The action of progabide against motor seizures elicited by pentylenetetrazol was studied in 7-, 12-, 18-, 25-day-old and adult rats. Progabide (dissolved in dimethylsulfoxide) was injected in doses from 12.5 to 150 mg/kg i.p. 30 min before pentylenetetrazol. Minimal seizures were not affected by solvent or progabide pretreatment. The action of progabide against major, i.e. generalized tonic-clonic seizures, changed with age: adult rats exhibited a tendency to suppression of whole major seizures, whereas specific suppression of the tonic phase was observed in rat pups during the first three weeks of life. The only effect seen in 25-day-old animals was prolongation of the latency of major seizures after the highest dose of progabide.
The anticonvulsant action of SL 75 102, a metabolite of Progabide, was studied in a model of pentylenetetrazol- induced motor seizures in adult and 12-day-old rats. SL 75 102 suppressed generalized tonic-clonic seizures in adult rats and restricted the tonic phase of these seizures in rat pups. SL 75 102 was less effective than Progabide. In addition, some minor differences in anticonvulsant actions of these two drugs were observed.
The action of two potential anticonvulsants, CM 40907 (10-50 mg/kg i.p.) and SR 41378 (1.25-20 mg/kg i.p.) against metrazol-induced seizures was studied in rats 7, 12, 18 and 25 days old. Two types of motor seizures - minimal, clonic and major, generalized tonic-clonic - were elicited by a 100-mg/kg dose of metrazol (s.c.) and their incidence and latency were evaluated. The severity of seizures was expressed as a score on a 5-point scale. Dimethylsulfoxide, an organic solvent, exhibited anticonvulsant action only in doses far exceeding those used for dissolving the two anticonvulsants. Both drugs suppressed minimal as well as major seizures in all age groups studied in a dose-dependent manner, SR 41378 being approximately four times more potent than CM 40907. The latencies could be measured only in animals given low doses of anticonvulsants. CM 40907 did not change the latencies whereas SR 41378 prolonged them. The severity of seizures was decreased again in a dose-dependent manner. There were only minor changes in the efficacy of CM 40907 among the four age groups. On the contrary, SR 41378 exhibited an extreme efficacy in 7-day-old rat pups, where even the 1.25 mg/kg dose signifcantly decreased the incidence and severity of seizures. The efficacy in the remaining three age groups was approximately at the same level as in adult rats.
The effects of two non-competitive NMDA antagonists - MK-801 and ketamine - were studied in a model of generalized seizures elicited by s.c. injection of strychnine (2 or 3 mg/kg) in adult rats. The animals were observed in isolation for 30 min after strychnine administration. Pretreatment with MK-801 (0.5 or 2 mg/kg i.p.) suppressed the tonic, but not the clonic phase of generalized seizures following both doses of strychnine. A similar action of ketamine (20 or 40 mg/kg i.p.) was indicated but it did not attain statistical significance. Strychnine-induced lethality was not changed significantly. A comparison with antiepileptic drugs demonstrated that only phénobarbital (10-80 mg/kg i.p.) was clearly effective against strychnine-induced seizures; carbamazepine (25 or 50 mg/kg i.p.) and partly phenytoin (30 or 60 mg/kg i.p.) were able to suppress the incidence of the tonic phase. Primidone (40 or 80 mg/kg i.p.) as well as the benzodiazepines bretazenil (0.1 or 1 mg/kg i.p.) and midazolam (two lower doses of 0.5 and 1 mg/kg i.p.) were without significant effect. The 2 mg/kg dose of midazolam was partly effective. Only phénobarbital, carbamazepine and the highest dose of midazolam prevented strychnine-induced lethality.