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Re-evaluation of estrogen-induced cortical and thalamic paroxysmal EEG activity in the cat
94
Electroencephalography and Clinical Neurophysiology, 1978, 4 4 : 9 4 - - 1 0 3 © Elsevier/North-Holland Scientific Publishers, Ltd.
RE-EVALUATION OF ESTROGEN-INDUCED CORTICAL AND THALAMIC PAROXYSMAL EEG ACTIVITY IN THE CAT STEPHAN C. LANGE * and ROBERT M. JULIEN **
Department of Medical Pharmacology and Therapeutics, University of California, Irvine, Calif. 9271 7 (U.S.A.) (Accepted for publication: June 9, 1977)
Since the report of Penfield and Jasper (1947) a number of laboratory studies have attempted to elucidate the site of origin of the spike--wave discharge of petit mal epilepsy. Most studies utilized EEG and behavioral observations using models of electrical stimulation (Hunter and Jasper 1949; Ingvar 1955; Guerrero-Figueroa et al. 1963; Marcus et al. 1966; Walker and Morello 1967; Wilder et al. 1968). In only one laboratory model (cortically-applied conjugated estrogens) has electrographic spike and wave discharge been correlated both with a behavioral absence (Marcus et al. 1968a) and with pharmacologic amelioration of epileptiform activity (Julien et al. 1975). The acceptance of estrogens as a laboratory model of petit mal epilepsy has been limited by the inability of others to reproduce petit real-like paroxysmal activity with conjugated estrogens either in the cat (Hardy 1970) or in the rat (McQueen and Woodbury 1975). Moreover, the role of thalamic structures in the development of estrogen-induced spike and wave discharges has not been evaluated despite the fact that 3 c/sec spike--wave activity is recordable in the thalamus during petit mal seizures (Williams 1953). Thus, although conjugated estrogens have been demonstrated to be epileptogenic, their validity as a model of petit mal epilepsy requires re-evaluation, * Present address: Department of Neurosurgery, University of Washington, Seattle, Wash., 98109 U.S.A. ** Present address: Good Samaritan Hospital, 1015
N.W. 22rid, Portland, Oreg. 97210, U.S.A.
This paper presents results of experiments conducted in cats to supply these data.
Methods
Acute experiments Experiments were performed in 50 adult cats (2.5--4.5 kg) of both sexes. Under halothane anesthesia, the trachea and the femoral artery and vein were cannulated. The animal was placed in a stereotaxic apparatus and the skull exposed. Sensory-motor cortex (anterior sigmoid gyrus) was exposed bilaterally. In 13 of the animals, bone overlying the n. ventralis anterior or n. centrum medianum of thalamus was also removed. Stainless-steel screws were implanted bilaterally over the anterior and posterior portions of suprasylvian gyri and a ground screw was located in frontal sinus. All wound margins were locally anesthetized with 20% benzocaine (Demetrescu and Julien 1974). General anesthesia was discontinued and the animal was paralyzed with D-tubocurarine (0.45 mg/kg/h) and ventilated to an end-tidal COs of 2.8--3.2%. Arterial blood pressure was continuously monitored and b o d y temperature was maintained at 37.5°C via a servo-controlled heating unit. Blood pressure, tracheal CO2, and ECoG were recorded on a polygraph. Agents evaluated included conjugated estrogens (Premarin), estrone-3-sulfate, piperazine estrone sulfate, diethylstilbesterol, testosterone
and
progesterone.
Concentra-
tions of each agent were prepared in a range
ESTROGENS AND EXPERIMENTAL EPILEPSY from 0.5 to 10% in distilled water or, if insoluble in water, in propylene glycol. Cortical application was accomplished either by topical application of pads of filter paper (0.6 cm X 0.8 cm, aqueous diluent) saturated with the steroid or by subpial injection (0.01 cc volume, aqueous or propylene glycol diluent), Thalamic injections of conjugated estrogens (1--2%, 10 gl, aqueous diluent) were made in n. ventralis anterior (A, 10; L, 5.6; H, +3) and n. centrum medianum (A, 6.8; L, 6.0; H, 1.0) through a stereotaxically m o u n t e d microsyringe. Subcortical electrical activity was recorded with stereotaxically located bipolar needle electrodes located in n. ventralis anterior, n. centrum medianum and n. medialis dorsalis (A, 9.5; L, 1.5; H, +3). Such activity was amplified (Grass P-15 preamplifiers) and displayed on a polygraph, In seven animals with ongoing paroxysmal activity from a unilateral cortical focus, electrolytic lesions were made in the ipsilateral n. ventralis anterior or n. centrum medianum. The effect of these lesions on estrogen-induced paroxysmal activity was subsequently recorded over a 2-h period. Thalamic sites for recording, drug injection and lesioning were determined by the coordinates of Snider and Niemer (1961) and confirmed histologically following termination of the experiments, sacrifice and formalin fixation of brain, Experiments on chronically isolated corticalslabs In seven animals, isolated slabs of suprasylvian gyrus were prepared according to the method of Sharpless and Halpern (1962). Under pentobarbital anesthesia and aseptic technique the skull was exposed and bone flaps overlying suprasylvian gyri were elevated bilaterally. Dura was reflected and areas of both gyri were surgically isolated. Following isolation, the dura was sutured and the bone flap was replaced. These animals were then maintained chronically for a period of 1--4 months following the initial surgery. On the day of acute experimentation, each animal was prepared under halothane anesthesia as
95 described above. The isolated cortical slabs were re-exposed, benzocaine powder applied to wound margins and the animal paralyzed, ventilated and monitored. Silver--silver chloride electrodes placed on the surface of the slabs were utilized to monitor the electrical activity of the isolated tissue. Screw electrodes located bilaterally over the anterior and posterior suprasylvian gyri recorded the electrical activity of adjacent intact cortex. After a period of control recording, pads of filterpaper(2mmX2mm)weresoakedinconcentrations of conjugated estrogens ranging from 0.5 to 2.0% and placed on the isolated tissue. Subsequent activity was recorded from both isolated and intact cortex. After sacrifice, brains were fixed in formalin and isolation of cortical slabs was microscopically confirmed.
Results Cortical application o f conjugated estrogens In control experiments, the application of water or propylene glycol by either sub-pial injection or placement of saturated filter paper to the anterior sigmoid gyrus had no effect on electroencephalographic activity over a 30 min period of observation. In 30 animals, either unilateral or bilateral application of 1--2% conjugated estrogens (CE) to the anterior sigmoid gyrus was followed within 30 min b y the development of 1--3 c/sec spike and wave discharge. Fig. 1 illustrates an experiment in which 2% CE was applied unilaterally to the left anterior sigmoid gyrus with recordings made from the left and right suprasylvian gyri and the right n. centrum medianum. In additional animals, similar thalamic recordings of cortical spike and wave discharge were made from the n. ventralis anterior and n. medialis dorsalis. As shown in Fig. 1, the spike and wave discharge from the unilateral focus is recordable in the contralateral homotopic cortex and in thalamic nuclei. With re-application of the agent at
96
S.C. LANGE, R.M. JULIEN.
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S t e r e o t a x i c injection o f CE (1--2%, 10 pl) into the thalamus o f 13 animals p r o d u c e d an e p i l e p t i f o r m p a t t e r n c h a r a c t e r i z e d b y 7--20 c/sec high-voltage poly-spike discharges comm e n c i n g within 15 min a f t e r injection. Fig. 2 illustrates the activity i n d u c e d by the injection o f CE into the n. ventralis anterior. As illustrated, high f r e q u e n c y poly-spike discharges d e v e l o p e d within 15 min and were r e c o r d e d b o t h in the contralateral thalamus and f r o m cerebral c o r t e x bilaterally. At n o time was low f r e q u e n c y , 1--4 c/sec activity or spike and wave discharges visualized a f t e r thalamic injection o f estrogen. S t e r e o t a x i c injection of 1 0 - - 2 0 pl distilled w a t e r into the thalamus in pre-CE c o n t r o l s had no observable e f f e c t on e l e c t r o e n c e p h a l o g r a p h i c activity.
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30 min intervals, spike and wave discharges could be m a i n t a i n e d f o r at least 3 h following initiation. In these e x p e r i m e n t s , although c o n c e n t r a tions o f 0.5--1,0% CE i n d u c e d high-voltage p a r o x y s m a l activity, c o n c e n t r a t i o n s of 2% m o s t c o n s i s t e n t l y i n d u c e d sustained episodes o f 1--3 c/sec spike and wave discharges. Such
T o d e t e r m i n e the e f f e c t o f a thalamic epileptogenic focus on ongoing cortical p a r o x y s mal discharge, CE (1--2%) was first topically applied t o the left a n t e r i o r sigmoid gyrus in seven animals and spike and wave activity was allowed t o develop. Following this, stereotaxic injections o f CE (1--2%, 10 gl) were m a d e in the n. ventralis a n t e r i o r or the n. cent r u m m e d i a n u m . As illustrated in Fig. 3, the resulting electrical activity consisted o f a cornbination o f cortical spike and wave discharges and bursts o f generalized 7 - - 2 0 c/sec poly-
discharges were e n h a n c e d in all animals b y maintaining end-tidal CO~ at 2 . 8 - 3 . 2 % . Levels o f CO2 greater t h a n 3.4% suppressed p a r o x y s m a l activity. T h e sex o f t h e animal had no e f f e c t on d e v e l o p m e n t o f CE-induced spike and wave discharge,
2 %CE in ventralis anterior 15 min post injection
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ESTROGENS AND EXPERIMENTAL EPILEPSY
97
CE. cortex and centrurn medianum
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Fig. 3. E]ectrographic activity resulting from app]ication of 2% CE to the left anterior sigmoid ~ r u s and injection into right centrum medianum (2%, 10 pl). Spike and wave discharge is apparent in combination with poly-spike bursts. Poly-spike activity such as indicated between the arrows was only visualized following the CE-thalamic injection.
spike discharges (Fig. 3, arrows). Sucti, Jn ablation of the cortical estrogen focus, although having no effect on the thalamic poly-spike epileptiform discharge, abolished the spike and wave paroxysms, Effect o f thalamic lesions on spike and wave discharges The influence of the thalamus on CE-induced spike and wave discharges was further investigated with electrolytic lesions of n. ventralis anterior in four animals and n. centrum medianum in three animals. Ventralis anterior lesions were stereotaxically located within an area of anterior 11.0--12.0 mm, lateral 3.0-6.0 mm and vertical 1.0--4.0 mm. Centrum medianum lesions were located within the area of anterior 6.5--7.2 mm, lateral 2.7--3.0 mm and vertical --1.0 to +1.0 mm. In each of the seven experiments, ipsilateral lesions in the thalamus were ineffective in decreasing either the amplitude or the frequency of epileptiform discharges induced from a unilateral cortical focus (Fig. 4). The epileptogenic agent used in this figure (1% piperazine-esterone-sulfate) is discussed below,
Acute experiments on chronically-isolated cortical tissue In the seven animals in which slabs of cerebral cortex had been chronically isolated for periods of 1---4 months, spike and wave discharges were initiated acutely by the topical application of CE (0.5--2%)to the re-exposed cortical slabs (Fig. 5). Such activity (occurring at a frequency of 1--3 c/sec) was initiated within 30 min of CE application and was maintained for 2 h with re-application of CE to the slabs at 30-min intervals. Neither the duration of cortical isolation (1--4 months) nor the sex of the particular animal appeared to affect the capacity of conjugated estrogens to induce the spike and wave paroxysms. Application of water-soaked filter paper had no effect on control slab activity. Capacity of various steroids to induce spike and wave discharge In 24 male and female cats, various steroids were topically applied to sensory-motor correx and electrographic effects recorded. In each of five animals, estrone-3-sulfate (1--2%, distilled water) induced generalized spike and
98
S.C. L A N G E , R.M. J U L I E N . Effects of Ipsilateral VA Lesion on Cortical
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Fig. 4. Epileptiform activity following application of 1% piperazine-estrone-sulfate to the right anterior sigmoid gyrus (upper traces). L o w e r set of traces are from the same animal 75 min after electrolytic lesion of the ipsilateral n. ventralis anterior. Thalamic lesions failed to decrease the f r e q u e n c y or amplitude o f cortical epileptif o r m activity over a 2-h period of observation. Note difference in time scale.
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ESTROGENS AND EXPERIMENTAL EPILEPSY
99
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wave activity occurring at a frequency of 2--3 c/sec within 15 min after cortical application (Fig. 6). Piperazine-estrone-sulfate (1--2%, distilled water) was also effective in inducing paroxysmal discharge in each of the six animals evaluated: low frequency (1.5--2.5 c/see) discharges occurred within 30 min after either unilateral (Fig. 7) or bilateral subpial injection.
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In six animals, diethylstilbesterol (1--5%, in distilled water) was ineffective in initiating epileptiform activity following bilateral topical application to sensory-motor cortex (Fig.
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Fig. 7. EEG activity before (control) and following application of 5% diethylstilbesterol (DES) and 1% piperazine-estrone-sulfate (ESP) to the left anterior sigmoid gyrus,
Fig, 8. Activity recorded from left and right suprasylvian gyri and right centrum medianum before (control) and after cortical application of 2% testoste_rone, 10% progesterone and 1% piperazine-esteronesulfate. See text for details.
100
7). Testosterone and progesterone (1--10%, propylene glycol) were similarly ineffective in inducing epileptiform activity after subpial injection in the nine animals evaluated (Fig. 8). Although, as illustrated in this figure, there was an increase in slow wave and spindle formation with the application of testosterone or progesterone in some of the animals, no poly-spike or spike and wave discharges developed over the 90-min period of observation. Subsequent administration of an epileptogenic estrogen (piperazine-esterone-sulfate, esterone-3-sulfate, or conjugated estrogens) indicated that the same cortex was capable of maintaining paroxysmal activity,
Discussion That estrogens possess a proconvulsant effect was indicated experimentally by electro-shock studies in rodents (Timiras 1968; Wooley and Timiras 1962). Marcus and Watson (1964) further demonstrated in cat the epileptogenic specificity of estrogens among all steroids they tested. Hardy (1970), in contrast, was unable to produce similar results in cats maintained under barbiturate anesthesia; non-anesthetized controls were not reported, Similarly, McQueen and Woodbury (1975) were unable to initiate spike and wave at a frequency greater than 1 c/sec in rat, although among all agents that these workers evaluated, only conjugated estrogens induced a spike and wave discharge, True or 'classical' spike--wave activity is to be differentiated from similar spike and wave patterns both clinically (Gastaut 1968; Blume et al. 1973) and experimentally (Ajmone Marson 1969). The paroxysmal discharges which follow the topical application of estrogen to cerebral cortex is not spike--wave; this is a term applied only to clinical petit mal. The 2--3 c/sec spike and wave bursts of these experiments do, however, compare well with the recordings from Weir's study (1965) of the electroencephalogram in clinical petit real. Review of the estrogen-induced spike and
S.C. LANGE, R.M. JULIEN.
wave recordings show the defined spike 1, a positive transient phase, spike 2 and the surface negative wave of Weir's criteria. Thus, specific estrogenic substances appear to induce from the cortex a spike and wave cornplex in the cat that appears electrographically similar to the EEG of petit mal or petit mal variant. A capacity of cerebral cortex to generate spike and wave discharge in the absence of subcortical influences is indicated by our findings of: (1) the differential effects of estrogen when applied to cortex and thalamus, (2) the failure of thalamic lesions to affect epileptiform activity from an ipsilateral cortical focus and (3) the production of spike and wave activity following estrogen application to chronically-isolated cortical tissue. In the present experiments, spike and wave activity occurred only with application of estrogens to cerebral cortex. Injection of estrogens into thalamic nuclei (Figs. 2 and 3) failed to initiate spike and wave discharges, inducing instead a high-voltage poly-spike pattern. These findings corroborate the experimental results of Marcus and Watson (1964) and Walker and Morello (1967) and the clinical findings of Goldring (1972) of a prime role of cerebral cortex in the spike--wave EEG of petit mal epilepsy. In addition to the bilateral loci employed by Marcus et al. (1966) and Julien et al. (1975) the present experiments have demonstrated that spike and wave discharges can also be initiated with unilateral cortical application of estrogens. The pathways through which this activity is projected from a unilateral cortical focus is unknown; however, thalamic lesions failed to significantly affect the cortical response (Fig. 4). This finding correlares with the poor clinical efficacy of thaiamic lesions in the treatment of epilepsy (Ojemann and Ward 1975). The importance of cerebral cortex in the development of estrogen-induced spike and wave discharge is further indicated by our findings utilizing the chronically-isolated slabs of suprasylvian cortex (Fig. 5). The spike and
E S T R O G E N S AND E X P E R I M E N T A L E P I L E P S Y
wave discharges resulting from the acute application of CE to this tissue are similar to those obtained from intact cortex: i.e., welldefined paroxysms of spike and wave discharges are noted despite the fact that this tissue is isolated from all subcortical influences (Sharpless and Halpern 1962). In view of the presence of cortical estrogen receptor sites in human fetus (Davies et al. 1975) some interactions between testosterone or progesterone and estrogen might be expected. With reports of both a conversion of testosterone to estrogen in brain (Naftolin et al. 1975) and of an anti-epileptic capacity of testosterone and progesterone (Timiras 1968), one would predict either augmentation or antagonism of estrogen-induced activity. In the present study, topical application of testosterone or progesterone neither induced epileptiform activity nor protected against estrogen's paroxysmal activity. Explanation for this lack of interaction may lie (1) in the different solubilities of testosterone, progesterone and estrogen, (2) in the free rather than conjugated forms of the non-estrogenic substances, or (3) in a high specificity of receptors in cerebral cortex for estrogen alone (Davies et al. 1975). All agents, however, were applied to a discrete cortical area during acute experiments; a condition which does not evaluate on a chronic basis the interaction betweet) progesterone, testosterone and estrogen, Clinically, there is no simple correlation between steroids and brain excitability and seizure development (Almquist 1955; Laidlow 1956: Logothetis et al. 1959). In the laboratory, this correlation is more apparent. Watersoluble, steroidal, estrogenic substances (i.e., conjugated estrogens, piperazine-estrone-sulfate, and estrone-3-sulfate) acutely applied to cerebral cortex (intact or chronically isolated) produce electrographic spike and wave patterns that are clearly epileptogenic. A nonsteroidal estrogen (diethylstilbesterol), testosterone and progesterone are non-epileptogenic (Figs. 7 and 8). In addition, although paroxysmal EEG patterns can be initiated by estro-
101
gens applied to both cortex and thalamic structures, the epileptiform pattern resulting from cortically-applied estrogens more closely corresponds to the EEG of clinical petit mal or petit mal variant. The relationship between estrogen levels in the brain, a possible cortical supersensitivity to estrogen, and the incidence of petit mal or petit mal variant remains to be shown. Summary Conjugated estrogens (Premarin), piperazine-esterone-sulfate (Ogen) and esterone-3sulfate were applied bilaterally or unilaterally to sensory-motor cortex in locally anesthetized, paralyzed cats. All these agents (1--2% concentration) initiated paroxysmal activity characterized by 2--3 c/sec spike and wave discharge that was generalized bilaterally over cortex and in the nuclei ventralis anterior, medialis dorsalis and centrum medianum of thalamus. In contrast, unilateral micro-injection (2%, 0.01 cc) of conjugated estrogens into thalamic nuclei resulted in 7--20 c/sec poly-spike activity recorded bilaterally over cortex and in the contralateral thalamus. Spike and wave discharges were not observed following thalamic injection of estrogens. Ipsilateral electrolytic lesions of either ventralis anterior or centrum medianum failed to decrease spike and wave discharge originating from a cortical focus. In chronically-isolated slabs of suprasylvian cortex, topically applied conjugated estrogens induced 1 - 3 c/sec spike and wave activity restricted to the isolated tissue in the absence of spread of activity to surrounding intact cortex. In contrast to the estrogenic steroids, progesterone, testosterone and diethylstilbesterol failed to initiate paroxysmal activity after bilateral topical application in concentrations of 10% although the application of either testosterone or progesterone was associated with spindle formation in some animals. These findings demonstrate a capacity of cerebral cortex to generate spike and wave
[02
S.C. LANGE, R.M. JULIEN.
discharge in the absence of subcortical influences, a generalization of spike and wave discharge from a unilateral cortical focus and an epileptogenic specificity o f estrogens. The experimental spike and wave complex produced by topically-applied estrogens is discussed in reference to the epileptiform EEG of clinical petit mal or petit mal variant.
R~sum~
Reevaluation de l'activitd EEG paroxystique corticale et thalamique induite par estrogenes chez l e c h a t L'application unis ou bilat~rale d'estrog~nes conjugu~s (Pr~marin) de sulfate de pip~razine-est~rone (Ogen) et de sulfate 3 est~rone a ~t~ r~alis~e sur le cortex sensorim o t e u r de chats sous anesth~sie locale et paralys~s. Tous ces agents (concentration de 1 ~ 2%) p r o v o q u e n t une activit~ paroxystique caract~ris~e par des d~charges de complexes pointe--ondes de 2 ~ 3 c/sec qui se g~n~ralisent de fa~on bilat~rale sur t o u t le cortex et dans les n o y a u x ventral int~rieur, dorsal m~dian et centra m~dian du thalamus, Au contraire, la micro-injection unilat~rale (2%; 0.01 cc) d'estrog~nes conjugu~s dans les n o y a u x thalamiques r~sulte en une activit~ de poly-pointes de 7 ~ 20 c/sec enregistr~e de faqon bilat~rale sur le cortex et darts le thalamus controlatdral. Des d~charges de cornplexes p o in te- - o n d es ne sont pas observ~es ~i la suite d'injection thalamique d'estrog~nes. Les l~sions ~lectrolytiques ipsilat~rales soit du n o y au ventral ant~rieur soit du n o y a u central m~dian ne produisent pas de diminution des d~charges de p o in t e - - onde s originaires d'un f o y e r cortical. Dans isol~es topique activit~ it~e au
des tranches de cor t e x suprasylvien de fa~on chronique, l'application d'estrog~nes conjugu~s pr ovoque une de p o in te- - onde s de 1 ~ 3 c/sec limtissu isol~ sans diffusion au cortex
intact p~riph~rique, Contrairement aux st~roides estrog~nes, la
progesterone, la testosterone et le diethylstibest~rol ne p r o v o q u e n t pas d'activit~ paroxyst i que par application topique bilat~rale pour des concentrations de 10% bien que l'application soit de testosterone soit de progest~rone s'associe ~ la f o r m a t i o n de fuseaux chez certains animaux. Ces donn~es m o n t r e n t la capacit~ du cortex c~r~bral ~ fabriquer des d~charges de p o n t e - ondes en l'absence d'influence sous-corticale, une g~n~ralisation des d~charges de poi nt e-ondes ~ partir d'un foyer cortical unilateral et une sp~cificit~ des estrog~nes en temps que facteur ~pileptog~ne. Le t ype de complexes pointe--ondes experimental provoqu~ par estrog~nes en application topique est discut~ par r~f~rence aux modifications EEG du PetitMal ou du Petit-Mal variant clinique.
The authors gratefully acknowledge the technical assistanceof Mr. Jay Manago. References Ajmone Marsan, C. Pathophysiology of EEG patterns characteristic of petit mal epilepsy: A critical review of some experiments. In H. Gastaut (Ed), The Pathogenesis of the Epilepsies. C.C. Thomas, Springfield, Ill., 1969. Almquist, R. The rhythm of epileptic attacks and its relationship to menstrual cycle. Acta psychiat. scand., 1955, 105: 1--116. B l u m e ,W.T., David, R.B. and Gomez, M.R. Generalized sharp and slow wave complexes: associated clinical features and long-term followup. Brain, 1973, 96: 289-306. Davies, J., Naftolin, F., Ryan, K.J. and Siu, J. A specific, high-affinity, limited-capacity estrogen binding component in the cytosol of human fetal pituitary and brain tissue. J. clin. Endocr., 1975, 40: 909-912. Demetrescu, M.C. and Julien, R.M. Local anesthetics and experimental epilepsy. Epilepsia (Amst.), 1974, 15: 234-248. Gastaut, H. Clinical and electroencephalographic correlates of generalized spike and wave bursts occurring spontaneously in man. Epilepsia (Amst.), 1968, 9: 179-184. Goldring, D. The role of prefrontal cortex in grand real convulsions. Arch. Neurol. (Chic,), 1972, 26: 109-119.
ESTROGENS AND EXPERIMENTAL EPILEPSY Geurrero-Figueroa, R., Barros, A., deBalbain Verster, F. and Heath, R.G. Experimental 'petit real' in kittens. Arch. Neurol. (Chic.), 1963, 9: 297--306. Hardy, R.W. Unit activity in Premarin-induced cortical epileptogenic foci. Epilepsia (Amst.), 1970, 11: 179--186. Hunter, J. and Ingvar, D.H. Pathways mediating metrazol induced irradiation of visual impulses. Electroenceph. clin. Neurophysiol., 1955, 17: 39-60. Hunter, J. and Jasper, H.H. Effects of thalamic stimulation in unanesthetized animals, Electroenceph. clin. Neurophysiol., 1955, 1: 305--324. Ingvar, D.H. Reproduction of the 3 cycle per second spike--wave pattern by subcortical electrical stimulation in cats. Acta physiol, scand., 1955, 33: 137--150. Julien, R.M., Fowler, G.W. and Danielson, M.G. The effects of antiepileptic drugs on estrogen-induced electrographic spike--wave discharge. J. Pharmacol. exp. Ther., 1975, 193: 647--656. Laidlow, J. Catamenial epilepsy. Lancet, 1956, 271: 1235. Logothetis, J. and Harner, R. Electrocortical activation by estrogens. Arch. Neurol. (Chic.), 1960, 3: 290--297. Marcus, E.M. and Watson, C.W. Reproduction in isolated cortex of cat brain of bilateral synchronous and symmetrical spike and slow wave pattern resembling petit mal. Trans. Amer. Neurolog. Ass., 1964, 89: 221--222. Marcus, E.M., Watson, C.W. and Goldman, P.L. Effects of steroids on cerebral electrical activity, Arch. Neurol. (Chic.), 1966, 15: 521--532. Marcus, E.M., Watson, C.W. and Simon, S.A. An experimental model of some varieties of petit real epilepsy: Electrical-behavioral correlations of acute bilateral epileptogenic foci in cerebral cortex. Epilepsia (Amst.), 1968, 9: 233--248. McQueen, J.K. and Woodbury, D.M. Attempts to produce spike and wave complexes in the electroencephalogram of the rat. Epilepsia (Amst.) 1975, 16: 295--299.
103 Naftolin, F., Ryan, K.J., Davies, I.J., Petro, Z. and Kuhn, M. The formation and metabolism of estrogen in brain tissue. Adv. Biosci., 1975, 15: 105. Ojemann, G.A. and Ward, A.A. Stereotaxic and other procedures for epilepsy. In D.P. Purpura, J.K. Penry and R.D. Walter (Eds.), Advances in Neurology, Vol. 8, Raven Press, New York, 1975. Penfield, W. and Jasper, H. Highest level seizures. Res. Publ. Ass. nerv. ment. Dis., 1947, 26: 252--271. Pollen, D.A., Perot, P. and Reid, K.H. Experimental bilateral wave and spike from thalamic stimulation in relation to level of arousal. Electroenceph. clin. Neurophysiol., 1963, 15: 1017--1028. Sharpless, S.K. and Halpern, L.M. The electrical excitability of chronically isolated cortex studied by means of permanently implanted electrodes. Electroenceph. clin. Neurophysiol., 1962, 14: 244--255. Snider, R.S. and Neimer, W.T. A stereotaxic atlas of the cat brain. University of Chicago Press, Chicago, 1961. Steriade, M. and Yossif, G. Spike and wave afterdischarges in cortical somatosensory neurons of cat. Electroenceph. clin. Neurophysiol., 1974, 37: 633--648. Timiras, P.S. The role of hormones in the development of seizures. In H. Jasper, A. Ward and A. Pope (Eds.), Basic Mechanisms of the Epilepsies, Little, Brown and Co., Boston, 1968. Walker, A.E. and Morello, G. Experimental petit mal. Trans. Amer. Neurol. Ass., 1967, 92: 57--61. Weir, B. The morphology of the spike--wave cornplex. Electroenceph. clin. Neurophysiol., 1965, 19: 284--289. Wilder, B.J., King, R.L. and Schmidt, R.P. Comparative study of secondary epileptogenesis. Epilepsia (Amst.), 1968, 9: 275--289. Williams, D. A study of thalamic and cortical rhythms in petit mal. Brain, 1953, 76: 50--69. Wooley, D.E. and Timiras, P.S. The gonad--brain relationship: Effects of female sex hormones on electroshock convulsions in the rat. Endocrinology, 1962, 70: 196--209.
Electroencephalography and Clinical Neurophysiology, 1978, 4 4 : 9 4 - - 1 0 3 © Elsevier/North-Holland Scientific Publishers, Ltd.
RE-EVALUATION OF ESTROGEN-INDUCED CORTICAL AND THALAMIC PAROXYSMAL EEG ACTIVITY IN THE CAT STEPHAN C. LANGE * and ROBERT M. JULIEN **
Department of Medical Pharmacology and Therapeutics, University of California, Irvine, Calif. 9271 7 (U.S.A.) (Accepted for publication: June 9, 1977)
Since the report of Penfield and Jasper (1947) a number of laboratory studies have attempted to elucidate the site of origin of the spike--wave discharge of petit mal epilepsy. Most studies utilized EEG and behavioral observations using models of electrical stimulation (Hunter and Jasper 1949; Ingvar 1955; Guerrero-Figueroa et al. 1963; Marcus et al. 1966; Walker and Morello 1967; Wilder et al. 1968). In only one laboratory model (cortically-applied conjugated estrogens) has electrographic spike and wave discharge been correlated both with a behavioral absence (Marcus et al. 1968a) and with pharmacologic amelioration of epileptiform activity (Julien et al. 1975). The acceptance of estrogens as a laboratory model of petit mal epilepsy has been limited by the inability of others to reproduce petit real-like paroxysmal activity with conjugated estrogens either in the cat (Hardy 1970) or in the rat (McQueen and Woodbury 1975). Moreover, the role of thalamic structures in the development of estrogen-induced spike and wave discharges has not been evaluated despite the fact that 3 c/sec spike--wave activity is recordable in the thalamus during petit mal seizures (Williams 1953). Thus, although conjugated estrogens have been demonstrated to be epileptogenic, their validity as a model of petit mal epilepsy requires re-evaluation, * Present address: Department of Neurosurgery, University of Washington, Seattle, Wash., 98109 U.S.A. ** Present address: Good Samaritan Hospital, 1015
N.W. 22rid, Portland, Oreg. 97210, U.S.A.
This paper presents results of experiments conducted in cats to supply these data.
Methods
Acute experiments Experiments were performed in 50 adult cats (2.5--4.5 kg) of both sexes. Under halothane anesthesia, the trachea and the femoral artery and vein were cannulated. The animal was placed in a stereotaxic apparatus and the skull exposed. Sensory-motor cortex (anterior sigmoid gyrus) was exposed bilaterally. In 13 of the animals, bone overlying the n. ventralis anterior or n. centrum medianum of thalamus was also removed. Stainless-steel screws were implanted bilaterally over the anterior and posterior portions of suprasylvian gyri and a ground screw was located in frontal sinus. All wound margins were locally anesthetized with 20% benzocaine (Demetrescu and Julien 1974). General anesthesia was discontinued and the animal was paralyzed with D-tubocurarine (0.45 mg/kg/h) and ventilated to an end-tidal COs of 2.8--3.2%. Arterial blood pressure was continuously monitored and b o d y temperature was maintained at 37.5°C via a servo-controlled heating unit. Blood pressure, tracheal CO2, and ECoG were recorded on a polygraph. Agents evaluated included conjugated estrogens (Premarin), estrone-3-sulfate, piperazine estrone sulfate, diethylstilbesterol, testosterone
and
progesterone.
Concentra-
tions of each agent were prepared in a range
ESTROGENS AND EXPERIMENTAL EPILEPSY from 0.5 to 10% in distilled water or, if insoluble in water, in propylene glycol. Cortical application was accomplished either by topical application of pads of filter paper (0.6 cm X 0.8 cm, aqueous diluent) saturated with the steroid or by subpial injection (0.01 cc volume, aqueous or propylene glycol diluent), Thalamic injections of conjugated estrogens (1--2%, 10 gl, aqueous diluent) were made in n. ventralis anterior (A, 10; L, 5.6; H, +3) and n. centrum medianum (A, 6.8; L, 6.0; H, 1.0) through a stereotaxically m o u n t e d microsyringe. Subcortical electrical activity was recorded with stereotaxically located bipolar needle electrodes located in n. ventralis anterior, n. centrum medianum and n. medialis dorsalis (A, 9.5; L, 1.5; H, +3). Such activity was amplified (Grass P-15 preamplifiers) and displayed on a polygraph, In seven animals with ongoing paroxysmal activity from a unilateral cortical focus, electrolytic lesions were made in the ipsilateral n. ventralis anterior or n. centrum medianum. The effect of these lesions on estrogen-induced paroxysmal activity was subsequently recorded over a 2-h period. Thalamic sites for recording, drug injection and lesioning were determined by the coordinates of Snider and Niemer (1961) and confirmed histologically following termination of the experiments, sacrifice and formalin fixation of brain, Experiments on chronically isolated corticalslabs In seven animals, isolated slabs of suprasylvian gyrus were prepared according to the method of Sharpless and Halpern (1962). Under pentobarbital anesthesia and aseptic technique the skull was exposed and bone flaps overlying suprasylvian gyri were elevated bilaterally. Dura was reflected and areas of both gyri were surgically isolated. Following isolation, the dura was sutured and the bone flap was replaced. These animals were then maintained chronically for a period of 1--4 months following the initial surgery. On the day of acute experimentation, each animal was prepared under halothane anesthesia as
95 described above. The isolated cortical slabs were re-exposed, benzocaine powder applied to wound margins and the animal paralyzed, ventilated and monitored. Silver--silver chloride electrodes placed on the surface of the slabs were utilized to monitor the electrical activity of the isolated tissue. Screw electrodes located bilaterally over the anterior and posterior suprasylvian gyri recorded the electrical activity of adjacent intact cortex. After a period of control recording, pads of filterpaper(2mmX2mm)weresoakedinconcentrations of conjugated estrogens ranging from 0.5 to 2.0% and placed on the isolated tissue. Subsequent activity was recorded from both isolated and intact cortex. After sacrifice, brains were fixed in formalin and isolation of cortical slabs was microscopically confirmed.
Results Cortical application o f conjugated estrogens In control experiments, the application of water or propylene glycol by either sub-pial injection or placement of saturated filter paper to the anterior sigmoid gyrus had no effect on electroencephalographic activity over a 30 min period of observation. In 30 animals, either unilateral or bilateral application of 1--2% conjugated estrogens (CE) to the anterior sigmoid gyrus was followed within 30 min b y the development of 1--3 c/sec spike and wave discharge. Fig. 1 illustrates an experiment in which 2% CE was applied unilaterally to the left anterior sigmoid gyrus with recordings made from the left and right suprasylvian gyri and the right n. centrum medianum. In additional animals, similar thalamic recordings of cortical spike and wave discharge were made from the n. ventralis anterior and n. medialis dorsalis. As shown in Fig. 1, the spike and wave discharge from the unilateral focus is recordable in the contralateral homotopic cortex and in thalamic nuclei. With re-application of the agent at
96
S.C. LANGE, R.M. JULIEN.
Thalamic injection of conjugated estrogens
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S t e r e o t a x i c injection o f CE (1--2%, 10 pl) into the thalamus o f 13 animals p r o d u c e d an e p i l e p t i f o r m p a t t e r n c h a r a c t e r i z e d b y 7--20 c/sec high-voltage poly-spike discharges comm e n c i n g within 15 min a f t e r injection. Fig. 2 illustrates the activity i n d u c e d by the injection o f CE into the n. ventralis anterior. As illustrated, high f r e q u e n c y poly-spike discharges d e v e l o p e d within 15 min and were r e c o r d e d b o t h in the contralateral thalamus and f r o m cerebral c o r t e x bilaterally. At n o time was low f r e q u e n c y , 1--4 c/sec activity or spike and wave discharges visualized a f t e r thalamic injection o f estrogen. S t e r e o t a x i c injection of 1 0 - - 2 0 pl distilled w a t e r into the thalamus in pre-CE c o n t r o l s had no observable e f f e c t on e l e c t r o e n c e p h a l o g r a p h i c activity.
' ' ' ~' ",~'~-~C~?:"".,'~'(]
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30 min intervals, spike and wave discharges could be m a i n t a i n e d f o r at least 3 h following initiation. In these e x p e r i m e n t s , although c o n c e n t r a tions o f 0.5--1,0% CE i n d u c e d high-voltage p a r o x y s m a l activity, c o n c e n t r a t i o n s of 2% m o s t c o n s i s t e n t l y i n d u c e d sustained episodes o f 1--3 c/sec spike and wave discharges. Such
T o d e t e r m i n e the e f f e c t o f a thalamic epileptogenic focus on ongoing cortical p a r o x y s mal discharge, CE (1--2%) was first topically applied t o the left a n t e r i o r sigmoid gyrus in seven animals and spike and wave activity was allowed t o develop. Following this, stereotaxic injections o f CE (1--2%, 10 gl) were m a d e in the n. ventralis a n t e r i o r or the n. cent r u m m e d i a n u m . As illustrated in Fig. 3, the resulting electrical activity consisted o f a cornbination o f cortical spike and wave discharges and bursts o f generalized 7 - - 2 0 c/sec poly-
discharges were e n h a n c e d in all animals b y maintaining end-tidal CO~ at 2 . 8 - 3 . 2 % . Levels o f CO2 greater t h a n 3.4% suppressed p a r o x y s m a l activity. T h e sex o f t h e animal had no e f f e c t on d e v e l o p m e n t o f CE-induced spike and wave discharge,
2 %CE in ventralis anterior 15 min post injection
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ESTROGENS AND EXPERIMENTAL EPILEPSY
97
CE. cortex and centrurn medianum
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spike discharges (Fig. 3, arrows). Sucti, Jn ablation of the cortical estrogen focus, although having no effect on the thalamic poly-spike epileptiform discharge, abolished the spike and wave paroxysms, Effect o f thalamic lesions on spike and wave discharges The influence of the thalamus on CE-induced spike and wave discharges was further investigated with electrolytic lesions of n. ventralis anterior in four animals and n. centrum medianum in three animals. Ventralis anterior lesions were stereotaxically located within an area of anterior 11.0--12.0 mm, lateral 3.0-6.0 mm and vertical 1.0--4.0 mm. Centrum medianum lesions were located within the area of anterior 6.5--7.2 mm, lateral 2.7--3.0 mm and vertical --1.0 to +1.0 mm. In each of the seven experiments, ipsilateral lesions in the thalamus were ineffective in decreasing either the amplitude or the frequency of epileptiform discharges induced from a unilateral cortical focus (Fig. 4). The epileptogenic agent used in this figure (1% piperazine-esterone-sulfate) is discussed below,
Acute experiments on chronically-isolated cortical tissue In the seven animals in which slabs of cerebral cortex had been chronically isolated for periods of 1---4 months, spike and wave discharges were initiated acutely by the topical application of CE (0.5--2%)to the re-exposed cortical slabs (Fig. 5). Such activity (occurring at a frequency of 1--3 c/sec) was initiated within 30 min of CE application and was maintained for 2 h with re-application of CE to the slabs at 30-min intervals. Neither the duration of cortical isolation (1--4 months) nor the sex of the particular animal appeared to affect the capacity of conjugated estrogens to induce the spike and wave paroxysms. Application of water-soaked filter paper had no effect on control slab activity. Capacity of various steroids to induce spike and wave discharge In 24 male and female cats, various steroids were topically applied to sensory-motor correx and electrographic effects recorded. In each of five animals, estrone-3-sulfate (1--2%, distilled water) induced generalized spike and
98
S.C. L A N G E , R.M. J U L I E N . Effects of Ipsilateral VA Lesion on Cortical
Focus
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Fig. 4. Epileptiform activity following application of 1% piperazine-estrone-sulfate to the right anterior sigmoid gyrus (upper traces). L o w e r set of traces are from the same animal 75 min after electrolytic lesion of the ipsilateral n. ventralis anterior. Thalamic lesions failed to decrease the f r e q u e n c y or amplitude o f cortical epileptif o r m activity over a 2-h period of observation. Note difference in time scale.
Control ,2.my intact
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ESTROGENS AND EXPERIMENTAL EPILEPSY
99
Control
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wave activity occurring at a frequency of 2--3 c/sec within 15 min after cortical application (Fig. 6). Piperazine-estrone-sulfate (1--2%, distilled water) was also effective in inducing paroxysmal discharge in each of the six animals evaluated: low frequency (1.5--2.5 c/see) discharges occurred within 30 min after either unilateral (Fig. 7) or bilateral subpial injection.
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In six animals, diethylstilbesterol (1--5%, in distilled water) was ineffective in initiating epileptiform activity following bilateral topical application to sensory-motor cortex (Fig.
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Fig. 7. EEG activity before (control) and following application of 5% diethylstilbesterol (DES) and 1% piperazine-estrone-sulfate (ESP) to the left anterior sigmoid gyrus,
Fig, 8. Activity recorded from left and right suprasylvian gyri and right centrum medianum before (control) and after cortical application of 2% testoste_rone, 10% progesterone and 1% piperazine-esteronesulfate. See text for details.
100
7). Testosterone and progesterone (1--10%, propylene glycol) were similarly ineffective in inducing epileptiform activity after subpial injection in the nine animals evaluated (Fig. 8). Although, as illustrated in this figure, there was an increase in slow wave and spindle formation with the application of testosterone or progesterone in some of the animals, no poly-spike or spike and wave discharges developed over the 90-min period of observation. Subsequent administration of an epileptogenic estrogen (piperazine-esterone-sulfate, esterone-3-sulfate, or conjugated estrogens) indicated that the same cortex was capable of maintaining paroxysmal activity,
Discussion That estrogens possess a proconvulsant effect was indicated experimentally by electro-shock studies in rodents (Timiras 1968; Wooley and Timiras 1962). Marcus and Watson (1964) further demonstrated in cat the epileptogenic specificity of estrogens among all steroids they tested. Hardy (1970), in contrast, was unable to produce similar results in cats maintained under barbiturate anesthesia; non-anesthetized controls were not reported, Similarly, McQueen and Woodbury (1975) were unable to initiate spike and wave at a frequency greater than 1 c/sec in rat, although among all agents that these workers evaluated, only conjugated estrogens induced a spike and wave discharge, True or 'classical' spike--wave activity is to be differentiated from similar spike and wave patterns both clinically (Gastaut 1968; Blume et al. 1973) and experimentally (Ajmone Marson 1969). The paroxysmal discharges which follow the topical application of estrogen to cerebral cortex is not spike--wave; this is a term applied only to clinical petit mal. The 2--3 c/sec spike and wave bursts of these experiments do, however, compare well with the recordings from Weir's study (1965) of the electroencephalogram in clinical petit real. Review of the estrogen-induced spike and
S.C. LANGE, R.M. JULIEN.
wave recordings show the defined spike 1, a positive transient phase, spike 2 and the surface negative wave of Weir's criteria. Thus, specific estrogenic substances appear to induce from the cortex a spike and wave cornplex in the cat that appears electrographically similar to the EEG of petit mal or petit mal variant. A capacity of cerebral cortex to generate spike and wave discharge in the absence of subcortical influences is indicated by our findings of: (1) the differential effects of estrogen when applied to cortex and thalamus, (2) the failure of thalamic lesions to affect epileptiform activity from an ipsilateral cortical focus and (3) the production of spike and wave activity following estrogen application to chronically-isolated cortical tissue. In the present experiments, spike and wave activity occurred only with application of estrogens to cerebral cortex. Injection of estrogens into thalamic nuclei (Figs. 2 and 3) failed to initiate spike and wave discharges, inducing instead a high-voltage poly-spike pattern. These findings corroborate the experimental results of Marcus and Watson (1964) and Walker and Morello (1967) and the clinical findings of Goldring (1972) of a prime role of cerebral cortex in the spike--wave EEG of petit mal epilepsy. In addition to the bilateral loci employed by Marcus et al. (1966) and Julien et al. (1975) the present experiments have demonstrated that spike and wave discharges can also be initiated with unilateral cortical application of estrogens. The pathways through which this activity is projected from a unilateral cortical focus is unknown; however, thalamic lesions failed to significantly affect the cortical response (Fig. 4). This finding correlares with the poor clinical efficacy of thaiamic lesions in the treatment of epilepsy (Ojemann and Ward 1975). The importance of cerebral cortex in the development of estrogen-induced spike and wave discharge is further indicated by our findings utilizing the chronically-isolated slabs of suprasylvian cortex (Fig. 5). The spike and
E S T R O G E N S AND E X P E R I M E N T A L E P I L E P S Y
wave discharges resulting from the acute application of CE to this tissue are similar to those obtained from intact cortex: i.e., welldefined paroxysms of spike and wave discharges are noted despite the fact that this tissue is isolated from all subcortical influences (Sharpless and Halpern 1962). In view of the presence of cortical estrogen receptor sites in human fetus (Davies et al. 1975) some interactions between testosterone or progesterone and estrogen might be expected. With reports of both a conversion of testosterone to estrogen in brain (Naftolin et al. 1975) and of an anti-epileptic capacity of testosterone and progesterone (Timiras 1968), one would predict either augmentation or antagonism of estrogen-induced activity. In the present study, topical application of testosterone or progesterone neither induced epileptiform activity nor protected against estrogen's paroxysmal activity. Explanation for this lack of interaction may lie (1) in the different solubilities of testosterone, progesterone and estrogen, (2) in the free rather than conjugated forms of the non-estrogenic substances, or (3) in a high specificity of receptors in cerebral cortex for estrogen alone (Davies et al. 1975). All agents, however, were applied to a discrete cortical area during acute experiments; a condition which does not evaluate on a chronic basis the interaction betweet) progesterone, testosterone and estrogen, Clinically, there is no simple correlation between steroids and brain excitability and seizure development (Almquist 1955; Laidlow 1956: Logothetis et al. 1959). In the laboratory, this correlation is more apparent. Watersoluble, steroidal, estrogenic substances (i.e., conjugated estrogens, piperazine-estrone-sulfate, and estrone-3-sulfate) acutely applied to cerebral cortex (intact or chronically isolated) produce electrographic spike and wave patterns that are clearly epileptogenic. A nonsteroidal estrogen (diethylstilbesterol), testosterone and progesterone are non-epileptogenic (Figs. 7 and 8). In addition, although paroxysmal EEG patterns can be initiated by estro-
101
gens applied to both cortex and thalamic structures, the epileptiform pattern resulting from cortically-applied estrogens more closely corresponds to the EEG of clinical petit mal or petit mal variant. The relationship between estrogen levels in the brain, a possible cortical supersensitivity to estrogen, and the incidence of petit mal or petit mal variant remains to be shown. Summary Conjugated estrogens (Premarin), piperazine-esterone-sulfate (Ogen) and esterone-3sulfate were applied bilaterally or unilaterally to sensory-motor cortex in locally anesthetized, paralyzed cats. All these agents (1--2% concentration) initiated paroxysmal activity characterized by 2--3 c/sec spike and wave discharge that was generalized bilaterally over cortex and in the nuclei ventralis anterior, medialis dorsalis and centrum medianum of thalamus. In contrast, unilateral micro-injection (2%, 0.01 cc) of conjugated estrogens into thalamic nuclei resulted in 7--20 c/sec poly-spike activity recorded bilaterally over cortex and in the contralateral thalamus. Spike and wave discharges were not observed following thalamic injection of estrogens. Ipsilateral electrolytic lesions of either ventralis anterior or centrum medianum failed to decrease spike and wave discharge originating from a cortical focus. In chronically-isolated slabs of suprasylvian cortex, topically applied conjugated estrogens induced 1 - 3 c/sec spike and wave activity restricted to the isolated tissue in the absence of spread of activity to surrounding intact cortex. In contrast to the estrogenic steroids, progesterone, testosterone and diethylstilbesterol failed to initiate paroxysmal activity after bilateral topical application in concentrations of 10% although the application of either testosterone or progesterone was associated with spindle formation in some animals. These findings demonstrate a capacity of cerebral cortex to generate spike and wave
[02
S.C. LANGE, R.M. JULIEN.
discharge in the absence of subcortical influences, a generalization of spike and wave discharge from a unilateral cortical focus and an epileptogenic specificity o f estrogens. The experimental spike and wave complex produced by topically-applied estrogens is discussed in reference to the epileptiform EEG of clinical petit mal or petit mal variant.
R~sum~
Reevaluation de l'activitd EEG paroxystique corticale et thalamique induite par estrogenes chez l e c h a t L'application unis ou bilat~rale d'estrog~nes conjugu~s (Pr~marin) de sulfate de pip~razine-est~rone (Ogen) et de sulfate 3 est~rone a ~t~ r~alis~e sur le cortex sensorim o t e u r de chats sous anesth~sie locale et paralys~s. Tous ces agents (concentration de 1 ~ 2%) p r o v o q u e n t une activit~ paroxystique caract~ris~e par des d~charges de complexes pointe--ondes de 2 ~ 3 c/sec qui se g~n~ralisent de fa~on bilat~rale sur t o u t le cortex et dans les n o y a u x ventral int~rieur, dorsal m~dian et centra m~dian du thalamus, Au contraire, la micro-injection unilat~rale (2%; 0.01 cc) d'estrog~nes conjugu~s dans les n o y a u x thalamiques r~sulte en une activit~ de poly-pointes de 7 ~ 20 c/sec enregistr~e de faqon bilat~rale sur le cortex et darts le thalamus controlatdral. Des d~charges de cornplexes p o in te- - o n d es ne sont pas observ~es ~i la suite d'injection thalamique d'estrog~nes. Les l~sions ~lectrolytiques ipsilat~rales soit du n o y au ventral ant~rieur soit du n o y a u central m~dian ne produisent pas de diminution des d~charges de p o in t e - - onde s originaires d'un f o y e r cortical. Dans isol~es topique activit~ it~e au
des tranches de cor t e x suprasylvien de fa~on chronique, l'application d'estrog~nes conjugu~s pr ovoque une de p o in te- - onde s de 1 ~ 3 c/sec limtissu isol~ sans diffusion au cortex
intact p~riph~rique, Contrairement aux st~roides estrog~nes, la
progesterone, la testosterone et le diethylstibest~rol ne p r o v o q u e n t pas d'activit~ paroxyst i que par application topique bilat~rale pour des concentrations de 10% bien que l'application soit de testosterone soit de progest~rone s'associe ~ la f o r m a t i o n de fuseaux chez certains animaux. Ces donn~es m o n t r e n t la capacit~ du cortex c~r~bral ~ fabriquer des d~charges de p o n t e - ondes en l'absence d'influence sous-corticale, une g~n~ralisation des d~charges de poi nt e-ondes ~ partir d'un foyer cortical unilateral et une sp~cificit~ des estrog~nes en temps que facteur ~pileptog~ne. Le t ype de complexes pointe--ondes experimental provoqu~ par estrog~nes en application topique est discut~ par r~f~rence aux modifications EEG du PetitMal ou du Petit-Mal variant clinique.
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