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Afferent vagal modulation of brain stem somatic reflex activity
EXPERIMENTAL
Afferent
NEUROLOGY
Vagal
27, 534-544
(19%)
Modulation Reflex
M. H.
CHASE,
Y.
of
Brain
Stem
Somatic
Activity
NAKAMURA,
AND
S.
TORII
’
Veteraw Administration Hospital, Sepulzleda, and the Department of .Inaio~rty and Physiology, Sckool of Medicine, Uninersity of California at Los Angeles, California 90024 Received
February
20, 1970
The influenceof cervical vagal afferent activity upon somaticreflexes was examined in immobilized, encephale isole cats. Antagonistic brain stem somatic reflexes, the masseteric (jaw closing) and the digastric (jaw opening), were induced in conjunction with stimulation of the cut central end of the cervical vagus nerve. Single pulse or pulse train vagal stimulation led to three sequential periods of masseteric reflex modulation : (a) facilitation, (b) depression, and (c) facilitation. Under a similar experimental paradigm the digastric reflex was first facilitated and then depressed. Repetitive vagal stimulation induced tonic facilitation of the masseteric reflex and tonic depression of the digastric reflex. These resultswere discussed in relation to the effectsexerted by vagal afferents upon the central nervous system and behavior, and the functional significance of visceralinformationreceivedby the brain. Introduction
We recently reported that excitation of vagal afferents can modulate the electroencephalographic (EEG) activity of the cerebral cortex and subcortical structures (9-l 1) . EEG synchronization and desynchronization were induced in conjunction with the excitation of specific afferents from the abdominal and thoracic cavities. Other studies have demonstrated that central vagal excitation may modify not only central neural activity (15, 17, 18, 25, 33) but also behaviors ranging from sleep to sham rage (1, 2, 19, 21, 26). Thus, it is clear that afferents which originally were thought to be concerned solely with visceral motor reflex activity are capable of influencing the electrical activity of the central nervous system (CNS) as 1 This research was supported by the United States Veterans Administration and by grants from the U.S. Public Health Service (MH-10083) and the National Science Foundation (GF 262). Bibliographic assistance was received from the UCLA Brain Information Service, which is part of the Neurological Information Network of NINDS and is supported under Contract DHEW PH-43-66-59. Part of this research was carried out at Toho University, Tokyo, Japan. 534
\‘AGAL
MODt?LA’l-IOS
OF
KEFLEXES
535
well as a variety of behaviors. To further our understanding of the mechanisms by which viscera1 afferents affect CNS activity and integrated patterns of behavior we were interested in determining whether a basic component of behavior, the somatic reflex, might he modified by afferent vagal excitation. Afferent vagal activity in the intact animal initiates visceral reflexes which affect a variety of peripheral systems (e.g., respiratory, circulatory) which in turn influence somatomotor activity (6, 14, 16, 20, 21, 30). In order to eliminate these indirect effects we decided that the preparation of choice would be the encephale isole animal which was immobilized and given artificial respiration. In this preparation the influence of central cervical vagal stimulation must be examined in conjunction with somatic reflexes which are organized entirely within the brain stem, and it was for this reason that we chose the monosynaptic masseteric and the polysynaptic digastric reflexes. We have previously studied these reflexes in immobilized preparations in conjunction with stimulation of cortical and subcortical areas (13, 24) and have correlated variations in reflex amplitude with various behavioral states in freely moving animals (7, 8). We now report on our current studies of vagal control of somatic reflex activity. Methods
Experiments were carried out on 26 adult cats. Each was first anesthetized with ether. The saphenous vein and trachea were then cannulated, and the animal was placed in a stereotaxic instrument. Anesthesia was maintained during subsequent surgical procedures by the intravenous injection of a short acting anesthetic agent, sodium methohesital (Hrevital ). The surgical procedures included (n) transection of the spinal cord at C,, (b) bilateral severance of the vagal and sympathetic trunks at a low cervical level, (r ) isolation of the right or left cervical vagus nerve from the adjacent sympathetic trunk and perineurium, and (d ) isolation and section of the right masseter nerve and the right mylohyoid nerve (i.e., digastric nerve branch to the anterior belly of the digastric muscle). The pattern of stimulation and recording is shown diagramatically in Fig. 1. A bipolar stimulating electrode was placed on the cut central end of the right or left cervical vagus nerve (Fig. 1A). -4 bipolar strut electrode was placed within the right mesencephalic nucleus of the Vth nerve (Fig. 1B) to induce the monosynaptic (jaw closing) masseteric reflex (Mass. R.). Screw electrodes were placed in the mandibular canal to induce the polysynaptic (jaw opening) digastric reflex (Dig. R.) by excitation of the inferior dental nerve (Fig, 1C). Bipolar recording electrodes were placed on the ipsilateral vagus nerve (Fig. 1A’) between the vagal stimulating electrode and the brain and on the cut central end of the masseter (Fig. 1B’)
536
CHASE,
NAKAMURA,
AND
TORI1
FIG. 1. Stimulation and recording paradigm. The masseteric reflex was induced by delivering an electrical stimulus to the mesencephalic trigeminal nucleus (B) and was monitored along the cut central end of the ipsilateral masseter nerve (Bl). The digastric reflex was induced by stimulation of the inferior dental nerve (C) and was recorded along the cut central end of the ipsilateral mylohyoid (digastric) nerve (Cl). A recording electrode was placed on the cervical vagus nerve (Al) approximately 5 cm central to the stimulating electrode (A) in order to monitor the induced afferent vagal activity.
and mylohyoid (Fig. 1C’) nerves. The exposed portions of the peripheral nerves were surrounded by a viscous solution of mineral oil and petroleum jelly. All wound edges and pressure points, as well as the nerve trunks supplying these areas, were infiltrated every 30 min with a local anesthetic, lidocaine (Xylocaine), throughout the course of the experiment. The animal’s body temperature was maintained at approximately 37C by a heating pad. After all surgical procedures were completed, Brevital anesthesia was discontinued, and gallamine triethiodide (Flaxedil) was administered. The animal was subsequently maintained by artificial respiration. Grass and Nihon Kohden stimulators were employed to induce activity along the vagus nerve and to elicit the Mass. R. and the Dig. R. The reflex responseswere displayed on an oscilloscope and photographed. For this investigation vagal excitation was carried out with stimuli which were sufficient to induce activity in all fiber groups which was determined by monitoring the induced vagal neurographic activity (9). A Nihon Kohden computer (ATAC-501) was used to obtain averaged reflex responses. Conditioning-test intervals were measured from the first vagal pulse to the onset of the pulse to the mesencephalicnucleus or inferior dental nerve. At the termination of each experiment the animal was dispatched with an overdose of sodium pentobarbital (Nembutal), and the brain was removed
I’AGAL
MODULATIOK
OF
for histologic determination of the placement mesencephalic trigeminal nucleus.
REFLEXES
of the electrode within
53i the
Results
SiJrglr Prrlsr 1 ‘nytrl Stilirulfltim. The amplitude of the Mass. K. varied xcoiding to the latency with d~ich it was evoked following single pulse stimdation of the cut central end of the cervical vagus nerve. X brief period of reflex facilitation occurred when the conditioning-test interval was between 2 and 5 met (Fig. 2 ). This initial facilitory phase was fol-
FIG. 2. The tnasseteric reflex was examined at various intervals following single pulse vagal stimulation. Consistent reflex depression was obtained at latencies from IO-35 msec. This phase was preceded by a brief period of facilitation and was followed by a long-lasting period of facilitation. The time course curve was generated by dividing the mean amplitude of ten reflexes preceded by a single vagal pulse by the mean amplitude of ten control responses. Examples of the raw data are shown which correspond to the points A, I3, and C on the time course curve (a: reflex control; b: reflex preceded by vagal stimulation). The reflex latency was measured from the beginning of the vagal pulse to the beginning of the pulse to the mesencephalic trigeminal nucleus. For this and the following figures the reflexes which are presented were elicited at the rate of I/set and represent the averaged pattern of reflex response to ten consecutive trials of reflex induction. Mesencephalic nucleus : 4 v, 0.2 msec; vagus : 10 v, 1 msec; calibration : 50 pv, 2 msec.
538
CHASE,
NAKAMURA,
AND
TORI1
lowed by a period of depression f ram 10-35 msec (Fig. 2A, B) . A second relatively long period of facilitation was observed which arose with a latency of approximately 35 msec and lasted for a period of more than 50 msec (Fig. 2C ). Reflex depression was more consistently obtained and was of greater magnitude than reflex facilitation. The Dig. R. showed an initial brief period (O-S msec) of facilitation (Fig. 3A, B) which was observed in most but not all trials. Reflex depression, which was consistently obtained, occurred with a latency of approximately 10 msec and lasted for over 100 msec (Fig. 3C). The initial period of Dig. R. depression overlapped the entire period of Mass. R. depression. The effectiveness of vagal stimulation to modify the Dig. R. was reduced when the conditioning vagal pulse was evoked at rates greater than l/set. Pulse Train Vagal Stimulation. When multiple pulses were used as the vagal conditioning stimulus, the degree of depression and facilitation of both the Mass. and Dig. R. was markedly enhanced. No qualitative change
I 0
10
20
30 40 CONDIlIOWIN6
-
50 ItSI
so 10 IWltRVll
IO
90
Ii0
WC
FIG. 3. The time course curve for the digastric reflex response to vagal stimulation was obtained according to the same paradigm described in the legend of Fig. 2 for the masseteric reflex. Early facilitation (A,B) of the digastric reflex was followed by a long-lasting period of depression (C). Inferior dental nerve : 1.2 v, .Ol msec ; vagus : 8 v, 1 msec ; calibration : 50 pv, 2 msec.
VAGAL
MODULATIOiY
OF
REFLEXES
539
in the pattern of refles response was observed when pulse trains were applied to the vagus nerve instead of single conditioning pulses. R~spmtsc~ Pattern of IndkGdrral Co~~~ponmts of t/w Digastric Reflex. Suprathreshold excitation of the inferior dental nerve led to a Dig. R. which was composed of two major components (Figs. -+A, SA). Liminal excitation resulted in the induction only of the first component (Figs. 4C, 5C). The influence of vagal stimulation upon each component of the Dig. R. was examined using short trains of conditioning pulses. Short Conditioning-Test Interval. When suprathreshold stimulation of the inferior dental nerve led to a response composed of two components (Fig. 4A), both increased slightly in amplitude when preceded by vagal pulses (Fig. 4D). This pattern of facilitation was also obtained with a control reflex of smaller amplitude (Fig. 4R,E). \Vhen a liminally induced reflex was used as a control ( Fig. -CC). its amplitude increased following
: VAht
DR VAGUS
‘4’
MSFC
FIG. 4. At short conditioning-test intervals the digastric reflex (DR) was facilitated; control on the left and vagus stimulation on the right. The averaged digastric reflex consisted of a response with two components (A, B), both of which increased in amplitude in conjunction with vagal stimulation (D, E). At low levels of inferior dental nerve excitation only the first component of the digastric reflex was induced (C) ; following vagal stimulation its amplitude increased and activity was observed at a latency corresponding to the second component (F). Inferior dental nerve : A-l.4 v, B-l.3 v, C-l v, .Ol msec; vagus: 10 v, 1 msec; calibration: 100 gv, 2 msec.
540
CHASE,
NAKAMURA,
AND
TORI1
FIG. 5. At long conditioning-test intervals the digastric reflex was depressed; control, left; vagus stimulation, right. When both components of the digastric reflex were present as a control (A) they were reduced in amplitude (D) in conjunction with vagal stimulation. When liminally induced the first (C) and second (B) components were suppressed (F, E). Inferior dental nerve: A-l.5 v, B-l.3 v, C-l v, .Ol msec; vagus : 10.0v, 1 msec; calibration: 100pv, 2 msec.
vagal stimulation, and a small response appeared at a latency corresponding to the period of the second reflex component (Fig. 4F). Long Conditioning-Test Interval. During the period of Dig. R. depression obtained with a single vagal pulse (Fig. 3C), both components of the reflex were reduced in amplitude (Fig. 5). The first component, even when supraliminally induced, was depressed, as was the second component (Fig. 5A,D). In Fig. SC, a liminally induced response was completely abolished by vagal stimulation (Fig. SF). Repetitive Yagul Stinzulution~ Repetitive vagal stimulation (10-200 cps) was applied for periods of 10 sec. in conjunction with the continuous induction of either test reflex (evoked at the rate of l/set) . The amplitude of the Mass. R. increased during this paradigm; the antidromic potential (13) remained unchanged (Fig. 6A). Both cotnponents of the Dig. R. were depressed (Fig. 6B). The Dig. R. was more consistently modified in this paradigm than was the Mass. R., and it appeared that the relative degree of depression of the Dig R. was greater than that of facilitation of the Mass. R. At the termination of stimulation facilitation of the Mass. R. continued for a few seconds while the Dig. R. remained depressed. This
VAGAL
A.MR
MODULATION
OF
541
REFLEXES
j-
$I,
JL
?-J--
B. OR -I
FIG. 6. High-frequency repetitive central vagal excitation masseteric reflex (MR) facilitation and digastric reflex (DR) control, left ; vagus stimulation, first 10 set of stimulation; trigeminal nucleus : 5 v, 2 msec; inferior dental nerve : 1.5 v, 1 msec ; calibration : 50 pv, 5 msec.
(100 cps) resulted in depression during the right. Mesencephalic .Ol msec ; vagus : 9 v,
of vagal stimulation was more pronounced and was of longer duration for the Dig. R. than for the Mass. R.
after-effect
Discussion
This report indicates that a direct interaction of striking magnitude exists between vagal afferents and the somatic motor system. However, it should not be surprising that there is such interaction since parasympathetic information conveyed from the viscera can influence a wide variety of activities. For example, many of the individual behaviors which comprise sham rage may be either augmented or depressedaccording to the excitation of specific groups of visceral afferent fibers or a lack of impulses along them (3.19,26). Additionally, the EEG pattern of the cerebral cortex and a variety of subcortical structures can be synchronized or desynchromized, dependent upon information conveyed by specific afferent vagal systems (9). Investigations which have analyzed somatic responsesfollowing excitation of visceral
organs
have dealt primarily
with
stimulation
of the carotid
chemoreceptors and baroreceptors ( 16,21--23,27-29,32). These studies are in essential agreement, namely, carotid baroreceptor stimulation induces somatomotor depression and chemoreceptor stimulation leads to somatomotor facilitation. Although excitation of the cervical vagus does not include carotid body afferents, there are receptors within the thoracic cavity subserving
similar
functions.
The origin
of those afferent
fihers which
are acti-
542
CHASE,
NAKAMURA,
AND
TORI1
vated by cervical vagal stimulation has been discussed (9,12). Certain studies have noted a depression in selected somatic reflexes following repetitive cervical vagal stimulation (4,5,30). However, Stoica, Guilleux, and Dell (31) reported facilitation of both the Mass. and Dig. R. and the induction of cortical slow waves following prolonged periods of repetitive cervical vagal excitation which presumably activated only low-threshold fibers. These studies were carried out in the immobilized preparation. They interpreted their results as due to a release of the reticular activating system We concur following cortical deactivation, i.e., cortical synchronization. that the Dig. R. is facilitated during cortical synchronization (7), but the Mass. R. is not (8). During alert behavior in the freely moving animal the Dig. R. is markedly decreased in amplitude, and the Mass. R. is facilitated when compared with the drowsy or quiet sleep states (7.8). Thus, the changes in reflex amplitude and EEG activity which we report in conjunction with repetitive vagal stimulation are qualitatively similar to those variations which occur spontaneously in the freely moving, unanesthetized preparation (7-9,12). In order to determine the precise behaviors which are correlated with the responses presented in this paper, it will be necessary to carry out studies in the freely moving animal which allow an assessment to be made of the conditions during which the various aspects of vagal control over central neural processes play a physiological role; until then one can only speculate as to the functional significance of visceral information which is received by the brain. Most probably the somatic responses presented in this paper are important in such processes as mastication, deglutition, and respiration. However, the electrical activity of the cortex and subcortex is also modified by the excitation of these afferent vagal fibers (9-11). We think it most probable that the modulation of the somatic reflexes presented in this paper represent only one aspect of an integrated group of neural responses initiated by afferent vagal stimulation. Thus, it is evident that the afferent vagal fiber systems play an important role not only in the regulation of a wide range of behaviors but also in their correlated patterns of central neural activity from the level of the cortical EEG to that of the monosynaptic and polysynaptic somatic reflex. References 1. BACCELLI, G., M. GUAZZI, A. LIBRETTI, and A. ZANCHETTI. 1963. Effects of pressoand chemoceptive components of the cat’s aortic nerve on sham rage behavior. Exfierientia 19 : 534-535. 2. BARTORELLI, C., E. BIZZI, A. LIBRETTI, and A. ZANCHETTI. 1960. Inhibitory control of lsinocarotid pressoceptive afferents on hypothalamic autonomic activity and sham rage behavior. .4rrh. Ital. Biol. 98 : 308-326.
VAGAL 3.
4. 5. 6. 7.
8.
9.
10.
11.
12. 13.
14. 15. 16. 17.
18.
19.
20. 21.
22.
JIOL)CL.-ZTIOS
0F
REFLEXES
543
BAUST, W., and H. HEINEMA~TN. 1967. The role of the baroreceptors and of blood pressure in the regulation of sleep and wakefulness. Ex). Brain Res. 3 : 12-24. BLIER, z. A., and N. KLEIThrAN. 1930. Conditions affecting the Iinguomaxillary reflex L47i~~~. J. Phy.Gol. 94: 118-124. CAKIIOT, H.. .4. CIILRBVLIEZ. and H. LAV(XEI<. 1923. L’inhihition et la dynamogenie etudiees sur le reflexe lingua-n:axillarie. c‘. K. Sot. liiol. 89: 146148. CHA~O~, G., -4. HUIXLIN, and J. VERROLXT. 1963. Influence des centres respiratoire#s et de PaCO, sur les reflexes masticateurs. J. Physiol. Paris 55: 225. CHASE, M. H., and C. D. CLEhtENrz. 1969. Amplitude changes of the digastric reflex during sleep and wakefulness. Fed. I’vor. Frd. .Imcv. Ser. E.r,b. Bio/. 28(2j : 587. CF~ASE, M. H., D. J. XCCIXTY, and MI. B. SrEa>rA.\I. 1968. Cyclic variation in the amplitude of a brain stem reflex during sleep and wakefulness. Exprrientin 24: 47-48. CHASE, M. H., Y. NAKAhruRA, C. D. CLE~~ENTE, and M. B. ST~R~~AN. 1967. Afferent vagal stimulation: Neurographic correlates of induced EEG synchronization and desynchronization. Bvairz Rrs. 5 : 231~249. CHASE, M. H., and Y. NAE;AMURA. 1968. Cortical and subcortical EEG patterns of response to afferent abdominal vagal stimulation : Neurographic correlates. Physiol. Bcltazl. 3 : 605-610. CHASE, M. H., M. B. STEHMAN, and C. D. CLEMESTR. 1966. Cortical and subcortical patterns of response to afferent vagal stimulation. Exp. Neural. 16: 36-49. CHASE. M. H., S. TORII, and Y. NAK.ZJII.HA. The influence of vagal afferent fiber activity on masticatory reflexes. /?.rp. Ncrcrol. 27 : 545-553. CLEMENTE, C. D., M. H. CHASE, T. A. KNAUSS, E. K. SAUEKLAND, and M. B. STERMAN. 1966. Inhibition of a monosynaptic reflex by electrical stimulation of the basal forebrain or the orbital gyrus in the cat. ErParicntia 22: 845. DELL, P., and M. BONVALLET. 1966. Influences d’origine cardio-vasculaire et respiratoire sur I’activiate somatique. .dcta Nrrrro~,cg. 28 : 148-168. DELL, P., and Y. PADEL. 1964. Endormissement rapide provcque par la stimulation selective d’afferences vagales chez le chat. RCZ. NeItrol. 111 : 381. FELIX, W. 1951. t)ber die Wirkung des Carotissinus auf Muskelleistung. I’jii,qcr.s .4vch. Gesnrrctc PEl)~siol. ibfr~tschcn Ticrc 253 : 351-354. GARNIER, L., and R/i. .\L~~IERT. 1964. Modifications de I’electroencephalogramme du chat consecutives a la stimulation du nerd vague. C. K. Ser. Biol. 158: 2405-2408. GRASTYAN, E., T. HASZN~S, K. LISSAK, L. MOLNAR, and 2. RU~SONYI. 1952. Activation of the brain stem activating system by vegetative afferents. .4ctn Pfrysiol. Arad. Sri. Hwrg. 9 : 103-122. GuA~~I, M., G. BACCELLI, and A. ZANCHETTI. 1968. Reflex chemoceptive regulation of arterial pressure during natural sleep in the cat. Anrrv. J. Physiol. 214 : 969-978. HEYMANS, C., and E. NEIL. 1958. “Reflexogenic Areas of the Cardiovascular System.” Churchill, London. KAADA, B. R. 1951. Somato-motor, autonomic and electroencephalographic responses to electrical stimulation of “rhinencephalic” and other structures in primates, cat and dog. Acta Phytiol. Stand. Suppl. 83, 24: l-285. KAUFMAN, W. 1938. Effects of chemical stimulation of the carotid body upon
544
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NAKAMURA.
AND
TORI1
the reflex contraction of the tibialis anticus muscle. Awzer. J. P!rysioZ. 123: 677-686. 23. KING, C. E., W. E. GAHKEY, and W. R. BRYAN. 1932. The effect of carbon dioxide, hyperventilation and anoxemia on the knee jerk. Amer. J. Physiol. 102 : 305-318. 24. NAKAMURA, Y., L. J. GOLDBERG, and C. D. CLEMENTE. 1967. Nature of suppression of the masseteric monosynaptic reflex induced by stimulation of the orbital gyros of the cat. Brain Res. 6: 184-198. 25. PADEL, Y., and P. DELL. 1965. Effets bulbaires et reticulaires des stimulations endormantes du tronc vago-aortique. J. Physiol. Paris 57 : 269-270. 26. PENALOZA-ROJAS, J. H. 1964. Electroencephalographic synchronization resulting from direct current application to the vagus nerves. Exp. Neural. 9: 367-371. 27. PINOTTI, O., and L. GRANATA. 1953, Effetto della stimolazione dei chemocettori carotidei sul riflesso linguo-mandibolare. Boll. Sot. Ital. Biol. Sper. 29: 375377. 23. PINOTTI, O., and L. GRANATA. 1954. Azione inhibitrice dei pressocettori carotidei #sul riflesso linguo-mandibolare. Boll. Sot. Ital. Biol. Sper. 30: 486488. 29. PINOTTI, O., and L. GKANATA. 1955. Azione inhibitrice dei pressocettori carotidei sull’attivita motoria, spontanea e riflessa, nel cane. drch. Sci. Biol. Bolognu 39: 59-71. 30. SCHWEITZER, A., and S. WRIGHT. 1937. Effects on the knee jerk of stimulation of the central end of the vagus and of various changes in the circulation and respiration. 1. Physiol. London 66 : 459-475. 31. STOICA, I., H. M. GUILLEUX, and P. DELL. 1%5. Variations des reflexes mono et polysynaptique au tours de stimulations vago-aortiques endormantes. J. Physiol. Paris 57 : 703-704. 32. TOUBNADE, A., and J. MALMEJAC. 1929. Diversite des actions reflexes que declenche l’excitation du sinus carotidien et de son nerf. C. R. Sot. Biol. 100: 708-711. 33. ZANCHETTI, A., S. C. WANG, and G. MORUZZI. 1952. The effect of vagal afferent stimulation on the EEG pattern of the cat. Electroencephalogr. C&z. Neurophysiol. 4 : 357-361.
Afferent
NEUROLOGY
Vagal
27, 534-544
(19%)
Modulation Reflex
M. H.
CHASE,
Y.
of
Brain
Stem
Somatic
Activity
NAKAMURA,
AND
S.
TORII
’
Veteraw Administration Hospital, Sepulzleda, and the Department of .Inaio~rty and Physiology, Sckool of Medicine, Uninersity of California at Los Angeles, California 90024 Received
February
20, 1970
The influenceof cervical vagal afferent activity upon somaticreflexes was examined in immobilized, encephale isole cats. Antagonistic brain stem somatic reflexes, the masseteric (jaw closing) and the digastric (jaw opening), were induced in conjunction with stimulation of the cut central end of the cervical vagus nerve. Single pulse or pulse train vagal stimulation led to three sequential periods of masseteric reflex modulation : (a) facilitation, (b) depression, and (c) facilitation. Under a similar experimental paradigm the digastric reflex was first facilitated and then depressed. Repetitive vagal stimulation induced tonic facilitation of the masseteric reflex and tonic depression of the digastric reflex. These resultswere discussed in relation to the effectsexerted by vagal afferents upon the central nervous system and behavior, and the functional significance of visceralinformationreceivedby the brain. Introduction
We recently reported that excitation of vagal afferents can modulate the electroencephalographic (EEG) activity of the cerebral cortex and subcortical structures (9-l 1) . EEG synchronization and desynchronization were induced in conjunction with the excitation of specific afferents from the abdominal and thoracic cavities. Other studies have demonstrated that central vagal excitation may modify not only central neural activity (15, 17, 18, 25, 33) but also behaviors ranging from sleep to sham rage (1, 2, 19, 21, 26). Thus, it is clear that afferents which originally were thought to be concerned solely with visceral motor reflex activity are capable of influencing the electrical activity of the central nervous system (CNS) as 1 This research was supported by the United States Veterans Administration and by grants from the U.S. Public Health Service (MH-10083) and the National Science Foundation (GF 262). Bibliographic assistance was received from the UCLA Brain Information Service, which is part of the Neurological Information Network of NINDS and is supported under Contract DHEW PH-43-66-59. Part of this research was carried out at Toho University, Tokyo, Japan. 534
\‘AGAL
MODt?LA’l-IOS
OF
KEFLEXES
535
well as a variety of behaviors. To further our understanding of the mechanisms by which viscera1 afferents affect CNS activity and integrated patterns of behavior we were interested in determining whether a basic component of behavior, the somatic reflex, might he modified by afferent vagal excitation. Afferent vagal activity in the intact animal initiates visceral reflexes which affect a variety of peripheral systems (e.g., respiratory, circulatory) which in turn influence somatomotor activity (6, 14, 16, 20, 21, 30). In order to eliminate these indirect effects we decided that the preparation of choice would be the encephale isole animal which was immobilized and given artificial respiration. In this preparation the influence of central cervical vagal stimulation must be examined in conjunction with somatic reflexes which are organized entirely within the brain stem, and it was for this reason that we chose the monosynaptic masseteric and the polysynaptic digastric reflexes. We have previously studied these reflexes in immobilized preparations in conjunction with stimulation of cortical and subcortical areas (13, 24) and have correlated variations in reflex amplitude with various behavioral states in freely moving animals (7, 8). We now report on our current studies of vagal control of somatic reflex activity. Methods
Experiments were carried out on 26 adult cats. Each was first anesthetized with ether. The saphenous vein and trachea were then cannulated, and the animal was placed in a stereotaxic instrument. Anesthesia was maintained during subsequent surgical procedures by the intravenous injection of a short acting anesthetic agent, sodium methohesital (Hrevital ). The surgical procedures included (n) transection of the spinal cord at C,, (b) bilateral severance of the vagal and sympathetic trunks at a low cervical level, (r ) isolation of the right or left cervical vagus nerve from the adjacent sympathetic trunk and perineurium, and (d ) isolation and section of the right masseter nerve and the right mylohyoid nerve (i.e., digastric nerve branch to the anterior belly of the digastric muscle). The pattern of stimulation and recording is shown diagramatically in Fig. 1. A bipolar stimulating electrode was placed on the cut central end of the right or left cervical vagus nerve (Fig. 1A). -4 bipolar strut electrode was placed within the right mesencephalic nucleus of the Vth nerve (Fig. 1B) to induce the monosynaptic (jaw closing) masseteric reflex (Mass. R.). Screw electrodes were placed in the mandibular canal to induce the polysynaptic (jaw opening) digastric reflex (Dig. R.) by excitation of the inferior dental nerve (Fig, 1C). Bipolar recording electrodes were placed on the ipsilateral vagus nerve (Fig. 1A’) between the vagal stimulating electrode and the brain and on the cut central end of the masseter (Fig. 1B’)
536
CHASE,
NAKAMURA,
AND
TORI1
FIG. 1. Stimulation and recording paradigm. The masseteric reflex was induced by delivering an electrical stimulus to the mesencephalic trigeminal nucleus (B) and was monitored along the cut central end of the ipsilateral masseter nerve (Bl). The digastric reflex was induced by stimulation of the inferior dental nerve (C) and was recorded along the cut central end of the ipsilateral mylohyoid (digastric) nerve (Cl). A recording electrode was placed on the cervical vagus nerve (Al) approximately 5 cm central to the stimulating electrode (A) in order to monitor the induced afferent vagal activity.
and mylohyoid (Fig. 1C’) nerves. The exposed portions of the peripheral nerves were surrounded by a viscous solution of mineral oil and petroleum jelly. All wound edges and pressure points, as well as the nerve trunks supplying these areas, were infiltrated every 30 min with a local anesthetic, lidocaine (Xylocaine), throughout the course of the experiment. The animal’s body temperature was maintained at approximately 37C by a heating pad. After all surgical procedures were completed, Brevital anesthesia was discontinued, and gallamine triethiodide (Flaxedil) was administered. The animal was subsequently maintained by artificial respiration. Grass and Nihon Kohden stimulators were employed to induce activity along the vagus nerve and to elicit the Mass. R. and the Dig. R. The reflex responseswere displayed on an oscilloscope and photographed. For this investigation vagal excitation was carried out with stimuli which were sufficient to induce activity in all fiber groups which was determined by monitoring the induced vagal neurographic activity (9). A Nihon Kohden computer (ATAC-501) was used to obtain averaged reflex responses. Conditioning-test intervals were measured from the first vagal pulse to the onset of the pulse to the mesencephalicnucleus or inferior dental nerve. At the termination of each experiment the animal was dispatched with an overdose of sodium pentobarbital (Nembutal), and the brain was removed
I’AGAL
MODULATIOK
OF
for histologic determination of the placement mesencephalic trigeminal nucleus.
REFLEXES
of the electrode within
53i the
Results
SiJrglr Prrlsr 1 ‘nytrl Stilirulfltim. The amplitude of the Mass. K. varied xcoiding to the latency with d~ich it was evoked following single pulse stimdation of the cut central end of the cervical vagus nerve. X brief period of reflex facilitation occurred when the conditioning-test interval was between 2 and 5 met (Fig. 2 ). This initial facilitory phase was fol-
FIG. 2. The tnasseteric reflex was examined at various intervals following single pulse vagal stimulation. Consistent reflex depression was obtained at latencies from IO-35 msec. This phase was preceded by a brief period of facilitation and was followed by a long-lasting period of facilitation. The time course curve was generated by dividing the mean amplitude of ten reflexes preceded by a single vagal pulse by the mean amplitude of ten control responses. Examples of the raw data are shown which correspond to the points A, I3, and C on the time course curve (a: reflex control; b: reflex preceded by vagal stimulation). The reflex latency was measured from the beginning of the vagal pulse to the beginning of the pulse to the mesencephalic trigeminal nucleus. For this and the following figures the reflexes which are presented were elicited at the rate of I/set and represent the averaged pattern of reflex response to ten consecutive trials of reflex induction. Mesencephalic nucleus : 4 v, 0.2 msec; vagus : 10 v, 1 msec; calibration : 50 pv, 2 msec.
538
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lowed by a period of depression f ram 10-35 msec (Fig. 2A, B) . A second relatively long period of facilitation was observed which arose with a latency of approximately 35 msec and lasted for a period of more than 50 msec (Fig. 2C ). Reflex depression was more consistently obtained and was of greater magnitude than reflex facilitation. The Dig. R. showed an initial brief period (O-S msec) of facilitation (Fig. 3A, B) which was observed in most but not all trials. Reflex depression, which was consistently obtained, occurred with a latency of approximately 10 msec and lasted for over 100 msec (Fig. 3C). The initial period of Dig. R. depression overlapped the entire period of Mass. R. depression. The effectiveness of vagal stimulation to modify the Dig. R. was reduced when the conditioning vagal pulse was evoked at rates greater than l/set. Pulse Train Vagal Stimulation. When multiple pulses were used as the vagal conditioning stimulus, the degree of depression and facilitation of both the Mass. and Dig. R. was markedly enhanced. No qualitative change
I 0
10
20
30 40 CONDIlIOWIN6
-
50 ItSI
so 10 IWltRVll
IO
90
Ii0
WC
FIG. 3. The time course curve for the digastric reflex response to vagal stimulation was obtained according to the same paradigm described in the legend of Fig. 2 for the masseteric reflex. Early facilitation (A,B) of the digastric reflex was followed by a long-lasting period of depression (C). Inferior dental nerve : 1.2 v, .Ol msec ; vagus : 8 v, 1 msec ; calibration : 50 pv, 2 msec.
VAGAL
MODULATIOiY
OF
REFLEXES
539
in the pattern of refles response was observed when pulse trains were applied to the vagus nerve instead of single conditioning pulses. R~spmtsc~ Pattern of IndkGdrral Co~~~ponmts of t/w Digastric Reflex. Suprathreshold excitation of the inferior dental nerve led to a Dig. R. which was composed of two major components (Figs. -+A, SA). Liminal excitation resulted in the induction only of the first component (Figs. 4C, 5C). The influence of vagal stimulation upon each component of the Dig. R. was examined using short trains of conditioning pulses. Short Conditioning-Test Interval. When suprathreshold stimulation of the inferior dental nerve led to a response composed of two components (Fig. 4A), both increased slightly in amplitude when preceded by vagal pulses (Fig. 4D). This pattern of facilitation was also obtained with a control reflex of smaller amplitude (Fig. 4R,E). \Vhen a liminally induced reflex was used as a control ( Fig. -CC). its amplitude increased following
: VAht
DR VAGUS
‘4’
MSFC
FIG. 4. At short conditioning-test intervals the digastric reflex (DR) was facilitated; control on the left and vagus stimulation on the right. The averaged digastric reflex consisted of a response with two components (A, B), both of which increased in amplitude in conjunction with vagal stimulation (D, E). At low levels of inferior dental nerve excitation only the first component of the digastric reflex was induced (C) ; following vagal stimulation its amplitude increased and activity was observed at a latency corresponding to the second component (F). Inferior dental nerve : A-l.4 v, B-l.3 v, C-l v, .Ol msec; vagus: 10 v, 1 msec; calibration: 100 gv, 2 msec.
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FIG. 5. At long conditioning-test intervals the digastric reflex was depressed; control, left; vagus stimulation, right. When both components of the digastric reflex were present as a control (A) they were reduced in amplitude (D) in conjunction with vagal stimulation. When liminally induced the first (C) and second (B) components were suppressed (F, E). Inferior dental nerve: A-l.5 v, B-l.3 v, C-l v, .Ol msec; vagus : 10.0v, 1 msec; calibration: 100pv, 2 msec.
vagal stimulation, and a small response appeared at a latency corresponding to the period of the second reflex component (Fig. 4F). Long Conditioning-Test Interval. During the period of Dig. R. depression obtained with a single vagal pulse (Fig. 3C), both components of the reflex were reduced in amplitude (Fig. 5). The first component, even when supraliminally induced, was depressed, as was the second component (Fig. 5A,D). In Fig. SC, a liminally induced response was completely abolished by vagal stimulation (Fig. SF). Repetitive Yagul Stinzulution~ Repetitive vagal stimulation (10-200 cps) was applied for periods of 10 sec. in conjunction with the continuous induction of either test reflex (evoked at the rate of l/set) . The amplitude of the Mass. R. increased during this paradigm; the antidromic potential (13) remained unchanged (Fig. 6A). Both cotnponents of the Dig. R. were depressed (Fig. 6B). The Dig. R. was more consistently modified in this paradigm than was the Mass. R., and it appeared that the relative degree of depression of the Dig R. was greater than that of facilitation of the Mass. R. At the termination of stimulation facilitation of the Mass. R. continued for a few seconds while the Dig. R. remained depressed. This
VAGAL
A.MR
MODULATION
OF
541
REFLEXES
j-
$I,
JL
?-J--
B. OR -I
FIG. 6. High-frequency repetitive central vagal excitation masseteric reflex (MR) facilitation and digastric reflex (DR) control, left ; vagus stimulation, first 10 set of stimulation; trigeminal nucleus : 5 v, 2 msec; inferior dental nerve : 1.5 v, 1 msec ; calibration : 50 pv, 5 msec.
(100 cps) resulted in depression during the right. Mesencephalic .Ol msec ; vagus : 9 v,
of vagal stimulation was more pronounced and was of longer duration for the Dig. R. than for the Mass. R.
after-effect
Discussion
This report indicates that a direct interaction of striking magnitude exists between vagal afferents and the somatic motor system. However, it should not be surprising that there is such interaction since parasympathetic information conveyed from the viscera can influence a wide variety of activities. For example, many of the individual behaviors which comprise sham rage may be either augmented or depressedaccording to the excitation of specific groups of visceral afferent fibers or a lack of impulses along them (3.19,26). Additionally, the EEG pattern of the cerebral cortex and a variety of subcortical structures can be synchronized or desynchromized, dependent upon information conveyed by specific afferent vagal systems (9). Investigations which have analyzed somatic responsesfollowing excitation of visceral
organs
have dealt primarily
with
stimulation
of the carotid
chemoreceptors and baroreceptors ( 16,21--23,27-29,32). These studies are in essential agreement, namely, carotid baroreceptor stimulation induces somatomotor depression and chemoreceptor stimulation leads to somatomotor facilitation. Although excitation of the cervical vagus does not include carotid body afferents, there are receptors within the thoracic cavity subserving
similar
functions.
The origin
of those afferent
fihers which
are acti-
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AND
TORI1
vated by cervical vagal stimulation has been discussed (9,12). Certain studies have noted a depression in selected somatic reflexes following repetitive cervical vagal stimulation (4,5,30). However, Stoica, Guilleux, and Dell (31) reported facilitation of both the Mass. and Dig. R. and the induction of cortical slow waves following prolonged periods of repetitive cervical vagal excitation which presumably activated only low-threshold fibers. These studies were carried out in the immobilized preparation. They interpreted their results as due to a release of the reticular activating system We concur following cortical deactivation, i.e., cortical synchronization. that the Dig. R. is facilitated during cortical synchronization (7), but the Mass. R. is not (8). During alert behavior in the freely moving animal the Dig. R. is markedly decreased in amplitude, and the Mass. R. is facilitated when compared with the drowsy or quiet sleep states (7.8). Thus, the changes in reflex amplitude and EEG activity which we report in conjunction with repetitive vagal stimulation are qualitatively similar to those variations which occur spontaneously in the freely moving, unanesthetized preparation (7-9,12). In order to determine the precise behaviors which are correlated with the responses presented in this paper, it will be necessary to carry out studies in the freely moving animal which allow an assessment to be made of the conditions during which the various aspects of vagal control over central neural processes play a physiological role; until then one can only speculate as to the functional significance of visceral information which is received by the brain. Most probably the somatic responses presented in this paper are important in such processes as mastication, deglutition, and respiration. However, the electrical activity of the cortex and subcortex is also modified by the excitation of these afferent vagal fibers (9-11). We think it most probable that the modulation of the somatic reflexes presented in this paper represent only one aspect of an integrated group of neural responses initiated by afferent vagal stimulation. Thus, it is evident that the afferent vagal fiber systems play an important role not only in the regulation of a wide range of behaviors but also in their correlated patterns of central neural activity from the level of the cortical EEG to that of the monosynaptic and polysynaptic somatic reflex. References 1. BACCELLI, G., M. GUAZZI, A. LIBRETTI, and A. ZANCHETTI. 1963. Effects of pressoand chemoceptive components of the cat’s aortic nerve on sham rage behavior. Exfierientia 19 : 534-535. 2. BARTORELLI, C., E. BIZZI, A. LIBRETTI, and A. ZANCHETTI. 1960. Inhibitory control of lsinocarotid pressoceptive afferents on hypothalamic autonomic activity and sham rage behavior. .4rrh. Ital. Biol. 98 : 308-326.
VAGAL 3.
4. 5. 6. 7.
8.
9.
10.
11.
12. 13.
14. 15. 16. 17.
18.
19.
20. 21.
22.
JIOL)CL.-ZTIOS
0F
REFLEXES
543
BAUST, W., and H. HEINEMA~TN. 1967. The role of the baroreceptors and of blood pressure in the regulation of sleep and wakefulness. Ex). Brain Res. 3 : 12-24. BLIER, z. A., and N. KLEIThrAN. 1930. Conditions affecting the Iinguomaxillary reflex L47i~~~. J. Phy.Gol. 94: 118-124. CAKIIOT, H.. .4. CIILRBVLIEZ. and H. LAV(XEI<. 1923. L’inhihition et la dynamogenie etudiees sur le reflexe lingua-n:axillarie. c‘. K. Sot. liiol. 89: 146148. CHA~O~, G., -4. HUIXLIN, and J. VERROLXT. 1963. Influence des centres respiratoire#s et de PaCO, sur les reflexes masticateurs. J. Physiol. Paris 55: 225. CHASE, M. H., and C. D. CLEhtENrz. 1969. Amplitude changes of the digastric reflex during sleep and wakefulness. Fed. I’vor. Frd. .Imcv. Ser. E.r,b. Bio/. 28(2j : 587. CF~ASE, M. H., D. J. XCCIXTY, and MI. B. SrEa>rA.\I. 1968. Cyclic variation in the amplitude of a brain stem reflex during sleep and wakefulness. Exprrientin 24: 47-48. CHASE, M. H., Y. NAKAhruRA, C. D. CLE~~ENTE, and M. B. ST~R~~AN. 1967. Afferent vagal stimulation: Neurographic correlates of induced EEG synchronization and desynchronization. Bvairz Rrs. 5 : 231~249. CHASE, M. H., and Y. NAE;AMURA. 1968. Cortical and subcortical EEG patterns of response to afferent abdominal vagal stimulation : Neurographic correlates. Physiol. Bcltazl. 3 : 605-610. CHASE, M. H., M. B. STEHMAN, and C. D. CLEMESTR. 1966. Cortical and subcortical patterns of response to afferent vagal stimulation. Exp. Neural. 16: 36-49. CHASE. M. H., S. TORII, and Y. NAK.ZJII.HA. The influence of vagal afferent fiber activity on masticatory reflexes. /?.rp. Ncrcrol. 27 : 545-553. CLEMENTE, C. D., M. H. CHASE, T. A. KNAUSS, E. K. SAUEKLAND, and M. B. STERMAN. 1966. Inhibition of a monosynaptic reflex by electrical stimulation of the basal forebrain or the orbital gyrus in the cat. ErParicntia 22: 845. DELL, P., and M. BONVALLET. 1966. Influences d’origine cardio-vasculaire et respiratoire sur I’activiate somatique. .dcta Nrrrro~,cg. 28 : 148-168. DELL, P., and Y. PADEL. 1964. Endormissement rapide provcque par la stimulation selective d’afferences vagales chez le chat. RCZ. NeItrol. 111 : 381. FELIX, W. 1951. t)ber die Wirkung des Carotissinus auf Muskelleistung. I’jii,qcr.s .4vch. Gesnrrctc PEl)~siol. ibfr~tschcn Ticrc 253 : 351-354. GARNIER, L., and R/i. .\L~~IERT. 1964. Modifications de I’electroencephalogramme du chat consecutives a la stimulation du nerd vague. C. K. Ser. Biol. 158: 2405-2408. GRASTYAN, E., T. HASZN~S, K. LISSAK, L. MOLNAR, and 2. RU~SONYI. 1952. Activation of the brain stem activating system by vegetative afferents. .4ctn Pfrysiol. Arad. Sri. Hwrg. 9 : 103-122. GuA~~I, M., G. BACCELLI, and A. ZANCHETTI. 1968. Reflex chemoceptive regulation of arterial pressure during natural sleep in the cat. Anrrv. J. Physiol. 214 : 969-978. HEYMANS, C., and E. NEIL. 1958. “Reflexogenic Areas of the Cardiovascular System.” Churchill, London. KAADA, B. R. 1951. Somato-motor, autonomic and electroencephalographic responses to electrical stimulation of “rhinencephalic” and other structures in primates, cat and dog. Acta Phytiol. Stand. Suppl. 83, 24: l-285. KAUFMAN, W. 1938. Effects of chemical stimulation of the carotid body upon
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the reflex contraction of the tibialis anticus muscle. Awzer. J. P!rysioZ. 123: 677-686. 23. KING, C. E., W. E. GAHKEY, and W. R. BRYAN. 1932. The effect of carbon dioxide, hyperventilation and anoxemia on the knee jerk. Amer. J. Physiol. 102 : 305-318. 24. NAKAMURA, Y., L. J. GOLDBERG, and C. D. CLEMENTE. 1967. Nature of suppression of the masseteric monosynaptic reflex induced by stimulation of the orbital gyros of the cat. Brain Res. 6: 184-198. 25. PADEL, Y., and P. DELL. 1965. Effets bulbaires et reticulaires des stimulations endormantes du tronc vago-aortique. J. Physiol. Paris 57 : 269-270. 26. PENALOZA-ROJAS, J. H. 1964. Electroencephalographic synchronization resulting from direct current application to the vagus nerves. Exp. Neural. 9: 367-371. 27. PINOTTI, O., and L. GRANATA. 1953, Effetto della stimolazione dei chemocettori carotidei sul riflesso linguo-mandibolare. Boll. Sot. Ital. Biol. Sper. 29: 375377. 23. PINOTTI, O., and L. GRANATA. 1954. Azione inhibitrice dei pressocettori carotidei #sul riflesso linguo-mandibolare. Boll. Sot. Ital. Biol. Sper. 30: 486488. 29. PINOTTI, O., and L. GKANATA. 1955. Azione inhibitrice dei pressocettori carotidei sull’attivita motoria, spontanea e riflessa, nel cane. drch. Sci. Biol. Bolognu 39: 59-71. 30. SCHWEITZER, A., and S. WRIGHT. 1937. Effects on the knee jerk of stimulation of the central end of the vagus and of various changes in the circulation and respiration. 1. Physiol. London 66 : 459-475. 31. STOICA, I., H. M. GUILLEUX, and P. DELL. 1%5. Variations des reflexes mono et polysynaptique au tours de stimulations vago-aortiques endormantes. J. Physiol. Paris 57 : 703-704. 32. TOUBNADE, A., and J. MALMEJAC. 1929. Diversite des actions reflexes que declenche l’excitation du sinus carotidien et de son nerf. C. R. Sot. Biol. 100: 708-711. 33. ZANCHETTI, A., S. C. WANG, and G. MORUZZI. 1952. The effect of vagal afferent stimulation on the EEG pattern of the cat. Electroencephalogr. C&z. Neurophysiol. 4 : 357-361.