Abstracts

Rationale: Tetramethylenedisulfotetramine (TETS) is a highly lethal neurotoxic rodenticide that acts as a noncompetitive GABAA receptor antagonist. Severe TETS intoxication in humans produces refractory convulsive status epilepticus (SE). We previously reported that the neurosteroid allopregnanolone enhances survival of mice in the TETS SE model and stops continued seizure activity faster than benzodiazepines such as midazolam and diazepam. Here we assess the effects of allopregnanolone on EEG measures in the TETS SE model. For comparison, some animals received midazolam at a dose equivalent by allometric scaling to that shown effective in the treatment of SE in humans (adult human dose: 10 mg; mg/kg mouse-to-human scaling factor: 0.081). Methods: Mice implanted with EEG electrodes were pretreated with a single dose of riluzole (10 mg/kg, IP) and 10 min later received a lethal dose of TETS (0.2 mg/kg, IP). Riluzole does not inhibit TETS-induced SE but does protect against the rapidly lethal effects of TETS in mice, providing a model of persistent seizure activity. Allopregnanolone (12 mg/kg, IM) and midazolam (1.8 mg/kg, IM) were administered 40 min after the first myoclonic twitch. Each 1 min epoch in the EEG recording during the 45 min period after treatment injection was scored for the presence of: isolated spikes/sharp waves (0.08-0.5 Hz), spikes/polyspikes/sharp waves clusters (0.5-2 Hz), and organized seizures. Rates are expressed as total number of rat-minutes with the observed behavior divided by total number of rat-minutes under observation and compared with Poisson regression models for longitudinal data. Results: Allopregnanolone decreased seizures (RR=0.21, 95% CI: 0.11, 0.38), spikes/polyspikes/sharp waves clusters (RR=0.20, 95% CI: 0.05, 0.88) and to the lesser extent isolated spikes/sharp waves (RR=0.42, 95% CI: 0.27, 0.66). In contrast, midazolam did not significantly reduce the rate of seizures (RR=0.68, 95% CI: 0.37, 1.26) but did reduce isolated spikes/sharp waves (RR=0.29, 95% CI: 0.15, 0.55) and spikes/polyspikes/sharp waves clusters (RR=0.51, 95% CI: 0.28, 0.94). Allopregnanolone versus midazolam contrasts were statistically significant for organized seizures (RR=0.41, 95% CI: 0.18, 0.92) and isolated spikes/sharp waves (RR=2.08, 95% CI: 1.04, 4.14) but not for spikes/polyspikes/sharp waves clusters (RR=0.39, 95% CI: 0.08, 1.84). Conclusions: Our results demonstrate that allopregnanolone is highly effective at reducing TETS-induced electrographic seizures and interictal-like activity. Midazolam, a benzodiazepine which is often used clinically in the treatment of SE, is less effective at reducing TETS-induced EEG seizures but effectively suppresses spikes and sharp waves. Our results indicate that the effects of allopregnanolone exceed those of midazolam on the electrographic features of TETS-induced SE. Allopregananolone's positive modulatory activity at extrasynaptic GABAA receptors that are not internalized during continuous seizures may account for its superiority over midazolam. Funding: NINDS grant #1U54NS079202, DZ, DJT, LO, PJL, MAR