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The effects of LY-201116, a 4-aminobenzamide, were examined in rats using the amygdala kindling model, both during acquisition of the kindled response and in fully kindled animals. Dose-response and timeresponse studies for efficacy and rotorod toxicity were completed following intraperitoneal injection of the drug. Afterdischarge duration, behavioral seizure response, kindled seizure threshold and EEG recordings were used to assess efficacy and toxicity of the drug. In the acquisition trial, the drug (7.5 mg/Kg) did not significantly alter the number of stimulations required to produce the first stage 5 kindled response nor did it modify afterdischarge durations. Doses of 11.25 and 15 mg/Kg suppressed afterdischarge and diminished behavioral responses significantly in fully kindled rats, but these doses were also neurotoxic as judged by rotorod performance. The non-selective anticonvulsant effect of 11.25 mg/Kg lasted at least 90 min. A dose of 15 mg/Kg raised kindled seizure threshold and diminished afterdischarge duration. Doses of 20, 30 and 40 mg/Kg produced spontaneous EEG spikes and seizures accompanied by behavioral convulsions. The drug thus exhibited non-selective anticonvulsant effects in fully kindled rats following doses of 11.25 or 15 mg/Kg, but exhibited proconvulsant activity following doses in the range of 20–40 mg/Kg.

A number of anticonvulsant drugs were studied for their efficacy in preventing seizures and death from intoxication with cocaine. Rats were first pretreated with the test drug then subjected to large doses of intraperitoneally administered cocaine. In this model, control animals developed seizures in approximately 6 min, followed by death in approximately 10 min. Statistically significant protection against seizures and death was afforded by pretreatment with diazepam, phenobarbitol and the blocker of the uptake of gamma-aminobutyric acid (GABA), SKF 100330A. Only partial protection was afforded by the N-methyl-d-aspartate (NMDA) antagonist MK 801, the benzodiazepine antagonist, flumazenil and the novel aminobenzamide, LY 201116. Valproic acid and phenytoin demonstrated limited efficacy against cocaine-induced seizures, without consistently reducing death. Carbamazepine and ethosuximide did not significantly reduce seizures or death. In this model of acute cocaine toxicity, the anticonvulsants diazepam, phenobarbital and the blocker of the uptake of GABA, SKF 100330A were the most effective in protecting rats from cocaine-induced seizures and death. These data offer insight into future approaches for the treatment of patients with the acute toxic effects of cocaine.

The effects of various doses of diazepam (0.5–4 mg/kg) and phenobarbital (7.5–60 mg/kg) were determined on prekindled and kindled amygdaloid seizures in the same rats. Diazepam was ineffective against the prekindled focal seizures, but demonstrated profound and statistically significant control of the kindled seizures. In the kindled state, diazepam reduced the afterdischarge duration and seizure rank score to prekindled levels. Only the largest sedating dose of phenobarbital produced a reduction of both prekindled afterdischarge duration and seizure rank score. Against the kindled seizure, phenobarbital showed a marked and statistically significant increase in effectiveness in all but the smallest dose tested. The afterdischarge duration of kindled seizures was reduced to prekindled levels by 15–60 mg/kg of phenobarbital, while seizure rank score was reduced to prekindled levels by 30 and 60 mg/kg phenobarbital. The effects of two doses of diazepam (0.5 and 2.5 mg/kg) and phenobarbital (7.5 and 30 mg/kg) were tested against prekindled and kindled pentylenetetrazol (PTZ)-induced seizures. Preliminary work with 3 doses of pentylenetetrazol (30, 40 and 60 mg/kg) demonstrated that repeated doses of 30 mg/kg readily kindled seizures without the significant mortality seen with larger doses. Both diazepam and phenobarbital were less effective against seizures kindled with 30 mg/kg pentylenetetrazol compared to prekindled seizures. The comparative lack of effect that was seen with diazepam and phenobarbital against the pentylenetetrazol kindled seizure at doses associated with control of the kindled amygdaloid seizure may reflect an underlying difference in the pathogenesis of kindling between these seizure models. Further, the lack of suppression of the prekindled amygdaloid afterdischarge duration by large doses of diazepam, in contrast to large doses of phenobarbital, may also reflect differences between the mechanisms of action of these two drugs. This paradigm provides a model for testing the effectiveness of anticonvulsants during the progressive development of various epileptogenic seizures.

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.

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.

The anticonvulsant effectiveness of the benzodiazepine antagonists RO 15-1788, CGS-8216 and PK-11195 were evaluated against threshold and suprathreshold (400 μA) stimulation in fully amygdaloid-kindled rats. Pretreatment with either RO 15-1788 (3, 10 and 30 mg/kg), CGS-8216 (3,10 and 30 mg/kg) or PK-11195 (10 and 60 mg/kg) failed in this study to modify consistently either the afterdischarge thresholds or elicited suprathreshold seizures or duration of afterdischarge. Using a double injection paradigm, the effectiveness of these three benzodiazepine antagonists to reverse the anticonvulsant and behavioral effects of diazepam were studied. When diazepam (3 mg/kg) was injected 15 min before or after a second injection of the vehicle control DMSO (0.25 mg/kg), a significant reduction in the duration of afterdischarge and seizure rank, elicited by a suprathreshold stimulation in amygdaloid-kindled rats, occurred. When either CGS 8216 (10 mg/kg)or RO 15-1788 (10 mg/kg) were given 15 min before diazepam (3 mg/kg) prior to stimulation, the anticonvulsant properties of diazepam were blocked. When RO 15-1788 (10 mg/kg) was given 15 min after diazepam, antagonism of the anticonvulsant effects on diazepam was shown. However, when either CGS-8216 (10 mg/kg) or PK-11195 (10 and 60 mg/kg) were given 15 min after diazepam (3 mg/kg), the anticonvulsant properties of diazepam were not blocked. The anticonvulsant effects of diazepam were reversed when CGS-8216 (10 mg/kg) was given 5 min after diazepam (3 mg/kg) or when a larger dose (30 mg/kg) was given at the same 15 min interval. Previous work has shown that the benzodiazepine antagonist, RO 15-1788 can inhibit the acquisition of amygdaloid-kindling, while the data in the present study point to the lack of significant anticonvulsant effectiveness of these three benzodiazepine antagonists in the fully amygdaloid-kindled model of epilepsy in the rat. Both of the “central” benzodiapine antagonists (RO 15-1788 and CGS-8216) demonstrated the ability to reverse the anticonvulsant effectiveness of diazepam in this model, when given before or after administration of diazepam. Appropriate doses and injection intervals were necessary to demonstrate the antagonism by CGS-8216 given after diazepam. Large doses of the “peripheral” benzodiazepine antagonist, PK-11195 failed to demonstrate intrinsic anticonvulsant properties or the ability to reverse the anticonvulsant effectiveness of diazepam in this model.

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.

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.

The effects of daily administration of pentylenetetrazol (PTZ) on the rate of the development of kindled amygdaloid seizures (KAS) were tested in the rat. Rats were pretreated for 6 days with 25 mg/kg PTZ or normal saline 15 min. prior to each daily amygdaloid stimulation. The PTZ group exhibited fully developed KAS, including a maximal behavioral ranking (BR) and an afterdischarge duration (AD) of over 90 sec, in 3.8 ± 0.3 stimulations compared to 8.0 ± 0.6 stimulations (ave. ± SEM) for the saline controls. Within 10 min after dosing, PTZ consistently induced intermittent spiking of 5 sec or less in the EEG and behaviorally induced head nodding and sniffing. However, chemical kindling due to the 6 repetitive doses of PTZ was not observed. When the PTZ pretreatment was stopped on the 7th day, the BR and AD of the PTZ pretreatment group decreased from 187% and 161% of control values, respectively, to 118% and 100% of control. It appears that PTZ augments both the AD and BR of the developing KAS but does not accelerate the actual rate of the development of the KAS.

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.

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.

The effects of 12 daily doses of 30 mg/kg GM1 ganglioside i.p. on the acquisition of kindled-amygdaloid seizures in the rat was studied. No modification in the rate of kindling or the expression of the elicited seizures was noted during the acquisition phase. Further studies with additional fully amygdaloid kindled rats failed to show significant modification of suprathreshold or threshold elicited seizures after single 30-60 mg/kg i.p. doses of GM1 ganglioside. Despite previous studies which have shown antibodies to GM1 ganglioside to be convulsive, no anticonvulsant activity was demonstrated in this study with exogenous GM1 ganglioside using a battery of kindled-amygdaloid seizure tests in the rat.

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.

The kindling phenomenon has become a useful animal model for studying the processes in the central nervous system involved in one type of epileptiform seizure response. A systematic, multipledose evaluation of 20 drugs known to have anticonvulsant properties and two new compounds (WB-CPI and SHK-I-11) is reported using a standard protocol with rats kindled by amygdaloid stimulation. Drugs which have a wide anticonvulsant spectrum of activity against various animal models of epilepsy were the most effective. The barbiturates, the benzodiazepines, a piperazine, an acetate derivative and WB-CPI (a significantly modified phenacylurea), were found to be the most effective in attenuating the induced seizures. Kindled amygdaloid seizures in the rat can be characterized as a model useful for the detection of a wide variety of anticonvulsants likely to be effective in many types of experimental seizures. The compound WB-CPI merits further neuropharmacological and psychopharmacological testing due to its activity in rats.

Amygdaloid kindled rats were utilized to determine the effects of the respiratory stimulant, doxapram (7.5-60 mg/kg) on seizures elicited by suprathreshold or threshold electrical stimulation. For comparison, a single dose of pentylenetetrazol (30 mg/kg), phenobarbital (40 mg/kg) and diazepam (2 mg/kg) were also tested in the same paradigm. With suprathreshold stimulation, doxapram did not increase the intensity of seizures. Neither the afterdischarge duration (AD) nor the behavioral rank (BR) were increased with doses high enough to cause systemic signs of toxicity. Similarly, the convulsant pentylenetetrazol did not increase AD or BR after suprathreshold stimulation. The anticonvulsants phenobarbital and diazepam significantly reduced both AD and BR after suprathreshold stimulation. Seizure thresholds tended to be higher after the various doses of doxapram with no consistent effect on elicited AD or BR. Pentylenetetrazol did not change threshold values, but was found to increase AD and BR at threshold. Both phenobarbital and diazepam raised thresholds with a significant decrease in elicited AD and BR. It would appear that the respiratory stimulant doxapram has little proconvulsant activity in this model of epilepsy.

The anticonvulsant properties of carbamazepine were evaluated in the kindled amygdaloid seizure model in rats. Carbamazepine significantly raised the threshold for seizures, reduced the duration of elicited afterdischarges and attenuated the severity of seizures in previously-kindled rats, at doses that did not cause sedation or ataxia. A similar reduction in the duration of elicited afterdischarges and severity of seizures was seen after suprathreshold stimulation (400 μA) with doses of carbamazepine that were without obvious sedative or ataxic effects. After acute intraperitoneal injections (solvent = 2% Tween-80 and70% propylene glycol), the maximum anticonvulsant effectiveness against suprathreshold stimulation was seen at 30 min. When administered daily (13 days) during acquisition or development of kindling, carbamazepine (25 and 50 mg/kg, i.p.) had variable effects on kindling. Neither dose consistently reduced the duration of elicited afterdischarges during the acquisition phase. Both groups tended to reduce the developing seizure, with the smaller dose of carbamazepine (25 mg/kg) resulting in a more consistent and significant reduction in severity of seizures. No significant differences in number of daily stimulations needed to reach fully kindled seizures were found. Previous studies have reported variable results with carbamazepine and the kindled amygdaloid seizure in rats. The present study provides a comprehensive evaluation of carbamazepine in this model of epilepsy and discusses the results with regard to the findings reported previously.