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The effects of chronic cocaine pretreatment on kindled seizures and behavioral stereotypies
EXPERIMENTAL
NEUROLOGY
64, 306-3 14 (1979)
The Effects of Chronic Cocaine Pretreatment on Kindled Seizures and Behavioral Stereotypies M. MARLYNE KILBEY,EVERETT H. ELLINWOOD, AND MARTHA E. EASLER Department
ofpsychiatry,
Duke
University Received
Medical August
Center,
Durham,
North
Carolina
27710
28, 1978
Male Sprague-Dawley rats were implanted with electrodes in the left basolateral amygdala and caudates. After recovery, rats received daily injections of 40 mg/kg cocaine or saline i.p. for 14 days. Daily electrostimulation (400 PA) of the left amygdala, i.e., kindling, was carried out until rats exhibited poststimulation clonic seizures on two consecutive days. Rats treated with cocaine prior to kindling reached criterion significantly faster than the controls. This difference, however, was wholly attributable to the faster kindling observed in subjects (Ss) in which cocaine-induced convulsions had been noted during the daily treatment. Augmentation of behavioral stereotypies was greater and propagation of afterdischarges to the caudate occurred significantly earlier in rats that had received cocaine prior to the initiation of kindling regardless of whether or not convulsions had occurred. These data in conjunction with those of other investigators suggest that chronic cocaine administration may deplete dopamine and thus diminish inhibitory neural function allowing earlier propagation of afterdischarges and augmenting drug-induced stereotypies.
INTRODUCTION Numerous experiments in our laboratory and others have shown a persistent augmentation of behavior, generally hyperactivity and stereotypy, after chronic cocaine administration for a period of 10 to 14 days (11, 12,14,21). Likewise, chronic administration was shown to lower thresholds for cocaine-induced convulsions and decrease the interval between convulsions (3, 14, 22, 23). Administration of cocaine resulted in increases in the amplitude of the electroencephalogram (EEG) in the basolateral amygdala that persisted for at least 20 days after discontinuaAbbreviations:
EEG-electroencephalogram;
DA-dopamine; 306
0014-4886/79/050306-09$02.00/O Copyright All rights
0 1979 by Academic Press, Inc. of reproduction in any form reserved.
Ss-subjects.
CHRONIC
COCAINE:
SEIZURES
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tion of chronic injections (22). Repeated injections of cocaine decreased striatal dopamine (DA) levels by 16% (24). It has been hypothesized that cocaine’s early and chronic effects on electrophysiological parameters of the limbic system may be reflected in the initial induction of abnormal behavior in animals and its subsequent augmentation after chronic injections. Chronic administration of cocaine is thought to augment stereotyped behavior and convulsion through a local neuronal reorganization in the limbic forebrain and an enhanced propagation of neural activity from these sites (5, 14). That process, of course, is analogous to the process thought to occur during “kindling” whereby daily applications of an originally subthreshold electrical stimulation, usually in the amygdala, come to elicit afterdischarges which spread to other brain structures and eventually result in fully expressed clonic convulsions (9). Kindling results in long-lasting depletion of DA in the amygdala (8). A pharmacological kindling process has been hypothesized to underlie the progressive behavioral disorders seen in stimulant-induced psychosis (7) and levodopa-induced psychosis (13). Thus, it seems important to determine whether or not previous treatment with drugs which induce abnormal behavior, presumably by acting on DA receptors, influence the kindling process. To evaluate this, we tested kindling in animals previously treated with cocaine for a 2-week period. METHODS Subjects. The subjects (Ss) were 89 male Sprague-Dawley rats weighing between 250 and 300 g at the beginning of the experiment. They were caged individually in plastic breeding cages and were maintained on a 12-h light:dark cycle. Food and water were available ad libitum. Procedure. The rats were implanted with electrodes in the left basolateral amygdala (-0.5 mm posterior to bregma; 4.6 mm lateral; 8.5 mm below the dura). In addition, for 68 of these rats, electrodes were implanted in the left and right caudate (1.9 mm anterior to bregma; +3.0 mm lateral; 4.0 mm below the dura). Stainless-steel screws were placed over the frontal sinus (13.0 mm anterior to bregma). Histology done at the completion of the experiment confirmed the location of the electrodes. A 3-week postoperative recovery period was used to insure the presence of normal electrophysiological activity at the implantation sites (4). Twentyfive Ss lost their head plugs, four died of drug administration, and nine did not develop convulsions. Thus, data are presented for 51 Ss. The experimental design is presented in Table 1. Electrostimulation was delivered to the left amygdala at 400 PA, for 2 s in I-ms pulses at 50 Hz. The kindling criterion consisted of two consecutive days on which the S
308
KILBEY,
ELLINWOOD, TABLE Experimental
Phase
AND EASLER 1 Paradigm
Description
Phase
1
Receive rats; 2-week acclimation period.
7
2
Surgery: implant monopolar electrodes.
Chronic repeat havior jection,
3
Recovery: 21-day period.
8
4
Habituate Ss in test cage (2 min). Administer 40 mg/kg cocaine, i.p. Rate behavior (10-s period) preiniection and once ner minute from”0 to 15 min postinjection. Use behavior ratings to form two matched groups.
Kindling period: plase S in test cage for 1 min. Record EEG for 1 min. Stimulate: 400 PA, 50 Hz, for 2 s. Record behavior and EEG through 2-min post-EEG discharges.
9
Post-kindling day 1: repeat phase 4 measures (all Ss receive coCaine).
10
Post-kindling day 10: repeat phase 4 measures (ah Ss receive coCaine).
5
Rest: 2-day period.
6
Chronic injection period: administer 40 mgikg cocaine or saline, i.p., for 13 days. Observe Ss for convulsions (O-20 min postinjection) in home cage. Rate behavior on days 1,5, and 9 during 3-h period.
Description injection period day 14: phase 4 measures of beafter cocaine or saline inas appropriate.
exhibited clonic seizures poststimulation. Behavior was rated using the scale developed by Ellinwood and Balster (6). Electrophysiologic data recorded were the number, latency, and duration of afterdischarges elicited by electrical stimulation at each electrode site. Data were analyzed using t-tests. RESULTS Kindling Effects. Ten Ss experienced drug-induced convulsions during the 1Cday chronic treatment period (phase 7) which preceded the kindling period. Seven of the ten Ss which convulsed had a single convulsion, two Ss convulsed twice, and one S had three convulsions. Seven convulsions occurred during the 1st week of the chronic treatment period and seven during the 2nd week. When brain stimulation was begun, Ss that had received cocaine kindled significantly faster, P 5 0.01. The mean number of days to criterion for cocaine-pretreated Ss was 12.2 ? 7.5 (SD), and it was 17.5 + 6.6 for saline-pretreated Ss. However, the difference was wholly attributable to faster kindling in those Ss that had convulsed
CHRONIC
COCAINE:
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STEREOTYPIES
(x = 7.2 ? 4.6) during chronic drug pretreatment, as the average number of days for those that had not convulsed was 14.8 -+ 7.5. These data are shown in Table 2. The mean number of afterdischarges for all days that afterdischarges were present, except for days on whichSs kindled, varied by electrode site. The greatest number of discharges occurred in the left amygdala. Fewer afterdischarges were found in the left caudate and still fewer in the right caudate (P 5 0.01). However chronic cocaine pretreatment did not result in a differential number of afterdischarges (P > 0.05) at any site as is shown in Table 3. Neither latency nor duration of afterdischarge in the, left amygdala site differed significantly as a function of treatment (P > 0.05). However, the duration of amygdala afterdischarge was significantly longer (P % 0.02 in Ss that had convulsed during pretreatment with cocaine (54.0 + 27.3 s) than in saline-pretreated Ss (33.8 & 23.6). The duration for cocainepretreated Ss that had not convulsed was 41.9 f 20.4 s which did not differ from the saline-pretreated Ss. Latency and duration of afterdischarges in right and left caudate sites did not vary as a function of pretreatment (P > 0.05). The speed with which discharges were propagated to the caudate was significantly faster for cocaine pretreated rats (P I 0.01). The salinepretreated group developed discharges 2.8 days after the kindling procedure was begun for the left caudate and at 3.8 days for the right. For the cocaine-pretreated Ss, the mean was 1.3 days for the left caudate and 1.2 for the right. Rats that had convulsed during treatment did not differ from those that had not in terms of the day on which propagation of afterdischarges to the right or left caudate was seen. These data are shown in Table 2. TABLE Mean
and Standard
Deviation
of Days
2
to Kindling
and Propagation Afterdischarge
Treatment Cocaine All Ss Convulsive Nonconvulsive
Kindling
only only
Saline * P 5 0.01 compared
Left
caudate
of Afterdischarge propagation Right
caudate
12.2 k 7.5* 7.2 T 4.6* 14.8 k 7.5
1.27 c 0.63* 1.30 k 0.67* 1.25 rt 0.62*
1.22 ” 0.61* 1.20 2 0.63* 1.25 k 0.62*
17.5 k 6.6
2.80
3.80
to saline-injected
controls.
+ 2.30
+ 4.60
310
KILBEY,
ELLINWOOD, TABLE
AND EASLER 3
Number of Afterdischarges Region Treatment
Left amygdala
Left caudate
Right caudate
Saline 40 mg/kg cocaine
95 -c 45” 107 2 50
71 + 47 88 k 52
73 k 46 87 f 52
Behavioral Effects. Behavioral ratings showed that Ss chronically pretreated with cocaine demonstrated augmented behavioral stereotypies when tested postkindling, whereas those pretreated with saline did not (Fig. 1). A lack of significant change in the saline group between cocaine tests on day 1 and the day after kindling (P > 0.05) shows that neither a single cocaine injection nor the kindling procedure potentiate stereotypies. As in a previous experiment (22), there were no significant differences in the behavioral augmentation between Ss that had convulsed during chronic pretreatment and those that had not (P > 0.05). DISCUSSION Recently, investigators (5, 15) suggested that the augmentation of abnormal behavior which occurs with chronic cocaine administration depends on mechanisms analagous to those believed to occur during “kindling,” i.e., a local neuronal reorganization at the site of stimulation and an enhanced propagation of neural activity from this stimulation site (2, 16- 18). The data of this experiment bear on this suggestion in several ways. If the repeated induction of amygdala spindles, known to occur with cocaine administration (22), mimics the effect of repeated electrical stimulation of this area, then pretreatment with cocaine should facilitate the rate of kindling. Experimental support for this hypothesis was not straightforward as those Ss that had experienced convulsions during the chronic drug treatment period accounted for the faster kindling which was obtained as a function of cocaine pretreatment. The rate of kindling within the group that had experienced convulsions did not appear to be a function of either the day on which the animal experienced convulsions or the number of convulsions. An animal that convulsed on day 3, for example, did not kindle until the 18th day whereas the Ss that had three convulsions kindled on day 9. The process by which prior drug-induced convulsions lead to facilitated kindling is not known. Spontaneously, audiogenically, chemically, or
CHRONIC
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9
8t
Time
in Minutes
FIG. 1. Mean behavioral rating of rats treated with saline or 40 mgikg cocaine during phases 4, 9, and 10. Ratings were made pre- and post-40 mg/kg cocaine during phase 4 (saline, & -; cocaine, 0- -) and phases 9 and 10 (saline, A-; cocaine O-). Behavioral ratings within treatments did not differ significantly at phases 9 and 10 postkindling (P > 0.05) and were combined. The standard errors for these data were approximately 6% of the mean values.
electrically induced seizures result in short-term elevations of seizure threshold (10, 20, 25) and long-term decreases. However, these appear to be specific to the modality used to induce the convulsion as prior chemical induction of seizures does not lower the threshold for electrically induced convulsions (25). Procaine coupled with electrical stimulation facilitated the rate of development of kindled seizures in comparison with Ss given saline plus electrical stimulation. However when Ss were retested in a seizures were retarded nondrug state, after 5 drug-free days, “kindled” (19). Thus, it appears experience with the combined effects of a local anesthetic drug and electrically induced seizures were not sufficient to
312
KILBEY,
ELLINWOOD,
AND
EASLER
facilitate “kindling” upon retesting in a nondrug state. The facilitation of “kindled” seizures found in a drug-free state in our experiment after chronic cocaine treatment which resulted in seizures suggest that cocaine-induced convulsions altered some mechanism basic to convulsions. This may involve synergistic effects of cocaine and kindling as both deplete DA stores (8, 24). As DA has been implicated as an inhibitory transmitter in the amygdala (1)) the longer duration of afterdischarges in the amygdala found in Ss that had experienced seizures during the chronic drug treatment period would be consonant with decreased DA levels also. Loss of inhibitory transmitter mechanisms due to DA depletion as a result of synergistic actions of chronic cocaine administration and seizure induction cannot explain cocaine’s augmentation of stereotypies as this occurred in allSs regardless of whether or not cocaine-induced convulsions had occurred. As faster propagation of afterdischarges to the caudate sites was seen in all Ss pretreated with cocaine also, these data suggest that chronic cocaine administration alone decreased inhibitory transmitter function allowing increased propagation of afterdischarges and augmented stereotypies. It is not known if cocaine induces spindles in the caudate as it does in the amygdala of rats, nor has the pehnomenon (18) of EEG spindle augmentation, reported to occur in the amygdala with chronic treatment, been evaluated at caudate or limbic sites. If faster amygdala-caudate pathway facilitation underlies augmentation of behavioral stereotypies, propagation of cocaine-induced spindles during chronic treatment should be coincident with the onset of augmented behavioral stereotypies, a hypothesis currently being tested. In summary, cocaine-induced convulsions during a period of chronic administration appears to facilitate “kindled” induction of seizures at a later time. This may reflect a synergism of relatively long-term cocaine-induced and seizure-induced dopamine depletion. Augmentation of behavioral stereotypy occurs in subjects pretreated with cocaine regardless of whether or not convulsions had been induced and may reflect localized long-term depletion of dopamine which impairs inhibitory function in the limbic system allowing propagation of afterdischarges from the amygdala to other sites. REFERENCES 1. BEN-AN, Y., AND J. S. KELLEY. 1976. Dopamine evoked inhibition of single cells of the feline putamen and basolateral amygdala. J. Physiol. (London) 356: l-22. 2. DOUGLAS, R. M., AND G. V. GODDARD. 1975. Long term potentiation of the perforant path-granule cell synapse in the rat hippocampus. Brain Res. 86: 205-215. 3. DOWNS, A. W., ANDN. B. EDDY. 1932. Theeffectofrepeateddosesofcocaineontherat. J. Pharmacol. Exp. Ther. 46: 199-200.
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4. EIDELBERG, E., AND C. M. WOODBURY. 1972. Electrical activity in the amygdala and its modification by drugs. Possible nature of synaptic transmitters. A review. Pages 609-622 in B. E. ELEFTHERIOU, Ed., The Neurobiology of the Amygdula. Plenum Press, New York. 5. ELLINWOOD, E. H., JR. 1974. Physiological effects of cocaine. Paper presented at National Institute on Drug Abuse Cocaine Conference, Washington, D.C. (Unpublished). 6. ELLINWOOD, E. H., JR., AND R. L. BALSTER. 1974. Rating the behavioral effects of amphetamine. Eur. J. Pharmacol. 28: 35-41. 7. ELLINWOOD, E. H., JR., J. S. STRIPLING, AND M. M. KILBEY. 1977. Chronic changes with amphetamine intoxication: Underlying processes. Pages 578-587 in E. USDIN AND J. BARCHAS, Eds., Neuroregulators and Hypotheses of Psychiatric Disorders. Oxford Univ. Press, London. 8. ENGEL, J., JR., AND N. S. SHARPLESS. 1977. Long-lasting depletion of dopamine in the rat amygdala induced by kindling stimulation. Bruin Res. 136: 381-386. 9. GODDARD, G. V. 1967. Development of epileptic seizures through brain stimulation at low intensity. Nature (London) 214: 1020-1021. 10. HERBERG, L. J., K. H. TRESS, AND J. E. BLUNDELL. 1969. Raising the threshold in experimental epilepsy by hypothalamic and septal stimulation and by audiogenic seizures. Bruin 92: 313-328. 11. Ho, B. T., D. L. TAYLOR, V. S. ESTEVEZ, L. F. ENGLERT, ANDM. L. MCKENNA. 1977. Behavioral effects of cocaine: metabolic and neurochemical approach. Pages 229-240 in E. H. ELLINWOOD AND M. M. KILBEY, Eds., Cocaine and Other Stimulants. Plenum Press, New York. 12. KILBEY, M. M., AND E. H. ELLINWOOD, JR. 1977. Chronic administration of stimulant drugs: response modification. Pages 409-429 in E. H. ELLINWOOD AND M. M. KILBEY, Eds., Cocaine and Other stimulants. Plenum Press, New York. 13. MOSKOVITZ, C., H. MOSES, AND H. L. KLAWANS. 1978. Levodopa-induced psychosis: a kindling phenomenon. Am. J. Psychiat. 135:6:669-675. 14. POST, R. M. 1977. Progressive changes in behavior and seizures following chronic cocaine administration: relationship to kindling and psychosis. Pages 353-372 in E. H. ELLINWOOD AND M. M. KILBEY, Eds., Cocaine and Other Stimulants. Plenum Press, New York. 15. POST, R. M., AND R. T. KOPANDA. 197.5. Cocaine, kindling, and reverse tolerance. Lancet 1: 409-410. 16. RACINE, R. J. 1972a. Modification of seizure activity by electrical stimulation: I. Afterdischarge threshold. Electroenceph. Clin. Neurophysiol. 32: 269-280. 17. RACINE. R. J. 1972b. Modification of seizure activity by electrical stimulation: II. Motor seizure. Electroenceph. Clin. Neurophysiol. 32: 281-294. 18. RACINE, R. J., J. G. GARTNER, AND W. M. BURNHAM. 1972. Epileptiform activity and neural plasticity in limbic structures. Brain Res. 47: 262-268. 19. RACINE, R. J., F. NEWBERRY, AND W. M. BURNHAM. 1975. Post-activation potentiation and the kindling phenomenon. Electroenceph. Clin. Neurophysiol. 39: 261-272. 20. RIFFEE, W. H., AND M. C. GERALD. 1977. The effects of chronic administration and withdrawal of (+) -amphetamine on seizure threshold and endogenous catecholamine concentrations and their rates of biosynthesis in mice. Psychopharmacobgy 51: 175- 179. 21. STRIPLING, J. S., AND E. H. ELLINWOOD, JR. 1977a. Potentiation of the behavioral and convulsant effects of cocaine by chronic administration in the rat. Pharmacol. Biochem. Behav. 6: 571-579.
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22. STRIPLING, J. S., AND E. H. ELLINWOOD, JR. 1977b. Augmentation of the behavioral and electrophysiologic response to cocaine by chronic administration in the rat. Exp. Neurol.
54: 546-564.
TATUM, A. L., AND M. H. SEWERS. 1929. Experimental cocaine addiction. J. Pharmacol. Exp. The-. 36: 401-410. 24. TAYLOR, D., AND B. T. Ho. 1977. Neurochemical effects of cocaine following acute and repeated injection. J. Neurosci. Res. 3: 9.5-101. 25. TRESS, K. H., AND L. J. HERBERG. 1972. Permanent reduction in seizure threshold resulting from repeated electrical stimulation. Exp. Neural. 37: 347-359. 23.
NEUROLOGY
64, 306-3 14 (1979)
The Effects of Chronic Cocaine Pretreatment on Kindled Seizures and Behavioral Stereotypies M. MARLYNE KILBEY,EVERETT H. ELLINWOOD, AND MARTHA E. EASLER Department
ofpsychiatry,
Duke
University Received
Medical August
Center,
Durham,
North
Carolina
27710
28, 1978
Male Sprague-Dawley rats were implanted with electrodes in the left basolateral amygdala and caudates. After recovery, rats received daily injections of 40 mg/kg cocaine or saline i.p. for 14 days. Daily electrostimulation (400 PA) of the left amygdala, i.e., kindling, was carried out until rats exhibited poststimulation clonic seizures on two consecutive days. Rats treated with cocaine prior to kindling reached criterion significantly faster than the controls. This difference, however, was wholly attributable to the faster kindling observed in subjects (Ss) in which cocaine-induced convulsions had been noted during the daily treatment. Augmentation of behavioral stereotypies was greater and propagation of afterdischarges to the caudate occurred significantly earlier in rats that had received cocaine prior to the initiation of kindling regardless of whether or not convulsions had occurred. These data in conjunction with those of other investigators suggest that chronic cocaine administration may deplete dopamine and thus diminish inhibitory neural function allowing earlier propagation of afterdischarges and augmenting drug-induced stereotypies.
INTRODUCTION Numerous experiments in our laboratory and others have shown a persistent augmentation of behavior, generally hyperactivity and stereotypy, after chronic cocaine administration for a period of 10 to 14 days (11, 12,14,21). Likewise, chronic administration was shown to lower thresholds for cocaine-induced convulsions and decrease the interval between convulsions (3, 14, 22, 23). Administration of cocaine resulted in increases in the amplitude of the electroencephalogram (EEG) in the basolateral amygdala that persisted for at least 20 days after discontinuaAbbreviations:
EEG-electroencephalogram;
DA-dopamine; 306
0014-4886/79/050306-09$02.00/O Copyright All rights
0 1979 by Academic Press, Inc. of reproduction in any form reserved.
Ss-subjects.
CHRONIC
COCAINE:
SEIZURES
AND
STEREOTYPIES
307
tion of chronic injections (22). Repeated injections of cocaine decreased striatal dopamine (DA) levels by 16% (24). It has been hypothesized that cocaine’s early and chronic effects on electrophysiological parameters of the limbic system may be reflected in the initial induction of abnormal behavior in animals and its subsequent augmentation after chronic injections. Chronic administration of cocaine is thought to augment stereotyped behavior and convulsion through a local neuronal reorganization in the limbic forebrain and an enhanced propagation of neural activity from these sites (5, 14). That process, of course, is analogous to the process thought to occur during “kindling” whereby daily applications of an originally subthreshold electrical stimulation, usually in the amygdala, come to elicit afterdischarges which spread to other brain structures and eventually result in fully expressed clonic convulsions (9). Kindling results in long-lasting depletion of DA in the amygdala (8). A pharmacological kindling process has been hypothesized to underlie the progressive behavioral disorders seen in stimulant-induced psychosis (7) and levodopa-induced psychosis (13). Thus, it seems important to determine whether or not previous treatment with drugs which induce abnormal behavior, presumably by acting on DA receptors, influence the kindling process. To evaluate this, we tested kindling in animals previously treated with cocaine for a 2-week period. METHODS Subjects. The subjects (Ss) were 89 male Sprague-Dawley rats weighing between 250 and 300 g at the beginning of the experiment. They were caged individually in plastic breeding cages and were maintained on a 12-h light:dark cycle. Food and water were available ad libitum. Procedure. The rats were implanted with electrodes in the left basolateral amygdala (-0.5 mm posterior to bregma; 4.6 mm lateral; 8.5 mm below the dura). In addition, for 68 of these rats, electrodes were implanted in the left and right caudate (1.9 mm anterior to bregma; +3.0 mm lateral; 4.0 mm below the dura). Stainless-steel screws were placed over the frontal sinus (13.0 mm anterior to bregma). Histology done at the completion of the experiment confirmed the location of the electrodes. A 3-week postoperative recovery period was used to insure the presence of normal electrophysiological activity at the implantation sites (4). Twentyfive Ss lost their head plugs, four died of drug administration, and nine did not develop convulsions. Thus, data are presented for 51 Ss. The experimental design is presented in Table 1. Electrostimulation was delivered to the left amygdala at 400 PA, for 2 s in I-ms pulses at 50 Hz. The kindling criterion consisted of two consecutive days on which the S
308
KILBEY,
ELLINWOOD, TABLE Experimental
Phase
AND EASLER 1 Paradigm
Description
Phase
1
Receive rats; 2-week acclimation period.
7
2
Surgery: implant monopolar electrodes.
Chronic repeat havior jection,
3
Recovery: 21-day period.
8
4
Habituate Ss in test cage (2 min). Administer 40 mg/kg cocaine, i.p. Rate behavior (10-s period) preiniection and once ner minute from”0 to 15 min postinjection. Use behavior ratings to form two matched groups.
Kindling period: plase S in test cage for 1 min. Record EEG for 1 min. Stimulate: 400 PA, 50 Hz, for 2 s. Record behavior and EEG through 2-min post-EEG discharges.
9
Post-kindling day 1: repeat phase 4 measures (all Ss receive coCaine).
10
Post-kindling day 10: repeat phase 4 measures (ah Ss receive coCaine).
5
Rest: 2-day period.
6
Chronic injection period: administer 40 mgikg cocaine or saline, i.p., for 13 days. Observe Ss for convulsions (O-20 min postinjection) in home cage. Rate behavior on days 1,5, and 9 during 3-h period.
Description injection period day 14: phase 4 measures of beafter cocaine or saline inas appropriate.
exhibited clonic seizures poststimulation. Behavior was rated using the scale developed by Ellinwood and Balster (6). Electrophysiologic data recorded were the number, latency, and duration of afterdischarges elicited by electrical stimulation at each electrode site. Data were analyzed using t-tests. RESULTS Kindling Effects. Ten Ss experienced drug-induced convulsions during the 1Cday chronic treatment period (phase 7) which preceded the kindling period. Seven of the ten Ss which convulsed had a single convulsion, two Ss convulsed twice, and one S had three convulsions. Seven convulsions occurred during the 1st week of the chronic treatment period and seven during the 2nd week. When brain stimulation was begun, Ss that had received cocaine kindled significantly faster, P 5 0.01. The mean number of days to criterion for cocaine-pretreated Ss was 12.2 ? 7.5 (SD), and it was 17.5 + 6.6 for saline-pretreated Ss. However, the difference was wholly attributable to faster kindling in those Ss that had convulsed
CHRONIC
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309
STEREOTYPIES
(x = 7.2 ? 4.6) during chronic drug pretreatment, as the average number of days for those that had not convulsed was 14.8 -+ 7.5. These data are shown in Table 2. The mean number of afterdischarges for all days that afterdischarges were present, except for days on whichSs kindled, varied by electrode site. The greatest number of discharges occurred in the left amygdala. Fewer afterdischarges were found in the left caudate and still fewer in the right caudate (P 5 0.01). However chronic cocaine pretreatment did not result in a differential number of afterdischarges (P > 0.05) at any site as is shown in Table 3. Neither latency nor duration of afterdischarge in the, left amygdala site differed significantly as a function of treatment (P > 0.05). However, the duration of amygdala afterdischarge was significantly longer (P % 0.02 in Ss that had convulsed during pretreatment with cocaine (54.0 + 27.3 s) than in saline-pretreated Ss (33.8 & 23.6). The duration for cocainepretreated Ss that had not convulsed was 41.9 f 20.4 s which did not differ from the saline-pretreated Ss. Latency and duration of afterdischarges in right and left caudate sites did not vary as a function of pretreatment (P > 0.05). The speed with which discharges were propagated to the caudate was significantly faster for cocaine pretreated rats (P I 0.01). The salinepretreated group developed discharges 2.8 days after the kindling procedure was begun for the left caudate and at 3.8 days for the right. For the cocaine-pretreated Ss, the mean was 1.3 days for the left caudate and 1.2 for the right. Rats that had convulsed during treatment did not differ from those that had not in terms of the day on which propagation of afterdischarges to the right or left caudate was seen. These data are shown in Table 2. TABLE Mean
and Standard
Deviation
of Days
2
to Kindling
and Propagation Afterdischarge
Treatment Cocaine All Ss Convulsive Nonconvulsive
Kindling
only only
Saline * P 5 0.01 compared
Left
caudate
of Afterdischarge propagation Right
caudate
12.2 k 7.5* 7.2 T 4.6* 14.8 k 7.5
1.27 c 0.63* 1.30 k 0.67* 1.25 rt 0.62*
1.22 ” 0.61* 1.20 2 0.63* 1.25 k 0.62*
17.5 k 6.6
2.80
3.80
to saline-injected
controls.
+ 2.30
+ 4.60
310
KILBEY,
ELLINWOOD, TABLE
AND EASLER 3
Number of Afterdischarges Region Treatment
Left amygdala
Left caudate
Right caudate
Saline 40 mg/kg cocaine
95 -c 45” 107 2 50
71 + 47 88 k 52
73 k 46 87 f 52
Behavioral Effects. Behavioral ratings showed that Ss chronically pretreated with cocaine demonstrated augmented behavioral stereotypies when tested postkindling, whereas those pretreated with saline did not (Fig. 1). A lack of significant change in the saline group between cocaine tests on day 1 and the day after kindling (P > 0.05) shows that neither a single cocaine injection nor the kindling procedure potentiate stereotypies. As in a previous experiment (22), there were no significant differences in the behavioral augmentation between Ss that had convulsed during chronic pretreatment and those that had not (P > 0.05). DISCUSSION Recently, investigators (5, 15) suggested that the augmentation of abnormal behavior which occurs with chronic cocaine administration depends on mechanisms analagous to those believed to occur during “kindling,” i.e., a local neuronal reorganization at the site of stimulation and an enhanced propagation of neural activity from this stimulation site (2, 16- 18). The data of this experiment bear on this suggestion in several ways. If the repeated induction of amygdala spindles, known to occur with cocaine administration (22), mimics the effect of repeated electrical stimulation of this area, then pretreatment with cocaine should facilitate the rate of kindling. Experimental support for this hypothesis was not straightforward as those Ss that had experienced convulsions during the chronic drug treatment period accounted for the faster kindling which was obtained as a function of cocaine pretreatment. The rate of kindling within the group that had experienced convulsions did not appear to be a function of either the day on which the animal experienced convulsions or the number of convulsions. An animal that convulsed on day 3, for example, did not kindle until the 18th day whereas the Ss that had three convulsions kindled on day 9. The process by which prior drug-induced convulsions lead to facilitated kindling is not known. Spontaneously, audiogenically, chemically, or
CHRONIC
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AND STEREOTYPIES
311
9
8t
Time
in Minutes
FIG. 1. Mean behavioral rating of rats treated with saline or 40 mgikg cocaine during phases 4, 9, and 10. Ratings were made pre- and post-40 mg/kg cocaine during phase 4 (saline, & -; cocaine, 0- -) and phases 9 and 10 (saline, A-; cocaine O-). Behavioral ratings within treatments did not differ significantly at phases 9 and 10 postkindling (P > 0.05) and were combined. The standard errors for these data were approximately 6% of the mean values.
electrically induced seizures result in short-term elevations of seizure threshold (10, 20, 25) and long-term decreases. However, these appear to be specific to the modality used to induce the convulsion as prior chemical induction of seizures does not lower the threshold for electrically induced convulsions (25). Procaine coupled with electrical stimulation facilitated the rate of development of kindled seizures in comparison with Ss given saline plus electrical stimulation. However when Ss were retested in a seizures were retarded nondrug state, after 5 drug-free days, “kindled” (19). Thus, it appears experience with the combined effects of a local anesthetic drug and electrically induced seizures were not sufficient to
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facilitate “kindling” upon retesting in a nondrug state. The facilitation of “kindled” seizures found in a drug-free state in our experiment after chronic cocaine treatment which resulted in seizures suggest that cocaine-induced convulsions altered some mechanism basic to convulsions. This may involve synergistic effects of cocaine and kindling as both deplete DA stores (8, 24). As DA has been implicated as an inhibitory transmitter in the amygdala (1)) the longer duration of afterdischarges in the amygdala found in Ss that had experienced seizures during the chronic drug treatment period would be consonant with decreased DA levels also. Loss of inhibitory transmitter mechanisms due to DA depletion as a result of synergistic actions of chronic cocaine administration and seizure induction cannot explain cocaine’s augmentation of stereotypies as this occurred in allSs regardless of whether or not cocaine-induced convulsions had occurred. As faster propagation of afterdischarges to the caudate sites was seen in all Ss pretreated with cocaine also, these data suggest that chronic cocaine administration alone decreased inhibitory transmitter function allowing increased propagation of afterdischarges and augmented stereotypies. It is not known if cocaine induces spindles in the caudate as it does in the amygdala of rats, nor has the pehnomenon (18) of EEG spindle augmentation, reported to occur in the amygdala with chronic treatment, been evaluated at caudate or limbic sites. If faster amygdala-caudate pathway facilitation underlies augmentation of behavioral stereotypies, propagation of cocaine-induced spindles during chronic treatment should be coincident with the onset of augmented behavioral stereotypies, a hypothesis currently being tested. In summary, cocaine-induced convulsions during a period of chronic administration appears to facilitate “kindled” induction of seizures at a later time. This may reflect a synergism of relatively long-term cocaine-induced and seizure-induced dopamine depletion. Augmentation of behavioral stereotypy occurs in subjects pretreated with cocaine regardless of whether or not convulsions had been induced and may reflect localized long-term depletion of dopamine which impairs inhibitory function in the limbic system allowing propagation of afterdischarges from the amygdala to other sites. REFERENCES 1. BEN-AN, Y., AND J. S. KELLEY. 1976. Dopamine evoked inhibition of single cells of the feline putamen and basolateral amygdala. J. Physiol. (London) 356: l-22. 2. DOUGLAS, R. M., AND G. V. GODDARD. 1975. Long term potentiation of the perforant path-granule cell synapse in the rat hippocampus. Brain Res. 86: 205-215. 3. DOWNS, A. W., ANDN. B. EDDY. 1932. Theeffectofrepeateddosesofcocaineontherat. J. Pharmacol. Exp. Ther. 46: 199-200.
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