The effect of cinromide on “kindled” seizures in the rat

Cinromide, an experimental anticonvulsant (Burroughs Wellcome Co.), was tested against focal cortical (simple partial analog), focal amygdala (complex partial analog), and generalized convulsive (tonic-clonic analog) seizures in the “kindled” rat. The toxicity in the CNS was measured by the ataxia scale devised by Desmedt. Niemegeers, Lewi and Janssen (Arzneimittel-Forsch.26: 1592–1602, 1976). Cinromide was found to suppress generalized convulsions in small, subtoxic doses, whereas larger, sometimes toxic doses were required to suppress focal seizure activity. The general pattern of response resembles that of the standard clinical anticonvulsants which the present authors have previously investigated. Cinromide, however, was relatively more potent against focal amygdala (complex partial analog) seizures than any drug previously tested, except carbamazepine. These data suggest that cinromide should be clinically effective, not only against tonic-clonic seizures, but also, toxicity permitting, against complex partial attacks as well.     

The anticonvulsant effects of diazepam and phenobarbital in prek1ndled and kindled cortical seizures

The effects of various doses of diazepam (0.5–4 mg/kg) and phenobarbital (15–60 mg/kg) were determined on prekindled (focal) and kindled (generalized) cortical seizures in the same rats. Only high sedating doses of diazepam or phenobarbital reduced the elicited afterdischarge duration (ADD) and behavioral response in the prekindled focal cortical seizure. Against the kindled seizure, both diazepam and phenobarbital showed a marked and statistically significant increase in effectiveness in all but the smallest doses tested. The ADD of the kindled cortical seizures was reduced to prekindled lengths by diazepam (1–4 mg/kg) or phenobarbital (30–60 mg/kg). The increased anticonvulsant effectiveness found in this study is similar to previous findings with diazepam and phenobarbital against prekindled and kindled amygdaloid seizures, but stands in contrast to findings with prekindled and kindled pentylenetetrazol seizures.     

Effect of cocaine and lidocaine on the development of kindled seizures

The effect of a subconvulsive dose of cocaine or lidocaine on the development of kindling was studied in male Long-Evans rats. Animals were divided into three groups and kindled by daily electrical stimulation of the pyriform cortex. Fifteen minutes before each stimulation each animal received an intraperitoneal injection of either saline, 20 mg/kg cocaine hydrochloride, or 20 mg/kg lidocaine hydrochloride. Following kindling the drug treatment was discontinued and the transfer of kindling to a nondrug state was assessed by test stimulations given 2, 6, and 48 days after the last day of kindling. Both cocaine and lidocaine dramatically accelerated the development of kindling. Furthermore, the duration of clonus at kindling criterion was significantly longer in lidocaine-treated animals than in animals treated with saline, and the onset of clonus in cocaine-treated animals occurred significantly sooner after stimulation. However, this performance did not transfer fully to the nondrug state, with some animals failing to exhibit clonus. Among those animals exhibiting clonus at nondrug tests, afterdischarge duration was significantly higher in cocaine-treated than in saline-treated animals, but clonus duration was no longer elevated in lidocaine-treated animals, and the latency to clonus rose dramatically in animals previously treated with either cocaine or lidocaine. These results indicate that a subconvulsive dose of cocaine or lidocaine can facilitate the development of kindling when the drug is active at the time of electrical stimulation, apparently by means of the local anesthetic action shared by the two drugs. The kindling produced in this fashion is not entirely equivalent to kindling produced by electrical stimulation alone.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of pentylenetetrazol, bicuculline and strychnine on the development of kindled seizures

Modification of the rate of acquisition of the kindled amygdaloid seizure by the convulsants pentylenetetrazol, bicuculline and strychnine was studied. Injections of saline, 25 mg/kg of pentylenetetrazol, 2 mg/kg of bicuculline or 1 mg/kg of strychnine were given 15 min prior to the daily electrical stimulation of the amygdala. The drug doses selected were capable of producing some behavioral and electrical epileptoid activity prior to stimulation without inducing generalized seizures. To determine whether pentylenetetrazol or bicuculline accelerated the rate of development of the kindled amygdaloid seizure or merely augmented the expression of each seizure, a crossover design was implemented. The crossover studies involved switching animals during the acquisition phase (between stimulations 3–6) from prestimulation saline to drug or drug to saline injections. It was found that pentylenetetrazol markedly augmented the expression of seizures during kindling development but the results of the crossover studies showed a less dramatic acceleration in the actual rate of the development of the fully generalized kindled amygdaloid seizure. The bicuculline-treated animals showed little augmentation in the expression of seizures during the kindling acquisition phase and in the actual rate of development of the kindled amygdaloid seizure. The strychnine treated animals showed no augmentation in expression of the seizures nor in the rate of development. The effects of prestimulation injections of bicuculline (1, 2 and 3 mg/kg) and strychnine (0.5, 1 and 2 mg/kg) on fully developed kindled amygdaloid seizures were also evaluated. Pretreatment with bicuculline minimally increased seizure afterdischarge duration at the highest dose. When fully kindled animals were pretreated with strychnine, a paradoxical decrease in afterdischarge length and an increase in severity (tonic hindlimb extension) was seen with the largest dose tested. This study emphasizes the potential importance of crossover studies in evaluating pharmacological manipulations of the rate of acquisition of the kindled seizure.     

Barbiturate serum levels and protection against kindled amygdaloid seizures in the rat

The barbiturates have been reported to be very effective against kindled amygdaloid seizures in the rat. In this study, the anticonvulsant effectiveness of pentobarbital, phenobarbital and primidone was studied in a systematic, multiple-dose evaluation. A correlation at 30 min between increased anti-convulsant protection and increased serum levels of pentobarbital and phenobarbital was seen. A possible correlation at 30 min, 2 hours and 48 hours between summed serum levels of the metabolites phenylethylmalonamide and phenobarbital was seen with the primidone treated animals. Serum primidone levels appeared to contribute little to the delayed protection against kindled amygdaloid seizures seen with primidone.     

Coadministration of gabapentin or MK-801 with lamotrigine slows tolerance to its anticonvulsant effects on kindled seizures

The development of tolerance to therapeutic effects of antiepileptic drugs can be a problem in the treatment of epilepsy, bipolar disorder, and pain syndromes. In the present study, acute treatment with the new antiepileptic drug lamotrigine (LTG, 15 mg/kg) markedly suppressed seizure stage and seizure duration in amygdala-kindled rats; but this antiseizure effect was rapidly lost following 4-8 days of repeated treatment. When gabapentin (GBP, 20 mg/kg) was coadministered with LTG, the ability of LTG to suppress seizure stage, seizure duration, and after-discharge (AD) duration was markedly extended. In addition, GBP coadministration with LTG decreased the number of animals that developed LTG-related running fits (Stage 6 seizures) and lengthened the number of days required to develop running fits or complete tolerance. Neither acute nor repeated treatment with MK-801 (0.3 mg/kg), a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, had effects on kindled seizures. However, cotreatment with MK-801 markedly extended the anticonvulsant effects of LTG on the three seizure indices and reduced running fits. These data indicate that cotreatment with either GBP or MK-801 slows tolerance development to the anticonvulsant effects of LTG on kindled seizures. Therapeutic implications of the present study remain to be explored.     

Adenosine antagonists. Lack of effect on the inhibition of kindled seizures in rats by carbamazepine

This study investigates the ability of adenosine antagonists to reverse the anticonvulsant effects of carbamazepine on amygdala-kindled seizures in order to elucidate the possible physiological relevance of the potent effects of carbamazepine on adenosine receptors. At large but subconvulsant doses, neither caffeine nor theophylline altered the anticonvulsant potency of carbamazepine, even though caffeine by itself significantly increased the duration of the kindled afterdischarge. The adenosine agonist cyclohexyladenosine (CHA), administered intraperitoneally at a dose that produced sedation, had no effect on the kindled seizures. Although carbamazepine potently displaces the binding of several adenosine ligands in vitro, the present data do not suggest that the anticonvulsant effects of carbamazepine on amygdalakindled seizures are mediated by an adenosine agonist-like action.     

Effect of cocaine and lidocaine on the expression of kindled seizures in the rat

The effect of cocaine and lidocaine on the expression of kindled seizures was studied in male Long-Evans rats. Animals were implanted with an electrode in either the olfactory bulb, prepyriform cortex, or basolateral amygdala and kindled by daily electrical stimulation. Each animal was then tested for the expression of kindled seizures following the intraperitoneal administration of saline, 20 mg/kg cocaine hydrochloride, or 20 mg/kg lidocaine hydrochloride. During testing the implantation site was stimulated every 60 sec at increasing current levels until an afterdischarge was elicited. Each animal was tested once under each drug at 96 hr intervals. The order of drug administration was counterbalanced across animals. Neither cocaine nor lidocaine had a significant effect on afterdischarge threshold. Both drugs significantly reduced the latency for clonus to occur following stimulation, a measure presumably related to the propagation of afterdischarges from the site of stimulation to other brain areas. In addition both cocaine and lidocaine significantly reduced the rated behavioral response to the stimulation due to a decrease in rearing and falling. Because they occurred with both cocaine and lidocaine, these effects appear to be of local anesthetic origin. In contrast, only cocaine significantly reduced afterdischarge duration, and only lidocaine significantly reduced clonus intensity. With the possible exception of clonus latency, these effects were present at all electrode sites studied. The results indicate that cocaine has pronounced effects on the expression of seizure activity in the olfactory forebrain, some of which are due to its local anesthetic action, and some not.     

Valproic acid serum levels and protection against kindled amygdaloid seizures in the rat

Valproic acid has been reported to be very effective against kindled amygdaloid Scizures in several species. In this study, the anticonvulsant effectiveness of valproic acid against kindled amygdaloid Scizures was studied in a systematic, multiple-dose evaluation in rats. A correlation at 30 min. between the degree of Scizure protection and increased serum levels of valproic acid was seen. At 30 min., the fifty percent effective dose (ED₅₀) was found to be 200 mg/kg. Additionally, the fifty percent effective serum level (ESL₅₀) was estimated to be 500 mg/L.     

Ketamine-induced changes in kindled amygdaloid seizures

The effects of ketamine on seizures kindled by repetitive electrical stimulation of the amygdala were determined in the rat. The response of fully developed kindled amygdaloid seizures (KAS) to 20, 40, 80 and 120 mg/kg (i.p.) ketamine, administered from 5 to 60 min prior to elicitation of seizures was examined. Ketamine reduced the afterdischarge duration (AD) and behavioral response (BR) in a dose-dependent fashion. However, the effect of ketamine on the afterdischarge duration and behavioral response was not clearly time-dependent for each dose (20–120 mg/kg). A dose-dependent increase in the seizure spiking frequencies in the amygdala and cortex during kindled amygdaloid seizures was also induced by ketamine. Blood plasma and brain levels of ketamine and its metabolites were determined 15 min after 20, 40, 80 and 120 mg/kg ketamine as well as 60 min after 80 mg/kg ketamine. Brain and plasma levels of ketamine and nor-ketamine were similar to those previously reported. Low plasma levels of dehydro-nor-ketamine were seen only at 60 min after 80 mg/kg ketamine. The decrease in afterdischarge duration and behavioral response and the increase in afterdischarge duration spiking frequency seen at 15 min correlated with elevated levels of ketamine and nor-ketamine in brain and plasma. However, by 60 min plasma levels of ketamine remained high, yet the brain levels of both ketamine and nor-ketamine had decreased. This is despite the fact that afterdishcarge duration and behavioral response were still attenuated and afterdischarge duration spiking frequency was still increased. Thus, the exact contribution by ketamine and nor-ketamine to the alteration of afterdischarge duration, behavioral response and afterdischarge spiking frequency cannot be made at this time. It was apparent that inhibition of the afterdischarge duration and behavioral response along with an increase in spiking frequency was not dependent on dehydro-nor-ketamine. The possibility that an unidentified metabolite may contribute to the modification of kindled amygdaloid seizures by ketamine is discussed.     

Anticonvulsive properties of F1933 (dulozafone) on kindled seizures in the rat

The anticonvulsive properties of a new compound: F1933 (Dulozafone) were investigated in the amygdala kindling model and compared with those of diazepam. Both drugs protected fully kindled rats against generalized seizures but failed to suppress partial ictal events (amygdala afterdischarges and limbic seizures). The anticonvulsive action of F1933, administered at the ED100, was nearly reversed by the specific antagonist of benzodiazepines receptors; R015-1788 (Flumazenil), suggesting that the effect of F1933 is mediated by this receptor. These results also emphasize the usefulness of kindling to test antiepileptic drugs and to confirm their supposed profile of action.     

Formamidine pesticides enhance susceptibility to kindled seizures in amygdala and hippocampus of the rat

Electrical kindling of the amygdala and hippocampus was used to evaluate the effects of two formamidines, chlordimeform (CDF) and amitraz (AMZ), upon seizures susceptibility in the rat. Male Long-Evans rats were implanted with electrodes in the amygdala or dorsal dentate gyrus, and injected IP daily with 40 mg/kg CDF, 50 mg/kg AMZ, or equal volumes of their respective vehicles. Afterdischarge (AD) thresholds were determined after the first injection. Animals were then stimulated twice daily, 2 and 4 hours postinjeciton, at a standard 200 microA stimulus intensity until three stage 5 generalized seizures ensued. Both CDF and AMZ significantly facilitated amygdaloid kindling rate, and CDF also facilitated hippocampal kindling rate. The effects of AMZ on hippocampal kindling were not assessed. AD durations were prolonged in the formamidine-treated groups, but there was no effect on AD thresholds. The alpha-2 adrenergic agonist and/or local anesthetic-like properties of these compounds may be responsible for these seizure enhancing effects.     

Effect of pentylenetetrazol-induced convulsions on the development and expression of limbic kindled seizures

Male Long-Evans rats experienced three convulsions induced by intravenously administered pentylenetetrazol (PTZ) and were then kindled by electrical stimulation of the olfactory bulb or amygdala. Pretreatment with PTZ did not alter the rate of kindling in either site but did enhance the expression of kindled seizures once generalization had occurred (PTZ-treated animals had significantly longer motor seizures, measured by clonus duration, than did saline-treated controls). This suggests that PTZ-induced convulsions have selective effects on areas of the brain that are involved in the expression of the motor seizure. In addition, rats treated with PTZ after kindling had convulsions that were significantly longer in duration than any of their three pre-kindling convulsions, indicating that kindling produced an increased sensitivity to PTZ's convulsant effects. Comparison of this experiment with previous research suggests that the ability of a drug treatment to generate a kindling-like effect is related to the pattern of seizure activity that it produces.     

The anticonvulsant properties of melatonin on kindled seizures in rats

The literature suggesting that the pineal gland and the indolamine, melatonin, have a significant role in regulating and modulating brain electrical activity is reviewed. The anticonvulsant properties of melatonin were investigated by testing acute doses of melatonin against two types of kindled Scizures in the rat. Against the electrically kindled amygdaloid Scizure, melatonin significantly reduced afterdischarge length at a non-sedative dose, but failed to modify Scizure rank scores. With larger doses of melatonin, which were associated with some sedation and ataxia, the Scizure rank score was reduced, but there was no additional reduction of afterdischarge length. Naloxone treatment (20 mg/kg, i.p.) did not reverse the sedation, ataxia, nor the anticonvulsant effects seen with the large dose of melatonin (200 mg/kg, i.p.). Additional animals were kindled with pentylenetetrazol injections (30 mg/kg, i.p.) given at 2–3 day intervals. Melatonin significantly reduced Scizure rank scores in these kindled animals at one dose (150 mg/kg, i.p.). A larger dose, associated with sedation and ataxia, did not result in any further reduction of Scizure rank scores. For comparison, large and small doses of both phenobarbital and diazepam were also tested against the pentylenetetrazol kindled Scizures. Neither phenobarbital (30 mg/kg) nor diazepam (2.5 mg/kg) induced a neurological deficit; however, both agents reduced Scizure rank to approximately the same score as did melatonin (150 mg/kg). This is the first report of a substantial anticonvulsant property of parenteral melatonin in two animal models of epilepsy. It would appear tha melatonin is most effective against the kindled pentylenetetrazol Scizure, and somewhat less effective against the electrically kindled amygdaloid Scizure. Further testing in other Scizure models and species is needed to define better the anticonvulsant profile of melatonin.     

Caffeine modification of kindled amygdaloid seizures

Rats were kindled during exposure to caffeine (50 mg/kg) or saline given IP twenty minutes before daily electrical stimulation of the amygdala until 3 kindled amygdaloid seizures (KAS) occured. They were then stimulated for 3 days without drug pretreatment followed by 5 additional days with drug pretreatment. There were no significant differences between the two groups in the number of daily stimulations or in the total seconds of cumulative afterdischarge (AD) needed to reach the first KAS. During kindling, the daily average AD tended to be longer in the caffeine treated group. This difference became significant (>200% saline) when the KAS was reached. When KAS animals were stimulated without caffeine pretreatment, the average AD returned to control lengths. When put back on caffeine pretreatment, the average AD was again increased. Caffeine (6–50 mg/kg, IP) was also evaluated in previously kindled rats using suprathreshold (400 μAMP) and threshold (20 μA increments) seizures. Caffeine had no consistent effect on threshold values. However, 12–50 mg/kg of caffeine increased seizure severity and AD durations after threshold stimulation. With suprathreshold stimulation, the length of the AD was significantly increased only after the highest dose of caffeine. It would appear that caffeine lengthens induced afterdischarges both during the acquisition phase of kindling and in the fully kindled subject. Caffeine does not appear to lower seizure thresholds or increase the rate of aquisition of the KAS in the doses tested in this model. It is postulated that caffeine may modify the KAS through an inhibition of the mechanisms which terminate the elicited AD.     

The effects of various anesthetics on amygdaloid kindled seizures

The effects of various doses of cataleptic anesthetics, gamma-butyrolactone (GBL), phencyclidine (PCP), and ketamine (KET), and the depressant anesthetics, pentobarbital (PB) and chloral hydrate (CH), on amygdaloid kindled seizures were tested in the rat. The seizure activity was monitored by behavioral observation and EEG recording. Anesthetic doses of the cataleptic anesthetics with the exception of KET had minimal effects on the afterdischarge duration (AD) and behavioral ranking (BR) of the elicited seizures. On the other hand, they were more inhibitory to the AD and BR than was the convulsant pentylenetetrazol (PTZ). The only cataleptic that induced spontaneous seizure activity at anesthetic doses was PCP, although KET induced epileptoid activity at supranesthetic doses. Ketamine, PB, and CH completely inhibited elicited seizure activity at anesthetic doses. In addition, rats were kindled by repetitive electrical stimulation during GBL-induced anesthesia or catalepsy. Although both these GBL groups averaged more stimulations to reach generalized seizures than the saline controls, GBL did not block the kindling process.     

Cysteamine suppresses kindled seizures in pentylenetetrazol-kindled rats

Rats were kindled by intraperitoneal injection of pentylenetetrazol (PTZ) (30 mg/kg) every 48 h. Once kindled, animals received a single injection of cysteamine (200 mg/kg) and subsequent responses to PTZ were observed. Cysteamine, an agent which depletes brain somatostatin and suppresses kindled seizures in amygdaloid-kindled rats, markedly suppressed the severity of PTZ-induced seizures in PTZ-kindled rats as well. However, it did not alter the convulsive response of non-kindled rats to a submaximal convulsive dose (50 mg/kg) of PTZ. The results support a role for somatostatin in kindling.     

The effect of a glycine derivative (CP 1552-S) on kindled seizures in rats

The effects of the glycine derivative, CP 1552-S (2-N-pentylaminoacetamide hydrochloride) were evaluated for potential anticonvulsant activity in rats which were cortically- or amygdaloid-kindled. Large doses (300-600 mg/kg, i.p.) of CP 1552 given 30 min before stimulation resulted in significant reductions in duration of afterdischarge after both partially-developed and fully-developed cortically-kindled seizures. The largest dose tested (600 mg/kg, i.p.) markedly reduced the duration of the elicited afterdischarge and the severity of seizure. This dose was associated with prestimulation sedation and a 50% incidence of post-afterdischarge spontaneous, electrical seizure activity. Against kindled amygdaloid seizures, CP 1552-S significantly reduced the duration of afterdischarge at 300 mg/kg (i.p.) without modifying the seizure and without prestimulation behavioral or electrical effects. The largest dose tested (600 mg/kg, i.p.) resulted in a significant reduction of the elicited duration of afterdischarge but was associated with a 25% incidence of prestimulation spontaneous electrical seizure activity and a 45% incidence of post-afterdischarge electrical seizure activity. When CP 1552-S (30-300 mg/kg, i.p.) was administered daily, prior to the amygdaloid kindling stimulus, no difference was noted in the rate of acquisition of the kindled amygdaloid response. It is concluded that the glycine derivative CP 1552-S, has little anticonvulsant activity against the acquisition or development of kindled amygdaloid seizures. It appears to have significant anticonvulsant effects against both cortically- and amygdaloid-kindled afterdischarges with little effect on the behavioral severity of the seizure. Further, large doses of CP 1552-S appeared to result in paradoxical post-afterdischarge and possibly prestimulation electrical seizure activity.     

Regional brain concentrations of cholecystokinin in the rat: the effects of kindled and non-kindled seizures

In an attempt to understand the neurochemical basis of kindling, this study investigated the effects on brain cholecystokinin (CCK) of amygdaloid kindled and non-kindled seizures. Thirteen brain regions were examined in rats sacrificed either 24 hr or 3 weeks after the last kindled seizure, or 24 hr after a suprathreshold stimulation-induced (non-kindled) seizure; and in sham kindled rats. There were no significant differences in CCK immunoreactivity between any of these groups. These results do not confirm a previous report of an increase in CCK in the hippocampus following amygdaloid kindling in the rat.     

The new antiepileptic drugs lamotrigine and felbamate are effective in phenytoin-resistant kindled rats

We evaluated the anticonvulsant efficacy of the antiepileptic drugs (AEDs) lamotrigine (LTG) and felbamate (FBM) in amygdala kindled rats that had been preselected with respect to their response to phenytoin. Anticonvulsant response was tested by determining the afterdischarge threshold (ADT), i.e., a sensitive measure for drug effects on focal seizure activity. By repeated testing with the phenytoin prodrug fosphenytoin, 3 groups of kindled rats were separated: rats in which consistent anticonvulsant effects were obtained (phenytoin responders), rats which showed no anticonvulsant response (phenytoin nonresponders), and rats with variable responses (variable phenytoin responders). The latter, largest group was used to evaluate at which doses LTG and FBM exerted significant anticonvulsant effects on ADT 1 h after i.p. drug administration. Effective doses were then used for drug testing in phenytoin responders and nonresponders. Both LTG and FBM proved to be effective anticonvulsant drugs in the kindling model by markedly increasing the ADT. Seizure severity and duration recorded at ADT currents were hardly reduced, indicating that both drugs predominantly affect induction of focal seizures and not seizure spread from the focus. In phenytoin nonresponders, LTG and FBM significantly increased ADT, which is in line with their proven efficacy in patients with refractory partial epilepsy in whom phenytoin has failed. However, LTG and, more markedly, FBM were clearly more efficacious in increasing ADT in phenytoin responders than in nonresponders, substantiating that the difference in phenytoin response between these groups of kindled rats extends to other AEDs. The data in this study reveal that phenytoin nonresponders are a unique model for the search for new AEDs with improved efficacy in refractory partial epilepsy.