct stimulation of left motor cortex were also recorded, as shown in Fig. 4 B and 4C. The site of the recording electrode in the motor nucleus of the facial nerve was reconfirmed by antidromic stimulation of the extra-temporal portion of the facial nerve, as shown in Fig. 5. Histological confirmation of positioning of the recording electrode in the motor nucleus of the facial nerve is shown in Fig. 6. The evoked EMG response of the orbicularis oris muscle elicited by direct stimulation of the peripheral facial nerve was demonstrated (Fig. 7) prior to the embolization procedure. The motor nucleus of the facial motor nucleus was activated by stimulation of contralateral motor cortex with different latencies ranging from 6.0 to 7.9 ms with a mean of 7.1 50.7 ms depending on the depth of anesthesia in each of the 10 animals examined because of subtle differences in change of synaptic delay. The latencies of evoked responses obtained from the extra-temporal portion of the facial nerve ranged from 7.4 to 10.1 ms with a mean of 8.5 t0.8 ms, and from the orbicularis oris muscle ranged from 8.7 to 14.7 ms with a mean of 10.7?2.0 ms. However, when the motor nucleus of the facial nerve was identified and the experimental sequence commenced, these latencies remained unchanged in each animal throughout the course of the experiment. Therefore, in the present report only one set of representative data recorded from cat No. 11 are given. Representative data in the left hand traces of Fig. 4A-C, show the latencies of each evoked response of the motor nucleus of the facial nerve and peripheral facial nerve and the EMG ofthe orbicularis oris muscle to direct stimulation of the contralateral motor cortex: 7.8. 8.8 and 10.1 ms, respectively. When embolization of the right internal maxillary artery was performed through a fine catheter with 1.5 ml of 1.OYo Avitene@(microfibril bovine collagen, Avicone Inc, Texas) for 40 min, no immediate obvious changes were observed in the previously described evoked
Fig. 8. Evoked EMG of orbicularis oris muscle elicited by peripheral VIIth nerve stimulation after establishment of facial paralysis (60 min after embolization).
940
n. frirani et at.
Acta Otolaryngol (Stockh) 111
1 0 o p v ~
Downloaded by [Purdue University Libraries] at 19:47 23 March 2016
5.0 msec.
Fig. 9. Evoked response of orbicularis oris muscle elicited by stronger stimulation of N. VlI after establishment of complete facial paralysis (60 min after embolization).
responses to direct stirnulation of the contralateral motor cortex, and contractile movements of the right orbicularis oris muscle were observed. Forty-five minutes after embolization, however, there was abrupt cessation of the evoked responses of the extra-temporal portion of the peripheral facial nerve and the EMG of the orbicularis oris muscle. The evoked response of the motor nucleus of the facial nerve still showed an active recording, as shown in the right hand traces of Fig. 4A-C. At that time, no visible contractile movement of the orbicularis oris muscle was observed. The evoked EMG response of orbicularis oris muscle could still be elicited by peripheral facial nerve stimulation after establishing complete facial nerve paralysis (Fig. 8). To confirm the conduction block in the temporal bone area. a much stronger orthodromic stimulus to the motor nucleus of the facial nerve was applied t o record the evoked response of orbicularis oris muscie (Fig. 9). and this was also applied to the extra-temporal portion of the peripheral facial nerve to elicit an antidromically evoked response of the motor nucleus of the facial nerve (Fig. 10). As is shown in Figs. 9 and 10, only a slight response was recorded.
DISCUSSION
In our previous report (3), we stated that the establishment of an animal model for ischemic or viral facial nerve paralysis is crucial to future developments in facial nerve research. The present results show that direct stimulation of the facial representation of the motor cortex in the experimental animal can produce a descending evoked potential distally in the end organ (the orbicularis oris muscle) through the motor nucleus of the facial nerve. Many of the recent developments in clinical intraoperative monitoring of the motor system have been made by Levy et al. (7-9). who reported techniques for stimulating the motor system and recording from the spinal cord of animals and humans. A descending signal originating from pyramidal cells activated by motor cortex stimulation elicits the motor-evoked potential
6.05 msec.
50
P.TL 5.0 m s e c .
Fig. 10. Evoked response of motor nucleus of N. VIl elicited by antidromic stimulation of the peripheral seventh nerve (60 min after embolization).
Downloaded by [Purdue University Libraries] at 19:47 23 March 2016
Acta Otolaryngol (Stockh) I 1 1
Facial nerve paralysis in an animal model 94 1
(MEP), and this MEP has been recorded traveling down the spinal cord, and finally activating muscle action potentials. When the lesion is created within the course of the pathway, the signal is almost completely abolished. Thus, the techniques for recording of MEPs have been utilized for intraoperative diagnostic and prognostic testing of cranial nerves. Recently in 1988, Estrem et al. (10) documented their data on MEPs of the facial musculature in dogs, and stated that magnetic stimulation of the motor cortex allows noninvasive study of the entire course of the facial nerve. In a similar manner, our present results clearly demonstrated that the lesion of established ischemic facial nerve paralysis with selective vascular embolization in the experimental animal model is located in the segment of the facial nerve within the temporal bone. The pathogenesis of Bell’s palsy still remains controversial, but there is some histologic and clinical evidence to suggest that the injury to the facial nerve occurs within its intratemporal course (11). In Gantz, Gmuer & Fisch’s paper, the site of the block of nerve impulse conduction was identified in 16 of 18 patients undergoing decompression for Bell’s palsy, and in whom the lesions extended for only a few millimeters and were proximal to the geniculate ganglion in 15 (94%) of these patients. Fisch & Felix (12) in 1983 reviewed anatomical, electrophysiological and histopathological data obtained in the acute phase of Bell’s palsy, and their results supported the entrapment neuropathy concept of Bell’s palsy. They postulated that the meatal foramen is by far the narrowest point of the entire Fallopian canal, and confirmed that the conduction block was situated between the geniculate ganglion and the meatal foramen in 94%of the patients, confirming the critical role of the meatal foramen and proximal labyrinthine segment in the pathogenesis of Bell’s palsy. Although, in the present experimental series, we could not define the precise location of the lesion of ischemic facial paralysis in our animal model as Fisch & Felix did, it is a useful animal model for facial nerve palsy, because the site of the lesion is within the temporal bone area. The other important point which should be discussed in this paper is that the present results are not in agreement with those reported by Frankander et al. (6) as described in the Introduction. In their experiment, despite a total absence of “open” vessels on the treated side, no light or electron microscopic signs of nerve damage were observed, and they concluded that intraneural vascular insufficiency in itself was not sufficient to cause facial palsy. Parry & Brown ( I 3) injected arachidonic acid, a potent stimulus to platelet aggregation and vasoconstriction, into the femoral artery of normal rats, and this resulted in the rapid onset of focal infarction of the proximal posterior tibia1 nerve in all animals, with distal evidence of Wallerian degeneration. A possible reason for the discrepancy between our data and that of Frankander et al. is thought to be related to the rapidity of development of vascular thrombosis. Another possible explanation is the occlusion of different vessels in experimental animals. Calcaterra et al. (14) in 1976 described two patients who, following embolization of vascular tumors with occlusion of the middle meningeal artery, developed total peripheral facial nerve paralysis which persisted for at least 6 months. This paper demonstrates the important role of the petrosal artery, a branch of the middle meningeal artery, in the vascular supply to the facial nerve. If the cobalt magnet in the experiment of Frankander et al. was placed more rostrally in the middle ear. thrombosis of the petrosal artery, with resulting facial nerve palsy. would be expected to occur. Further histological studies clarifying the location of lesions in ischemic facial paralysis are in progress.
ACKNOWLEDGMENTS The authors wish to thank Professor Takeo Kumoi for his generous advice and help with this study.
942 H.iritani et at.
Ada Otolaryngol (Stockh) 1 I 1
Downloaded by [Purdue University Libraries] at 19:47 23 March 2016
REFERENCES I. Balkany TB. The intrinsic vasculature of the cat facial nerve. Laryngoscope 1986; 96: 70-7. 2. Blunt MJ. The Dossible role of vascular changes in the etiology of Bell's palsy. J Laryngol 1956; 70: 701-13. 3. Iritani H, Nishimura Y, Minatogawa T et al. An animal model for ischemic facial nerve paralysis with a selective embolization. Ear Res Jpn 1989; 20: 195-6. 4. Korthals JK. Wisniewski HM. Peripheral nerve ischemia: Part I. Experimental model. J Neurol Sci 197%24: 65-76. 5. Hess K. Eames RA, Darveniza P. Gilliatt RW. Acute ischemic neuropathy in the rabbit. J Neurol Sci 1979; 4 4 19-43. 6. Frankander L. Thomander L, Bagger-Sjobick D. Experimental thrombosis of the microcirculation in the intratympanic portion of the facial nerve. An experimental study in the rabbit. In: Castro D, ed. The facial nerve. Amstelveen, Netherlands: Kugler, 1990: 131-3. 7. Levy WJ. York DH. Evoked potentials from the motor tracts in humans. Neurosurgery 1983; 12: 422-9. 8. Levy WJ. York DH. McCaffrey M,Tanzer F. Motor evoked potentials from transcranial stimulation of the motor cortex in humans. Neurosurgery 1984; 15: 287-302. 9. Levy WJ, Mctaffrey M. York DH. Tanzer F. Motor evoked potentials from transcranial stimulation of the motor cortex in cats. Neurosurgery 1984; 15: 214-27. 10. Estrem SA. Haghighi S, Levy WJ. Wertheimer R, Kendall M. Motorevoked potentials of facial musculature in dogs. Laryngoscope 198% 98: 1012-5. 11. Gantz BJ, Gmuer A, Fisch U. lntraoperative evoked electromyography in Bell's palsy. Am J Otolaryngo1 1982; 3: 273-8. 12. Fisch U. Felix H. On the pathogenesis of Bell's palsy. Acta Otolaryngol (Stockh) 1983; 95: 532-8. 13. Parry GJ. Brown MJ. Arachidonate-induced experimental nerve infarction. J Neurol Sci 1981; 5 0 123-33. 14. Calcaterra TC. Rand RW,Bentson JR. ischemic paralysis ofthe facial nerve: A possible etiologic factor in Bell's palsy. Laryngoscope 1976; 86: 92-7. Manuscript received Nocrrnber 9. 1990: accrpied March 22. I991
Address for correspondence: H. Iritani, Department of Otolaryngology, Hyogo College of Medicine, 1-1, Mukogawa-cho, Nishinomiya 663, Japan
