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The effects of amantadine, rimantadine and levodopa on the frequency of fibrillation potentials in denervated muscle
174
Electroencephalography and clinical N europto'siology, 1984, 57:174-177 Elsevier Scientific Publishers Ireland, Ltd.
T H E E F F E C T S O F A M A N T A D I N E , R I M A N T A D I N E AND L E V O D O P A O N T H E F R E Q U E N C Y OF F I B R I L L A T I O N P O T E N T I A L S IN D E N E R V A T E D M U S C L E ISRAEL YAAR
Neurophysiology Laboratory, Neurology Service. VAMC, Davis Park, Providence, R1 02908 (U.S.A.)
(Accepted for publication: July 8, 1983)
Catecholaminergic receptors exist throughout the CNS (Lindwell et al. 1974), and the peripheral neuromuscular system as well (Bowman and Roper 1966). Amantadine exerts a direct dopaminergic, and probably some additional effects of its own, on CNS neurons (Vermier et al. 1969; Bailey and Stone 1975), and on the peripheral neuromuscular system (Calesnich and Perko 1973; Tsai et al. 1978). Rimantadine, as an amantadine analog, has a non-dopaminergic direct effect on CNS neurons (Stone 1978), but is not known to have peripheral activities (Tsai et al. 1978). In this study we investigated the effects of amantadine, rimantadine and levodopa on the frequency of fibrillation potentials (FPs) in surgically denervated gastrocnemius-soleus muscle of rats.
Method and Material
Fifty-nine rats, type OM, 180-220 g were denervated under pentothal anesthesia (25-50 m g / k g : the right sciatic nerves were exposed in mid-thigh and segments 0.5 cm long were cut away. Then, for 11 days the rats were held in metabolic cages and fed on regular food. On the 12th and 13th days, in the afternoons, 19 rats were injected with 1 ml normal saline intraperitoneally (i.p.), 20 rats were injected i.p. with 1 ml of rimantadine (10 mg in normal saline), 13 rats were injected i.p. with 1 ml of amantadine (10 mg in normal saline) and 7 rats were injected i.p. with 1 ml of levodopa (10 mg in normal saline). On the 14th day the same injections were given but then, 2 h later electromyographic (EMG) recordings were performed. The E M G was performed with the rats
completely relaxed under pentothal anesthesia (25-50 mg/kg). The E M G amplifier filter settings were 300-10K c/sec. The same needle electrode, Disa 13L51, was used for all the rats. The E M G fiberoptic paper recorder (TECA) was set to record continuously in a raster mode for 5 sec, at sweep speed of 17 m s e c / c m and amplification of 100 ~V/cm. The needle electrode was inserted into the calf muscles and 3 consecutive recordings of 5 sec duration each were performed, each recording from a different location inside the muscle bulk. Adequate time of about 10 sec was allowed for insertional activities to subside completely. The animal's ambient temperature was kept reasonably warm with an infrared lamp. Fibrillation potentials were counted manually governed by the following quantitative and qualitative criteria: amplitudes within 20 and 300/~V; durations less than 2 msec; fast positive to negative deflections with sharp peaks. The animals were coded, fibrillations were counted, and only then was the code broken. The 3 counts for each animal were averaged. Statistical analysis was performed by analysis of variance, F tests for the Mahalonobis distance between groups and t test.
Results
The mean number of fibrillations for each group and its standard error are given in Table I. One-way analysis of variance (SPSS one-way) for the 4 groups revealed an overall significance: F = 3.26, df= 3; 55 and P = 0.028. The amantadine and the levodopa groups were found to be significantly different from the saline injected control group at
0013-4649/84/$03.00 © 1984 Elsevier Scientific Publishers Ireland, Ltd.
AMANTADINE, RIMANTADINE, LEVODOPA AND FIBRILLATIONS TABLE I Means of fibrillation potentials recorded in the test groups. Group
No. of animals
Mean no. of fibrillations
S.E.
Saline Rimantadine Amantadine Levodopa
19 20 13 7
99.0 77.5 65.5 43.4
13.0 8.6 10.9 5.9
One-way analysis of variance: F = 3.26, df = 3; 55, P = 0.028 TABLE II Mahalonobis distances: F statistics and significances between pairs of groups. Each statistic has 1 and 55 dr. Group Rimantadine Amantadine Levodopa
F= P= F= P= F= P=
Saline
Rimantadine
Amantadine
2.3 0.1 4.5 0.04 8.2 0.006
0.6 0.4 3.1 0.08 *
1.2 0.3
Canonical discriminant function: X2 = 9.1, df = 3, P = 0.028. * t test: t = 3.27, df = 25, P = 0.003.
the P = 0.05 level by the same test. F o u r g r o u p s ' m u l t i v a r i a t e F tests ( M a h a l o n o b i s distances) (Table II) showed significant differences b e t w e e n the saline injected c o n t r o l g r o u p ' s c e n t r o i d and the a m a n t a d i n e a n d the l e v o d o p a injected g r o u p s ' c e n t r o i d s (SPSS discriminant). Also, a t test ( T a b l e II) showed a significant difference b e t w e e n levodopa and rimantadine.
Discussion This study disclosed that b o t h t e v o d o p a and a m a n t a d i n e are effective, and r i m a n t a d i n e is ineffective, at least in the doses that were used, in reducing the frequency of F P s in surgically den e r v a t e d rat g a s t r o c n e m i u s - s o l e u s muscles. It is c o m m o n l y a c c e p t e d that F P s arise as a result of the various p l a s m a l e m m a l (PL) changes that take place in response to the d i s c o n t i n u e d t r a n s p o r t of as yet u n i d e n t i f i e d m y o t r o p h i c factor ( M F ) by the axon. This p o s t u l a t e d M F is considered not to be A C h a n d to be i n d e p e n d e n t of the
175
a x o n a l electrical activity ( R o b e r t a n d Oester 1970; M c C o m a s 1977; Rogus et al. 1977). T h e r e are several changes in the PL functional a n d structural characteristics, each of them m a y result in FPs ( B o w m a n a n d R o p e r 1966; M c C o m a s 1977; V r b o v a et al. 1978): (1) fall in the PL resting p o t e n t i a l , its r e d u c e d p e r m e a b i l i t y to K + and C1 , a n d changes in its action potential; (2) a m a n i - f o l d increase in e x t r a j u n c t i o n a l A C h R ( E J - A C h R ) , a n d increased EJ sensitivity to A C h ; (3) a two-fold increase in PL b e t a - a d r e n e r g i c receptors. Changes in P L ionic c o n d u c t a n c e a n d ( N a + + K +) p u m p activities are p r o b a b l y most i m p o r t a n t in initiating FPs. Both A C h R a n d the b e t a - a d r e n ergic receptors are c o u p l e d to ionic channels (Bowm a n a n d N o t t 1970; Eldefrawi et al. 1977; McC o m a s 1977; Rogus et al. 1977; A l b u q u e r q u e et al. 1978). The last is c o u p l e d to a d e n y l a t e cyclase ( R o g u s et al. 1977; R e d d y a n d Engel 1979). In the C N S b o t h a m a n t a d i n e a n d l e v o d o p a are c a p a b l e in activating b e t a - c a t e c h o l a m i n e r g i c rec e p t o r s ( D A receptor) ( B o w m a n and N o t t 1970; Stone 1976, 1978; Tsai et al. 1978). A m a n t a d i n e seems to have a d d i t i o n a l n o n - D A activities too (Stone 1978). R i m a n t a d i n e , though much m o r e active on C N S n e u r o n s than a m a n t a d i n e , does not act through D A receptors (Stone 1978). In the skeletal muscle it was f o u n d that a m a n t a d i n e acts on the ion c o n d u c t a n c e m o d u l a tor of the A C h R ( N a s t u k et al. 1976; Eldefrawi et al. 1977; A l b u q u e r q u e et al. 1978; Tsai et al. 1978), reducing the sensitivity of the E J - A C h R to i o n t o p h o r e t i c a l l y a p p l i e d ACh. It was also f o u n d that on J - A C h R a m a n t a d i n e has the same effect, reducing the sensitivity of the p o s t - j u n c t i o n a l m e m b r a n e to A C h with the p r o d u c t i o n of neurom u s c u l a r block. W h e n a p p l i e d for long p e r i o d s a m a n t a d i n e also depolarizes the EJ-PL. R i m a n t a d i n e was f o u n d to be inactive in these respects (Tsai et al. 1978). A m a n t a d i n e effect was pinp o i n t e d to ionic channels of the J- a n d E J - A C h R s ( A l b u q u e r q u e et al. 1978). L e v o d o p a is m e t a b o l i z e d to d o p a m i n e (DA), e p i n e p h r i n e and n o r e p i n e p h r i n e (Louis et al. 1974). These c a t e c h o l a m i n e s a u g m e n t PL b e t a 2 - a d r e n ergic receptors activity ( B o w m a n a n d N o t t 1970, 1978; M a r s d e n a n d M e a d o w s 1970; N o t t 1975) by c o u p l i n g to a d e n y l a t e cyclase a n d increased c A M P
176 synthesis ( R e d d y a n d Engel 1978). This releases an u n i d e n t i f i e d factor that acts directly on ( N a + + K + ) - A T P a s e . It is also p o s s i b l e t h a t the c a t e c h o l a m i n e s interact directly with the P L a d e n y l a t e cyclase, an i n t e r a c t i o n that requires a c e r t a i n c o n f i g u r a t i o n of the c a t e c h o l a m i n e molecule, and is not m e d i a t e d by b e t a - a d r e n e r g i c rec e p t o r s (Cheng et al. 1977; R e d d y a n d Engel 1979). Speculating on the basis of the a b o v e d a t a it seems that a m a n t a d i n e might reduce F P s b y its effect on the J- a n d E J - A C h R s ionic channels, a n d the l e v o d o p a effects are p r o b a b l y m e d i a t e d b y its m e t a b o l i t e s , acting on the PL b e t a - a d r e n e r g i c receptors, or directly on the P L ( N a + + K +)-ATPase.
I. YAAR logique normal, et 3 groupes, avec injection i.p. d ' a m a n t a d i n e , de r i m a n t a d i n e ou de l e v o d o p a (50 m g / k g de c h a q u e substance) p e n d a n t 3 j o u r s cons6cutifs. Le 146me jour, 2 h apr6s la 3~me injection, I ' E M G du gastrocnbmien-soleus 6tait recueilli, sous anesth6sie au p e n t o t h a l , et les potentiels de fibrillation 6taient compt+s. L ' a n a l y s e statistique a montr6 une r6duction significative des fibrillations, apr6s injection de l e v o d o p a et d ' a m a n t a d i n e . La r i m a n t a d i n e n'a pas modifi6 la fr6quence des fibrillations. On sugg6re que la levod o p a et l ' a m a n t a d i n e ont un effet stabilisateur sur la m e m b r a n e p l a s m a t i q u e d6nerv6e. The author wishes to thank Mr. Gregory Zirzow for his technical assistance, and Mrs. Deloris N. Brown for typing this manuscript.
Summary Right m i d - t h i g h sciatic d e n e r v a t i o n was perf o r m e d in 59 rats. Eleven d a y s later they were assigned into 4 groups: a c o n t r o l g r o u p that was injected i n t r a p e r i t o n e a l l y with n o r m a l saline, a n d 3 test groups that were injected i n t r a p e r i t o n e a l l y with a m a n t a d i n e , r i m a n t a d i n e or l e v o d o p a (50 m g / k g each), for 3 consecutive days. O n the fourteenth day, 2 h after the third injection, electrom y o g r a p h y of the soleus-gastrocnemius muscles was p e r f o r m e d u n d e r p e n t o t h a l anesthesia. F i b r i l l a t i o n p o t e n t i a l s were counted. T h e statistical analysis showed significant r e d u c t i o n of fibrillations s e c o n d a r y to l e v o d o p a a n d to a m a n t a d i n e injections. R i m a n t a d i n e d i d not change the frequency of fibrillations. A stabilizing effect of l e v o d o p a a n d a m a n t a d i n e on the d e n e r v a t e d p l a s m a l e m m a is postulated.
R6sum6 Effets de l'amantadine, de la rimantadine et la levodopa sur la frOquence des potentiels de fibrillation clans les muscles dOnervks O n a effectu6 chez 59 rats, une d 6 n e r v a t i o n du sciatique /l mi-cuisse, /i droite. Onze j o u r s apr6s, les a n i m a u x ont 6t6 divis6s en 4 groupes: un g r o u p e t6moin, avec injection i.p. de s6rum physio-
References Albuquerque, E.X., Eldefrawi, A.T., Eldefrawi, M.E., Mansour, N.S. and Tsai, M.C. Amantadine neuromuscular blockade by suppression of the acetylcholine receptor. Science, 1978. 199: 788-790. Bailey, E.V. and Stone, T.W. The mechanism of action of amantadine in parkinsonism: a review. Arch. Int. Pharmacol., 1975, 216: 246-262. Bowman, W.C. and Nott, M.W. Actions of some sympathomimetic bronchodilator and beta-adrenergic blocking drugs on contractions of cat soleus muscle. Brit. J. Pharmacol., 1970, 38: 37-49. Bowman, W.C. and Non, M.W. Peripheral muscle effects of levodopa in the anaesthesized cat. Clin. exp. Pharmacol. Physiol., 1978, 5: 305-312. Bowman, W.C. and Roper, C. Adrenotropic receptors in skeletal muscle. Ann. N.Y. Acad. Sci., 1966, 139: 741-753. Calesnich, B. and Perko, A.P. Action of levodopa and dopamine on skeletal muscle contraction. Drug. Inf. J.. 1973, 7: 48-50. Cheng, L.C., Rogus, E.M. and Zierler, K. Catechol, a structural requirement for (Na++K+)-ATPase stimulation in rat skeletal muscle membranes. Biochim. Biophys. Acta (Amst.), 1977, 464: 338-346. Eldefrawi, A.T., Eldefrawi, M.E., Albuquerque, E.X., Oliveira, A.C., Mansour, N.S., Adler, M., Daly, J., Brown, G.B., Burgermeister, W. and Witkop, B. Perhydrohistrionicotoxin: a potential ligand for the ion conductance modulator of the acetylcholine receptor. Proc. nat. Acad. Sci. (Wash.), 1977, 74: 2172-2176. Lindwell, O., Bj~rklund, A., Moore, R.Y. and Stener, U. Mesencephalic dopamine neurons projecting to neocortex. Brain Res., 1974, 81: 325-331. Louis, W.J., Doyle, A.E. and Sampson, R.G. The metabolic
A M A N T A D I N E , R I M A N T A D I N E , LEVODOPA A N D F I B R I L L A T I O N S fate of levodopa in m a n and animals. Clin. exp. Pharmacol. Physiol., 1974, 1: 341-346. Marsden, C.D. and Meadows, J.C. The effect of adrenaline on the contraction of h u m a n muscle. J. Physiol. (Lond.), 1970, 207: 429-448. McComas, A.J. Neuromuscular Functions and Disorders. Butterworths, Boston, MA, 1977: 72-79. Nastuk, W.L., Su, P.C. and Doubilet, P. Anticholinergic and membrane activities of amantadine in neuromuscular transmission. Nature (Lond.), 1976, 264: 76-79. Nie, N.H., Hull, C.H., Jenkins, J.G. and Bent, D.H. Statistical Package for the Social Sciences. McGraw-Hill, New York, 1975. Nott, M. Actions of levodopa on the cat soleus muscle. Clin. exp. Pharmacol. Physiol., 1975, 2: 413. Reddy, N B . and Engel, W.K. Differential effects of denervation on skeletal muscle adenylate cyclase (AC) and adrenergic receptor binding. Neurology (Minneap.), 1978, 28: 399-400. Reddy, N.B. and Engel, W.K. In vitro characterization of skeletal muscle beta-adrenergic receptors coupled to adenylate cyclase. Biochim. Biophys. Acta (Amst.), 1979, 585: 343-359.
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Robert, E.D. and Oester, Y.T. Nerve impulses and trophic effect. Arch. Neurol. (Chic.), 1970, 22: 57-63. Rogus, E.M., Cheng, L.C. and Ziegler, L. Beta adrenergic affect on Na+-K + transport in rat skeletal muscle. Biochim. Biophys. Acta (Amst.), 1977, 46: 347-355. Stone, T.W. Responses of neurones in the cerebral cortex and caudate nucleus to amantadine, amphetamine and dopamine. Brit. J. Pharmacol., 1976, 56: 101-110. Stone, T.W. Comparison of neuronal responses to amantadine and rimantadine: use of alpha-flupenthixol. Exp. Neurol., 1978, 62: 489-493. Tsai, M.C., Mansour, N.S., Eldefrawi, A.T., Eldefrawi, M.E. and Albuquerque, E.X. Mechanisms of action of amantadine on neuromuscular transmission. Mol. Pharmacol., 1978, 14: 787-803. Vermier, V.G., Harmon, J.B., Stump, J.M., Lynes, T.E., Marvel, J.P. and Smith, D.H. The toxicologic and pharmacologic properties of amantadine hydrochloride. Toxicol. appl. Pharmacol., 1969, 15: 642-665. Vrbova, G., Gordon T. and Jones, R. Nerve-Muscle Interaction. C h a p m a n and Hall, London, 1978: 81-104.
Electroencephalography and clinical N europto'siology, 1984, 57:174-177 Elsevier Scientific Publishers Ireland, Ltd.
T H E E F F E C T S O F A M A N T A D I N E , R I M A N T A D I N E AND L E V O D O P A O N T H E F R E Q U E N C Y OF F I B R I L L A T I O N P O T E N T I A L S IN D E N E R V A T E D M U S C L E ISRAEL YAAR
Neurophysiology Laboratory, Neurology Service. VAMC, Davis Park, Providence, R1 02908 (U.S.A.)
(Accepted for publication: July 8, 1983)
Catecholaminergic receptors exist throughout the CNS (Lindwell et al. 1974), and the peripheral neuromuscular system as well (Bowman and Roper 1966). Amantadine exerts a direct dopaminergic, and probably some additional effects of its own, on CNS neurons (Vermier et al. 1969; Bailey and Stone 1975), and on the peripheral neuromuscular system (Calesnich and Perko 1973; Tsai et al. 1978). Rimantadine, as an amantadine analog, has a non-dopaminergic direct effect on CNS neurons (Stone 1978), but is not known to have peripheral activities (Tsai et al. 1978). In this study we investigated the effects of amantadine, rimantadine and levodopa on the frequency of fibrillation potentials (FPs) in surgically denervated gastrocnemius-soleus muscle of rats.
Method and Material
Fifty-nine rats, type OM, 180-220 g were denervated under pentothal anesthesia (25-50 m g / k g : the right sciatic nerves were exposed in mid-thigh and segments 0.5 cm long were cut away. Then, for 11 days the rats were held in metabolic cages and fed on regular food. On the 12th and 13th days, in the afternoons, 19 rats were injected with 1 ml normal saline intraperitoneally (i.p.), 20 rats were injected i.p. with 1 ml of rimantadine (10 mg in normal saline), 13 rats were injected i.p. with 1 ml of amantadine (10 mg in normal saline) and 7 rats were injected i.p. with 1 ml of levodopa (10 mg in normal saline). On the 14th day the same injections were given but then, 2 h later electromyographic (EMG) recordings were performed. The E M G was performed with the rats
completely relaxed under pentothal anesthesia (25-50 mg/kg). The E M G amplifier filter settings were 300-10K c/sec. The same needle electrode, Disa 13L51, was used for all the rats. The E M G fiberoptic paper recorder (TECA) was set to record continuously in a raster mode for 5 sec, at sweep speed of 17 m s e c / c m and amplification of 100 ~V/cm. The needle electrode was inserted into the calf muscles and 3 consecutive recordings of 5 sec duration each were performed, each recording from a different location inside the muscle bulk. Adequate time of about 10 sec was allowed for insertional activities to subside completely. The animal's ambient temperature was kept reasonably warm with an infrared lamp. Fibrillation potentials were counted manually governed by the following quantitative and qualitative criteria: amplitudes within 20 and 300/~V; durations less than 2 msec; fast positive to negative deflections with sharp peaks. The animals were coded, fibrillations were counted, and only then was the code broken. The 3 counts for each animal were averaged. Statistical analysis was performed by analysis of variance, F tests for the Mahalonobis distance between groups and t test.
Results
The mean number of fibrillations for each group and its standard error are given in Table I. One-way analysis of variance (SPSS one-way) for the 4 groups revealed an overall significance: F = 3.26, df= 3; 55 and P = 0.028. The amantadine and the levodopa groups were found to be significantly different from the saline injected control group at
0013-4649/84/$03.00 © 1984 Elsevier Scientific Publishers Ireland, Ltd.
AMANTADINE, RIMANTADINE, LEVODOPA AND FIBRILLATIONS TABLE I Means of fibrillation potentials recorded in the test groups. Group
No. of animals
Mean no. of fibrillations
S.E.
Saline Rimantadine Amantadine Levodopa
19 20 13 7
99.0 77.5 65.5 43.4
13.0 8.6 10.9 5.9
One-way analysis of variance: F = 3.26, df = 3; 55, P = 0.028 TABLE II Mahalonobis distances: F statistics and significances between pairs of groups. Each statistic has 1 and 55 dr. Group Rimantadine Amantadine Levodopa
F= P= F= P= F= P=
Saline
Rimantadine
Amantadine
2.3 0.1 4.5 0.04 8.2 0.006
0.6 0.4 3.1 0.08 *
1.2 0.3
Canonical discriminant function: X2 = 9.1, df = 3, P = 0.028. * t test: t = 3.27, df = 25, P = 0.003.
the P = 0.05 level by the same test. F o u r g r o u p s ' m u l t i v a r i a t e F tests ( M a h a l o n o b i s distances) (Table II) showed significant differences b e t w e e n the saline injected c o n t r o l g r o u p ' s c e n t r o i d and the a m a n t a d i n e a n d the l e v o d o p a injected g r o u p s ' c e n t r o i d s (SPSS discriminant). Also, a t test ( T a b l e II) showed a significant difference b e t w e e n levodopa and rimantadine.
Discussion This study disclosed that b o t h t e v o d o p a and a m a n t a d i n e are effective, and r i m a n t a d i n e is ineffective, at least in the doses that were used, in reducing the frequency of F P s in surgically den e r v a t e d rat g a s t r o c n e m i u s - s o l e u s muscles. It is c o m m o n l y a c c e p t e d that F P s arise as a result of the various p l a s m a l e m m a l (PL) changes that take place in response to the d i s c o n t i n u e d t r a n s p o r t of as yet u n i d e n t i f i e d m y o t r o p h i c factor ( M F ) by the axon. This p o s t u l a t e d M F is considered not to be A C h a n d to be i n d e p e n d e n t of the
175
a x o n a l electrical activity ( R o b e r t a n d Oester 1970; M c C o m a s 1977; Rogus et al. 1977). T h e r e are several changes in the PL functional a n d structural characteristics, each of them m a y result in FPs ( B o w m a n a n d R o p e r 1966; M c C o m a s 1977; V r b o v a et al. 1978): (1) fall in the PL resting p o t e n t i a l , its r e d u c e d p e r m e a b i l i t y to K + and C1 , a n d changes in its action potential; (2) a m a n i - f o l d increase in e x t r a j u n c t i o n a l A C h R ( E J - A C h R ) , a n d increased EJ sensitivity to A C h ; (3) a two-fold increase in PL b e t a - a d r e n e r g i c receptors. Changes in P L ionic c o n d u c t a n c e a n d ( N a + + K +) p u m p activities are p r o b a b l y most i m p o r t a n t in initiating FPs. Both A C h R a n d the b e t a - a d r e n ergic receptors are c o u p l e d to ionic channels (Bowm a n a n d N o t t 1970; Eldefrawi et al. 1977; McC o m a s 1977; Rogus et al. 1977; A l b u q u e r q u e et al. 1978). The last is c o u p l e d to a d e n y l a t e cyclase ( R o g u s et al. 1977; R e d d y a n d Engel 1979). In the C N S b o t h a m a n t a d i n e a n d l e v o d o p a are c a p a b l e in activating b e t a - c a t e c h o l a m i n e r g i c rec e p t o r s ( D A receptor) ( B o w m a n and N o t t 1970; Stone 1976, 1978; Tsai et al. 1978). A m a n t a d i n e seems to have a d d i t i o n a l n o n - D A activities too (Stone 1978). R i m a n t a d i n e , though much m o r e active on C N S n e u r o n s than a m a n t a d i n e , does not act through D A receptors (Stone 1978). In the skeletal muscle it was f o u n d that a m a n t a d i n e acts on the ion c o n d u c t a n c e m o d u l a tor of the A C h R ( N a s t u k et al. 1976; Eldefrawi et al. 1977; A l b u q u e r q u e et al. 1978; Tsai et al. 1978), reducing the sensitivity of the E J - A C h R to i o n t o p h o r e t i c a l l y a p p l i e d ACh. It was also f o u n d that on J - A C h R a m a n t a d i n e has the same effect, reducing the sensitivity of the p o s t - j u n c t i o n a l m e m b r a n e to A C h with the p r o d u c t i o n of neurom u s c u l a r block. W h e n a p p l i e d for long p e r i o d s a m a n t a d i n e also depolarizes the EJ-PL. R i m a n t a d i n e was f o u n d to be inactive in these respects (Tsai et al. 1978). A m a n t a d i n e effect was pinp o i n t e d to ionic channels of the J- a n d E J - A C h R s ( A l b u q u e r q u e et al. 1978). L e v o d o p a is m e t a b o l i z e d to d o p a m i n e (DA), e p i n e p h r i n e and n o r e p i n e p h r i n e (Louis et al. 1974). These c a t e c h o l a m i n e s a u g m e n t PL b e t a 2 - a d r e n ergic receptors activity ( B o w m a n a n d N o t t 1970, 1978; M a r s d e n a n d M e a d o w s 1970; N o t t 1975) by c o u p l i n g to a d e n y l a t e cyclase a n d increased c A M P
176 synthesis ( R e d d y a n d Engel 1978). This releases an u n i d e n t i f i e d factor that acts directly on ( N a + + K + ) - A T P a s e . It is also p o s s i b l e t h a t the c a t e c h o l a m i n e s interact directly with the P L a d e n y l a t e cyclase, an i n t e r a c t i o n that requires a c e r t a i n c o n f i g u r a t i o n of the c a t e c h o l a m i n e molecule, and is not m e d i a t e d by b e t a - a d r e n e r g i c rec e p t o r s (Cheng et al. 1977; R e d d y a n d Engel 1979). Speculating on the basis of the a b o v e d a t a it seems that a m a n t a d i n e might reduce F P s b y its effect on the J- a n d E J - A C h R s ionic channels, a n d the l e v o d o p a effects are p r o b a b l y m e d i a t e d b y its m e t a b o l i t e s , acting on the PL b e t a - a d r e n e r g i c receptors, or directly on the P L ( N a + + K +)-ATPase.
I. YAAR logique normal, et 3 groupes, avec injection i.p. d ' a m a n t a d i n e , de r i m a n t a d i n e ou de l e v o d o p a (50 m g / k g de c h a q u e substance) p e n d a n t 3 j o u r s cons6cutifs. Le 146me jour, 2 h apr6s la 3~me injection, I ' E M G du gastrocnbmien-soleus 6tait recueilli, sous anesth6sie au p e n t o t h a l , et les potentiels de fibrillation 6taient compt+s. L ' a n a l y s e statistique a montr6 une r6duction significative des fibrillations, apr6s injection de l e v o d o p a et d ' a m a n t a d i n e . La r i m a n t a d i n e n'a pas modifi6 la fr6quence des fibrillations. On sugg6re que la levod o p a et l ' a m a n t a d i n e ont un effet stabilisateur sur la m e m b r a n e p l a s m a t i q u e d6nerv6e. The author wishes to thank Mr. Gregory Zirzow for his technical assistance, and Mrs. Deloris N. Brown for typing this manuscript.
Summary Right m i d - t h i g h sciatic d e n e r v a t i o n was perf o r m e d in 59 rats. Eleven d a y s later they were assigned into 4 groups: a c o n t r o l g r o u p that was injected i n t r a p e r i t o n e a l l y with n o r m a l saline, a n d 3 test groups that were injected i n t r a p e r i t o n e a l l y with a m a n t a d i n e , r i m a n t a d i n e or l e v o d o p a (50 m g / k g each), for 3 consecutive days. O n the fourteenth day, 2 h after the third injection, electrom y o g r a p h y of the soleus-gastrocnemius muscles was p e r f o r m e d u n d e r p e n t o t h a l anesthesia. F i b r i l l a t i o n p o t e n t i a l s were counted. T h e statistical analysis showed significant r e d u c t i o n of fibrillations s e c o n d a r y to l e v o d o p a a n d to a m a n t a d i n e injections. R i m a n t a d i n e d i d not change the frequency of fibrillations. A stabilizing effect of l e v o d o p a a n d a m a n t a d i n e on the d e n e r v a t e d p l a s m a l e m m a is postulated.
R6sum6 Effets de l'amantadine, de la rimantadine et la levodopa sur la frOquence des potentiels de fibrillation clans les muscles dOnervks O n a effectu6 chez 59 rats, une d 6 n e r v a t i o n du sciatique /l mi-cuisse, /i droite. Onze j o u r s apr6s, les a n i m a u x ont 6t6 divis6s en 4 groupes: un g r o u p e t6moin, avec injection i.p. de s6rum physio-
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