Abstracts

RATIONALE: Benign familial neonatal convulsions, an inherited epilepsy, is caused by mutations in either the KCNQ2 or KCNQ3 subunit of the M-type K+ channel which underlies the M current. The M current regulates the subthreshold electrical excitability of most neurons. Linopirdine [DuP 996, 3,3-bis(4-pyridinylmethyl)-1-phenylindolin-2-one] enhances depolarization-induced release of several neurotransmitters in the central nervous system through inhibition of M current. This study was designed to evaluate the effects of linopirdine in seizure genesis in normal and epilepsy-prone mice.
METHODS: Experiments were performed on adult wild-type CF1, C57BL/6J and FVB/NJ mouse strains, the Frings audiogenic seizure-susceptible mouse strain, and the BALB.B6-[italic]Szt1[/italic]/+ mouse strain known to have a spontaneous deletion which truncates the [italic]Kcnq2[/italic] gene, causing a dominant susceptibility to electroshock and pentylenetetrazol (PTZ)-induced seizures. This study investigated the proconvulsive properties of linopirdine (10, 20 and 30 mg/kg, ip) administered alone and in combination with a convulsive dose of PTZ sufficient to produce a minimal clonic seizure in 25% (CD25) of the mice tested. For the combination study, the CD25 for PTZ was administered 15 min after linopirdine (20 mg/kg). Alterations in both behavior and EEG were monitored for 45 min after injection of linopirdine. EEG spectral analysis was performed.
RESULTS: By itself, linopirdine at 10, 20 and 30 mg/kg did not induce seizures in CF1 (n=9), C57BL/6J (n=10) or FVB/NJ (n=3) mice. At 30 mg/kg, body tremors and limb shakes were observed. In Frings mice, 10 mg/kg linopirdine produced whole body tremors; whereas 20 and 30 mg/kg linopirdine produced clonic seizure activity, followed by tonic extension and death at 30 mg/kg. In BALB.B6-[italic]Szt1[/italic]/+ mice, 30 mg/kg linopirdine produced severe body tremors and limb shakes, although only two out of the five mice tested displayed seizure activity. In the PTZ-linopirdine combination study, there was a significant increase in the number of animals exhibiting clonic seizures in the group that received 20 mg/kg linopirdine 15 min before CD25 PTZ injection, compared with animals that received only PTZ (p[lt]0.01 in all strains tested, binomial test). EEG spectral analysis confirmed that onset of seizure significantly increased the spectrum power in the low frequency band (delta wave). However, it was interesting that this increase started earlier than the onset of behavioral seizure, and it took more time for the EEG to recover.
CONCLUSIONS: These results suggest that 1) linopirdine facilitates PTZ-induced seizures in wild-type CF1, C57BL/6J and FVB/NJ mice, and 2) Frings and BALB.B6-[italic]Szt1[/italic]/+ mice, which are genetically epilepsy-prone, are more sensitive to linopirdine than the CF1, C57BL/6J and FVB/NJ mice. This data suggests that the M current is involved in seizure susceptibility, and linopirdine decreases seizure threshold by modulating the function of these channels.
[Supported by: NIH: 5-RO1-NS-40246 (WNF, HSW)]