The influence of curare on hypothalamic excitability and the electroencephalogram

THE INFLUENCE AND

OF CURARE

ON HYPOTHALAMIC

THE ELECTROENCEPHALOGRAM

EXCITABILITY 1

E. GEI.LUOaN, P h . D . Laboratory of Neurophyslology, Del)artment of Physiology, University of Minnesota, Minneapolis, Minn. (Received for publication: March 4, 1958) Previous investigations (Bernhaut, Gellhorn and Rasmussen 1953) showed that proprioceptive impulses elicited in the muscles and joints by passive movements of the limbs cause a marked excitation of the sympathetic division of the hypothalamus and a diffuse excitation of the cerebral cortex. There exists a parallelism between the two excitatory processes. Reduction in hypothalamic excitability by barbiturates (Gellhorn 1953), or hypothalamie lesions (Koella and Gellhorn 1953), reduce or abolish the diffuse hypothalamiccortical discharge, whereas the inhalation of 10 per cent CO2 increases hypothalamie excitability and the proprioceptively induced diffuse excitation of the cerebral cortex (Gellhorn 1953). These observations suggest that curare, by reducing or abolishing proprioeeptive discharges, should reduce hypothalamic excitability and thereby, through the diminution of hypothalamic-eortical discharges, increase s y n c h r o n y in the E E G . Since the influence of curare on the excitability of the hypothalamus does not seem to have been investigated, and most authors deny an effect of curare on the E E G (Bovet and Longo 1953; Smith, Brown, Toman and Goodman 1947) the action of Intocostrin and Anectine on hypothalamus and E E G was studied. METHODS The experiments were performed on 12 cats. The animals were operated under ether anesthesia or after intravenous injection of Pentothal and local anesthesia. The experimental observations were carried out several hours later. I n one group of animals Hess electrodes were inserted in the posterior hypo-

thalamus and the blood pressure (from the femoral artery) and the normal and the acutely denervated nictitating membrane (n.m.) were recorded with a Brush Strain Gauge Analyzer by means of Statham pressure and displacement transducers. The hypothalamus was stimulated with a Grass square wave generator. The site of the electrode was verified histologically. I n the second group of experiments the E E G taken from the intact skull, and the potentials from the posterior hypothalamus (Hess electrodes) were recorded by means of an eight channel Grass electroencephalograph. The E E G was analyzed with an Offner Analyzer. Intocostrin (20 units/cc.) was used intramuscularly in doses from 0.22 to 0.5 ee/kg. 2 and Anectine was applied intravenously in doses from 0.4 to 1.5 m g / k g . 3 RESULTS

I. The influence of Intocostrin and Anectine on the Excitability of the Posterior Hypothalamus. 4 The typical action of Intocostrin on the excitability of the sympathetic division of the hypothalamus is illustrated in figure 1. A f t e r repeated tests, performed at intervals of 2-3 rain., had shown that the response of the hypothalamus to a certain stimulus remained constant, Intoeostrin was injected. The effect of the stimulus on the n.m. was then distinctly lessened (B). As the time interval was increased a n d / o r slightly higher doses were employed, the sympathetic reactivity decreased f u r t h e r (C, D). Finally, the slope 2 In a few instances Intocostrin was given i.v. in doses up to 0.1 cc/kg. The drugs were kindly supplied by E. R. Squibb and Sons and Burroughs Wellcome & Co. respectively. 4 With the assistance of E. S. Redgate.

1 These studies were aided by a grant from the Louis W. and Maud Hill Family Foundation. [ 697 ]

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GELLHORI~

of the pressor a c t i o n was lessened ( D ) . I t is w o r t h y of emphasis t h a t m a r k e d effects of c u r a r e on the r e s p o n s i v e n e s s of the n.m. a n d s m a l l effects on the p r e s s o r response were seen r e g u l a r l y a l t h o u g h the blood p r e s s u r e was n o t lowered. I n one e x p e r i m e n t i n

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Fig. 1 The effect of Intocostrin on hypothalamic sympathetic reactivity of a cat. Stimulation of the posterior hypothalamus: 2.5 V., 207/sec., 0.8 mscc., 8 sec. A, Control; B, 4 min. after injection of Intocostrin (0.25 cc/kg, i.m.); C and D, r~spectively, 10 and 20 min. later after further injection of 0.1 cc/kg, of Intocostrin i.v. NM, nictitating membrane; BP, blood pressure. Note that the contraction of the nictitating membrane and the pressor effect of hypothalamic stimulation decline progressively. which 10 rain. f o l l o w i n g the i n j e c t i o n of 0.33 cc/kg, of I n t o c o s t r i n (i.m.) the blood p r e s s u r e fell f r o m 152 mm. to 132 ram. H G the d i m i n i s h e d response of the n.m. a n d the blood p r e s s u r e to h y p o t h a l a m i c s t i m u l a t i o n could haI'dly be a t t r i b u t e d to a c o n c o m i t a n t ina d e q u a c y of cerebral o x y g e n a t i o n . The long d u r a t i o n of the a c t i o n of I n t o c o s t r i n f r e q u e n t l y p r e v e n t e d the d e m o n s t r a tion t h a t its effect was reversible. The t r a n s i e n t action of A n e c t i n e , however, was re-

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BP OO Fig. 2 The effect of Anectine on hypothalamic reactivity. Cat, 41~ kg., prepared with 25 mg/kg. Pentothal i.v. and local application of procaine several hours earlier. Stimulation of the posterior hypothalamus: 2.0 V., 207/sec., 0.8 msec., 3 sec. A, Control; C, 36 sec. after injection of Anectine (0.44 mg/kg, i.v.). B, 4 min. after C. DNI~[, denervated nictitating membrane. s y m p a t h e t i c r e s p o n s i v e n e s s of the hypot h a l a m u s is i n c r e a s e d d u r i n g a s p h y x i a . Since c u r a r i z a t i o n lessens h y p o t h a l a m i c e x c i t a b i l i t y it a p p e a r e d likely t h a t it w o u l d c o u n t e r a c t 1 Immediately on injection of Anectine the denervated n.m. relaxed. As soon as the effect passed it resumed its previous state. The nature of this relaxation has not been investigated.

CURARE, HYPOTHALAMUS AND EEG this action of asphyxia. A p p r o p r i a t e experiments showed indeed that the increased sympathetic responsiveness indicated by the greater contraction of the n.m. on hypothalamic stimulation in asphyxia m a y be absent a f t e r curarization. I t is concluded f r o m the experiments of this section t h a t curarization lessens hypothalamie sympathetic excitability. II. The Influence of Intocostrin and Anectine

on Hypothalamic and Cortical Potentials. On injection of Intocostrin or Ancctine in the doses indicated earlier, characteristic changes in cortical and hypothalamic po-

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potentials a p p e a r e d in the hypothalamic and cortical records and persisted for several minutes. This change was accompanied by a marked increase in the integrated amplitude of the potentials of low frequencies as the analysis of the h y p o t h a l a m o g r a m (A 1) shows. Similar changes occurred, as the analysis of other experiments disclosed, in cortical potentials. P a r t C of figure 3 illustrates the reversibility of these effects on cortical and hypothalamic potentials and on the analysis of the latter. Similar results were obtained on injection of Intocostrin, the chief difference being the longer action of this drug. There seemed to

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C Fig. 3 The effect of Anectine on cortical and hypothalamie potentials. Cat, 3.4 kg. Bipolar recordings from: 1, left and right hypothalamus; 2, left motor-parietal cortex; 3, left and right motor cortex. A. 1, analysis of # 1 (hypothalamus). Calibration: 50 /~V. and 5 sec. A. control before injection; B, 3 rain. after injection of 0.6 mg/kg. Anectine i.v.; C. 8 min. after B. The blood pressure was unchanged (110 mm Hg) throughout the experiment. :~requcncies analyzed by the Offner apparatus are in order as following: 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 7, 8, 9, 10~ 1l, 12, 13, 14, 15, 16, 18, 20, 22, 24, 27, and 30.

tentials occurred although the blood pressure did not fall. F i g u r e 3 shows t h a t in a cat in which u n d e r control conditions no grouped potentials a p p e a r e d in the h y p o t h a l a m o g r a m and only a few in the cerebral cortex, the injection of Anectine (0.6 m g / k g , i.v.) altered the records fundamentally. L a r g e grouped

be one difference however, between the two groups of observations. Anectine produced commonly a transient excitatory phase before the grouped potentials in cortex and h y p o t h a l a m u s appeared. This phase was clearly seen in experiments in which a few grouped potentials were present in cortex and

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h y p o t h a l a m u s u n d e r c o n t r o l c o n d i t i o n s as in f i g u r e 4 A. The f i r s t h a l f of f i g u r e 4 B i l l u s t r a t e s t h e f a c t t h a t the e x c i t a t o r y s t a t e b e g i n n i n g a b o u t 30 sec. a f t e r the i n j e c t i o n

low f r e q u e n c y showed a d e c r e a s e d , a n d those of h i g h f r e q u e n c y a n i n c r e a s e d , i n t e g r a t e d a m p l i t u d e . F o l l o w i n g this e x c i t a t o r y p h a s e the blood p r e s s u r e r e t u r n s to t h e c o n t r o l level,

Fig. 4 The immediate effects of Anectine on hypothalamic and cortical potentials of the cat. 1. Bipolar recordings from: 1, r. hypothalamus; 2, left and right posterior h~pothalamus; 3, left and right motor cortex; 4, blood pressure; 5, analysis of # 2 (hypothalamus). A, Control; B, 30 sec. after injection of Anectine 1 mg/kg, i.v. Calibration 50 t~V. and 5 sec. is c h a r a c t e r i z e d b y : 1, a s l i g h t rise of the blood p r e s s u r e ; 2, a d i s a p p e a r a n c e of g r o u p e d p o t e n t i a l s seen in the c o n t r o l r e c o r d ; 3, a d i m i n u t i o n in t h e i n t e g r a t e d a m p l i t u d e of the p o t e n t i a l s of low f r e q u e n c i e s . T h i s l a t t e r

w h e r e a s the c o r t i c a l a n d h y p o t h a l a m i c pot e n t i a l s disclose g r o u p e d p o t e n t i a l s ( r i g h t h a l f of f i g u r e 4) b e f o r e c o n t r o l c o n d i t i o n s w e r e restored. W h e t h e r the a p p e a r a n c e of t h e t r a n s i e n t

Fig. 5 The effect of nociceptive stimulation on hypothalamic and cortical potentials as influenced by Anectine. Cat, 2.5 kg. Bipolar recordings from: 1, left hypothalamus; 2, left and right hypothalamus; 3, left and right motor cortex; 4, left and right auditory cortex; 5, blood pressure. Calibration: 100 t~V. and 5 sec. A, before; B, 9 rain. after the injection of 0.44 cc/kg. Intocostrin i.m. Between the arrows the tail was immersed in water of 55°C. for 30 sec. p h e n o m e n o n is s h o w n i n f i g u r e 4 f o r t h e h y p o t h a l a m u s . I n o t h e r e x p e r i m e n t s i t was s h o w n t h a t i t a p p e a r e d to a n even m o r e m a r k e d d e g r e e in t h e c o r t e x : t h e p o t e n t i a l s o f

e x c i t a t o r y p h a s e in t h e A n e c t i n e e x p e r i m e n t s b u t n o t in those i n v o l v i n g I n t r o c o s t r i n is d u e to s i g n i f i c a n t d i f f e r e n c e s in the a c t i o n of t h e two d r u g s or to d i f f e r e n c e s in t h e a d m i n i s t r a -

CURARE, HYPOTHALAMUS

tion has not been investigated. The intravenous injection of effective doses of Intocostrin lowers the blood pressure, an effect carefully avoided in our experiments in order to s t u d y the effects of curarization at constant circulatory conditions. The experiments described in this p a p e r seem to indicate that the responsiveness of the h y p o t h a l a m u s to direct stimulation is lessened on injection of Intocostrin and Anectine. The alterations of the hypothalam o g r a m indicates likewise t h a t these drugs reduce hypothalamic excitation. Since the effect of nociceptive stimulation depends-on hypothalamic excitability (Bernhaut, Gellhorn, and Rasmussen 1953) nociceptive stimuli were applied before and a f t e r curarization while cortical and hypothalamic potentials were recorded. F i g u r e 5 illustrates a typical experiment. A weak nociceptive stimulus produced in this " l i g h t " cat a prolonged excitation in cortex and h y p o t h a l a m u s since the grouped potentials d i s a p p e a r e d following the stimulus and did not r e t u r n during the time recorded in figure 5 A. A f t e r curarization, however, the excitatory effect was greatly reduced in duration as the r e t u r n of the grouped potentials in the right section of figure 5 B shows. DISCUSSION

The experiments show that curarization leads to a diminution in the responsiveness of the sympathetic division of the h y p o t h a l a m u s to electrical stimulation and to a diminished state of excitation of this structure as ~ndieared by the h y p o t h a l a m o g r a m and its frequency analysis. The a p p e a r a n c e of grouped potentials in the cerebral cortex as the result of curarization and the lessened effect of noeiceptive stimuli on cortex and hypothalamus can likewise be explained by the reduction in hypothalamic excitability. Curarization exerts an effet similar to that seen when the excitability of the posterior hypothalamus is reduced by the i n t r a h y p o t h a l a m i e injection of b a r b i t u r a t e s (Gellhorn, unpublished experiments) or the production of lesions in this area (Koella and Gellhorn 1958). Since the blood pressure was not lowered by

AND EEG

701

Intoeostrin and Anectine in the doses used in our experiments the reduction in hypothalamic and cortical excitability cannot be due to changes in cerebral oxygenation. 1 The direct and indirect (cortical) effects of the reduced hypothalamic excitability seem to be the result of the elimination of proprioceptive impulses by curarization. T h a t proprioceptive impulses cause an excitation of the posterior h y p o t h a l a m u s and elicit a hypothalamic-cortical discharge was shown by Bernhaut, Rasmussen and Gellhorn (1953). The effects of curare suggest that the physiological muscle tone contributes to hypothalamic and cortical excitation. The frequently observed occurrence of increased muscle tension in states of emotion seems to be not only the result of increased central sympathetic and somatic discharges whose parallelism at the hypothalamic level was emphasized by Hess (1947) but also to the seconda r y contribution of the increased proprioceptire impulses to the state of excitation of the sympathetic division of the h y p o t h a l a m u s and of the cerebral cortex. The value of a t h e r a p y of muscular relaxation (Jacobson 1929) appears, therefore, well founded physiologically in states of emotional tension, regardless of the mechanism by which this relaxation is achieved. In this connection it m a y be mentioned that, as shown elsewhere (Gellhorn 1957 pp. 144) small doses of curare which do not interfere with respiration reduce the excitability of the posterior h y p o t h a l a m u s and the emotional reactivity of the unanesthetized cat. Conversely, it was suggested by Ge]lhorn, Koella and Ballin (1954, 1955) that the interaction of sensory stimuli with the diffuse afferent system activated by stimulation of the posterior h y p o t h a l a m u s contributes to conscious perception. This interpretation was supported by recent observations on unanethetized cats in which sensory stimuli to which 1 P u r p u r a a n d G r n n d f e s t (1956) f o u n d th~qt ,qfter a d m i n i s t r a t i o n of t u b o c u r a r i n e in doses of 3 to 5 m g / k g , i.v. n o r m a l a n d convulsive a c t i v i t y d i s a p p e a r in t h e E E G . I t is well known t h a t such e n o r m o u s doses, p a r t i c u l a r l y if a d m i n i s t e r e d i n t r a v e n o u s l y , cause a m a r k e d fall in t h e blood pressure. The l a t t e r was n o t recorded in their e x p e r i m e n t s .

702

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the animal failed to react under control conditions, elicited specific effects (the cat followed a moving visual object with the eyes etc.) after minimal stimulation of the posterior hypothalamus (Gellhorn 1957 pp. 197). I t is, therefore, understandable that the complete relaxation in a darkened quiet room leads not only to lessened emotional tension but also to a peculiar " e m p t i n e s s " of the conscious state ("Bewusstseinsleere ohne Bewusstlosigkeit' ', B u y t e n d i j k 1955). I f curare is applied in similar doses to those used in our experiments in moderately deep anesthesia it fails to alter the E E G . For this reason our work was carried out several hours after the initial anesthesia, at a time when the E E G revealed no or only a few grouped potentials. The common occurrence of slow potentials in the E E G of the unanesthetized rabbit (as the figures in Bovet and Longo's paper (1953) show) makes this animal rather unsuited for the study of curare on the E E G . The failure of curare to alter the E E G in man, reported by Smith, Brown, Toman and Goodman (1947), seemed to be explainable on a similar basis. The experimental subjects were already relaxed, the E E G in a state of moderate synchrony (alpha potentials) so that f u r t h e r relaxation by curare was ineffective (see the similar interpretation of the failure of chlorpromazine to alter the human E E G by Shagass 1955). Finally, attention is called to the work of yon E u l e r and SSderberg (1957) who, through adequate stimulation of the anterior hypothalamus induced an increased synchrony in the E E G and a diminution in the discharges from the muscles spindles. Since anterior and posterior hypothalamus are reciprocally related in their excitability (Gellhorn, Nakao, and Redgate 1956) it may be said that in yon E u l e r ' s experiments the posterior hypothalamus was inhibited. This inhibition was accompanied by the same central (cortical) and peripheral effects (diminished activity of the muscle spindles) that are seen when the activity of the muscle spindles is reduced by curare. In yon E u l e r ' s and SSderberg's work a diminution in the reactivity of the sympathetic division of the hypothalamus

must have occurred through reciprocal action from the anterior hypothalamus, whereas in our curare experiments it resulted from the diminution of proprioceptive impulses impinging on the posterior hypothalamus. SUMMARY The action on the posterior hypothalamus and the E E G of Intocostrin and Anectine in small doses which do not lower the blood pressure was studied in cats. It was found that the excitability of the sympathetic division of the hypothalamus was decreased by curarization as indicated by the diminished response of the nictitating membrane to, and the lessened pressor effect of, hypothalamic stimulation. At the same time the E E G showed an increased synchrony. The reduction in hypothalamic sympathetic reactivity and the associated reduction in the state of cortical excitation account for the diminution in emotional reactivity which is associated with the relaxation of the skeletal muscles. L'action sur l'hypothalamus post~rieur et sur I ' E E G de petites doses d'Intocostrine et d'Anectine ne produisant pas d'abaissement de la pression art~rielle a ~t~ ~tudi~e chez des chats. I1 a ~t~ trouv~ que l'excitabilit~ de la portion sympathique de l'hypothalamus est diminu~e par curarisation, puisque la stimulation hypothalamique produit nne r~ponse diminu~e de la membrane nictitante et une action hypertensive diminu~e apr~s administration de ces m~dicaments curarisants. Simultan~ment les trac~s E E G montrent une synchronization augment~e. La r~duction de la r~activit~ sympathique de l'hypothalamus et la diminution de l'~tat d'excitabilit~ du cortex expliquent la diminution de la r~activit~ ~motionnelle qu'on trouve ~tre associ~e avec le rel~chement du tonus des muscles strips. ZUSAMMEN•ASSUNG Die W i r k u n g yon Curare-artigen Pharmaka wie Intocostrin und Anectine auf den Hypothalamus posterior und das E E G , in Dosen, die den B l u t d r u c k nicht herabsetzen, wurde untersucht. Es ergab sich, dass die sympathische Erregbarkeit des Hypothalamus

CURARE, H Y P O T H A L A M U S AND E E G

durch Curare vermindert wurde, da die Kontraktion der l~Iembrana nictitans und die Blutdrucksteigerung auf Reizung des Hypothalamus kleiner ausfiel als in entsprechenden Kontroll-Versuchen. Ausserdem trat eine Synchronie in dem Hypothalamogramm und im EEG auf. Die GrSsse der integrierten Potentiale (Analyse yon Hypothalamogramm und EEG) nahm fiir die kleinen Frequenzen zu und fiir die hSheren Frequenzen ab. Die verminderte Reaktionsweise des Hypothalamus und die damit verbundene reduzierte Erregbarkeit der Hirnrinde liegen der verringerten emotionalen Erregbarkeit des Menschen zu Grunde, die mit der Erschlaffung der quergestreiften Muskulatur einhergeht. REFERENCES BERNHAUT, M., GELLHORN, E. 3nd RASMUSSEN, A. T. Experimental contributions to the problem of consciousness. J. Neuropbysiol., 1 9 5 , 16: 21-35. BOVET, D. and LONOO, V. G. Action of natural and synthetic curares on the cortical activity of the rabbit. E E G Clin. Neurophysiol., 1953, ~: 225234. BUYTEI~DIJK, F. J. J. Ueber den Sehmerz. Psyche, 1953, 9: 436-452. GELLHORN, E. The hypothalamic-cortical system in b a r b i t u r a t e anesthesia. Arch. Internat. Pharmacodyn., 1953, 93: 434-442.

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GELLHORN, E. On the physiological action of COs on cortex and hypothalamus. E E G Clin. Neurophysiol., 1953, 5: 401-413. GELLHORN, E. Autonomic Imbalance and the Itypothalamus. University of Minnesota Press, Minneapolis, 1957. GELLHORN, E., ~ORTELL, 1~. and CARLSOn, H. B. Fundamental differences in the excitability of somatic and autonomic centers in response to anoxia. Amer. J. Physiol., 1942, 135: 641-649. GELLHORN, E., NAKAO, ]:~. and REDGATE, E. The influence of lesions in the anterior and posterior hypothalamus on tonic and phasic autonomic reactions. J. Physiol., 1956, 131: 402-423. HESS, W. R. Vegetative Funktionen und Zwischenhim. Basel, 1947. JACOBSON, E. Progressive Relaxation. Chicago, 1929. KOELLA, W. P. and GELLHORN, E. The influence of diencephalic lesions upon the action of nociceptive impulses and hypereapnia on the electrical activity of the c a t ' s brain. J. comp. Neurol., 1953, 100: 243-255. PURPURA, D. P. and GRUrrDFEST, H. Nature of dendritie potentials and synaptie mechanisms in cerebral cortex of cat. J. Neurophysiol., 1956, ~9: 573-595. SHAGASS, C. Effect of intravenous ehlorpromazine on the electroencephalogram. EEG Clin. Neurophysiol., 1955, 7: 306-308. SMIT~, S. M., BROWN, tI. O., TO~A~, J. E. P. and GOODMAN, L. S. The lack of cerebral effects of d-tubocurarine. Anaesthesiol., 1947, 8: 1-14. voN EULER, C. and S~JDEEBEEG, U. The influence of hypothalamie thermoeeptive structures on the electroencephalogram and gamma motor activity. E E G Clin. Neurophysiol., 1957, 9: 391-408.

~eference: GELLHOR~, E. The influence of curare on hypothalaml¢ excitability and the electroencephalogram. E E G Clin. Neurophysiol., 1958, I0: 697-703.