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Spinal electrogram of the cat. II. Supraspinal influences
111
Electroencephalography and Clinical Neurophysiology Elsevier Publishing Company, Amsterdam - Printed in The Netherlands
SPINAL E L E C T R O G R A M OF T H E CAT. II. SUPRASPINAL INFLUENCES 1 H . LEVITAN 2, E. L. GASTEIGER, H . KASPRZAK AND H . BRUST-CARMONA ~
Department of Physical Biology, New York State Veterinary College and Section of Neurobiology and Behavior, Cornell University, Ithaca, N.Y. 14850 (U.S.A.)
(Accepted for publication: December 11, 1967)
INTRODUCTION
Our parallel studies (Brust-Carmona et al. 1968) have shown that the spinal electrogram (SEG) is composed mainly of two components: a diphasic background activity (BA) and negative sharp waves (NSW). The BA is related to, and largely dependent upon, input coming to the cord segment from the periphery but the sharp waves are autochthonous to the cord and do not depend on peripheral activation. In the present study the relationship between NSW and the output from the spinal cord was further explored in experiments based on the findings of Niemer and Magoun (1947) and Sprague and Chambers (1954) that reticular formation (RF) stimulation modifies muscular tone. METHODS AND MATERIAL
Preparatory surgery was performed on twentyfive cats anesthetized with ether. Except as noted below the methods were as described in the preceding paper (Brust-Carmona et al. 1968). An attempt was made to correlate motor activity with the SEG in 17 experiments. E M G recordings were made from pairs of stainless steel pins inserted into flexor and extensor muscles of the preparation's hind and forelimbs. The
EMGs were recorded with an amplifying system like that used for the SEG. In 4 experiments variations in the amplitudes of the cord dorsum potential (CDP) and the dorsal root potential (DRP) were correlated with the amplitude of the SEG. These potentials were evoked by stimulating the exposed sciatic nerve at a frequency between 0.5 and 1.0/sec. In twelve cats with dorsal roots intact and 5 with dorsal roots sectioned the brain-stem was stimulated through a coaxial bipolar electrode. Animal and stimulating electrode were mounted in a K o p f stereotaxic instrument and the electrode was placed in the brain-stem RF according to the Verhaart atlas (1964) and then adjusted according to the response of the musculature. The electrode was inserted parallel and caudal to the bony tentorium at an angle of 22 ° to the frontal plane. The region of the brain-stem explored extended from 6 mm anterior to 12 mm posterior, from 2 mm above to 8 mm below and laterally from the midline to 2.5 mm left. Although this volume of brain-stem was not probed in its entirety all the areas stimulated fell within its bounds. The stimulus current consisted of diphasic rectangular 0.1~).3 msec pulses applied at 60-300 p/sec (Grass $4 stimulator and isolation unit). RESULTS
1 This work was supported by U.S. Public Health Service Grants NB-04408, 5 TI GM223 and 5 K 3 NB6877. 2 Now at the Department of Anatomy, University of California, School of Medicine, Los Angeles, Calif. 90024. While o n leave from the Departamento de Fisiologia, Facultad de Medicina, Universidad Nacional de M6xico, M6xico 20, D.F., M6xico.
Tonic influence of the brain-stem Spinalization of the decerebrate cat by occluding the circulation to the brain-stem caused a transient de'wession of the SEG, a change which paralleled in time the transient increase in arterial blood pressure commonly seen under these Electroenceph. clin. Neurophysiol., 1968, 25: 111-118
H. LEVITAN
112
conditions. Both components of the SEG then progressively increased until in 15 min they reached levels 4-5 times greater than those for the decerebrate condition (see parallel change in Fig. 4 of Brust-Carmona et al. 1968). By this
et
a/.
time, the blood pressure had settled to the low levels characteristic of high spinal preparations. Subsequent surgical transection of the medullacord junction produced no response or a very brief one. These changes occurred whether the dorsal roots were intact or sectioned.
Effects of RF stimulation on SEG and muscular activity
Fig. 1
Concomitant decrease in SEG with increase in motor activity produced by reticular formation stimulation [P 8, L 2, H -11. LLs = SEG from sixth lumbar segment, left of cord midline; dorsal roots intact; LFF = EMG from left forelimb flexors; LHE = EMG from left hind limb extensors; LHF = EMG from left hind limb flexors.
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The response to brain-stem stimulation varied according to the electrode placement, the initial muscle tone and the afferent input to the spinal cord. In general, stimulation of the RF at sites producing increased motor tone caused a reduction of the SEG (Fig. I), whereas stimulation at sites producing decreased motor tone enhanced the SEG (Fig. 2). Regions of the brain-stem causing inhibition of motor activity appeared to be scarcer than those causing excitation and in some cats inhibitory sites escaped detection entirely. Apparently they are very localized since displacement of the stimulating electrode as little as 1 mm often resulted in a different response. The intensity of RF stimulation required to
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Fig. 2 Increase in sharp wave activity in deafTerented lumbar cord during inhibition of forelimb musculature by reticular formation stimulation [A 5.7, L 2.0, H -1.91 (on+ff). Also inhibited but not shown was right hind limb extensor. RLa = SEG from right side of lumbar La; RFF = EMG from right forelimb flexors; LFE = EMG from left forelimb extensors. Persistent, periodic spikes in lower trace are electrocardiogram. Electroenceph. din. Neurophysiol., 1968,25: 11l-l 18
l 13
SEG" SUPRA,SPINAL INFLUENCES
i
Fig. 3 Alteration of the SEG by stimulation of the facilitatory reticular formation [P 3.1, L 0, H -2.8] before and after Flaxedil. Before Flaxedil: RF stimulation increased SEG in lumbar cord (LT) and motor activity as measured by ventral root discharge (LTVR). After Flaxedil: RF stimulation decreased the SEG while still evoking motoneurortal discharge.
produce a motor response was lower than, or equal to, that which produced an alteration in the SEG. Forelimb muscles were more sensitive to stimulation, but greater stimulus intensity caused a more diffuse motor response which extended eventually to the fore- and hind limbs of both sides. The response of motor activity and SEG to RF stimulation began with the onset of stimulus and ceased with its termination. Exceptions were observed for motor responses. These include: build up of response or delayed onset (Fig. 2), waning of activity during the stimulus period (RHE in Fig. 4), or a failure of the activity to return to pre-stimulus level--particularly following inhibitory stimulation (LFF in Fig. 1). These variations were most apparent for low in-
tensity stimulation. Motor activation with inhibition of the SEG produced by RF stimulation, illustrated in Fig. 1, was obtained in a preparation with intact dorsal roots. A recording on an expanded time base revealed that the BA component was not markedly changed by moderate stimulation although the NSWs were greatly reduced. However, with more intense stimulation at this site both a greater motor response, especially in the forelimbs, and an unexpected increase of SEG were observed. It was difficult to determine whether this increase of the SEG was due to a change in its BA or NSW component 1. To maintain the BA component 1 An increase in the BA component would be expected
if there were an increase in activity coming into the cord via the intact dorsal roots (Brust-Carmona et al. 1968). Electroenceph. clin. Neurophydol., 1968, 25: 111-118
114
H. LEVITAN et al.
c o n s t a n t despite stimulation, 4-10 m g o f Flaxedil were given i.v. in three cases where stimuli facilit a t o r y for m o t o r activity also increased the SEG. Under these conditions R F s t i m u l a t i o n increased m o t o r activity as m e a s u r e d by ventral r o o t discharge, decreased the N S W , b u t d i d n o t alter the BA (Fig. 3). Thus, it is p r o b a b l e t h a t increase o f the S E G prior to a d m i n i s t e r i n g Flaxedil was largely due to heightened B A which occurred reflexly with increased m u s c u l a r activity. The differential effects on B A a n d N S W components o f repeated s t i m u l a t i o n o f various intensities at n u m e r o u s R F sites was studied further in five cats with l u m b a r deafferentation. It was observed in these p r e p a r a t i o n s that only when the forelimbs were a c t i v a t e d d i d an increase in BA o c c u r (Fig. 4), similar to that described a b o v e when d o r s a l l u m b a r r o o t s were intact. Therefore, changes in the c o m p o n e n t s o f the l u m b a r S E G were correlated with a c t i v a t i o n or i n h i b i t i o n o f fore- and h i n d l i m b tone in 200 responses (Table I). A n increase in B A was f o u n d to be c o r r e l a t e d with increased forelimb tone in 78 o f 106 instances (74%). I n t r a v e n o u s injection o f Flaxedil again b l o c k e d the increase o f B A suggesting t h a t the forelimb afferents were facilitating the l u m b a r BA. N o correlation c o u l d be discerned between changes in hind limb m o t o r activity a n d B A in these deafferented animals since h i n d limb t o n e increased, decreased or r e m a i n e d u n c h a n g e d with a b o u t equal frequency. W h e n b o t h fore- a n d hind limb tone increased concurrently, the increase in B A was observed but it was a c c o m p a n i e d by decrease in N S W (Fig. 4). ~LL~ . . . .
i LFF
~
+ '+'~+! 'l+m"+'v +
+ + Rt,,E +
I aJml~%+,+,~ .+ +
.....
o~+
I
!
Fig. 4 Concurrent increase in BA and fore- and hind limb muscular activity with decrease in NSWs in response to RF stimulation [P 8, L 2, H 0]. LL6 = SEG from left side of segment L6 in lumbar deafferented cord; LFF = EMG from left forelimb flexor; RI-IE = EMG from right hind limb extensor.
A s s o c i a t i o n o f N S W activity with changes in hind limb muscle tone showed close correlation. Of the 37 instances in which an increase in N S W activity coincided with a change in hind limb activity, 29 were associated with a decrease in tone (79%). Conversely a decrease in N S W activity was associated with an increase in hind TABLE 1 Relation between components of SEG and electromyogram of fore- and hind limb muscles for five lumbar deafferented cats in response to RF stimulation SEG
BAincrease NSWincrease NSWdecrease
EMG Fore limbs 0
Hind limbs -+- -- 0
78 18 10 40 36 12 25 4 10
33 29 35 8 29 41 18 4 14
Mixed responses of flexor and extensor muscles (fore- and hind limb responses treated independently) were scored according to the dominant effects. BA := background activity; NSW := negative sharp wave activity. ÷ = increase; . . . . . decrease; 0 ~ no change in muscular activity. limb tone in 18 o f 22 cases (82%). In 41 instances R F s t i m u l a t i o n p r o d u c e d an increase in N S W s w i t h o u t a n y change in hind limb m u s c u l a r tone. The m a j o r i t y o f these o c c u r r e d in animals with an absence o f tonic hind limb activity following d e c e r e b r a t i o n or previous i n h i b i t o r y s t i m u l a t i o n ; p r e s u m a b l y no inhibition o f m u s c u l a r activity could occur. O n 14 occasions N S W s were depressed without change in hind limb tone. Increase o f N S W s could not be correlated with forelimb activity. However, the N S W s consistently decreased when forelimb tone increased. This change was like t h a t seen in the case o f increased hind limb tone a n d indicates that the N S W s are decreased with heightened efferent activity o f the spinal cord. Variations in the frequency a n d strength o f R F stimulus altered the t h r e s h o l d b u t n o t the c h a r a c t e r o f the response. W h e n the c h a r a c t e r o f the response did change, the stimulating electrode was usually in an i n h i b i t o r y area. The effects o f the R F on the S E G were not restricted to a single spinal segment b u t extended s i m u l t a n e o u s l y over segments L~, L6 a n d LT. Electroenceph. clin. Neurophysiol., 1968, 25: 111-118
SEG: SUPRASPINALINFLUENCES
Changes in peripherally evoked po tentials R F stimulation which attenuated the NSWs simultaneously reduced the spinal cord potentials, CDP and DRP, evoked by single shocks to the sciatic nerve (Fig. 5), All but the early spike components of the evoked potentials were reduced in amplitude, but particularly marked was the reduction of the P wave and D R V components. A concomitant increase in the N S W and evoked potentials was never observed. The temporal correspondence between attenuation of the N S W and reduction of CDP and D R P was close, both with onset and cessation of R F stimulation. The stimulation threshold for the two
115
influences also corresponded well. R F stimulation producing decrease in NSW and evoked afferent activity enhanced motor tone at the same time (Fig. 5). Also illustrated is the finding that peripheral stimulation itself could cause alteration in the lumbar SEG. Maximal stimuli to the sciatic nerve at rates greater than about 0.5 sec depressed the sharp wave activity.
Concomitant blood pressure changes R F stimulation which caused enhancement of both BA and N S W was accompanied by transient decrease in arterial blood pressure, whereas stimulation which caused depression of sponta-
STIM.
CDP
:7
DRP
LL7
•
~
•
~,,T
Fig. 5 Concurrent decrease of SEG and evoked potentials from the cord dorsum (CDP) and dorsalroot (DRP) with increased motoneuronal activity (LLTVR) in response to RF stimulation [A 0.5, L 2, H -3.7]. The times single shocks were delivered to the sciatic are indicated on the third channel; when initiated they decreased the NSWs. Shock artifact has been removed from the top trace to make clear the changes in the SEG. The resulting evoked potentials, CDP and DR.P, are represented before, during and after RF stimulation, from left to right. LL7 = SEG from left L7 segment; L L 7 V R = activity of left ventral root of L~ segment.
Eleetroenceph. clin. Neurophysiol., 1968, 25: 111-118
116
H. LEVITAN CI ~/[.
RET~ULAR s~lle
Ka
STIMULATION
EPINEPHRINE
IN,I C T I O N
lqlljmm[
t. I
I
I
Fig. 6 The independence of SEG and blood pressure changes caused by R F stimulation [A 1.3, L 1.5, H -1.9] as shown by relative constancy of SEG when blood pressure was increased by injection of epinephrine.
neous activity was accompanied by transient increase in the arterial blood pressure. Since these changes in SEG and blood pressure wet e consistent with those seen with spinalization, it was possible that the variation in SEG was due to blood pressure changes rather than directly to RF stimulation. To determine the validity of this possible inverse relationship, an i.v. injection of epinephrine (30 #g) was administered (4 animals) to produce a rise in blood pressure comparable to that caused by reticular stimulation. The SEG was not altered significantly (Fig. 6). In addition, infusion of 20-40 ml of Dextran (6 animals) produced an increase in blood pressure without a change in the SEG. Therefore, the concomitant variations in SEG and blood pressure did not appear to be directly related even though they were provoked from the same region of the RF. DISCUSSION
This study has confirmed the existence of a powerful influence of brain-stem structures on the SEG. Although no histological verification of stimulus sites was made, electrode placement was guided by physiological responses--analogous to those obtained by RF stimulation.
Sprague and Chambers (1954) in their study of descending reticular influence reported difficulties comparable to ours in locating and "holding" a brain-stem region which inhibited motor activity. The prolonged effects of reticular stimulation on motor activity which they found were attributed to reticulo-cerebellar pathways and were abolished by cerebellectomy. In the present experiments the cerebellum was intact, which may account for the prolonged excitation or inhibition of muscular activity following the cessation of reticular stimulation. Llinas and Terzuolo (1964) have shown that a sustained potential is evoked within spinal motoneurons in response to RF stimulation. Further investigations of sustained voltage shifts at the spinal level would be useful in determining mechanisms underlying the SEG. The large rhythmic potentials of strychnineevoked convulsions in the spinal cord can be enhanced and inhibited by vestibular input (Gernandt and Terzuolo 1955); these effects were also interpreted to be mediated by the RF. The importance of supraspinal influence on SEG is further demonstrated upon spinalization of the decerebrate preparation. This procedure increases the SEG similarly to that reported by Mark and Gasteiger (1953) for spinalization of intact anesthetized preparations. The changes we Electroenceph. clin. Neurophysiol., 1968, 25:111-118
117
SEG" SUPRASPINAL INFLUENCES
observed were more pronounced and could be studied in terms of components of the SEG, probably due to the absence of anesthetics. A long lasting (7 h) decrease in SEG with spinalization was reported by Horsten (1947). A similar depression was routinely observed by us, but its time course was very short (10 min). Both alpha and gamma motoneurons are under supraspinal control (Granit and Kaada 1952; Sasaki et al. 1960). Thus RF stimulation which caused increased contraction of extrafusal muscles, possibly producing Golgi tendon organ discharge, might also activate the intrafusal muscles of spindle organs. These changes would cause an increase of afferent activity coming to the cord. This seemed to be the case, for (1) BA was decreased markedly when tonic afferent influences were eliminated by dorsal root section, and (2) the phasic increase of BA which was associated with increased muscular activity was prevented by Flaxedilization. The observation that BA continued to increase in response to RF stimulation for cats with lumbar rhizotomy, indicated that this component of the SEG is related not only to the input at the lumbar level but at other spinal levels as well. Presumably there are other determinants of BA, for the above explanation leads one to predict a decrease in BA when decerebrate rigidity is eliminated by spinalization. However, BA increased despite decreased motor activity and afferent input. The variations in the NSW component of the SEG have been associated throughout this study with the afferent and efferent activity of the cord. The following discussion considers the implications of such associations. It was observed that RF stimulation simultaneously depressed the sharp wave activity and the central action of peripherally evoked potentials, while spinalization caused an increase in both. Since the most marked effects were on the P wave and DRV of the evoked potentials, the possibility that these potentials and the NSWs have a common origin has been considered, but is not supported by other experiments (BrustCarmona et al. 1968). The NSW activity bore an inverse relationship to the amount of motor activity emanating from the cord when modulated by supraspinal
structures. This relation to motor activity implies that the NSWs reflect an inhibitory role as seen in their increase with termination of decerebrate rigidity by spinalization and their decrease in response to convulsants such as strychnine (Brust-Carmona et al. 1968). Our results from study of supraspinal influences emphasize again a more intimate coupling of NSWs to efferent than to afferent activity. Although the reciprocal relation between NSWs and motor activity is an arresting phenomenon, the essentiality of the NSWs in supraspinal influences has not been established. SUMMARY
In acute experiments with unanesthetized decerebrate and spinal cats, the spinal electrogram (SEG) was recorded with either intact or acutely transected dorsal roots. Only variations in the autochthonous negative sharp waves (NSW) and background activity (BA) were noted. Both these components of the SEG were attenuated in the decerebrate cat, as demonstrated by their increase in amplitude with spinalization. Electrical stimulation of brain-stem areas could enhance or depress the amplitude and frequency of occurrence of the NSWs of the lumbar cord. Decrease in NSWs was accompanied by: (a) increased lumbar motoneuronal excitability as manifested by increased hind limb muscle activity, and (b) decreased amplitude of peripherally evoked potentials. Increase in NSWs was accompanied by decreased excitability of lumbar motoneurons. BA was dependent upon input to the region of the lumbar cord under observation, from either the periphery or intraspinal sources. Its amplitude was markedly reduced by lumbar deafferentation, but was increased by descending impulses induced by forelimb muscle activity. BA was not directly affected by stimulation of brain-stem centers; the changes observed were due to an increase or decrease in input from muscles of the fore- and/or hind limbs. It now has been shown that the well-studied influence of brain-stem structures on spinal reflexes can be broadened to include the cord spontaneous activity. Electroenceph. clin. Neurophysiol., 1968, 25: 111-118
1 18
H. LEVITANet al. RI~SUMI~
L'I~LECTROGRAMME SPINAL DU CHAT. II. INFLUENCES SUPRASPINALES Dans des exp6riences aigu6s chez des chats d6c6r6br6s non-anesth6si6s et des chats spinaux non-anesth6si6s, l'61ectrogramme spinal (SEG) est enregistr6 aussi bien avec les racines post6rieures intactes ou coup6es par section transversale aiguS. Les auteurs notent seulement des variations des "negative sharp waves" autochtones (NSW) et de l'activit6 de fond (BA). Ces deux composantes du SEG sont att6nu6s chez des chats d6c6r6br6s c o m m e cela est d6montr6 par l'augmentation de leur amplitude avec la "spinalization". La stimulation 61ectrique des aires c6r6brales suppressives peut 616ver ou d6primer l'amplitude et la fr6quence de survenue des N S W s au niveau de la moelle lombaire. La diminution des N S W s est accompagn6e par: (a) l'616vation de l'excitabilit6 des motoneurones lombaires c o m m e cela est manifest6 par l'616vation de l'excitabilit6 des membres post6rieurs, et (b) la diminution de l'amplitude des potentiels 6voqu6s p6riph6riques L'616vation des N S W s s'accompagne de la diminution de l'excitabilit6 des motoneurones lombaires. BA d6pendait des aff6rences dans la r6gion lombaire sous observation, /t la fois de sources p6riph6riques ou spinales. Son amplitude est nettement r6duite par d6saff6rentation lombaire, mais est 61ev6e par des impulsions descendantes induites par l'activit6 musculaire des membres ant6rieurs. BA n'est pas directement affect6e par la stimulation des centres c6r6braux suppressifs; les variations observ6es son dues
une augmentation ou une diminution dans l'arriv6e depuis les muscles de membres ant6rieurs et/ou des membres post6rieurs. I1 est maintenant d6montr6 que les influences bien 6tudi6es des structures c6r6brales suppressives sur les r6flexes spinaux peuvent ~tre 6tendues fi l'activit6 spontan6e de la moelle. REFERENCES BRUST-CARMONA,H., LEVITAN, H., KASPRZAK,H. and GASTEIGER, E. L. Spinal electrogram of the cat. I. Study of origin by degeneration and ischemia. Electroenceph, clin. Neurophysiol., 1968, 25:101-110. GERNANDT,B. E. and TERZUOLO,C. A. Effect of vestibular
stimulation on strychnine-induced activity of the spinal cord. Amer. J. Physiol., 1955, 183: 1-8. GRANIT,R. and KAADA,B. R. Influence of stimulation of central nervous structures on muscle spindles in cat. Acta physiol, scand., 1952, 27: 130-160. HORSTEN,G. P. i . L'activit6 61ectrique spontan6e de la moelle 6pini~re des mammif~res. Arch. int. Physiol., 1947, 55: 304-306. LLINAS, R. and TERZUOLO,C. A. Mechanisms of supraspinal actions upon spinal cord activities. Reticular inhibitory mechanisms on alpha-extensor motoneurons. J. Neurophysiol., 1964, 27: 579-591. MARK,V. H. and GASTEIGER,E. L. Observations on the role of afferent and descending impulses on the spontaneous potentials of the spinal cord. Electroenceph. clin. Neurophysiol., 1953, 5: 251-258. NIEMER,W. T. and MAGOUN,H. W. Reticulospinal tracts influencing motor activity. J. comp. Neurol., 19,17, 87: 367-379. SASAKI,K., NANIKAWA,A. and HASmROMOTO,S. S. The effects of mid-brain stimulation upon alpha motoneurons in lumbar cord. Jap. J. Physiol., 1960, 10: 303316. SPRAGUE,J. M. and CHAMBERS,W. W. Control of posture by reticular formation and cerebellum in the intact, anesthetized and unanesthetized and in the decerebrate cat. Amer. J. Physiol., 1954, 176: 52-64. VERHAART,W. J. C. A stereotaxic atlas o f the brain stem of the cat: 2 vols. Davis, Philadelphia, 1964.
Reference: LEVITAN,H., GASTEIGER,E. L., KASPRZAK,H. and BRUST-CARMONA,H. Spinal electrogram of the cat. II.
Supraspinal influences. Electroenceph, clin. Neurophysiol., 1968, 25:111-118.
Electroencephalography and Clinical Neurophysiology Elsevier Publishing Company, Amsterdam - Printed in The Netherlands
SPINAL E L E C T R O G R A M OF T H E CAT. II. SUPRASPINAL INFLUENCES 1 H . LEVITAN 2, E. L. GASTEIGER, H . KASPRZAK AND H . BRUST-CARMONA ~
Department of Physical Biology, New York State Veterinary College and Section of Neurobiology and Behavior, Cornell University, Ithaca, N.Y. 14850 (U.S.A.)
(Accepted for publication: December 11, 1967)
INTRODUCTION
Our parallel studies (Brust-Carmona et al. 1968) have shown that the spinal electrogram (SEG) is composed mainly of two components: a diphasic background activity (BA) and negative sharp waves (NSW). The BA is related to, and largely dependent upon, input coming to the cord segment from the periphery but the sharp waves are autochthonous to the cord and do not depend on peripheral activation. In the present study the relationship between NSW and the output from the spinal cord was further explored in experiments based on the findings of Niemer and Magoun (1947) and Sprague and Chambers (1954) that reticular formation (RF) stimulation modifies muscular tone. METHODS AND MATERIAL
Preparatory surgery was performed on twentyfive cats anesthetized with ether. Except as noted below the methods were as described in the preceding paper (Brust-Carmona et al. 1968). An attempt was made to correlate motor activity with the SEG in 17 experiments. E M G recordings were made from pairs of stainless steel pins inserted into flexor and extensor muscles of the preparation's hind and forelimbs. The
EMGs were recorded with an amplifying system like that used for the SEG. In 4 experiments variations in the amplitudes of the cord dorsum potential (CDP) and the dorsal root potential (DRP) were correlated with the amplitude of the SEG. These potentials were evoked by stimulating the exposed sciatic nerve at a frequency between 0.5 and 1.0/sec. In twelve cats with dorsal roots intact and 5 with dorsal roots sectioned the brain-stem was stimulated through a coaxial bipolar electrode. Animal and stimulating electrode were mounted in a K o p f stereotaxic instrument and the electrode was placed in the brain-stem RF according to the Verhaart atlas (1964) and then adjusted according to the response of the musculature. The electrode was inserted parallel and caudal to the bony tentorium at an angle of 22 ° to the frontal plane. The region of the brain-stem explored extended from 6 mm anterior to 12 mm posterior, from 2 mm above to 8 mm below and laterally from the midline to 2.5 mm left. Although this volume of brain-stem was not probed in its entirety all the areas stimulated fell within its bounds. The stimulus current consisted of diphasic rectangular 0.1~).3 msec pulses applied at 60-300 p/sec (Grass $4 stimulator and isolation unit). RESULTS
1 This work was supported by U.S. Public Health Service Grants NB-04408, 5 TI GM223 and 5 K 3 NB6877. 2 Now at the Department of Anatomy, University of California, School of Medicine, Los Angeles, Calif. 90024. While o n leave from the Departamento de Fisiologia, Facultad de Medicina, Universidad Nacional de M6xico, M6xico 20, D.F., M6xico.
Tonic influence of the brain-stem Spinalization of the decerebrate cat by occluding the circulation to the brain-stem caused a transient de'wession of the SEG, a change which paralleled in time the transient increase in arterial blood pressure commonly seen under these Electroenceph. clin. Neurophysiol., 1968, 25: 111-118
H. LEVITAN
112
conditions. Both components of the SEG then progressively increased until in 15 min they reached levels 4-5 times greater than those for the decerebrate condition (see parallel change in Fig. 4 of Brust-Carmona et al. 1968). By this
et
a/.
time, the blood pressure had settled to the low levels characteristic of high spinal preparations. Subsequent surgical transection of the medullacord junction produced no response or a very brief one. These changes occurred whether the dorsal roots were intact or sectioned.
Effects of RF stimulation on SEG and muscular activity
Fig. 1
Concomitant decrease in SEG with increase in motor activity produced by reticular formation stimulation [P 8, L 2, H -11. LLs = SEG from sixth lumbar segment, left of cord midline; dorsal roots intact; LFF = EMG from left forelimb flexors; LHE = EMG from left hind limb extensors; LHF = EMG from left hind limb flexors.
?
.av’
The response to brain-stem stimulation varied according to the electrode placement, the initial muscle tone and the afferent input to the spinal cord. In general, stimulation of the RF at sites producing increased motor tone caused a reduction of the SEG (Fig. I), whereas stimulation at sites producing decreased motor tone enhanced the SEG (Fig. 2). Regions of the brain-stem causing inhibition of motor activity appeared to be scarcer than those causing excitation and in some cats inhibitory sites escaped detection entirely. Apparently they are very localized since displacement of the stimulating electrode as little as 1 mm often resulted in a different response. The intensity of RF stimulation required to
ok
Fig. 2 Increase in sharp wave activity in deafTerented lumbar cord during inhibition of forelimb musculature by reticular formation stimulation [A 5.7, L 2.0, H -1.91 (on+ff). Also inhibited but not shown was right hind limb extensor. RLa = SEG from right side of lumbar La; RFF = EMG from right forelimb flexors; LFE = EMG from left forelimb extensors. Persistent, periodic spikes in lower trace are electrocardiogram. Electroenceph. din. Neurophysiol., 1968,25: 11l-l 18
l 13
SEG" SUPRA,SPINAL INFLUENCES
i
Fig. 3 Alteration of the SEG by stimulation of the facilitatory reticular formation [P 3.1, L 0, H -2.8] before and after Flaxedil. Before Flaxedil: RF stimulation increased SEG in lumbar cord (LT) and motor activity as measured by ventral root discharge (LTVR). After Flaxedil: RF stimulation decreased the SEG while still evoking motoneurortal discharge.
produce a motor response was lower than, or equal to, that which produced an alteration in the SEG. Forelimb muscles were more sensitive to stimulation, but greater stimulus intensity caused a more diffuse motor response which extended eventually to the fore- and hind limbs of both sides. The response of motor activity and SEG to RF stimulation began with the onset of stimulus and ceased with its termination. Exceptions were observed for motor responses. These include: build up of response or delayed onset (Fig. 2), waning of activity during the stimulus period (RHE in Fig. 4), or a failure of the activity to return to pre-stimulus level--particularly following inhibitory stimulation (LFF in Fig. 1). These variations were most apparent for low in-
tensity stimulation. Motor activation with inhibition of the SEG produced by RF stimulation, illustrated in Fig. 1, was obtained in a preparation with intact dorsal roots. A recording on an expanded time base revealed that the BA component was not markedly changed by moderate stimulation although the NSWs were greatly reduced. However, with more intense stimulation at this site both a greater motor response, especially in the forelimbs, and an unexpected increase of SEG were observed. It was difficult to determine whether this increase of the SEG was due to a change in its BA or NSW component 1. To maintain the BA component 1 An increase in the BA component would be expected
if there were an increase in activity coming into the cord via the intact dorsal roots (Brust-Carmona et al. 1968). Electroenceph. clin. Neurophydol., 1968, 25: 111-118
114
H. LEVITAN et al.
c o n s t a n t despite stimulation, 4-10 m g o f Flaxedil were given i.v. in three cases where stimuli facilit a t o r y for m o t o r activity also increased the SEG. Under these conditions R F s t i m u l a t i o n increased m o t o r activity as m e a s u r e d by ventral r o o t discharge, decreased the N S W , b u t d i d n o t alter the BA (Fig. 3). Thus, it is p r o b a b l e t h a t increase o f the S E G prior to a d m i n i s t e r i n g Flaxedil was largely due to heightened B A which occurred reflexly with increased m u s c u l a r activity. The differential effects on B A a n d N S W components o f repeated s t i m u l a t i o n o f various intensities at n u m e r o u s R F sites was studied further in five cats with l u m b a r deafferentation. It was observed in these p r e p a r a t i o n s that only when the forelimbs were a c t i v a t e d d i d an increase in BA o c c u r (Fig. 4), similar to that described a b o v e when d o r s a l l u m b a r r o o t s were intact. Therefore, changes in the c o m p o n e n t s o f the l u m b a r S E G were correlated with a c t i v a t i o n or i n h i b i t i o n o f fore- and h i n d l i m b tone in 200 responses (Table I). A n increase in B A was f o u n d to be c o r r e l a t e d with increased forelimb tone in 78 o f 106 instances (74%). I n t r a v e n o u s injection o f Flaxedil again b l o c k e d the increase o f B A suggesting t h a t the forelimb afferents were facilitating the l u m b a r BA. N o correlation c o u l d be discerned between changes in hind limb m o t o r activity a n d B A in these deafferented animals since h i n d limb t o n e increased, decreased or r e m a i n e d u n c h a n g e d with a b o u t equal frequency. W h e n b o t h fore- a n d hind limb tone increased concurrently, the increase in B A was observed but it was a c c o m p a n i e d by decrease in N S W (Fig. 4). ~LL~ . . . .
i LFF
~
+ '+'~+! 'l+m"+'v +
+ + Rt,,E +
I aJml~%+,+,~ .+ +
.....
o~+
I
!
Fig. 4 Concurrent increase in BA and fore- and hind limb muscular activity with decrease in NSWs in response to RF stimulation [P 8, L 2, H 0]. LL6 = SEG from left side of segment L6 in lumbar deafferented cord; LFF = EMG from left forelimb flexor; RI-IE = EMG from right hind limb extensor.
A s s o c i a t i o n o f N S W activity with changes in hind limb muscle tone showed close correlation. Of the 37 instances in which an increase in N S W activity coincided with a change in hind limb activity, 29 were associated with a decrease in tone (79%). Conversely a decrease in N S W activity was associated with an increase in hind TABLE 1 Relation between components of SEG and electromyogram of fore- and hind limb muscles for five lumbar deafferented cats in response to RF stimulation SEG
BAincrease NSWincrease NSWdecrease
EMG Fore limbs 0
Hind limbs -+- -- 0
78 18 10 40 36 12 25 4 10
33 29 35 8 29 41 18 4 14
Mixed responses of flexor and extensor muscles (fore- and hind limb responses treated independently) were scored according to the dominant effects. BA := background activity; NSW := negative sharp wave activity. ÷ = increase; . . . . . decrease; 0 ~ no change in muscular activity. limb tone in 18 o f 22 cases (82%). In 41 instances R F s t i m u l a t i o n p r o d u c e d an increase in N S W s w i t h o u t a n y change in hind limb m u s c u l a r tone. The m a j o r i t y o f these o c c u r r e d in animals with an absence o f tonic hind limb activity following d e c e r e b r a t i o n or previous i n h i b i t o r y s t i m u l a t i o n ; p r e s u m a b l y no inhibition o f m u s c u l a r activity could occur. O n 14 occasions N S W s were depressed without change in hind limb tone. Increase o f N S W s could not be correlated with forelimb activity. However, the N S W s consistently decreased when forelimb tone increased. This change was like t h a t seen in the case o f increased hind limb tone a n d indicates that the N S W s are decreased with heightened efferent activity o f the spinal cord. Variations in the frequency a n d strength o f R F stimulus altered the t h r e s h o l d b u t n o t the c h a r a c t e r o f the response. W h e n the c h a r a c t e r o f the response did change, the stimulating electrode was usually in an i n h i b i t o r y area. The effects o f the R F on the S E G were not restricted to a single spinal segment b u t extended s i m u l t a n e o u s l y over segments L~, L6 a n d LT. Electroenceph. clin. Neurophysiol., 1968, 25: 111-118
SEG: SUPRASPINALINFLUENCES
Changes in peripherally evoked po tentials R F stimulation which attenuated the NSWs simultaneously reduced the spinal cord potentials, CDP and DRP, evoked by single shocks to the sciatic nerve (Fig. 5), All but the early spike components of the evoked potentials were reduced in amplitude, but particularly marked was the reduction of the P wave and D R V components. A concomitant increase in the N S W and evoked potentials was never observed. The temporal correspondence between attenuation of the N S W and reduction of CDP and D R P was close, both with onset and cessation of R F stimulation. The stimulation threshold for the two
115
influences also corresponded well. R F stimulation producing decrease in NSW and evoked afferent activity enhanced motor tone at the same time (Fig. 5). Also illustrated is the finding that peripheral stimulation itself could cause alteration in the lumbar SEG. Maximal stimuli to the sciatic nerve at rates greater than about 0.5 sec depressed the sharp wave activity.
Concomitant blood pressure changes R F stimulation which caused enhancement of both BA and N S W was accompanied by transient decrease in arterial blood pressure, whereas stimulation which caused depression of sponta-
STIM.
CDP
:7
DRP
LL7
•
~
•
~,,T
Fig. 5 Concurrent decrease of SEG and evoked potentials from the cord dorsum (CDP) and dorsalroot (DRP) with increased motoneuronal activity (LLTVR) in response to RF stimulation [A 0.5, L 2, H -3.7]. The times single shocks were delivered to the sciatic are indicated on the third channel; when initiated they decreased the NSWs. Shock artifact has been removed from the top trace to make clear the changes in the SEG. The resulting evoked potentials, CDP and DR.P, are represented before, during and after RF stimulation, from left to right. LL7 = SEG from left L7 segment; L L 7 V R = activity of left ventral root of L~ segment.
Eleetroenceph. clin. Neurophysiol., 1968, 25: 111-118
116
H. LEVITAN CI ~/[.
RET~ULAR s~lle
Ka
STIMULATION
EPINEPHRINE
IN,I C T I O N
lqlljmm[
t. I
I
I
Fig. 6 The independence of SEG and blood pressure changes caused by R F stimulation [A 1.3, L 1.5, H -1.9] as shown by relative constancy of SEG when blood pressure was increased by injection of epinephrine.
neous activity was accompanied by transient increase in the arterial blood pressure. Since these changes in SEG and blood pressure wet e consistent with those seen with spinalization, it was possible that the variation in SEG was due to blood pressure changes rather than directly to RF stimulation. To determine the validity of this possible inverse relationship, an i.v. injection of epinephrine (30 #g) was administered (4 animals) to produce a rise in blood pressure comparable to that caused by reticular stimulation. The SEG was not altered significantly (Fig. 6). In addition, infusion of 20-40 ml of Dextran (6 animals) produced an increase in blood pressure without a change in the SEG. Therefore, the concomitant variations in SEG and blood pressure did not appear to be directly related even though they were provoked from the same region of the RF. DISCUSSION
This study has confirmed the existence of a powerful influence of brain-stem structures on the SEG. Although no histological verification of stimulus sites was made, electrode placement was guided by physiological responses--analogous to those obtained by RF stimulation.
Sprague and Chambers (1954) in their study of descending reticular influence reported difficulties comparable to ours in locating and "holding" a brain-stem region which inhibited motor activity. The prolonged effects of reticular stimulation on motor activity which they found were attributed to reticulo-cerebellar pathways and were abolished by cerebellectomy. In the present experiments the cerebellum was intact, which may account for the prolonged excitation or inhibition of muscular activity following the cessation of reticular stimulation. Llinas and Terzuolo (1964) have shown that a sustained potential is evoked within spinal motoneurons in response to RF stimulation. Further investigations of sustained voltage shifts at the spinal level would be useful in determining mechanisms underlying the SEG. The large rhythmic potentials of strychnineevoked convulsions in the spinal cord can be enhanced and inhibited by vestibular input (Gernandt and Terzuolo 1955); these effects were also interpreted to be mediated by the RF. The importance of supraspinal influence on SEG is further demonstrated upon spinalization of the decerebrate preparation. This procedure increases the SEG similarly to that reported by Mark and Gasteiger (1953) for spinalization of intact anesthetized preparations. The changes we Electroenceph. clin. Neurophysiol., 1968, 25:111-118
117
SEG" SUPRASPINAL INFLUENCES
observed were more pronounced and could be studied in terms of components of the SEG, probably due to the absence of anesthetics. A long lasting (7 h) decrease in SEG with spinalization was reported by Horsten (1947). A similar depression was routinely observed by us, but its time course was very short (10 min). Both alpha and gamma motoneurons are under supraspinal control (Granit and Kaada 1952; Sasaki et al. 1960). Thus RF stimulation which caused increased contraction of extrafusal muscles, possibly producing Golgi tendon organ discharge, might also activate the intrafusal muscles of spindle organs. These changes would cause an increase of afferent activity coming to the cord. This seemed to be the case, for (1) BA was decreased markedly when tonic afferent influences were eliminated by dorsal root section, and (2) the phasic increase of BA which was associated with increased muscular activity was prevented by Flaxedilization. The observation that BA continued to increase in response to RF stimulation for cats with lumbar rhizotomy, indicated that this component of the SEG is related not only to the input at the lumbar level but at other spinal levels as well. Presumably there are other determinants of BA, for the above explanation leads one to predict a decrease in BA when decerebrate rigidity is eliminated by spinalization. However, BA increased despite decreased motor activity and afferent input. The variations in the NSW component of the SEG have been associated throughout this study with the afferent and efferent activity of the cord. The following discussion considers the implications of such associations. It was observed that RF stimulation simultaneously depressed the sharp wave activity and the central action of peripherally evoked potentials, while spinalization caused an increase in both. Since the most marked effects were on the P wave and DRV of the evoked potentials, the possibility that these potentials and the NSWs have a common origin has been considered, but is not supported by other experiments (BrustCarmona et al. 1968). The NSW activity bore an inverse relationship to the amount of motor activity emanating from the cord when modulated by supraspinal
structures. This relation to motor activity implies that the NSWs reflect an inhibitory role as seen in their increase with termination of decerebrate rigidity by spinalization and their decrease in response to convulsants such as strychnine (Brust-Carmona et al. 1968). Our results from study of supraspinal influences emphasize again a more intimate coupling of NSWs to efferent than to afferent activity. Although the reciprocal relation between NSWs and motor activity is an arresting phenomenon, the essentiality of the NSWs in supraspinal influences has not been established. SUMMARY
In acute experiments with unanesthetized decerebrate and spinal cats, the spinal electrogram (SEG) was recorded with either intact or acutely transected dorsal roots. Only variations in the autochthonous negative sharp waves (NSW) and background activity (BA) were noted. Both these components of the SEG were attenuated in the decerebrate cat, as demonstrated by their increase in amplitude with spinalization. Electrical stimulation of brain-stem areas could enhance or depress the amplitude and frequency of occurrence of the NSWs of the lumbar cord. Decrease in NSWs was accompanied by: (a) increased lumbar motoneuronal excitability as manifested by increased hind limb muscle activity, and (b) decreased amplitude of peripherally evoked potentials. Increase in NSWs was accompanied by decreased excitability of lumbar motoneurons. BA was dependent upon input to the region of the lumbar cord under observation, from either the periphery or intraspinal sources. Its amplitude was markedly reduced by lumbar deafferentation, but was increased by descending impulses induced by forelimb muscle activity. BA was not directly affected by stimulation of brain-stem centers; the changes observed were due to an increase or decrease in input from muscles of the fore- and/or hind limbs. It now has been shown that the well-studied influence of brain-stem structures on spinal reflexes can be broadened to include the cord spontaneous activity. Electroenceph. clin. Neurophysiol., 1968, 25: 111-118
1 18
H. LEVITANet al. RI~SUMI~
L'I~LECTROGRAMME SPINAL DU CHAT. II. INFLUENCES SUPRASPINALES Dans des exp6riences aigu6s chez des chats d6c6r6br6s non-anesth6si6s et des chats spinaux non-anesth6si6s, l'61ectrogramme spinal (SEG) est enregistr6 aussi bien avec les racines post6rieures intactes ou coup6es par section transversale aiguS. Les auteurs notent seulement des variations des "negative sharp waves" autochtones (NSW) et de l'activit6 de fond (BA). Ces deux composantes du SEG sont att6nu6s chez des chats d6c6r6br6s c o m m e cela est d6montr6 par l'augmentation de leur amplitude avec la "spinalization". La stimulation 61ectrique des aires c6r6brales suppressives peut 616ver ou d6primer l'amplitude et la fr6quence de survenue des N S W s au niveau de la moelle lombaire. La diminution des N S W s est accompagn6e par: (a) l'616vation de l'excitabilit6 des motoneurones lombaires c o m m e cela est manifest6 par l'616vation de l'excitabilit6 des membres post6rieurs, et (b) la diminution de l'amplitude des potentiels 6voqu6s p6riph6riques L'616vation des N S W s s'accompagne de la diminution de l'excitabilit6 des motoneurones lombaires. BA d6pendait des aff6rences dans la r6gion lombaire sous observation, /t la fois de sources p6riph6riques ou spinales. Son amplitude est nettement r6duite par d6saff6rentation lombaire, mais est 61ev6e par des impulsions descendantes induites par l'activit6 musculaire des membres ant6rieurs. BA n'est pas directement affect6e par la stimulation des centres c6r6braux suppressifs; les variations observ6es son dues
une augmentation ou une diminution dans l'arriv6e depuis les muscles de membres ant6rieurs et/ou des membres post6rieurs. I1 est maintenant d6montr6 que les influences bien 6tudi6es des structures c6r6brales suppressives sur les r6flexes spinaux peuvent ~tre 6tendues fi l'activit6 spontan6e de la moelle. REFERENCES BRUST-CARMONA,H., LEVITAN, H., KASPRZAK,H. and GASTEIGER, E. L. Spinal electrogram of the cat. I. Study of origin by degeneration and ischemia. Electroenceph, clin. Neurophysiol., 1968, 25:101-110. GERNANDT,B. E. and TERZUOLO,C. A. Effect of vestibular
stimulation on strychnine-induced activity of the spinal cord. Amer. J. Physiol., 1955, 183: 1-8. GRANIT,R. and KAADA,B. R. Influence of stimulation of central nervous structures on muscle spindles in cat. Acta physiol, scand., 1952, 27: 130-160. HORSTEN,G. P. i . L'activit6 61ectrique spontan6e de la moelle 6pini~re des mammif~res. Arch. int. Physiol., 1947, 55: 304-306. LLINAS, R. and TERZUOLO,C. A. Mechanisms of supraspinal actions upon spinal cord activities. Reticular inhibitory mechanisms on alpha-extensor motoneurons. J. Neurophysiol., 1964, 27: 579-591. MARK,V. H. and GASTEIGER,E. L. Observations on the role of afferent and descending impulses on the spontaneous potentials of the spinal cord. Electroenceph. clin. Neurophysiol., 1953, 5: 251-258. NIEMER,W. T. and MAGOUN,H. W. Reticulospinal tracts influencing motor activity. J. comp. Neurol., 19,17, 87: 367-379. SASAKI,K., NANIKAWA,A. and HASmROMOTO,S. S. The effects of mid-brain stimulation upon alpha motoneurons in lumbar cord. Jap. J. Physiol., 1960, 10: 303316. SPRAGUE,J. M. and CHAMBERS,W. W. Control of posture by reticular formation and cerebellum in the intact, anesthetized and unanesthetized and in the decerebrate cat. Amer. J. Physiol., 1954, 176: 52-64. VERHAART,W. J. C. A stereotaxic atlas o f the brain stem of the cat: 2 vols. Davis, Philadelphia, 1964.
Reference: LEVITAN,H., GASTEIGER,E. L., KASPRZAK,H. and BRUST-CARMONA,H. Spinal electrogram of the cat. II.
Supraspinal influences. Electroenceph, clin. Neurophysiol., 1968, 25:111-118.