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Unilateral peri-substantia nigra catecholaminergic lesion and amygdala kindling
388
Brain Research, 370(1986) 388-392 Elsevier
BRE 21492
Unilateral peri-substantia nigra catecholaminergic lesion and amygdala kindling BRUCE J. ALBALA l , SOLOMON L. MOSHI~,1,2, JOSEPH F. CUBELLS 3, NANSIE S. SHARPLESS 1.4and MAYNARD H. MAKMAN5-6 Departments oflNeurology, 2pediatrics, SNeuroscience, 4psychiatry, 5Biochemistry and 6Molecular Pharmacology, Albert Einstein College of Medicine. Bronx, NY 10461 ( U. S. A.) (Accepted December 17th, 1985) Key words: seizure - - epilepsy - - convulsion - - kindling - - substantia nigra - - catecholamine - - amygdala - - rat
Recent evidence suggests that the substantia nigra (SN) may be involved in the modulation of kindled seizures in adult rats. In this report we investigated the role of the dopaminergic nigrostriatal pathway in mediating the SN effect on seizures by lesioning this pathway with unilateral infusions of 6-hydroxydopamine (6-OHDA) in the vicinity of the right SN with or without desmethylimipramine pretreatment. Our data suggest that the facilitation of amygdala kindling observed following 6-OHDA lesion in the vicinity of the ipsilateral SN is due to norepinephrine depletion of the ipsilateral forebrain. Selective destruction of the nigrostriatal dopaminergic neurons neither facilitates nor inhibits the development of amygdala-kindled convulsions in adult rats.
Recent evidence has suggested that the substantia nigra (SN) has a crucial role in seizures 4.6,1°,1a. Electrophysiological studies have indicated that the epileptiform activity propagates through the SN and deoxyglucose metabolic studies have uniformly demonstrated increased metabolic activity in the SN following diverse generalized seizures in mature animals (see refs. 4 and 14 for review). While these studies suggest that the SN plays at least a passive role in seizure mechanisms, lesion and stimulation (chemical and electrical) studies have d e m o n s t r a t e d that manipulation of the SN results in modification of seizures as well (see refs. 4 and 14 for review). Thus the available data convincingly implicate the SN in the seizure process whether it be the p r o p a g a t i o n or termination of seizures. The specific nigral pathway which might subserve these events is as yet unknown. The present study was u n d e r t a k e n to examine the influence of one of the m a j o r SN efferents, the dopaminergic nigrostriatal pathway 7,13, on seizures electrically kindled from the amygdala of the adult rat. Male S p r a g u e - D a w l e y rats, weighing 200-250 g, were randomly divided into 3 groups. Two groups of rats were unilaterally lesioned with 8/~g of 6-hydrox-
ydopamine ( 6 - O H D A ) in buffered ascorbate vehicle infused just above the pars c o m p a c t a of the right SN as previously described 5 at the rate of 0.2/~i/min for a total of 5 min. To protect the adjacent norepinephrine neurons, one group of rats was p r e t r e a t e d with desmethylimipramine ( D M I ; 25 mg/kg, i.p.) administered 30 min prior to the acute infusion of 6 - O H D A . Thus, the 3 groups of animals consisted of 6 - O H D A treated (n = 10), D M I + 6 - O H D A - t r e a t e d (n = 5) and N A I V E rats (n = 7) which were only handled. As a preliminary behavioral assessment of the efficacy of the unilateral perinigral lesion all rats were systemically (i.p.) administered an a p o m o r p h i n e (2 mg/kg) challenge two weeks after surgery. The degree of rotation resulting from the d o p a m i n e agonist was measured in an a u t o m a t e d r o t a m e t e r bowl apparatus for 20 min 5. F o r all animals, except for the group of animals later i m p l a n t e d with electrodes in the amygdala contralateral to the side of lesion, analyses of d o p a m i n e ( D A ) and n o r e p i n e p h r i n e (NE) concentrations of striatum and amygdala were later carried out. These analyses served as the final indicators of the extent of the lesion. Initial selection of animals for electrode implantation was based on the be-
Correspondence: S.L. Mosh6, Department of Neurology, Albert Einstein College of Medicine. F, G-9, 1300 Morris Park Avenue, Bronx. NY 10461, U.S.A.
389 havioral response to apomorphine of 3 or more rotations per minute (rpm) contraversive to the side of the lesion. There was no significant difference observed for this behavior between rats later implanted ipsilaterally (X = 7.9 rpm) or contralaterally (X = 7.6 rpm) with an amygdala electrode. Four weeks after the lesion procedure the rats were again anesthetized and implanted in the amygdala with a chronic bipolar electrode (Plastic Products MS 303/2) as previously described 15. Four rats in the 6 - O H D A group were implanted in the left amygdala contralaterally to the lesion, while all others were implanted in the right, ipsilateral amygdala. After one week of recovery the amygdala afterdischarge (AD) threshold (defined as the lowest current which produced an A D ) was determined 15. The kindling procedure consisted of hourly, one second suprathreshold stimulations of 400 ~ A (peak to peak) sinusoidal current. The behavioral seizures were classified into 5 stages as described by Racine16: stage 0 was characterized by behavioral arrest, stage 1 by chewing, stage 2 by head nodding, stage 3 by unilateral forelimb clonus, stage 4 by the addition of bilateral symmetrical forelimb clonus with rearing and stage 5 by all these behaviors and falling. All animals were kindled until they exhibited 3 generalized stage 5 motor convulsions. Two weeks after the last seizure the rats were decapitated, the brains were removed and placed in icecold saline. The electrode tip location was ascer-
tained at this point with the aid of a dissecting microscope and the amygdata and striatum from the ipsilaterally implanted rats were removed from both hemispheres as previously described 15. The tissues were immediately frozen on dry-ice, weighed, homogenized in ice-cold 0.1 N HC104, and then stored frozen at - 3 0 °C until analyzed for D A and NE. After adjustment to p H 6.1, the extracts were passed through small cation exchange columns and then the catecholamines in the column eluates were adsorbed onto alumina at pH 8.4. The alumina was washed, eluted with 0.1 M oxalic acid, and aliquots of the eluates were analyzed by high-performance liquid chromatography with electrochemical detection (column: Biophase ODS-5 tim from Bioanalytical Systems; mobile phase: 0.1 M chloroacetate, pH 3.0, 1 mM NazEDTA, 0.14 mM sodium octylsulfate, and 4% methanol at 1.0 ml/min). Quantitation was performed by determination of peak heights relative to the height of an internal standard (dihydroxybenzylamine) added to the extracts prior to column adsorption. The statistical methods used for the analysis of the data consisted of one-way analysis of variance with post hoc comparisons (t-tests). The kindling data are presented in Table I. The 6-OHDA-lesioned rats that were stimulated in the ipsilateral to the lesion amygdala exhibited longer ADs, more severe seizures at threshold stimulation and kindled significantly faster than any other group. The D M I + 6-OHDA-lesioned rats and the 6-
TABLE I Kindling parameters of amygdala seizures in rats with right peri-substantia nigra lesions
Values are means _+S.E.M. ADT = AD threshold; the term kindling rate is defined as the number of AD producing stimulations required for the development of the first stage 5 (K5) generalized convulsion. The various kindling stages are described in the text. The letters depict the individual group differences within a row (post hoc t-tests), n.s., not significant. Right amygdala kindling
ADT (,uA) ADT duration (s) Kindling stage at ADT Kindling rate AD duration at K5 (s) n
* P < 0.03, relative to B and C. ** P < 0.03, relative to B, C and D.
Left amygdala kindling
(A) 6-OHDA
(B) DM1 + 6-OHDA
(C) NAIVE
(D) 6-OHDA
116.7+21.0 57.3+12.0" 2.0+0.7** 3.3_+0.2** 102.8_+21.0
240.0+68.0 22.0-+4.0 0.2_+0.2 9.6_+2.3 75.6_+13.0
246.4_+44.0 27.7_+4.0 0.0 10.4_+1.4 63.6_+13.0
181.3+60.0 32.5-+8.0 0.5-+0.3 11.5_+1.8 67.5_+25.0
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390
OHDA
rats that were kindled f r o m the a m y g d a l a
6-OHDA
and N A I V E
groups. The D A concentra-
contralateral to the SN lesion did not significantly dif-
tions were significantly lower in the right striatum (le-
fer from the N A I V E
sioned side) of the 6 - O H D A
rats in any of the kindling pa-
rameters. The D A
rats than in the N A I V E and N E concentrations
of the left and
right striatum are p r e s e n t e d in Fig. I A and B. T h e
and D M I + 6 - O H D A
(F2.~5 = 142.8, P = 0.000).
The lesioned groups did not differ from each other (t-test, P > 0.7).
concentrations of N E and D A in the left striatum
The 6 - O H D A - i n d u c e d
changes in the a m y g d a l a
(contralateral to the lesion) did not significantly dif-
paralleled those o b s e r v e d in the striatum (Fig. 1C
fer a m o n g the treatment groups (k2,t_~ = 0.07 and 1.5,
and D). The N E and D A concentrations of the left
respectively). T h e 6 - O H D A
lesion significantly low-
ered the N E concentrations
in the right striatum
amygdala did not differ significantly a m o n g the 3 groups (F2,15 = 0.43 and 0.05, respectively).
The
(k2.t5 = 8.8, P < 0.01) w h i l e the D M I pretreatment
6-OHDA
lesion of the SN significantly l o w e r e d the
clearly protected the N E concentration in the D M I +
N E concentration of the a m y g d a l a on the kindled
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Fig. 1. Striatal (A, B) and amygdala (C, D) catecholamine concentrations (ng/gram of wet tissue) in 6-OHDA SN-lesioned rats and NAIVE controls two weeks after the last amygdala kindled seizure. Each bar is the mean + S.E.M.; n: 6-OHDA = 6, DMI + 6-OHDA = 5, NAIVE = 7. A: striatal DA concentrations; * P < 0.001, post hoc t-tests from NAIVE. B: striatal NE concentrations; • P < 0.01, post hoc t-tests from NAIVE and DMI + 6-OHDA. C: amygdala DA concentrations; * P < 0.02, post hoc t-tests from NAIVE. D: amygdala NE concentrations; * P < 0.05, post hoc t-tests from NAIVE and DMI + 6-OHDA. There are no statistically significant differences in the concentrations of either catecholamine in the left striata or amygdala among the groups.
391 right side as compared to both the DMI + 6-OHDA and NAIVE rats (F2,15 = 6.3, P < 0.01). The amygdala NE concentrations did not significantly differ between the latter two groups (t-test, P > 0.3). The DA concentrations of the right - - kindled - - amygdala was significantly lower for both the 6-OHDA and DMI + 6-OHDA groups as compared to N A I V E (F2,15 = 10.6, P < 0.01) but did not differ from each other (t-test, P > 1.0). Thus all catecholaminergic depletions occurred ipsilaterally to the SN lesion. The lowered striatal and amygdala DA and NE levels in the present experiments are not the result of kindling per se 3 or of a direct local action of 6-OHDA due to globally diffuse spread of 6-OHDA to the amygdala. While kindling has been shown to affect the amine content of the kindled structure 3, one would expect similar changes in all 3 treatment groups as long as the rats were equivalently kindled. All animals in the present study were kindled to the same generalized stage 5 seizure level; the NAIVE group and DMI + 6-OHDA group also did not differ in any of the kindling parameters. The N A I V E animals did not demonstrate any significant hemispheric differences in D A or NE concentrations in either the striatum or amygdala. Therefore the observed depletions are not the result of the kindling process or the resulting seizures. If the catecholamine depletion were the result of direct chemical spread, then the infused droplet would be expected to cross the midline long before it could spread from the SN to the amygdala. Such a spread across the midline should result in contralateral biochemical effects, produced by the contralateral lesion of the contiguous SN in the other hemisphere. Yet the biochemical concentrations of DA and NE levels in the contralateral striata and amygdala of all tested animals did not differ among treatment groups. Furthermore, rats kindled from the contralateral amygdala did not exhibit any increases in seizure susceptibility. It is more likely that the catecholamine depletions observed are the result of the ipsilateral destruction of catecholaminergic
projections to the striatum and amygdala 11,~3. In this respect, our method of inducing the catecholaminergic depletions is different from those previously described, in which 6-OHDA was either infused intraventricularly (thereby producing diffuse effects) H2 or in the kindled site 8. Furthermore, in previous studies 1.9 the extent of striatal DA depletion (40-65%) was not sufficient to rule out the influence of the nigrostriatal pathway in kindling. The main conclusion of our study is that in adult rats virtually complete destruction of the perinigral dopaminergic projections to the striatum or amygdala does not modify kindling. While these results do not entirely rule out the participation of the dopaminergic nigrostriatal pathway in the nigral-mediated seizure modification, they strongly suggest that the presence of this specific pathway is not necessary for the development or suppression of generalized kindled seizures. Hence, the nigral effects on seizures may be mediated by other SN efferents. The rats which received 6-OHDA without DMI pretreatment showed significant facilitation in the development and generalization of kindled seizures. NE depletion of the amygdala or other areas is probably responsible for the enhancement of kindling observed in the 6-OHDA group. This is consistent with previous studies implicating NE in the rapid propagation and generalization of seizures 1.2.s,9,12. In our study, all NE depletions were found to be ipsilateral to the lesion and kindling was enhanced only when the ipsilateral amygdala were stimulated. These resuits support the hypothesis that the propagation of seizures from a kindled focus occurs within the ipsilateral hemisphereS.
1 Corcoran, M.E. and Mason, S.T., Role of forebrain catecholamines in amygdaloid kindling, Brain Research, 190 (1980) 473-484. 2 Ehlers, C.L., Clifton, D.K. and Sawyer, C.H., Facilitation of amygdalakindling in the rat by transected ascending noradrenergic pathways, Brain Research, 189 (1980) 274-278. 3 Engel, J., Jr. and Sharpless, N.S., Long-lastingdepletion of
dopamine in the rat amygdalainduced by kindling stimulation, Brain Research, 136 (1977) 381-386. 4 Gale, K., Mechanisms of seizure control mediated by gamma-aminobutyric acid: role of the substantia nigra, Fed. Proc. Fed. Am. Soc. Exp. Biol., 44 (1985) 2414-2424, 5 Hirschhorn, I.D., Hittner, D., Gardner, E.L., Cubells, J. and Makman, M,H., Evidence for a role of endogenous
Supported in part by Grants NS 20253 and NS 09649 from the NINCDS and a grant from the Epilepsy Foundation of America. We thank Ms. Mariann Downing for her expert technical assistance and Ms. Donna Platyan for her help in the preparation of the manuscript.
392
6
7
8
9
10
11
opioids in the nigrostriatal system: influence ot naloxone and morphine on nigrostriatal dopaminergic st, persensitivit y, Brain Research, 270 (1983) 109-117. ladarola, M.J. and Gale, K., Substantia nigra: site of anticonvulsant activity mediated by gamma-aminobutyric acid, Science, 218 (1982) 1237-124t). Loughlin, S.E. and Fallon, J.H., Substantia nigra and ventral tegmental area projections to cortex: topography and collateralization, Neuroscience, 11 (1984) 425-435. Mclntyre, D.C., Amygdala kindling in rats: facilitation after local amygdala norepinephrine depletion with 6-hydroxydopamine, Exp. Neurol., 69 (1980) 395-407. Mclntyre, D.C., Saari, M. and Pappas, B.A., Potentiation of amygdala kindling in adult or infant rats by injection of 6hydroxydopamine, Exp. Neurol., 63 (1979) 527-544. McNamara, J.O., Galloway, M.T., Rigsbee, L.C. and Shin, C., Evidence implicating substantia nigra in regulation of kindled seizure threshold, J. Neurosci., 4 (1984) 2410-2417. Meibach, R.C. and Katzman, R., Origin, course and termi-
nation of dopaminergic substantia nigra neurons projecting to the amygdaloid complex m the cat, Neuroscience, 6 (1981) 2159-2171. 12 Mohr, E. and Corcoran, M.E., Depletion ol noradremdinc and amygdaloid kindling, Exp. Neurol., 72 (1981) 507-51 I. 13 Moore, R.Y. and Bloom, F.E,, Central catecholamine neuron systems: anatomy and physiology of the norepinephrine and epinepht'ine systems, Annu. Rev. Neurosci, 2 (1979) 113-168.
14 Mosh6, S,L., Ackermann, R.F., Albala, B.J. and Okada. R., The role of substantia nigra in seizures of developing animals. In .I.A. Wada (Ed.), Kindling, Vol. 3, Raven press. New York, in press. 15 Moshe, S.L., Sharpless, N.S. and Kaplan, J., Kindling in developing rats: variability of afterdischarge thresholds with age, Brain Research. 211 ( 1981 ) 190-195. 16 Racine, R.J., Modification of seizure activity by electrical stimulation. II. Motor seizures. Electroencephalogr. Clin. Neurophysiol., 32 (1972) 281-294.
Brain Research, 370(1986) 388-392 Elsevier
BRE 21492
Unilateral peri-substantia nigra catecholaminergic lesion and amygdala kindling BRUCE J. ALBALA l , SOLOMON L. MOSHI~,1,2, JOSEPH F. CUBELLS 3, NANSIE S. SHARPLESS 1.4and MAYNARD H. MAKMAN5-6 Departments oflNeurology, 2pediatrics, SNeuroscience, 4psychiatry, 5Biochemistry and 6Molecular Pharmacology, Albert Einstein College of Medicine. Bronx, NY 10461 ( U. S. A.) (Accepted December 17th, 1985) Key words: seizure - - epilepsy - - convulsion - - kindling - - substantia nigra - - catecholamine - - amygdala - - rat
Recent evidence suggests that the substantia nigra (SN) may be involved in the modulation of kindled seizures in adult rats. In this report we investigated the role of the dopaminergic nigrostriatal pathway in mediating the SN effect on seizures by lesioning this pathway with unilateral infusions of 6-hydroxydopamine (6-OHDA) in the vicinity of the right SN with or without desmethylimipramine pretreatment. Our data suggest that the facilitation of amygdala kindling observed following 6-OHDA lesion in the vicinity of the ipsilateral SN is due to norepinephrine depletion of the ipsilateral forebrain. Selective destruction of the nigrostriatal dopaminergic neurons neither facilitates nor inhibits the development of amygdala-kindled convulsions in adult rats.
Recent evidence has suggested that the substantia nigra (SN) has a crucial role in seizures 4.6,1°,1a. Electrophysiological studies have indicated that the epileptiform activity propagates through the SN and deoxyglucose metabolic studies have uniformly demonstrated increased metabolic activity in the SN following diverse generalized seizures in mature animals (see refs. 4 and 14 for review). While these studies suggest that the SN plays at least a passive role in seizure mechanisms, lesion and stimulation (chemical and electrical) studies have d e m o n s t r a t e d that manipulation of the SN results in modification of seizures as well (see refs. 4 and 14 for review). Thus the available data convincingly implicate the SN in the seizure process whether it be the p r o p a g a t i o n or termination of seizures. The specific nigral pathway which might subserve these events is as yet unknown. The present study was u n d e r t a k e n to examine the influence of one of the m a j o r SN efferents, the dopaminergic nigrostriatal pathway 7,13, on seizures electrically kindled from the amygdala of the adult rat. Male S p r a g u e - D a w l e y rats, weighing 200-250 g, were randomly divided into 3 groups. Two groups of rats were unilaterally lesioned with 8/~g of 6-hydrox-
ydopamine ( 6 - O H D A ) in buffered ascorbate vehicle infused just above the pars c o m p a c t a of the right SN as previously described 5 at the rate of 0.2/~i/min for a total of 5 min. To protect the adjacent norepinephrine neurons, one group of rats was p r e t r e a t e d with desmethylimipramine ( D M I ; 25 mg/kg, i.p.) administered 30 min prior to the acute infusion of 6 - O H D A . Thus, the 3 groups of animals consisted of 6 - O H D A treated (n = 10), D M I + 6 - O H D A - t r e a t e d (n = 5) and N A I V E rats (n = 7) which were only handled. As a preliminary behavioral assessment of the efficacy of the unilateral perinigral lesion all rats were systemically (i.p.) administered an a p o m o r p h i n e (2 mg/kg) challenge two weeks after surgery. The degree of rotation resulting from the d o p a m i n e agonist was measured in an a u t o m a t e d r o t a m e t e r bowl apparatus for 20 min 5. F o r all animals, except for the group of animals later i m p l a n t e d with electrodes in the amygdala contralateral to the side of lesion, analyses of d o p a m i n e ( D A ) and n o r e p i n e p h r i n e (NE) concentrations of striatum and amygdala were later carried out. These analyses served as the final indicators of the extent of the lesion. Initial selection of animals for electrode implantation was based on the be-
Correspondence: S.L. Mosh6, Department of Neurology, Albert Einstein College of Medicine. F, G-9, 1300 Morris Park Avenue, Bronx. NY 10461, U.S.A.
389 havioral response to apomorphine of 3 or more rotations per minute (rpm) contraversive to the side of the lesion. There was no significant difference observed for this behavior between rats later implanted ipsilaterally (X = 7.9 rpm) or contralaterally (X = 7.6 rpm) with an amygdala electrode. Four weeks after the lesion procedure the rats were again anesthetized and implanted in the amygdala with a chronic bipolar electrode (Plastic Products MS 303/2) as previously described 15. Four rats in the 6 - O H D A group were implanted in the left amygdala contralaterally to the lesion, while all others were implanted in the right, ipsilateral amygdala. After one week of recovery the amygdala afterdischarge (AD) threshold (defined as the lowest current which produced an A D ) was determined 15. The kindling procedure consisted of hourly, one second suprathreshold stimulations of 400 ~ A (peak to peak) sinusoidal current. The behavioral seizures were classified into 5 stages as described by Racine16: stage 0 was characterized by behavioral arrest, stage 1 by chewing, stage 2 by head nodding, stage 3 by unilateral forelimb clonus, stage 4 by the addition of bilateral symmetrical forelimb clonus with rearing and stage 5 by all these behaviors and falling. All animals were kindled until they exhibited 3 generalized stage 5 motor convulsions. Two weeks after the last seizure the rats were decapitated, the brains were removed and placed in icecold saline. The electrode tip location was ascer-
tained at this point with the aid of a dissecting microscope and the amygdata and striatum from the ipsilaterally implanted rats were removed from both hemispheres as previously described 15. The tissues were immediately frozen on dry-ice, weighed, homogenized in ice-cold 0.1 N HC104, and then stored frozen at - 3 0 °C until analyzed for D A and NE. After adjustment to p H 6.1, the extracts were passed through small cation exchange columns and then the catecholamines in the column eluates were adsorbed onto alumina at pH 8.4. The alumina was washed, eluted with 0.1 M oxalic acid, and aliquots of the eluates were analyzed by high-performance liquid chromatography with electrochemical detection (column: Biophase ODS-5 tim from Bioanalytical Systems; mobile phase: 0.1 M chloroacetate, pH 3.0, 1 mM NazEDTA, 0.14 mM sodium octylsulfate, and 4% methanol at 1.0 ml/min). Quantitation was performed by determination of peak heights relative to the height of an internal standard (dihydroxybenzylamine) added to the extracts prior to column adsorption. The statistical methods used for the analysis of the data consisted of one-way analysis of variance with post hoc comparisons (t-tests). The kindling data are presented in Table I. The 6-OHDA-lesioned rats that were stimulated in the ipsilateral to the lesion amygdala exhibited longer ADs, more severe seizures at threshold stimulation and kindled significantly faster than any other group. The D M I + 6-OHDA-lesioned rats and the 6-
TABLE I Kindling parameters of amygdala seizures in rats with right peri-substantia nigra lesions
Values are means _+S.E.M. ADT = AD threshold; the term kindling rate is defined as the number of AD producing stimulations required for the development of the first stage 5 (K5) generalized convulsion. The various kindling stages are described in the text. The letters depict the individual group differences within a row (post hoc t-tests), n.s., not significant. Right amygdala kindling
ADT (,uA) ADT duration (s) Kindling stage at ADT Kindling rate AD duration at K5 (s) n
* P < 0.03, relative to B and C. ** P < 0.03, relative to B, C and D.
Left amygdala kindling
(A) 6-OHDA
(B) DM1 + 6-OHDA
(C) NAIVE
(D) 6-OHDA
116.7+21.0 57.3+12.0" 2.0+0.7** 3.3_+0.2** 102.8_+21.0
240.0+68.0 22.0-+4.0 0.2_+0.2 9.6_+2.3 75.6_+13.0
246.4_+44.0 27.7_+4.0 0.0 10.4_+1.4 63.6_+13.0
181.3+60.0 32.5-+8.0 0.5-+0.3 11.5_+1.8 67.5_+25.0
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390
OHDA
rats that were kindled f r o m the a m y g d a l a
6-OHDA
and N A I V E
groups. The D A concentra-
contralateral to the SN lesion did not significantly dif-
tions were significantly lower in the right striatum (le-
fer from the N A I V E
sioned side) of the 6 - O H D A
rats in any of the kindling pa-
rameters. The D A
rats than in the N A I V E and N E concentrations
of the left and
right striatum are p r e s e n t e d in Fig. I A and B. T h e
and D M I + 6 - O H D A
(F2.~5 = 142.8, P = 0.000).
The lesioned groups did not differ from each other (t-test, P > 0.7).
concentrations of N E and D A in the left striatum
The 6 - O H D A - i n d u c e d
changes in the a m y g d a l a
(contralateral to the lesion) did not significantly dif-
paralleled those o b s e r v e d in the striatum (Fig. 1C
fer a m o n g the treatment groups (k2,t_~ = 0.07 and 1.5,
and D). The N E and D A concentrations of the left
respectively). T h e 6 - O H D A
lesion significantly low-
ered the N E concentrations
in the right striatum
amygdala did not differ significantly a m o n g the 3 groups (F2,15 = 0.43 and 0.05, respectively).
The
(k2.t5 = 8.8, P < 0.01) w h i l e the D M I pretreatment
6-OHDA
lesion of the SN significantly l o w e r e d the
clearly protected the N E concentration in the D M I +
N E concentration of the a m y g d a l a on the kindled
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Fig. 1. Striatal (A, B) and amygdala (C, D) catecholamine concentrations (ng/gram of wet tissue) in 6-OHDA SN-lesioned rats and NAIVE controls two weeks after the last amygdala kindled seizure. Each bar is the mean + S.E.M.; n: 6-OHDA = 6, DMI + 6-OHDA = 5, NAIVE = 7. A: striatal DA concentrations; * P < 0.001, post hoc t-tests from NAIVE. B: striatal NE concentrations; • P < 0.01, post hoc t-tests from NAIVE and DMI + 6-OHDA. C: amygdala DA concentrations; * P < 0.02, post hoc t-tests from NAIVE. D: amygdala NE concentrations; * P < 0.05, post hoc t-tests from NAIVE and DMI + 6-OHDA. There are no statistically significant differences in the concentrations of either catecholamine in the left striata or amygdala among the groups.
391 right side as compared to both the DMI + 6-OHDA and NAIVE rats (F2,15 = 6.3, P < 0.01). The amygdala NE concentrations did not significantly differ between the latter two groups (t-test, P > 0.3). The DA concentrations of the right - - kindled - - amygdala was significantly lower for both the 6-OHDA and DMI + 6-OHDA groups as compared to N A I V E (F2,15 = 10.6, P < 0.01) but did not differ from each other (t-test, P > 1.0). Thus all catecholaminergic depletions occurred ipsilaterally to the SN lesion. The lowered striatal and amygdala DA and NE levels in the present experiments are not the result of kindling per se 3 or of a direct local action of 6-OHDA due to globally diffuse spread of 6-OHDA to the amygdala. While kindling has been shown to affect the amine content of the kindled structure 3, one would expect similar changes in all 3 treatment groups as long as the rats were equivalently kindled. All animals in the present study were kindled to the same generalized stage 5 seizure level; the NAIVE group and DMI + 6-OHDA group also did not differ in any of the kindling parameters. The N A I V E animals did not demonstrate any significant hemispheric differences in D A or NE concentrations in either the striatum or amygdala. Therefore the observed depletions are not the result of the kindling process or the resulting seizures. If the catecholamine depletion were the result of direct chemical spread, then the infused droplet would be expected to cross the midline long before it could spread from the SN to the amygdala. Such a spread across the midline should result in contralateral biochemical effects, produced by the contralateral lesion of the contiguous SN in the other hemisphere. Yet the biochemical concentrations of DA and NE levels in the contralateral striata and amygdala of all tested animals did not differ among treatment groups. Furthermore, rats kindled from the contralateral amygdala did not exhibit any increases in seizure susceptibility. It is more likely that the catecholamine depletions observed are the result of the ipsilateral destruction of catecholaminergic
projections to the striatum and amygdala 11,~3. In this respect, our method of inducing the catecholaminergic depletions is different from those previously described, in which 6-OHDA was either infused intraventricularly (thereby producing diffuse effects) H2 or in the kindled site 8. Furthermore, in previous studies 1.9 the extent of striatal DA depletion (40-65%) was not sufficient to rule out the influence of the nigrostriatal pathway in kindling. The main conclusion of our study is that in adult rats virtually complete destruction of the perinigral dopaminergic projections to the striatum or amygdala does not modify kindling. While these results do not entirely rule out the participation of the dopaminergic nigrostriatal pathway in the nigral-mediated seizure modification, they strongly suggest that the presence of this specific pathway is not necessary for the development or suppression of generalized kindled seizures. Hence, the nigral effects on seizures may be mediated by other SN efferents. The rats which received 6-OHDA without DMI pretreatment showed significant facilitation in the development and generalization of kindled seizures. NE depletion of the amygdala or other areas is probably responsible for the enhancement of kindling observed in the 6-OHDA group. This is consistent with previous studies implicating NE in the rapid propagation and generalization of seizures 1.2.s,9,12. In our study, all NE depletions were found to be ipsilateral to the lesion and kindling was enhanced only when the ipsilateral amygdala were stimulated. These resuits support the hypothesis that the propagation of seizures from a kindled focus occurs within the ipsilateral hemisphereS.
1 Corcoran, M.E. and Mason, S.T., Role of forebrain catecholamines in amygdaloid kindling, Brain Research, 190 (1980) 473-484. 2 Ehlers, C.L., Clifton, D.K. and Sawyer, C.H., Facilitation of amygdalakindling in the rat by transected ascending noradrenergic pathways, Brain Research, 189 (1980) 274-278. 3 Engel, J., Jr. and Sharpless, N.S., Long-lastingdepletion of
dopamine in the rat amygdalainduced by kindling stimulation, Brain Research, 136 (1977) 381-386. 4 Gale, K., Mechanisms of seizure control mediated by gamma-aminobutyric acid: role of the substantia nigra, Fed. Proc. Fed. Am. Soc. Exp. Biol., 44 (1985) 2414-2424, 5 Hirschhorn, I.D., Hittner, D., Gardner, E.L., Cubells, J. and Makman, M,H., Evidence for a role of endogenous
Supported in part by Grants NS 20253 and NS 09649 from the NINCDS and a grant from the Epilepsy Foundation of America. We thank Ms. Mariann Downing for her expert technical assistance and Ms. Donna Platyan for her help in the preparation of the manuscript.
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