Enhancement of anti-absence effects of ethosuximide by low doses of a noncompetitive α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist in a genetic animal model of absence epilepsy

N-Acetyl-1-(4-chlorophenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (THIQ-10c) is a noncompetitive α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist that has been demonstrated to antagonize generalized tonic–clonic seizures in different animal models of epilepsy. In the study described here, we tested the potential effect of such a compound alone or co-administered with ethosuximide in a genetic animal model of absence epilepsy, the WAG/Rij rat. The intraperitoneal or intracerebroventricular microinjection of THIQ-10c alone was unable to significantly modify the number and duration of spike-and-wave discharges (SWDs). In contrast, intracerebroventricular administration of AMPA induced a dose-dependent increase in the number of SWDs. THIQ-10c dose-dependently antagonized this effect. Furthermore, co-administration of THIQ-1c with ethosuximide (50 mg/kg, intraperitoneally) was able to significantly increase the efficacy of the anti-absence drug. In conclusion, although noncompetitive AMPA receptor antagonists alone might not be useful in the treatment of absence epilepsy because of their low therapeutic index, combining them with ethosuximide might be helpful in controlling absence seizures in patients not tolerating this drug or in refractory patients.