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Afferent nerve information underlying the effects of electroacupuncture in rat
EXPERIMENTAL
Afferent
65, 457-461 (1979)
NEUROLOGY
Nerve
information Underlying the Effects Electroacupuncture in Rat
KAZUO Department
of Physiology,
TODA
AND MASAMICHI
Faculty of Dentistry, Bunkyo-ku, Tokyo Received
February
of
ICHIOKA’
Tokyo Medical 113 Japan
and Dental
University
16, 1979
In the previous reports, the authors revealed that electroacupuncture stimulation produces analgesic effects in rats probably identical to those observed in man (3-6). In electroacupuncture mechanisms, peripheral afferent nerve impulse evoked by stimulation of the meridian points has been suggested to be essential for those effects (1, 2). The present study reports the effects of direct electrical stimulation of peripheral nerves, not the stimulation of meridian points, as conditioning stimulation in order to determine the role of peripheral nerve impulses on electrically induced acupuncture effects. The experiments were carried out on anesthetized Wistar albino rats weighing 350 to 450 g as reported elsewhere (3,4). The radial, median, and ulnar nerves of the brachial plexus were exposed on both sides. Each nerve was stimulated with a bipolar electrode (interpolar distance of 2 mm) to which constant current rectangular pulses of 0.1 ms duration were applied at 45 Hz for 15 min under the same conditions as electroacupuncture stimulation described elsewhere (3, 4). The stimulus intensity was about eight times stronger than that producing the minimum compound action potential which was recorded from each nerve with a bipolar electrode (interpolar distance of 3 mm) situated central to the stimulating electrode. To apply noxious stimuli, a pair of stainless-steel wire stimulating electrodes (interpolar distance of 1.5 mm) of 0.1 mm diameter, insulated Abbreviation: dEMG--digastric electromyogram. 1 The authors wish to express thanks to Dr. T. Sato for valuable discussions and to Dr. H. Tanaka and Dr. A. Iriki for their technical assistance. This work was supported in part by grant 348327 (1978 and 1979) from the Ministry of Education, Culture and Science of Japan. 457 0014-4886/79/080457-05$02.00/O Copyright 0 1979 by Academic Press, Inc. All rights of reproduction in any form reserved.
458
TODA AND ICHIOKA
except for the tips, was inserted into the tooth pulp of the right lower incisor. Test stimulation of the pulp nerve was applied electrically by rectangular pulses with duration of 0.1 ms at 2 Hz. The entire tooth was covered with dental cement or wax to isolate the electrodes from the saliva. The effect of conditioning stimulation was estimated by the degree of suppression of the digastric electromyogram (dEMG) in jaw-opening reflex. This was recorded from the right anterior belly of the digastric muscle utilizing a bipolar needle electrode (interpolar distance of 4 mm) electrically summated with an integrator of 400 ms time constant (3). The dEMG activity was obtained by averaging about 10 successive integrated dEMG responses. The body temperature of the animals was maintained between 37 + 0.2”C with a heating pad. A typical example of the effects of direct ipsilateral radial nerve stimulation with eight times threshold intensity on the integrated dEMGs evoked by tooth pulp nerve stimulation with an intensity of about 1.5 times above the threshold is shown in Fig. 1. The horizontal bar indicates a period of 15min conditioning stimulation of the radial nerve. The dEMG responses were gradually suppressed during conditioning stimulation and the after effect remained for about 55 min. Figure 2 shows the relationship between ipsilateral radial (0), median (A), and ulnar (0) nerve stimulation and the dEMG responses elicited by tooth pulp stimulation. The horizontal bar under the abscissa indicates 15 min conditioning stimulation delivered to each of the three nerves. A maximum 50% suppression of the control was obtained following radial nerve stimulation. On the other hand, stimulation of the median or ulnar nerve, induced a maximum suppression of about 75 and 90%, respectively. The maximum suppression appeared 5 to 15 min after the onset of the stimulation. The effects were statistically significant when compared with those obtained without conditioning stimulation (Cl) (Z’ < 0.05).
0 I ON
25
5
10
15
25
LO
70
min
I OFF 5lllV 1
5sec FIG. 1. Effect of conditioning electrical stimulation of the radial nerve on the integrated dEMGs of the anterior belly evoked by lower incisor tooth pulp stimulation. The horizontal bar indicates a 15-min conditioning stimulation. Each record consisted of about 10 successive integrated dEMG responses.
ELECTROACUPUNCTURE
459
IN RAT
0
CONTROL
0
RADIAL
A
MEDIAN
0
ULNAR
I PS I
I
III
0 1
5
1
I
1
I
10
15
25
40
I
70 mln
I TIME
AFTER
CONDITIONING
STIMULATION
2. Effects of the conditioning electrical stimulation of the ipsilateral radial (O), median and ulnar nerves (0) on the dEMG responses. In both this and the next figure, the horizontal bar under the abscissa indicates 15-min conditioning stimulation and the control (Cl) represents the case without conditioning stimulation. Ordinate: relative amplitude of dEMG; abscissa: time in minutes after the conditioning stimulation. Vertical bars indicate SE N = 10. FIG.
(A),
The effects of contralateral radial (O), median (A), and ulnar (+) nerve stimulation on the dEMGs are shown in Fig. 3. Conditioning stimulation of radial, median, and ulnar nerves suppressed the dEMG responses to about 65, 70, and 90% of the control, respectively. The suppressing effects of radial or median nerve stimulation were statistically significant (8’ < O.OS), but that of ulnar nerve stimulation was not (Z’ > 0.05). When ipsilateral and contralateral radial nerves were stimulated simultaneously, the maximum suppression was to about 50% of control, which was almost equivalent to those values obtained when only the ipsilateral radial nerve was stimulated. In the present experiments, the effectiveness of conditioning stimulation was found in 10 of 11 rats. No effect was observed in one rat, even when each of the three nerves was stimulated with strong intensity. The present study revealed that stimulation of the radial nerve produced the most effective suppression of the dEMG when studied in the jaw-opening reflex. Maximum suppression during direct stimulation of the
TODA AND ICHIOKA
n l
RADIAL
A
MEDIAN
l
ULNAR
CONTRA 50
CONTROL
1
0 1 LII 0
1 5 TIME
IO
15 AFTER
I
I
25
LO
CONDITIONING
f 70 rmn
STIMULATION
FIG. 3. Effects of conditioning electrical stimulation of the contralateral radial (O), median (A), and ulnar (e) nerves on the dEMG responses. Ordinate: relative amplitude of dEMG; abscissa: time in minutes after the conditioning stimulation. Vertical bars indicate SE, N = 10. Note that the effects of the conditioning stimulation were smaller than those shown in Fig. 2.
radial nerve was almost as effective as that during the electroacupuncture stimulation applied to the Ho-Ku point (3,4). Furthermore, the time course of direct nerve stimulation effects was similar to that of electroacupuncture stimulation. These facts suggest that afferent impulses for suppressing the jaw-opening reflex evoked by electroacupuncture stimulation to the Ho-Ku point are mainly conducted along the radial nerve. The conditioning stimulation delivered to the ipsilateral nerves is more effective than that delivered to contralateral nerves. This difference seems to suggest that the specific jaw-opening reflex suppressive fibers from the ipsilateral Ho-Ku point is projected to the central nervous areas responsible for suppressing the jaw-opening reflex. REFERENCES 1. Acupuncture Anesthesia Research Unit. 1974. The peripheral afferent pathway in acupuncture analgesia. Chin. Med. J. 6: 360-364. 2. Shanghai Acupuncture Anesthesia coordinating Group. 1975. Acupuncture anesthesia.
ELECTROACUPUNCTURE
3. 4.
5. 6.
IN RAT
461
An anesthesic method combining traditional Chinese and western medicine. Chin. Med. J. 1: 13-27. TODA, K. 1978. Effects of electroacupuncture on rat jaw opening reflex elicited by tooth pulp stimulation. Jup. J. Physiol. 28: 485-497. TODA, K., AND M. ICHIOKA. 1978. Electroacupuncture: Relations between forelimb afferent impulses and suppression of jaw opening reflex in the rat. Exp. Neural. 61: 465-470. TODA, K., M. ICHIOKA, H. SUDA, AND A. IRIKI. 1979. Effects of electroacupuncture on the somatosensory evoked response in rat. Exp. Neural. 63: 652-658. TODA, K., M. ICHIOKA, A. IRIKI, AND H. SUDA. 1979. Electroacupuncture effects on the field potentials in the caudal part of the spinal trigeminal nucleus evoked by tooth pulp stimulation in rat. Exp. Neurol. 64: 704-709.
Afferent
65, 457-461 (1979)
NEUROLOGY
Nerve
information Underlying the Effects Electroacupuncture in Rat
KAZUO Department
of Physiology,
TODA
AND MASAMICHI
Faculty of Dentistry, Bunkyo-ku, Tokyo Received
February
of
ICHIOKA’
Tokyo Medical 113 Japan
and Dental
University
16, 1979
In the previous reports, the authors revealed that electroacupuncture stimulation produces analgesic effects in rats probably identical to those observed in man (3-6). In electroacupuncture mechanisms, peripheral afferent nerve impulse evoked by stimulation of the meridian points has been suggested to be essential for those effects (1, 2). The present study reports the effects of direct electrical stimulation of peripheral nerves, not the stimulation of meridian points, as conditioning stimulation in order to determine the role of peripheral nerve impulses on electrically induced acupuncture effects. The experiments were carried out on anesthetized Wistar albino rats weighing 350 to 450 g as reported elsewhere (3,4). The radial, median, and ulnar nerves of the brachial plexus were exposed on both sides. Each nerve was stimulated with a bipolar electrode (interpolar distance of 2 mm) to which constant current rectangular pulses of 0.1 ms duration were applied at 45 Hz for 15 min under the same conditions as electroacupuncture stimulation described elsewhere (3, 4). The stimulus intensity was about eight times stronger than that producing the minimum compound action potential which was recorded from each nerve with a bipolar electrode (interpolar distance of 3 mm) situated central to the stimulating electrode. To apply noxious stimuli, a pair of stainless-steel wire stimulating electrodes (interpolar distance of 1.5 mm) of 0.1 mm diameter, insulated Abbreviation: dEMG--digastric electromyogram. 1 The authors wish to express thanks to Dr. T. Sato for valuable discussions and to Dr. H. Tanaka and Dr. A. Iriki for their technical assistance. This work was supported in part by grant 348327 (1978 and 1979) from the Ministry of Education, Culture and Science of Japan. 457 0014-4886/79/080457-05$02.00/O Copyright 0 1979 by Academic Press, Inc. All rights of reproduction in any form reserved.
458
TODA AND ICHIOKA
except for the tips, was inserted into the tooth pulp of the right lower incisor. Test stimulation of the pulp nerve was applied electrically by rectangular pulses with duration of 0.1 ms at 2 Hz. The entire tooth was covered with dental cement or wax to isolate the electrodes from the saliva. The effect of conditioning stimulation was estimated by the degree of suppression of the digastric electromyogram (dEMG) in jaw-opening reflex. This was recorded from the right anterior belly of the digastric muscle utilizing a bipolar needle electrode (interpolar distance of 4 mm) electrically summated with an integrator of 400 ms time constant (3). The dEMG activity was obtained by averaging about 10 successive integrated dEMG responses. The body temperature of the animals was maintained between 37 + 0.2”C with a heating pad. A typical example of the effects of direct ipsilateral radial nerve stimulation with eight times threshold intensity on the integrated dEMGs evoked by tooth pulp nerve stimulation with an intensity of about 1.5 times above the threshold is shown in Fig. 1. The horizontal bar indicates a period of 15min conditioning stimulation of the radial nerve. The dEMG responses were gradually suppressed during conditioning stimulation and the after effect remained for about 55 min. Figure 2 shows the relationship between ipsilateral radial (0), median (A), and ulnar (0) nerve stimulation and the dEMG responses elicited by tooth pulp stimulation. The horizontal bar under the abscissa indicates 15 min conditioning stimulation delivered to each of the three nerves. A maximum 50% suppression of the control was obtained following radial nerve stimulation. On the other hand, stimulation of the median or ulnar nerve, induced a maximum suppression of about 75 and 90%, respectively. The maximum suppression appeared 5 to 15 min after the onset of the stimulation. The effects were statistically significant when compared with those obtained without conditioning stimulation (Cl) (Z’ < 0.05).
0 I ON
25
5
10
15
25
LO
70
min
I OFF 5lllV 1
5sec FIG. 1. Effect of conditioning electrical stimulation of the radial nerve on the integrated dEMGs of the anterior belly evoked by lower incisor tooth pulp stimulation. The horizontal bar indicates a 15-min conditioning stimulation. Each record consisted of about 10 successive integrated dEMG responses.
ELECTROACUPUNCTURE
459
IN RAT
0
CONTROL
0
RADIAL
A
MEDIAN
0
ULNAR
I PS I
I
III
0 1
5
1
I
1
I
10
15
25
40
I
70 mln
I TIME
AFTER
CONDITIONING
STIMULATION
2. Effects of the conditioning electrical stimulation of the ipsilateral radial (O), median and ulnar nerves (0) on the dEMG responses. In both this and the next figure, the horizontal bar under the abscissa indicates 15-min conditioning stimulation and the control (Cl) represents the case without conditioning stimulation. Ordinate: relative amplitude of dEMG; abscissa: time in minutes after the conditioning stimulation. Vertical bars indicate SE N = 10. FIG.
(A),
The effects of contralateral radial (O), median (A), and ulnar (+) nerve stimulation on the dEMGs are shown in Fig. 3. Conditioning stimulation of radial, median, and ulnar nerves suppressed the dEMG responses to about 65, 70, and 90% of the control, respectively. The suppressing effects of radial or median nerve stimulation were statistically significant (8’ < O.OS), but that of ulnar nerve stimulation was not (Z’ > 0.05). When ipsilateral and contralateral radial nerves were stimulated simultaneously, the maximum suppression was to about 50% of control, which was almost equivalent to those values obtained when only the ipsilateral radial nerve was stimulated. In the present experiments, the effectiveness of conditioning stimulation was found in 10 of 11 rats. No effect was observed in one rat, even when each of the three nerves was stimulated with strong intensity. The present study revealed that stimulation of the radial nerve produced the most effective suppression of the dEMG when studied in the jaw-opening reflex. Maximum suppression during direct stimulation of the
TODA AND ICHIOKA
n l
RADIAL
A
MEDIAN
l
ULNAR
CONTRA 50
CONTROL
1
0 1 LII 0
1 5 TIME
IO
15 AFTER
I
I
25
LO
CONDITIONING
f 70 rmn
STIMULATION
FIG. 3. Effects of conditioning electrical stimulation of the contralateral radial (O), median (A), and ulnar (e) nerves on the dEMG responses. Ordinate: relative amplitude of dEMG; abscissa: time in minutes after the conditioning stimulation. Vertical bars indicate SE, N = 10. Note that the effects of the conditioning stimulation were smaller than those shown in Fig. 2.
radial nerve was almost as effective as that during the electroacupuncture stimulation applied to the Ho-Ku point (3,4). Furthermore, the time course of direct nerve stimulation effects was similar to that of electroacupuncture stimulation. These facts suggest that afferent impulses for suppressing the jaw-opening reflex evoked by electroacupuncture stimulation to the Ho-Ku point are mainly conducted along the radial nerve. The conditioning stimulation delivered to the ipsilateral nerves is more effective than that delivered to contralateral nerves. This difference seems to suggest that the specific jaw-opening reflex suppressive fibers from the ipsilateral Ho-Ku point is projected to the central nervous areas responsible for suppressing the jaw-opening reflex. REFERENCES 1. Acupuncture Anesthesia Research Unit. 1974. The peripheral afferent pathway in acupuncture analgesia. Chin. Med. J. 6: 360-364. 2. Shanghai Acupuncture Anesthesia coordinating Group. 1975. Acupuncture anesthesia.
ELECTROACUPUNCTURE
3. 4.
5. 6.
IN RAT
461
An anesthesic method combining traditional Chinese and western medicine. Chin. Med. J. 1: 13-27. TODA, K. 1978. Effects of electroacupuncture on rat jaw opening reflex elicited by tooth pulp stimulation. Jup. J. Physiol. 28: 485-497. TODA, K., AND M. ICHIOKA. 1978. Electroacupuncture: Relations between forelimb afferent impulses and suppression of jaw opening reflex in the rat. Exp. Neural. 61: 465-470. TODA, K., M. ICHIOKA, H. SUDA, AND A. IRIKI. 1979. Effects of electroacupuncture on the somatosensory evoked response in rat. Exp. Neural. 63: 652-658. TODA, K., M. ICHIOKA, A. IRIKI, AND H. SUDA. 1979. Electroacupuncture effects on the field potentials in the caudal part of the spinal trigeminal nucleus evoked by tooth pulp stimulation in rat. Exp. Neurol. 64: 704-709.