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Inhibitory effects of 6-hydroxydopamine on the clonic convulsions induced by electroshock and decapitation
Ncuropharmucology, 1975. 14, 579-583. Pergamon Press Printed in G:. Britain.
INHIBITORY EFFFKTS OF 6-HYDROXYDOPAMINE ON THE CLONIC CONVULSIONS INDUCED BY ELE~ROSHOCK AND DECAPITATION T. FUKUDA,Y. ARAKIand N. SUENAGA Department of Pharmacology, Faculty of Medicine, Kyushu University, Fukuoka 812, Japan (Accepted 18 December 1974) Summary-Effects of intraven~i~ul~r injection of 6-hy~oxydopamine f6-OHDA) on maximal electroshock seizures and decapitation convulsions were investigated in mice. The incidence of the clonic phase of maximal electroshock seizure was suppressed by 6-OHDA. The time course of the suppression was in good agreement with the decreased level of whole brain norepinephrine. The incidence of clonic convulsions following decapitation was also suppressed by 6-OHDA. On the contrary, the tonic phase of maximal electroshock seizure was potentiated by the treatment. The incidence of the clonic phase of maximal electroshock seizure and of de~p~tation convulsions were well correlated in 6-OHDA treated mice which had been exposed to maximal electroshock seizure and then decapitated. It is suggested that the central catecholaminergic mechanism concerned with the clonic phase in maximal electroshock seizure is analogous to that concerned with decapitation convulsions and different from that underlying the tonic phase of maximal electroshock seizure.
Recent investigations suggest that brain catecholamines play a role in the manifestation of convulsions. Post-decapitation convulsions in rats and mice are inhibited by pretreatment with reserpine or other amine depleting agents (FRIEDMAN, 1964; KAMATand SETH, 1971; EICHBAUM and YASAKA,1973). On the other hand, reserpine is known to increase the su~eptibility of animals to electroshock seizures (CHFZN, ENSOR and BOHNER, 1954; DE SCHAEPDRYVER, PIET-ITand DELAUNOIS, 1962; AZZARO,WENGER, CRAIGand STITZEL,1972; KILIANand FREY,1973; WENGER,STITZELand CRAIG,1973). Since decapitation convulsions consist mainly of the clonic component and maximal electroshock seizures begin with the tonic and end with the clonic phase, the differentiation of the mechanisms underlying the clonic on the one hand and the tonic convulsions on the other appears necessary. In the present experiments, this differentiation was attempted by employing Ghydroxydopamine (6-OHDA), a selective destructor of catecholaminergic nerve terminals in the brain CHOPIN and TRANZER,1973). METHODS
The experiments were performed on CF 1 strain adult male mice weighing 2%35g. maximal electroshock seizures were induced by a current of .5OmA, 60 Hz, O-2 set through cornea1 electrodes. For 6-OHDA pretreatment, a small incision was made on the skin of the head under light ether anaesthesia and a microsyringe needle was inserted through the skull to a depth of 25 mm, 1 mm lateral to the midline and 2 mm rostra1 to the lambda. Various doses (5-F-100 pg/animal) of 6-OHDA dissolved in 5 ~1 of 0.9% NaCl with ascorbic acid (1 mg/ml), were injected into the lateral ventricle. Control mice were treated with the vehicle in the same manner. The accuracy of localization in this method was ascertained by injection of trypan-blue solution. In the first experiment, effects of various doses of intraventricular 6-OHDA on the incidence and average duration of the clonic phase of maximal electroshock seizure were observed in five groups of 10 mice. Each group %& tieated with 0, 5, 10, 20 or 100 pg 6-OHDA and the maximal electroshock seizure test was carried out 2, 7 and 14 days after the treatment. Ninety mice including 20 vehicle injected mice were used in the second experiment. Seven groups of 10 mice were pretreated with 50 pg 6-OHDA; maximal electroshock 579
580
T.
FUKUDA, Y. ARAKI
and N.
SUENAGA
Table 1. Average duration and percent incidence of clonic convulsion during maximal electroshock seizures after various dose of 6-OHDA 2 Days* Dose of 6-OHDA (Pg)
n
Vehicle 5 10 20 100
10 10 10 10 10
Duration wt
14 Days
I Days
Incidence (%I .________ 6.9 f 0.56 100 5.0 * 1.20 90 1.4 f. 0.54*** 50 0.6 ) 0.32*** 20 0.5 * 0.31*** 131
Duration (set) 6.0 f 5.0 + 3.8 f 2.0 + 0.5 +
0.68 1.11 0.92 0.76** 0.33***
Incidence (%) 100 90 70 40 14a
Duration @ec) 63 + 64 j, 3.9 * 3.9 f 0.5 +
0.85 0.96 1.02 1.40 0.33***
Incidence (%I 100 100 70 50 145
* Days after intraventricular injection. t Average + SE. $ Incidence out of eight mice. # Incidence out of seven mice. ** P < 0.01: *** P < 0.001.
seizures were induced in each group 3, 6, 24 and 48 hr, and 7, 14 and 21 days after the injection. One minute after the recovery from postictal coma, the mice were decapitated and norepinephrine (NE) and dopamine (DA) levels of the whole brain were determined fluorophotometrically by the method of SHELLENBERGER and GORDON (1971). In the third experiment, the maximal electroshock seizure test and decapitation were carried out on the same individuals in 26 vehicle injected mice and 42 mice treated with 50 pg 6-OHDA. The duration of tonic flexion, tonic extension and clonic convulsion, and the latent period of clonic phase after the end of tonic phase in maximal electroshock seizure were recorded 48 hr after the injection. The latent period and the duration of clonic convulsion after decapitation were measured 52 hr after the treatment. Also, 20 other mice treated with 50 pg 6-OHDA and not subjected to maximal electroshock seizure were decapitated 48 hr after the injection and the parameters of seizure were measured. The statistical significance of differences between means was calculated by Student’s t-test. RESULTS
EfjTects of 6-OHDA on the clonic phase of the maximal brain catecholamine levels
electroshock
seizure and on whole
The clonic phase in maximal electroshock seizure was manifest in all of the mice injected with vehicle. Average duration and incidence of the clonic phase in four groups of mice pretreated with various doses of 6-OHDA are shown in Table 1. It is evident that the incidence was diminished and the average duration was shortened by 6-OHDA pretreatment. The doses of 20 and 100 !Lg 6-OHDA reduced the incidence of the clonic phase by 80 and 87 per cent respectively on the second day. A gradual recovery was observed in the pretreated mice, except for the group pretreated with 100 pg of 6-OHDA, in which no recovery was noted within two weeks. Furthermore, 2 mice and 1 mouse pretreated with 100 pg 6-OHDA died during the tonic phase of maximal electroshock seizure induced on the 2nd and 7th day respectively. The time course of the inhibitory effect of 6-OHDA on the incidence and duration of the clonic phase was examined in the animals pretreated with 50 pg, which was considered as an adequate dose from the previous experiment. As shown in Figure 1, the average duration of the clonic phase began to reduce at 3 hr and reached the minimum at 48 hr after the injection. This inhibition was maintained for 21 days (end of the session). Figure 2 represents the levels of whole brain catecholamines in mice treated with intraventricular 6-OHDA. The level of NE was already decreased at 3 hr after the injection, and this low level was maintained throughout the session. On the contrary, the content of DA sustained the normal level for 24 hr after the injection. It was reduced to about one-half at 48 hr, where it remained until the 14th day, and recovered to
Clonic convulsions inhibited bv 6-OHDA
5
0
0
3
6
24
46
6 OHDA
581
‘..14”21
hr
Days
Fig. 1. The time course of inhibitory effects of 6-OHDA on the duration of clonic convulsion during maximal electroshock seizures (MES). 6-Hydroxydopamine in the dose of 50 pg/animal was injected intraventricularly in 7 groups of mice (10 mice per group). Ordinate: duration of clonic convulsion during MES. Abscissa: time after the injection of 6-OHDA. At each time a different group of mice was used.
within 80% of the control value after 21 days. The time course of inhibition clonic phase was in good agreement with the NE rather than the DA level. Effects of 6-OHDA on the duration of each convulsive phase during maximal seizure and of decapitation convulsion
of the
electroshock
As shown in Table 2, the average duration of tonic extension and the latent period of the clonic phase in maximal electroshock seizure were significantly prolonged by pretreatment with 50 ,ug 6-OHDA, whereas the average duration of the clonic phase was shortened by the treatment. Similar results were obtained in the clonic convulsion induced by decapitation: longer latency and shortened duration were evident in the 6OHDA treated group. Though the post-decapitation clonic convulsion Appeared in all vehicle-injected mice, it was absent in 20 of 42 treated mice. Moreover, most 6-OHDAtreated mice which did not exhibit clonic convulsion during maximal electroshock seizure did not show decapitation convulsion either. .The average duration and latency of decapitation convulsion measured in 20 mice treated with 50 pg 6-OHDA and not subjected to maximal electroshock seizure were 8.1 f 1.50 and 13.8 + 2.24 (set f S.E.) respectively. These values are significantly different (P -C OGOl) from the values of vehicle-injected mice, and not significantly different
:r
f
: d1 6
24
I
hr
Days
Fig. 2. Contents of norepinephrine (NE) and dopamine (DA) in the whole brain after intraventricular injection of 50 pg 6-OHDA. Control mice were treated with vehicle. Each bar represents the mean content in 10 mice (control: 20 mice), and the vertical line shows standard error of the mean.
T.
582
FUKUDA, Y. ARAKIand N. SUENAGA
Table 2. Average duration and latency of maximal electroshock seizures and decapitation convulsions Maximal electroshock seizures’ --. Treatment
.___._~_ Tonic Rexion
3,
hC)t
Duration Tonic extension
Latency of clonic phase
Clonic convulsion
MC)
NC)
Dccapitstion*
---.
WI
Duration or ‘XIlV”lSiOtl (4
Latency of convulsion WC)
____..
Vehicle 6-OHDA
26 42
I.7 f 0.09 13 f 0~08
5.7 f 0.22 2.0 i 03F**
12.9 f 1335 14.4 f 0.22’“’
2.1 + 0~20 ‘4.0 + @86**
14.9 4 0-4x 5.8 + I.lo***
65 + 0.30 1.56***
1I.h f
* In 6-OHDA treated group, maximal electroshock seizures test was performed 48 hr after injection, and decapitation 4 hr later on the same individuals. t Averagef S. E.
** P < 0.01, *** P < 0001.
from the values of 6-OHDA-treated seizure (Table 2).
mice decapitated
4 hr after maximal electroshock
DISCUSSION
The earlier data indicating that the depletion of brain catecholamines by systemic administration of reserpine or a-methyl-p-tyrosine inhibits post-decapitation convulsions (FRIEDMAN, 1964; KAMAT and SHETH, 1971; EICHBAUM and YASAKA, 1973) were confirmed by the present study, in which cerebral catecholamines were selectively depleted by intraventricularly injected 6-OHDA. This effect of 6-OIIDA was mentioned by CLARK, LAVERTY and PHELAN (1972) but they did not describe it in detail. KAMAT and SHETH(1971) suggested that de~pi~tio~ con~lsions may be a release phenomenon from a cerebral tonic inhibition of spinal interneurones. Since this inhibition is supposed to be mediated by monoaminergic pathways, depletion of monoamines would reduce the severity of the rebound and, therefore, of clonic convulsions. The present results are consistent with this hypothesis. The present demonstration that the clonic component in maximal electroshock seizure is also suppressed by 6-OHDA is novel. The suppression was clear-cut and proportional to the dose. The exact parallelism in time course between this inhibition and the decrease in brain NE level after 6-OHDA treatment demonstrated at present, suggests that cerebral noradrenergic neurones are also involved in the clonic convulsion phase of maximal electroshock seizure. In this respect, DA level in the brain appears to be not related to the genesis of clonic convulsion, since only a slight depletion of DA is yielded by 6-OHDA as described by many other investigators (BELL, IVERSENand URETSKY, 1970; LAVERTY and TAYLOR, 1970; BREESE and TRAYLOR, 1971). As the GOHDA-induced attenuation of the clonic phase of maximal electroshock seizure was closely correlated with the suppression of decapi~tion convulsions, these two types of clonic convulsions have a common mechanism, possibly related to a release phenomenon in which NE may be involved. The tonic phase in maximal electroshock seizure, on the contrary, was potentiated by 6-OHDA. The duration of tonic extension was prolonged and the mortality during tonic convulsion was increased. Such effects of 6-OHDA in rats were reported by BROWING and MAYNERT (1970), and the similar effect of reserpination was demonstrated by many investigators (CHEN et al,, 1954; AZZARO et al., 1972; JOBE, STULL and GEIGER, 1974). Furthermore, CORCORAN,FIBIGER,MCGEER and WADA (1973) observed a potentiation of pentylenetetrazol seizures by intraventricular 6-OHDA. Similarly, we found that the convulsant EDso of pentylenetetrazol was significantly lowered by 6-OHDA (unpublished data). It appears that the mechanism for the tonic phase in maximal electroshock seizure and for the chemically induced clonic convulsion is different from that underlying the clonic seizure as a release phenomenon. REFERENCES R., CRAIG, C. R. and STITZEL, R. E. (1972). Reserpine induced alterations in brain amines and their relationship to changes in the incidence of minimal electroshock seizures in mice. .I. Pharmuc. exp. Ther. 180: 558-568.
AZZARO,
A.
J., WENGER,
G.
Clonic convulsions inhibited by 6-OHDA
583
BELL, L. J., IVERSEN,L. L. and URETSKY,N. J. (1970). Time course of the effects of 6-hydroxydopamine in catecholamine-containing neurons in rat hypothalamus and striatum. Br. J. Pharmac. 40: 79c-799. BREESE,G. R. and TRAYLOR,T. D. (1971). Depletion of brain noradrenaline and dopamine by 6-hydroxydopamine. Br. J. Phrmuc. 42: 8&99. BROWING,F. E. and MAYNI’RT.E. W. (1970). Increased seizure susceptibility in h-OHDA treated rats. Fedn Proc. Fedn Am. Sots esp. Biol. 29: 966. CHIN,
G..
ENSOR,C. and BOHNER,B. (1954). A facilitative action of reserpine on the central nervous system.
Proc. Sot. exp. Biol. Med. 86: 507T510.
D. W. J., LAVERTY.R. and PHELAN.E. L. (1972). Long-lasting peripheral and central effects of 6hydroxydopamine in rats. Br. J. Pharmac. 44: 233-243. CORCORAN.M. E.. FIHIG~.R,H. C.. McGI:~:K. E. G. and WAUA. J. A. (1973). Potentiation of leptazol seizures by 6-hydroxydopamine. J. Pharm. Pharmac. 25: 497-499. DF: SCHAEI~~RYVER. A. F.. PII~TTE.Y. and DELAUNOIS. A. L. (1962). Brain amines and electroshock threshold. CLARK,
Arc/n ir~t.Pharmacodyn. Thbr. 140: 358-367.
EICHBAUM. F. W. and YASAKA,W. J. (1973). Inhibition of post-decapitation
convulsions by reserpine. Esperierl-
tin 29: 816817.
FRIEDMAN.A. H. (1964). Alteration of motor effects of acute decapitation by tremorine and other compounds. Fedn Proc. Fedrl Am. Sots exp. Biol. 23: 560.
JOBE.P. C., STULL, R. E. and GEIGER.P. F. (1974). The relative significance of norepinephrine, dopamine and 5-hydroxytryptamine in electroshock seizure in the rat. N~,r,~op/~rrrr,locolo~~ 13: 961-968. KAMAT,U. G. and SHETH,U. K. (1971). The role of central monoamines in decapitation convulsions of mice. Neuropharmacology 10: 571-579. KILIAN,M. and FREY,H. H. (1973). Central monoamines and convulsive thresholds in mice and rats. Neuropharmacology IZ: 681-692. LAVERTY. R. and TAYLOR,K. M. (1970). Effects of intraventricular 2,4,5-trihydroxyphenylethylamine (6-hydroxydopamine) on rat behavior and brain catecholamine metabolism. Br. J. Pharmac. 40: 836846. SHELLENBERGER, M. K. and GORDON,J. H. (1971). A rapid simplified procedure for simultaneous assay of norepinephrine, dopamine and 5-hydroxytryptamine from discrete brain areas. Analyt. Biochem. 39: 356-372. THOENEN,H. and TRANZER,J. P. (1973). The pharmacology of 6-hydroxydopamine. A. Rev. Pharmac. 13: I 69- 180.
W~NGER,G. R., STITZEL,R. E. and CRAIG,C. R. (1973)rThe role of biogenic amines in the reserpine-induced alteration of minimal electroshock seizure thresholds in the mouse. Neuropharmacology 12: 693-703.
INHIBITORY EFFFKTS OF 6-HYDROXYDOPAMINE ON THE CLONIC CONVULSIONS INDUCED BY ELE~ROSHOCK AND DECAPITATION T. FUKUDA,Y. ARAKIand N. SUENAGA Department of Pharmacology, Faculty of Medicine, Kyushu University, Fukuoka 812, Japan (Accepted 18 December 1974) Summary-Effects of intraven~i~ul~r injection of 6-hy~oxydopamine f6-OHDA) on maximal electroshock seizures and decapitation convulsions were investigated in mice. The incidence of the clonic phase of maximal electroshock seizure was suppressed by 6-OHDA. The time course of the suppression was in good agreement with the decreased level of whole brain norepinephrine. The incidence of clonic convulsions following decapitation was also suppressed by 6-OHDA. On the contrary, the tonic phase of maximal electroshock seizure was potentiated by the treatment. The incidence of the clonic phase of maximal electroshock seizure and of de~p~tation convulsions were well correlated in 6-OHDA treated mice which had been exposed to maximal electroshock seizure and then decapitated. It is suggested that the central catecholaminergic mechanism concerned with the clonic phase in maximal electroshock seizure is analogous to that concerned with decapitation convulsions and different from that underlying the tonic phase of maximal electroshock seizure.
Recent investigations suggest that brain catecholamines play a role in the manifestation of convulsions. Post-decapitation convulsions in rats and mice are inhibited by pretreatment with reserpine or other amine depleting agents (FRIEDMAN, 1964; KAMATand SETH, 1971; EICHBAUM and YASAKA,1973). On the other hand, reserpine is known to increase the su~eptibility of animals to electroshock seizures (CHFZN, ENSOR and BOHNER, 1954; DE SCHAEPDRYVER, PIET-ITand DELAUNOIS, 1962; AZZARO,WENGER, CRAIGand STITZEL,1972; KILIANand FREY,1973; WENGER,STITZELand CRAIG,1973). Since decapitation convulsions consist mainly of the clonic component and maximal electroshock seizures begin with the tonic and end with the clonic phase, the differentiation of the mechanisms underlying the clonic on the one hand and the tonic convulsions on the other appears necessary. In the present experiments, this differentiation was attempted by employing Ghydroxydopamine (6-OHDA), a selective destructor of catecholaminergic nerve terminals in the brain CHOPIN and TRANZER,1973). METHODS
The experiments were performed on CF 1 strain adult male mice weighing 2%35g. maximal electroshock seizures were induced by a current of .5OmA, 60 Hz, O-2 set through cornea1 electrodes. For 6-OHDA pretreatment, a small incision was made on the skin of the head under light ether anaesthesia and a microsyringe needle was inserted through the skull to a depth of 25 mm, 1 mm lateral to the midline and 2 mm rostra1 to the lambda. Various doses (5-F-100 pg/animal) of 6-OHDA dissolved in 5 ~1 of 0.9% NaCl with ascorbic acid (1 mg/ml), were injected into the lateral ventricle. Control mice were treated with the vehicle in the same manner. The accuracy of localization in this method was ascertained by injection of trypan-blue solution. In the first experiment, effects of various doses of intraventricular 6-OHDA on the incidence and average duration of the clonic phase of maximal electroshock seizure were observed in five groups of 10 mice. Each group %& tieated with 0, 5, 10, 20 or 100 pg 6-OHDA and the maximal electroshock seizure test was carried out 2, 7 and 14 days after the treatment. Ninety mice including 20 vehicle injected mice were used in the second experiment. Seven groups of 10 mice were pretreated with 50 pg 6-OHDA; maximal electroshock 579
580
T.
FUKUDA, Y. ARAKI
and N.
SUENAGA
Table 1. Average duration and percent incidence of clonic convulsion during maximal electroshock seizures after various dose of 6-OHDA 2 Days* Dose of 6-OHDA (Pg)
n
Vehicle 5 10 20 100
10 10 10 10 10
Duration wt
14 Days
I Days
Incidence (%I .________ 6.9 f 0.56 100 5.0 * 1.20 90 1.4 f. 0.54*** 50 0.6 ) 0.32*** 20 0.5 * 0.31*** 131
Duration (set) 6.0 f 5.0 + 3.8 f 2.0 + 0.5 +
0.68 1.11 0.92 0.76** 0.33***
Incidence (%) 100 90 70 40 14a
Duration @ec) 63 + 64 j, 3.9 * 3.9 f 0.5 +
0.85 0.96 1.02 1.40 0.33***
Incidence (%I 100 100 70 50 145
* Days after intraventricular injection. t Average + SE. $ Incidence out of eight mice. # Incidence out of seven mice. ** P < 0.01: *** P < 0.001.
seizures were induced in each group 3, 6, 24 and 48 hr, and 7, 14 and 21 days after the injection. One minute after the recovery from postictal coma, the mice were decapitated and norepinephrine (NE) and dopamine (DA) levels of the whole brain were determined fluorophotometrically by the method of SHELLENBERGER and GORDON (1971). In the third experiment, the maximal electroshock seizure test and decapitation were carried out on the same individuals in 26 vehicle injected mice and 42 mice treated with 50 pg 6-OHDA. The duration of tonic flexion, tonic extension and clonic convulsion, and the latent period of clonic phase after the end of tonic phase in maximal electroshock seizure were recorded 48 hr after the injection. The latent period and the duration of clonic convulsion after decapitation were measured 52 hr after the treatment. Also, 20 other mice treated with 50 pg 6-OHDA and not subjected to maximal electroshock seizure were decapitated 48 hr after the injection and the parameters of seizure were measured. The statistical significance of differences between means was calculated by Student’s t-test. RESULTS
EfjTects of 6-OHDA on the clonic phase of the maximal brain catecholamine levels
electroshock
seizure and on whole
The clonic phase in maximal electroshock seizure was manifest in all of the mice injected with vehicle. Average duration and incidence of the clonic phase in four groups of mice pretreated with various doses of 6-OHDA are shown in Table 1. It is evident that the incidence was diminished and the average duration was shortened by 6-OHDA pretreatment. The doses of 20 and 100 !Lg 6-OHDA reduced the incidence of the clonic phase by 80 and 87 per cent respectively on the second day. A gradual recovery was observed in the pretreated mice, except for the group pretreated with 100 pg of 6-OHDA, in which no recovery was noted within two weeks. Furthermore, 2 mice and 1 mouse pretreated with 100 pg 6-OHDA died during the tonic phase of maximal electroshock seizure induced on the 2nd and 7th day respectively. The time course of the inhibitory effect of 6-OHDA on the incidence and duration of the clonic phase was examined in the animals pretreated with 50 pg, which was considered as an adequate dose from the previous experiment. As shown in Figure 1, the average duration of the clonic phase began to reduce at 3 hr and reached the minimum at 48 hr after the injection. This inhibition was maintained for 21 days (end of the session). Figure 2 represents the levels of whole brain catecholamines in mice treated with intraventricular 6-OHDA. The level of NE was already decreased at 3 hr after the injection, and this low level was maintained throughout the session. On the contrary, the content of DA sustained the normal level for 24 hr after the injection. It was reduced to about one-half at 48 hr, where it remained until the 14th day, and recovered to
Clonic convulsions inhibited bv 6-OHDA
5
0
0
3
6
24
46
6 OHDA
581
‘..14”21
hr
Days
Fig. 1. The time course of inhibitory effects of 6-OHDA on the duration of clonic convulsion during maximal electroshock seizures (MES). 6-Hydroxydopamine in the dose of 50 pg/animal was injected intraventricularly in 7 groups of mice (10 mice per group). Ordinate: duration of clonic convulsion during MES. Abscissa: time after the injection of 6-OHDA. At each time a different group of mice was used.
within 80% of the control value after 21 days. The time course of inhibition clonic phase was in good agreement with the NE rather than the DA level. Effects of 6-OHDA on the duration of each convulsive phase during maximal seizure and of decapitation convulsion
of the
electroshock
As shown in Table 2, the average duration of tonic extension and the latent period of the clonic phase in maximal electroshock seizure were significantly prolonged by pretreatment with 50 ,ug 6-OHDA, whereas the average duration of the clonic phase was shortened by the treatment. Similar results were obtained in the clonic convulsion induced by decapitation: longer latency and shortened duration were evident in the 6OHDA treated group. Though the post-decapitation clonic convulsion Appeared in all vehicle-injected mice, it was absent in 20 of 42 treated mice. Moreover, most 6-OHDAtreated mice which did not exhibit clonic convulsion during maximal electroshock seizure did not show decapitation convulsion either. .The average duration and latency of decapitation convulsion measured in 20 mice treated with 50 pg 6-OHDA and not subjected to maximal electroshock seizure were 8.1 f 1.50 and 13.8 + 2.24 (set f S.E.) respectively. These values are significantly different (P -C OGOl) from the values of vehicle-injected mice, and not significantly different
:r
f
: d1 6
24
I
hr
Days
Fig. 2. Contents of norepinephrine (NE) and dopamine (DA) in the whole brain after intraventricular injection of 50 pg 6-OHDA. Control mice were treated with vehicle. Each bar represents the mean content in 10 mice (control: 20 mice), and the vertical line shows standard error of the mean.
T.
582
FUKUDA, Y. ARAKIand N. SUENAGA
Table 2. Average duration and latency of maximal electroshock seizures and decapitation convulsions Maximal electroshock seizures’ --. Treatment
.___._~_ Tonic Rexion
3,
hC)t
Duration Tonic extension
Latency of clonic phase
Clonic convulsion
MC)
NC)
Dccapitstion*
---.
WI
Duration or ‘XIlV”lSiOtl (4
Latency of convulsion WC)
____..
Vehicle 6-OHDA
26 42
I.7 f 0.09 13 f 0~08
5.7 f 0.22 2.0 i 03F**
12.9 f 1335 14.4 f 0.22’“’
2.1 + 0~20 ‘4.0 + @86**
14.9 4 0-4x 5.8 + I.lo***
65 + 0.30 1.56***
1I.h f
* In 6-OHDA treated group, maximal electroshock seizures test was performed 48 hr after injection, and decapitation 4 hr later on the same individuals. t Averagef S. E.
** P < 0.01, *** P < 0001.
from the values of 6-OHDA-treated seizure (Table 2).
mice decapitated
4 hr after maximal electroshock
DISCUSSION
The earlier data indicating that the depletion of brain catecholamines by systemic administration of reserpine or a-methyl-p-tyrosine inhibits post-decapitation convulsions (FRIEDMAN, 1964; KAMAT and SHETH, 1971; EICHBAUM and YASAKA, 1973) were confirmed by the present study, in which cerebral catecholamines were selectively depleted by intraventricularly injected 6-OHDA. This effect of 6-OIIDA was mentioned by CLARK, LAVERTY and PHELAN (1972) but they did not describe it in detail. KAMAT and SHETH(1971) suggested that de~pi~tio~ con~lsions may be a release phenomenon from a cerebral tonic inhibition of spinal interneurones. Since this inhibition is supposed to be mediated by monoaminergic pathways, depletion of monoamines would reduce the severity of the rebound and, therefore, of clonic convulsions. The present results are consistent with this hypothesis. The present demonstration that the clonic component in maximal electroshock seizure is also suppressed by 6-OHDA is novel. The suppression was clear-cut and proportional to the dose. The exact parallelism in time course between this inhibition and the decrease in brain NE level after 6-OHDA treatment demonstrated at present, suggests that cerebral noradrenergic neurones are also involved in the clonic convulsion phase of maximal electroshock seizure. In this respect, DA level in the brain appears to be not related to the genesis of clonic convulsion, since only a slight depletion of DA is yielded by 6-OHDA as described by many other investigators (BELL, IVERSENand URETSKY, 1970; LAVERTY and TAYLOR, 1970; BREESE and TRAYLOR, 1971). As the GOHDA-induced attenuation of the clonic phase of maximal electroshock seizure was closely correlated with the suppression of decapi~tion convulsions, these two types of clonic convulsions have a common mechanism, possibly related to a release phenomenon in which NE may be involved. The tonic phase in maximal electroshock seizure, on the contrary, was potentiated by 6-OHDA. The duration of tonic extension was prolonged and the mortality during tonic convulsion was increased. Such effects of 6-OHDA in rats were reported by BROWING and MAYNERT (1970), and the similar effect of reserpination was demonstrated by many investigators (CHEN et al,, 1954; AZZARO et al., 1972; JOBE, STULL and GEIGER, 1974). Furthermore, CORCORAN,FIBIGER,MCGEER and WADA (1973) observed a potentiation of pentylenetetrazol seizures by intraventricular 6-OHDA. Similarly, we found that the convulsant EDso of pentylenetetrazol was significantly lowered by 6-OHDA (unpublished data). It appears that the mechanism for the tonic phase in maximal electroshock seizure and for the chemically induced clonic convulsion is different from that underlying the clonic seizure as a release phenomenon. REFERENCES R., CRAIG, C. R. and STITZEL, R. E. (1972). Reserpine induced alterations in brain amines and their relationship to changes in the incidence of minimal electroshock seizures in mice. .I. Pharmuc. exp. Ther. 180: 558-568.
AZZARO,
A.
J., WENGER,
G.
Clonic convulsions inhibited by 6-OHDA
583
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