Anticonvulsant effect of BmK IT2, a sodium channel-specific neurotoxin, in rat models of epilepsy

Abstract

Background and purpose: The sodium channel is a primary target for treating central nervous system disorders such as epilepsy. In this study the anticonvulsant effect of BmK IT2, a sodium channel-specific neurotoxin, was evaluated in different animal models of epilepsy.

Experimental approach: Experiments were performed on freely moving rats made epileptic by administration of either pentylenetetrazole (PTZ) or pilocarpine. BmK IT2 (0.05-0.5 microg in 2 microl) was microinjected into the CA1 area and its effects on PTZ-induced widespread, seizure-like behaviour and cortex epileptiform EEG, as well as on pilocarpine-induced seizure-like behaviour and c-Fos expression were studied.

Key results: Intrahippocampal application of BmK IT2 dose-dependently inhibited PTZ-induced seizure-like behaviour, and reduced the numbers and duration of the high amplitude and frequency discharges (HAFDs) of the epileptiform EEG component induced by PTZ. Similarly, in the pilocarpine-induced status epilepticus (SE) model, BmK IT2 significantly prolonged the latency to onset of the SE, reduced the severity of SE and suppressed hippocampal c-Fos expression during SE.

Conclusions and implications: BmK IT2 showed anticonvulsant activity as it inhibited the widespread seizures induced by PTZ and pilocarpine-induced SE in rats. This activity might be due to the modulation of sodium channels in the hippocampus. Hence, BmK IT2 could be used as a novel tool to explore the molecular and pathological mechanisms of epilepsy with regard to the involvement of sodium channels.

Figure 1

Representative normal and epileptiform EEG traces recorded from rat cortex directly above the hippocampus. (a) Normal EEG before PTZ injection; (b) and (c), HAFDs and spikes appeared during seizures after PTZ injection. Note that all EEG recordings were obtained from a rat with saline microinjected into hippocampal CA1 area before and after PTZ injection.

Figure 2

Effects of BmK IT2 on electrographic seizures induced by PTZ. The EEG results in the saline (n=6) or BmK IT2 (0.05, 0.1, 0.5 μg, n=6 for each dose) groups were counted for 2 h and averaged. (a) Effects of BmK IT2 on the latency to the first EEG seizure induced by PTZ. (b) A quantitative comparison of spikes between the saline and BmK IT2 groups during the first 2 h after PTZ injection. (c)A quantitative comparison of the HAFDs between the saline and BmK IT2 groups during the first 2 h after PTZ injection. (d) A comparison of the duration of the HAFDs between the saline and BmK IT2 groups during the first 2 h after PTZ injection. Data are presented as mean±s.e.mean. ^*P<0.05 and ^***P<0.005 compared with the saline group (One-way ANOVA, Tukey's test).

Figure 3

Effects of BmK IT2 on behavioural seizures induced by pilocarpine. (a) The seizure scores of the saline (n=8) and BmK IT2 (n=6 for each dose)-treated groups. (b) The latency to SE onset after the injection of saline or BmK IT2. Data are presented as mean±s.e.mean. ^*P<0.05 and ^***P<0.005 compared with the saline group (One-way ANOVA, Tukey's test).

Figure 4

Representative microphotographs of the suppressive effect of BmK IT2 on hippocampal c-Fos expression induced by pilocarpine. The sections show the c-Fos expression in the ipsilateral and contralateral sides of the hippocampus after the intrahippocampal administration of saline or BmK IT2. Panels (A) and (a), (B) and (b), (C) and (c), (D) and (d), (E) and (e), (F) and (f), (G) and (g), (H) and (h) were taken from the same section, respectively.

Figure 5

Histograms of the number of labelled FLI neurons in the ipsilateral (a) and contralateral (b) hippocampus in the saline and BmK IT2 groups. The number of labelled FLI neurons in the hippocampus from 9 to 11 sections of each animal was counted and averaged (n=6–8) 2 h after the injection of pilocarpine. Data are shown as mean±s.e.mean. ^*P<0.05 and ^***P<0.005 compared with the saline group (One-way ANOVA, Tukey's test).