252
Electroencephalography and Clinical Neurophysiology, 1977, 4 2 : 2 5 2 - - 2 5 8 © Elsevier/North-Holland Scientific Publishers Ltd
Laboratory note ELECTROCORTICOGRAPHIC CHANGES INDUCED BY TOPICALLY APPLIED SUCCINYLCHOLINE AND BIPERIDEN /JNER TAN
A tatiirk Universitesi, Fizyoloji Enstitiisii, Erzurum (Turkey) (Accepted for publication: June 15, 1976)
The neuromuscular blocking agent succinylcholine (SCh) consists of two acetylcholine (ACh) molecules and mimicks the actions of ACh in many respects. SCh elicits massive afferent discharge from the muscle spindles (Granit et al. 1953) presumably by causing contracture of the nuclear bag fibres (Smith 1966). Moreover, it depolarizes the end-plate-free part of the muscle membrane (Ras et al. 1972) and reacts with the cholinoceptive sites at the first node of the m o t o r nerve terminal (Blaber and Goode 1968). The effects of this depolarizing agent on the cerebral cortex, which is known to be rich in cholinoceptive neurones (Crawford and Curtis 1966; Krnjevi6 and Phillis 1963a,b,c) has not been investigated. It is known that excess ACh elicits epileptiform discharges (Chatfield and Dempsey 1942; Echlin and McDonald 1954; Echlin 1959; Ferguson and Jasper 1971), probably by depolarizing these cells extensively. On the other hand, topical atropine also produces convulsive activity (Daniels and Spehlman 1973) although it is a well known antimuscarinic agent. The antiparkinson drug biperiden also possesses antimuscarinic properties (Fried 1963). Therefore, it might be expected that topically applied biperiden would also produce epileptiform activity. In the present study an attempt was made to elucidate the ECoG effects of topical SCh and biperiden with respect to cortical transmission and convulsive phenomena.
Methods
The experiments were performed on 11 unanaesthetized cats with spinal transection at C1 and maintained under artificial respiration. The animals were anaesthetized with ether during surgical procedures. They were then paralysed with gallamine triethiodide to avoid artefacts in the ECoG. All contact points were anaesthetized locally with lidocaine. The left cerebral cortex was exposed by craniotomy. The dura was removed and usually three recording wick elec-
trodes were placed over the somatomotor (electrode 1 ), temporal (electrode 2) and posterior parietal {electrode 3) cortex as shown in Fig. 2. Recordings were made bipolarly between electrodes 1 and 2, 2 and 3 and 1 and 3 using a time constant of 10 msec. A polyethylene cannula was introduced into the right femoral artery to monitor blood pressure. Temperature was maintained between 36.5 and 37.5°C with a heating pad. In order to produce evoked potentials, clicks were generated by 0.2 msec pulses applied to a loudspeaker. For topical application of substances, 2 × 2 mm 2 of blotting paper was immersed in neutral solutions containing SCh-chloride (Fake, Istanbul) or biperiden hydrochloride (Knoll, Ludwigshafen). When thoroughly soaked, the paper was placed over the cerebral cortex lying under one of the recording electrodes for at least 10 min.
Results
Convulsant effect of topical SCh In all 11 experiments, topical application of 5-20% SCh produced large amplitude intermittent sharp waves ("spikes"). In 5 of 11 experiments intermittent spike activity changed to a well developed seizure activity. SCh action usually appeared within 2 min following application and lasted for as long as 1 h when the absorbent tissue was not removed from the cortical surface. Otherwise, it lasted for about 30 min if the absorbent tissue was removed within 10 min. Fig. 1 summarizes the main effects of topical SCh. In the control period, the ECoGs recorded between electrodes 1 and 2 (Ai) and 2 and 3 (A2) showed fast activity. Two min after application of a 5% solution of SCh under electrode 1 intermittent spike activity was recorded between electrodes 1 and 2 (B1). No change was observed in the other records (B2). Eight sec later double spikes began to occur (CI).
ECoG, S U C C I N Y L C H O L I N E A N D B E P E R I D E N
253 (El,2). This convulsive discharge lasted for a b o u t 23 sec, as seen in F and G. Fig. 2 illustrates the effect o f topical SCh on acoustically evoked cortical responses. Before SCh clicks p r o d u c e d small evoked potentials visible in record 2 (CON), i.e., between electrodes 2 and 3. Ten rain after topical application of 2% SCh under electrode 2, the same clicks elicited m u c h larger cortical potentials and one click evoked two responses (SChl : trace 2). Click-evoked responses were also recorded in the other cortical areas after SCh, as seen in records 1 and 3 (between electrodes 1 and 2, and 1 and 3, respectively). A n o t h e r application of a 2% solution of SCh to the same cortical area further increased the evoked potential amplitude in all three recording sites (SCh2). After washing out the temporal c o r t e x with saline, evoked potentials returned to their control amplitude (SAL).
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Fig. 1. Effect of topical succinylcholine on ECoG. A : Control period; 1 and 2, ECoGs recorded between the electrodes 1 and 2 and 2 and 3, respectively. B, C, D and E: 2, 8, 10 and 26 rain after the application o f a 5% SCh solution under electrode 1 (indicated in Fig. 2). E, F and G are successive records. Vertical bar, 150 pV.
In all 7 experiments, topical biperiden induced at least i n t e r m i t t e n t spike activity which developed occasionally into long-lasting convulsive discharge when the c o n c e n t r a t i o n was high enough. The effect of 0.5--1% biperiden appeared usually within 10 rain and lasted for a b o u t 2 h when the absorbent tissue was not r e m o v e d from the cortical surface. Fig. 3 illustrates one experiment. In the control period, ECoG was recorded between electrodes 1 and 2 (A). Ten rain after the topical application of a 1% solution of biperiden to cortical area 1, large amplitude diphasic i n t e r m i t t e n t spikes appeared at a rate of a p p r o x i m a t e l y 1 per 3--5 see (B) which increased within the 21st rain (C) and c o n t i n u e d in the same m a n n e r up to the 28th min of application (D). The i n t e r m i t t e n t spike activity lasted for a b o u t 2 h, as seen in E. A f t e r the ECoG had returned to normal, it was recorded between electrodes 2 and 3 (CON, first horizontal cut-out after E). Ten rain after topical application of a 1% solution of biperiden to the cortical area 2, i n t e r m i t t e n t spikes with after-discharges appeared (BIP). These biperiden spikes diminished within 1 min following intravenous injection of 0.1 mg/kg eserine sulphate and then disappeared c o m p l e t e l y 14 min after injection (ESER). Click-evoked responses recorded between electrodes 2 and 3 (CON, below) also increased after the same biperiden application (BIP) and decreased after the same eserine injection (ESER).
SCh--biperiden interaction However, 10 min after application of SCh the single spikes reappeared, as seen in D I . The spike rate increased within the 26th min o f application and the o t h e r records also showed simultaneous spike activity
SCh-induced spikes were depressed by topical biperiden (9 experiments). Fig. 4 illustrates the effects o f topical biperiden on the SCh-induced spike activi-
254
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Fig. 2. Effect o f topical succinylcholine on cortical click response. CON: Control period. 1, 2 and 3 are records f r o m electrodes i and 2, 2 and 3 and 1 and 3, respectively (see insert). Clicks are indicated by dots. SChl, 10 rain after application of a 2% (subconvulsive) SCh solution u n d e r electrode 2. SCh2, 10 min after a further application of 2% SCh to the same area. SAL, 10 min after washing away the SCh. Vertical bar, 150 pV.
ty. Single and double spikes appeared within 2 min following topical application of a 5% solution of SCh to the cortical surface underlying electrode 1 (B). A f t e r a further application of a 5% SCh solution to the same cortical area the spike amplitude and frequency increased (C). In D, 0.5% biperiden was d r o p p e d on the paper lying over the c o r t e x under electrode 1.
Within 2 min spike amplitudes increased (D) and int e r m i t t e n t burst activity appeared 30 sec later (E), i.e., SCh effect was p o t e n t i a t e d by biperiden. Within the 6th min triplets disappeared but spike amplitudes increased further (F). SCh spikes began to decrease in the 10th min (G) and almost disappeared in the 12th min of biperiden application (H).
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Fig. 3. Action of topical biperiden on ECoG and acoustically evoked potentials. A: ECoG recorded between electrodes i and 2 (electrode position, see Fig. 2). B: Biperiden spikes 10 rain after topical application of a 1 % solution of biperiden under electrode 1. C and D: 21 and 28 rain later. E: 2 h after biperiden application. Vertical bar, 150 ]~V. Below: same experiments, with recording between electrodes 2 and 3. CON, control ECoG, BIP, 10 rain after application of a 1% biperden solution under electrode 2. ESER, 14 rain after intravenous injection of 0.1 mg/kg eserine. Last 3 records: click-evoked responses recorded between electrodes 2 and 3. CON, control period. BIP, 15 rain after application of 1% biperiden to the cortical area 2. ESER, 20 min after the same eserine injection as above. Clicks are indicated by dots. Vertical bar, 150 pV.
Discussion
The above results indicate that topical application of the neuromuscular blocking agent SCh and antiparkinsonian agent biperiden can both induce epileptiform discharge in the ECoG. The effect of topi-
cally applied SCh lasted much longer than that when given intravenously. Inactivation of SCh by pseudocholinesterase probably did not occur in the cerebral cortex. SCh may act by mimicking the action of ACh on the cerebral cortex since topical ACh application also elicits convulsive activity (Echlin and McDonald
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1954; Echlin 1959; Ferguson and Jasper 1971). It is conceivable that the cholinoceptive sites of the cortical cholinergic neurones may have been affected by SCh. In accordance with this assumption, SCh also caused a large increase of the cortical click-evoked response. There is indeed evidence that an increase in the ACh output can be produced by stimulating the specific auditory afferent pathways (Mitchell 1963; Neal et al. 1968). On the other hand, suppression of SCh spikes by application of the cholinolytic agent biperiden also supports the view that SCh acts on the cholinoceptive sites of the cortical neurones. The initial potentiation of the SCh spikes by biperiden may be due to a distinct mechanism. Accord-
ingly, it was shown here that the topical application of biperiden may produce epileptiform ECoG activity. The depression of the SCh spikes occurring after additional application of biperiden may be accounted for by the antimuscarinic action of the latter substance, since the cortical cholinergic receptors show muscarinic properties (Krnjevi~ and Phillis 1963c). The epileptiform activity that appeared following biperiden may be the result of at least two mechanisms for the following reasons: (i) biperiden may block presumed cholinergic inhibitory synapses at the cortical neurones (Randi~ et al. 1964; Phillis and York 1968; Jordan and Phillis 1972) and thus cause disinhibition leading to accumulation of ACh, which
ECoG, SUCCINYLCHOLINE AND BEPERIDEN may result in bursting or epileptogenic activity; (ii) biperiden may block the muscarinic excitatory synapses at the cortical neurones (Krnjevid and Phillis 1963c) and thus diminish the desynchronizing drive exerted on the cortex by the ascending reticular activatory system as suggested by others for the genesis of penicillin epilepsy (Guberman and Gloor 1974; Testa and Gloor 1974). Experiments with chronic foci also suggest that neuronal deafferentation may contribute to generation of epileptiform activity (Ward 1969). The first possibility may be correct since topical SCh is convulsant as is its agonist ACh and this action is antagonized by topical application of the cholinolytic agent biperiden. The second possibility may also be correct since convulsive action of topical biperiden was antagonized by eserine. Consequently, it can be suggested that the epileptogenic activity of the cholinolytic agents may be the result of a dual inhibitory action on both the inhibitory and the excitatory muscarinic cortical synapses.
257 duit des pointes intermittentes de grande amplitude ~voluant parfois en une activit6 convulsive prolong6e (selon la concentration). Les potentiels ~voqu~s acoustiques ont accus~ une augmentation d'amplitude, apr6s application topique de 2% succinylcholine. Celle, de bip~riden (0.5--1%) a 6galement suscit~ des pointes, se d6veloppant parfois en une activit~ critique durable selon la concentration. Ces effets du bipdriden 6taient diminu~s par injection i.v. de 0,1 mg/kg d'~s~rine. Les pointes produites par la succinylcholine dtaient d'abord accrues, et ult~rieurement r~duites par le bip~riden. Ces donn~es sugg~rent que la succinylcholine agft en mimant les effets de l'ac6tylcholine et que le bipdriden d6termine des activitds paroxystiques en bloquant les synapses muscarinique excitatrices et inhibitrices, ces deux types de synapses contribuant, on le suppose, au phdnom6ne paroxystique.
References Summary ECoG effects of topically applied succinylcholine and biperden were investigated in unanaesthetized cats with high cervical transection. Topical application of 5% succinylcholine produced large amplitude intermittent spikes which developed into long-lasting seizure activity, depending upon the concentration. Acoustically evoked cortical potentials showed increase in amplitude following topical application of 2% succinylcholine. Topical biperiden (0.5--1%) also induced intermittent spikes which developed into seizure activity, depending upon the concentration. The biperiden effects were diminished by i.v. injection of 0.1 mg/kg eserine. Succinylcholine-induced spikes were first increased and then decreased by topical biperiden. It is suggested that topical succinylcholine may act by mimicking acetylcholine actions and that topical biperiden may induce paroxysms by blocking the inhibitory and excitatory muscarinic synapses, both being assumed to contribute to the mechanism of the epileptic phenomenon.
R~sum~ Altdrations ECoG prbduites par application topique de succinylcholine et de bip~riden Les effets 61ectrocorticographique d'appiication locale de succinylcholine et de bipdriden ont ~t~ dtudids sur le chat apr~s transection cervicale haute. L'application topique de succinylcholine (~ 5%) a pro-
Blaber, L.C. and Goode, J.W. A comparison of the action of facilitatory and depolarizing drugs at the mammalian motor nerve terminal. Int. J. Neuropharmacol., 1968, 7: 429--440. Chatfield, P.O. and Dempsey, E.W. Some effects of prostigmine and acetylcholine on cortical potentials. Amer. J. Physiol., 1942, 135: 633--640. Crawford, J.M. and Curtis, D.R. Pharmacological studies on feline Betz cells. J. Physiol. (Lond.), 1966, 186: 121--138. Daniels, J.C. and Spehlman, R. The convulsant effects of topically applied atropine. Electroenceph. clin. Neurophysiol., 1973, 34: 83--87. Echlin, F.A. The supersensitivity of chronically isolated cerebral cortex as a mechanism in focal epilepsy. Electroenceph. clin. Neurophysiol., 1959, 11: 697--772. Echlin, F.A. and McDonald, J. The supersensitivity of chronically isolated and partially isolated cerebral cortex as a mechanism in focal cortical epilepsy. Trans. Amer. neurol. Ass., 1954, 79: 75--79. Ferguson, J.H. and Jasper, H.H. Laminar DC studies of acetylcholine activated epileptiform discharge in cerebral cortex. Electroenceph. clin. Neurophysiol., 1 9 7 1 , 3 0 : 377--390. Fried, D.G. Antiparkinsonism drug therapy. Clin. Pharmacol. Ther., 1963, 4: 815--822. Granit, R., Skoglund, S. and Thesleff, S. Activation of muscle spindles by succinylcholine and decamethonium. The effects of curare. Acta physiol. scand., 1953, 28: 134--151. Guberman, A. and Gloor, P. Cholinergic drug studies of generalized penicillin epilepsy in the cat. Brain Res., 1974, 78: 203--222.
258 Jordan, L.M. and Phillis, J.W. Acetylcholine inhibition in the intact and chronically isolated cerebral cortex. Brit. J. Pharmacol., 1972, 45: 584--595. Krnjevi~, K. and Phillis, J.W. Iontophoretic studies of neurones in the mammalian cerebral cortex. J. Physiol. (Lond.), 1963a, 165: 274--304. Krnjevid, K. and Phillis, J.W. Acetylcholine sensitive cells in the cerebral cortex. J. Physiol. (Lond.), 1963b, 166: 296--327. Krnjevid, K. and Phillis, J.W. Pharmacological properties of acetylcholine sensitive cells in the cerebral cortex. J. Physiol. (Lond.), 196~c, 166: 328--350. Mitchell, J.F. The spontaneous and evoked release of acetylcholine from the cerebral cortex. J. Physiol. (Lond.), 1963, 165: 98--116. Neal, M.J., Hemsworth, B.A. and Mitchell, J.F. The excitation of central cholinergic mechanism by stimulation of the auditory pathway. Life Sci., 1968, 7: 757--763. Phillis, J.W. and York, D.H. Pharmacological studies
U. TAN on a cholinergic inhibition in the cerebral cortex. Brain Res., 1968, 10: 297--306. Randid, M., Siminoff, R. and Straughan, D.W. Acetylcholine depression of cortical neurons. Exp. Neurol., 1964, 9: 236--242. Ras, R., Den Hertog, A. and Lammers, W. The effects of suxamethonium on the striated muscle fibre outside the endplate regions.Pfliigers Arch. ges. Physiol., 1972, 333: 187--196. Smith, R.S. Properties of intrafusal muscle fibres. In R. Granit (Ed.}, Muscular afferents and motor control. Almqvist and Wiksell, Stockholm, 1966: 69--80. Testa, G. and Gloor, P. Generalized penicillin epilepsy in the cat: effect of midbrain cooling. Electroenceph, clin. Neurophysiol., 1974, 36: 517--524. Ward, A.A. The epileptic neuron: chronic foci in animals and man. In H.H. Jasper et al. (Eds.), Basic mechanisms of the epilepsies. Little, Brown and Co., Boston, Mass., 1969: 263--288.
Electroencephalography and Clinical Neurophysiology, 1977, 4 2 : 2 5 2 - - 2 5 8 © Elsevier/North-Holland Scientific Publishers Ltd
Laboratory note ELECTROCORTICOGRAPHIC CHANGES INDUCED BY TOPICALLY APPLIED SUCCINYLCHOLINE AND BIPERIDEN /JNER TAN
A tatiirk Universitesi, Fizyoloji Enstitiisii, Erzurum (Turkey) (Accepted for publication: June 15, 1976)
The neuromuscular blocking agent succinylcholine (SCh) consists of two acetylcholine (ACh) molecules and mimicks the actions of ACh in many respects. SCh elicits massive afferent discharge from the muscle spindles (Granit et al. 1953) presumably by causing contracture of the nuclear bag fibres (Smith 1966). Moreover, it depolarizes the end-plate-free part of the muscle membrane (Ras et al. 1972) and reacts with the cholinoceptive sites at the first node of the m o t o r nerve terminal (Blaber and Goode 1968). The effects of this depolarizing agent on the cerebral cortex, which is known to be rich in cholinoceptive neurones (Crawford and Curtis 1966; Krnjevi6 and Phillis 1963a,b,c) has not been investigated. It is known that excess ACh elicits epileptiform discharges (Chatfield and Dempsey 1942; Echlin and McDonald 1954; Echlin 1959; Ferguson and Jasper 1971), probably by depolarizing these cells extensively. On the other hand, topical atropine also produces convulsive activity (Daniels and Spehlman 1973) although it is a well known antimuscarinic agent. The antiparkinson drug biperiden also possesses antimuscarinic properties (Fried 1963). Therefore, it might be expected that topically applied biperiden would also produce epileptiform activity. In the present study an attempt was made to elucidate the ECoG effects of topical SCh and biperiden with respect to cortical transmission and convulsive phenomena.
Methods
The experiments were performed on 11 unanaesthetized cats with spinal transection at C1 and maintained under artificial respiration. The animals were anaesthetized with ether during surgical procedures. They were then paralysed with gallamine triethiodide to avoid artefacts in the ECoG. All contact points were anaesthetized locally with lidocaine. The left cerebral cortex was exposed by craniotomy. The dura was removed and usually three recording wick elec-
trodes were placed over the somatomotor (electrode 1 ), temporal (electrode 2) and posterior parietal {electrode 3) cortex as shown in Fig. 2. Recordings were made bipolarly between electrodes 1 and 2, 2 and 3 and 1 and 3 using a time constant of 10 msec. A polyethylene cannula was introduced into the right femoral artery to monitor blood pressure. Temperature was maintained between 36.5 and 37.5°C with a heating pad. In order to produce evoked potentials, clicks were generated by 0.2 msec pulses applied to a loudspeaker. For topical application of substances, 2 × 2 mm 2 of blotting paper was immersed in neutral solutions containing SCh-chloride (Fake, Istanbul) or biperiden hydrochloride (Knoll, Ludwigshafen). When thoroughly soaked, the paper was placed over the cerebral cortex lying under one of the recording electrodes for at least 10 min.
Results
Convulsant effect of topical SCh In all 11 experiments, topical application of 5-20% SCh produced large amplitude intermittent sharp waves ("spikes"). In 5 of 11 experiments intermittent spike activity changed to a well developed seizure activity. SCh action usually appeared within 2 min following application and lasted for as long as 1 h when the absorbent tissue was not removed from the cortical surface. Otherwise, it lasted for about 30 min if the absorbent tissue was removed within 10 min. Fig. 1 summarizes the main effects of topical SCh. In the control period, the ECoGs recorded between electrodes 1 and 2 (Ai) and 2 and 3 (A2) showed fast activity. Two min after application of a 5% solution of SCh under electrode 1 intermittent spike activity was recorded between electrodes 1 and 2 (B1). No change was observed in the other records (B2). Eight sec later double spikes began to occur (CI).
ECoG, S U C C I N Y L C H O L I N E A N D B E P E R I D E N
253 (El,2). This convulsive discharge lasted for a b o u t 23 sec, as seen in F and G. Fig. 2 illustrates the effect o f topical SCh on acoustically evoked cortical responses. Before SCh clicks p r o d u c e d small evoked potentials visible in record 2 (CON), i.e., between electrodes 2 and 3. Ten rain after topical application of 2% SCh under electrode 2, the same clicks elicited m u c h larger cortical potentials and one click evoked two responses (SChl : trace 2). Click-evoked responses were also recorded in the other cortical areas after SCh, as seen in records 1 and 3 (between electrodes 1 and 2, and 1 and 3, respectively). A n o t h e r application of a 2% solution of SCh to the same cortical area further increased the evoked potential amplitude in all three recording sites (SCh2). After washing out the temporal c o r t e x with saline, evoked potentials returned to their control amplitude (SAL).
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Fig. 1. Effect of topical succinylcholine on ECoG. A : Control period; 1 and 2, ECoGs recorded between the electrodes 1 and 2 and 2 and 3, respectively. B, C, D and E: 2, 8, 10 and 26 rain after the application o f a 5% SCh solution under electrode 1 (indicated in Fig. 2). E, F and G are successive records. Vertical bar, 150 pV.
In all 7 experiments, topical biperiden induced at least i n t e r m i t t e n t spike activity which developed occasionally into long-lasting convulsive discharge when the c o n c e n t r a t i o n was high enough. The effect of 0.5--1% biperiden appeared usually within 10 rain and lasted for a b o u t 2 h when the absorbent tissue was not r e m o v e d from the cortical surface. Fig. 3 illustrates one experiment. In the control period, ECoG was recorded between electrodes 1 and 2 (A). Ten rain after the topical application of a 1% solution of biperiden to cortical area 1, large amplitude diphasic i n t e r m i t t e n t spikes appeared at a rate of a p p r o x i m a t e l y 1 per 3--5 see (B) which increased within the 21st rain (C) and c o n t i n u e d in the same m a n n e r up to the 28th min of application (D). The i n t e r m i t t e n t spike activity lasted for a b o u t 2 h, as seen in E. A f t e r the ECoG had returned to normal, it was recorded between electrodes 2 and 3 (CON, first horizontal cut-out after E). Ten rain after topical application of a 1% solution of biperiden to the cortical area 2, i n t e r m i t t e n t spikes with after-discharges appeared (BIP). These biperiden spikes diminished within 1 min following intravenous injection of 0.1 mg/kg eserine sulphate and then disappeared c o m p l e t e l y 14 min after injection (ESER). Click-evoked responses recorded between electrodes 2 and 3 (CON, below) also increased after the same biperiden application (BIP) and decreased after the same eserine injection (ESER).
SCh--biperiden interaction However, 10 min after application of SCh the single spikes reappeared, as seen in D I . The spike rate increased within the 26th min o f application and the o t h e r records also showed simultaneous spike activity
SCh-induced spikes were depressed by topical biperiden (9 experiments). Fig. 4 illustrates the effects o f topical biperiden on the SCh-induced spike activi-
254
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ty. Single and double spikes appeared within 2 min following topical application of a 5% solution of SCh to the cortical surface underlying electrode 1 (B). A f t e r a further application of a 5% SCh solution to the same cortical area the spike amplitude and frequency increased (C). In D, 0.5% biperiden was d r o p p e d on the paper lying over the c o r t e x under electrode 1.
Within 2 min spike amplitudes increased (D) and int e r m i t t e n t burst activity appeared 30 sec later (E), i.e., SCh effect was p o t e n t i a t e d by biperiden. Within the 6th min triplets disappeared but spike amplitudes increased further (F). SCh spikes began to decrease in the 10th min (G) and almost disappeared in the 12th min of biperiden application (H).
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Fig. 3. Action of topical biperiden on ECoG and acoustically evoked potentials. A: ECoG recorded between electrodes i and 2 (electrode position, see Fig. 2). B: Biperiden spikes 10 rain after topical application of a 1 % solution of biperiden under electrode 1. C and D: 21 and 28 rain later. E: 2 h after biperiden application. Vertical bar, 150 ]~V. Below: same experiments, with recording between electrodes 2 and 3. CON, control ECoG, BIP, 10 rain after application of a 1% biperden solution under electrode 2. ESER, 14 rain after intravenous injection of 0.1 mg/kg eserine. Last 3 records: click-evoked responses recorded between electrodes 2 and 3. CON, control period. BIP, 15 rain after application of 1% biperiden to the cortical area 2. ESER, 20 min after the same eserine injection as above. Clicks are indicated by dots. Vertical bar, 150 pV.
Discussion
The above results indicate that topical application of the neuromuscular blocking agent SCh and antiparkinsonian agent biperiden can both induce epileptiform discharge in the ECoG. The effect of topi-
cally applied SCh lasted much longer than that when given intravenously. Inactivation of SCh by pseudocholinesterase probably did not occur in the cerebral cortex. SCh may act by mimicking the action of ACh on the cerebral cortex since topical ACh application also elicits convulsive activity (Echlin and McDonald
256
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Fig. 4. Antagonization of SCh spikes by topical biperiden. 1, 2 and 3: ECoGs recorded between electrodes 1 and 2, 2 and 3, and 1 and 3, respectively. A : Control period. B: 2 min after topical application of 5% SCh under electrode 2. C: 10 min after a further SCh application to the same area at same concentration. D: 2 rain after application of 0.5% biperiden on the SCh paper placed over cortical area 2. E, F, G and H: 2 min 30 sec, 6 min, 10 rain, and 12 min after biperiden, respectively. Vertical bar, 150 pV.
1954; Echlin 1959; Ferguson and Jasper 1971). It is conceivable that the cholinoceptive sites of the cortical cholinergic neurones may have been affected by SCh. In accordance with this assumption, SCh also caused a large increase of the cortical click-evoked response. There is indeed evidence that an increase in the ACh output can be produced by stimulating the specific auditory afferent pathways (Mitchell 1963; Neal et al. 1968). On the other hand, suppression of SCh spikes by application of the cholinolytic agent biperiden also supports the view that SCh acts on the cholinoceptive sites of the cortical neurones. The initial potentiation of the SCh spikes by biperiden may be due to a distinct mechanism. Accord-
ingly, it was shown here that the topical application of biperiden may produce epileptiform ECoG activity. The depression of the SCh spikes occurring after additional application of biperiden may be accounted for by the antimuscarinic action of the latter substance, since the cortical cholinergic receptors show muscarinic properties (Krnjevi~ and Phillis 1963c). The epileptiform activity that appeared following biperiden may be the result of at least two mechanisms for the following reasons: (i) biperiden may block presumed cholinergic inhibitory synapses at the cortical neurones (Randi~ et al. 1964; Phillis and York 1968; Jordan and Phillis 1972) and thus cause disinhibition leading to accumulation of ACh, which
ECoG, SUCCINYLCHOLINE AND BEPERIDEN may result in bursting or epileptogenic activity; (ii) biperiden may block the muscarinic excitatory synapses at the cortical neurones (Krnjevid and Phillis 1963c) and thus diminish the desynchronizing drive exerted on the cortex by the ascending reticular activatory system as suggested by others for the genesis of penicillin epilepsy (Guberman and Gloor 1974; Testa and Gloor 1974). Experiments with chronic foci also suggest that neuronal deafferentation may contribute to generation of epileptiform activity (Ward 1969). The first possibility may be correct since topical SCh is convulsant as is its agonist ACh and this action is antagonized by topical application of the cholinolytic agent biperiden. The second possibility may also be correct since convulsive action of topical biperiden was antagonized by eserine. Consequently, it can be suggested that the epileptogenic activity of the cholinolytic agents may be the result of a dual inhibitory action on both the inhibitory and the excitatory muscarinic cortical synapses.
257 duit des pointes intermittentes de grande amplitude ~voluant parfois en une activit6 convulsive prolong6e (selon la concentration). Les potentiels ~voqu~s acoustiques ont accus~ une augmentation d'amplitude, apr6s application topique de 2% succinylcholine. Celle, de bip~riden (0.5--1%) a 6galement suscit~ des pointes, se d6veloppant parfois en une activit~ critique durable selon la concentration. Ces effets du bipdriden 6taient diminu~s par injection i.v. de 0,1 mg/kg d'~s~rine. Les pointes produites par la succinylcholine dtaient d'abord accrues, et ult~rieurement r~duites par le bip~riden. Ces donn~es sugg~rent que la succinylcholine agft en mimant les effets de l'ac6tylcholine et que le bipdriden d6termine des activitds paroxystiques en bloquant les synapses muscarinique excitatrices et inhibitrices, ces deux types de synapses contribuant, on le suppose, au phdnom6ne paroxystique.
References Summary ECoG effects of topically applied succinylcholine and biperden were investigated in unanaesthetized cats with high cervical transection. Topical application of 5% succinylcholine produced large amplitude intermittent spikes which developed into long-lasting seizure activity, depending upon the concentration. Acoustically evoked cortical potentials showed increase in amplitude following topical application of 2% succinylcholine. Topical biperiden (0.5--1%) also induced intermittent spikes which developed into seizure activity, depending upon the concentration. The biperiden effects were diminished by i.v. injection of 0.1 mg/kg eserine. Succinylcholine-induced spikes were first increased and then decreased by topical biperiden. It is suggested that topical succinylcholine may act by mimicking acetylcholine actions and that topical biperiden may induce paroxysms by blocking the inhibitory and excitatory muscarinic synapses, both being assumed to contribute to the mechanism of the epileptic phenomenon.
R~sum~ Altdrations ECoG prbduites par application topique de succinylcholine et de bip~riden Les effets 61ectrocorticographique d'appiication locale de succinylcholine et de bipdriden ont ~t~ dtudids sur le chat apr~s transection cervicale haute. L'application topique de succinylcholine (~ 5%) a pro-
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