Cyclothiazide induces seizure behavior in freely moving rats

Abstract

We have previously demonstrated that cyclothiazide (CTZ) is a potent convulsant drug inducing robust epileptiform activity in hippocampal neurons both in vitro and in vivo. Here we further establish an animal model for CTZ-induced behavioral seizures in freely moving rats. Microinjection of CTZ into the left ventricle dose-dependently induced robust seizure behaviors within 3h after administration. At a dose of 0.75 μmol, CTZ induced Racine score IV-V seizure behaviors in 71% (n=14) of the rats were tested. In addition, CTZ also induced epileptiform EEG activity accompanying behavioral seizures. The convulsant action of CTZ on both behavior and EEG was blocked by pretreatment with clinical anticonvulsant drug diazepam (n=5). In conclusion, our results demonstrate that CTZ is capable of inducing behavioral seizures in intact animals. Since CTZ acts on both GABAergic and glutamatergic systems, this new animal epilepsy model will be useful for anticonvulsant drug testing and general epilepsy research.

Fig. 1. Dose-dependent effect of CTZ in inducing seizure behaviors in freely moving rats

Bar histograms showing (A) the percentage of rats had Racine score I - V behavior and (B) the behavioral seizure score of the animals in DMSO control (n=8), CTZ at 0.25 μmol (n=5), 0.5 μmol (n=4) and 0.75 μmol (n=14), as well as CTZ (0.75μmol) after diazepam (10 mg kg^-1, n=5) groups. ** P<0.005 compared to the control group; ## P<0.005 compared to the CTZ at 0.75 μmol group.

Fig 2. Behavioral characterization of seizures elicited by CTZ in freely moving rats

Bar histograms showing the group data of CTZ-induced seizure in freely moving rats on (A) seizure numbers, and (B) seizure duration. * P<0.05, **P<0.005 compared to DMSO control group.

Fig. 3. Representative traces showing epileptiform EEG activities associated with behavioral seizures in a freely moving rat

Traces showing the original EEG recordings (A) before and (B) after CTZ injection in one anaesthetized rat. Part of the top traces taken from indicated area were expanded to illustrate the detail (middle and bottom traces). Seizure behavior-associated epileptiform EEG activity was marked with bar on top of the traces.

Fig. 4. Representative example of epileptiform EEG patterns elicited by CTZ

(A) Control EEG recording; (B) EEG recording after DMSO administration; (C-E) EEG recording after CTZ administration: (C) spike or sharp wave (indicated by arrows), (D) HAFDs, (E) continuous spikes with high amplitude (> 15 s).

Fig. 5. Typical electroencephalographic characteristics of seizures elicited by CTZ

Bar histograms showing the group data of DMSO control and CTZ-induced (0.75 μmol, n=8) epileptiform EEG components of (A) spontaneous seizure number, (B) HAFDs number, (C) HAFDs duration, (D) EEG score. *P<0.05, **P<0.005 compared to the DMSO control group.