Bidirectional transfer between electrical and flurothyl kindling in mice: Evidence for common processes in epileptogenesis

Purpose: This study sought to determine whether there was a transfer of seizure susceptibility between two models of epileptogenesis, electrical kindling and a newly described model of flurothyl kindling. In this study, we determined the effects of preexposure to one kindling agent on the seizure responsiveness to the other. Methods: Mice were divided into three groups: (a) six mice (FLK) were kindled with flurothyl, rechallenged with flurothyl after a 28-day incubation phase, implanted with olfactory bulb (OB) electrodes, and electrically kindled; (b) six mice (ELK) were implanted with OB electrodes, electrically kindled to six stage 5 seizures, and given one flurothyl trial 3 days later and a second flurothyl trial after a 28-day incubation period; and (c) six mice (IMP) were implanted with OB electrodes, tested with flurothyl at the same times as the ELK group, and later electrically kindled. Results: Mice that were previously kindled with flurothyl (FLK) had significantly faster electrical kindling rates to one stage 5 seizure or to six stage 5 seizures compared with animals in the ELK and IMP groups. Mice that were previously exposed to either electrical kindling or flurothyl kindling had significantly diminished latencies to generalized seizure onset (flurothyl-induced seizure thresholds) either before or after a 28-day incubation period compared with the IMP control mice. In addition, both the FLK and ELK groups had significantly increased percentages of mice expressing forebrain-brainstem seizures, compared with the IMP group, following either rechallenge with flurothyl after a 28-day incubation or focal electrical kindling. Conclusions: These findings indicate a near-complete bidirectional transfer between these electrical and flurothyl kindling models. Mice that were previously exposed to either electrical or flurothyl kindling have increased seizure susceptibilities and altered seizure phenotypes when exposed to the other seizure paradigm. overall, these studies indicate that previous seizures are the critical determinant of the bidirectional transfer of seizure susceptibility observed, and not the electrical or pharmacologic properties of the original kindling agent. Finally, the observation of near identity in transfer characteristics between electrical and flurothyl kindling models suggests that the proepileptogenic processes initiated by exposure to either model are similar.