Effects of carbamazepine, AF-CX 921, and AF-CX 1325 on epileptic discharges and seizures in hippocampally kindled rats

Use of maximal dentate activation to study the effect of drugs on kindling and kindled responses

Maximal dentate activation is a paroxysmal event characterized by the appearance of bursts of large amplitude population spikes in the dentate gyrus that has been shown to be associated with the production of afterdischarges in limbic circuits. Repeated elicitation of maximal dentate activation in the anesthetized rat produces a progressive increase in afterdischarge duration. The present work examined the role of NMDA receptor activation in this process. The effects of MK-801 (a systemically active NMDA receptor complex antagonist) and imipramine and desipramine (tricyclic antidepressants recently reported to have NMDA receptor-coupled channel blocking properties) were studied. MK-801, at 0.5 mg/kg, prevented the lengthening of the duration of maximal dentate activation. At 2 mg/kg, MK-801 also shortened the duration of maximal dentate activation already established. Imipramine showed a similar dose-dependent response pattern with 15 mg/kg and 50 mg/kg respectively. Desipramine (50 mg/kg) was similar to imipramine (50 mg/kg) in its effect. Thus, the drugs studied were effective at shortening limbic epileptiform discharges. These results support the use of this model to examine drug effects and strengthen the hypothesis that NMDA receptors play a critical role in seizure generation in the limbic system and, specifically, in the lengthening of the duration of maximal dentate activation.

Differences in antiepileptic drug efficacy in hippocampally kindled normal and microcephalic rats

The difference in antiepileptic drug efficacy was investigated in two groups of animals: 5 normal and 4 microcephalic rats. The latter were produced by a single i.p. injection of 30 mg/kg methylazoxymethanol acetate in the mother on the 15th day of gestation. Hippocampal kindling was performed to a seizure criterion in all animals followed by testing of the antiepileptic drugs vs placebo. Besides carbamazepine (CBZ), two new anticonvulsants were tested: (E)-2-[(alpha-amino)phenylmethylene]-benzo-[b]-thiophene-3(2H)-one (AF-CX 921) and its metabolite (E)-2-[alpha-amino)phenylmethylene]-benzo-[b]-thiophene-3(2H)-one- 1- oxide (AF-CX 1325). Frequency of occurrence and duration of afterdischarges and seizures were statistically examined. The duration of early afterdischarges (AD1) tended to be shorter in microcephalic than in normal animals in control and placebo periods. In contrast, during treatment with the antiepileptic drugs, AD1 durations were longer in microcephalic than in normal animals. This suggests that the drugs inhibited AD1 to a lesser extent in the microcephalics. Two other characteristics of EEG epileptic activity, focal spiking (FS) and late afterdischarges (AD2) also varied in the two groups. Both were significantly lower in occurrence in the microcephalic rats independent of treatment. Three types of behavioral manifestations were also examined: convulsive seizures (CS), epileptic behavior (EB) and quiet states (Q). The two groups of animals responded differently to the drugs with respect to Q and CS. In the microcephalics, AFCX 1325 and AFCX 921 were superior to CBZ, which in turn, was superior to placebo.(ABSTRACT TRUNCATED AT 250 WORDS)