Abstracts

Rationale: Pharmacoresistance develops quickly during repetitive seizures, and refractory status epilepticus (RSE) remains a therapeutic challenge. The outcome of RSE is poor, with high mortality and morbidity. New treatments are needed. Deep hypothermia (20ºC) is used clinically during cardiac surgery and neurosurgery, and has proved safe and effective in those indications. We tested the hypothesis that deep hypothermia reduces RSE and its long-term consequences in a rat model of SE induced by lithium and pilocarpine and refractory to midazolam.Methods: Male Wistar rat (300-400 grams; Charles River) were implanted with skull screw electrodes one week before the experiment. Rats received lithium chloride (3 mEq/kg) subcutaneously and, 16 h later, all rats received scopolamine methyl bromide (1mg/kg), and SE was induced with i.p. pilocarpine hydrochloride (60 mg/kg). Twelve min after the second stage 3 or higher seizure (to make sure that self-sustaining seizures were well established), they received midazolam (3 mg/kg ip) and scopolamine (2 mg/kg i.p.), and rats that stopped seizing were removed from the study. In the hypothermic group, body temperature was brought to 20±1°C with ice packs, and maintained at that temperature for 30 min. Re-warming was initiated with a warming jacket until rectal temperature reached 36±1°C. Pilot experiments show that rectal and surface cortex temperatures were quite close. Several EEG measures were recorded in both hypothermic (n=17) and normothermic (n=20) animals. Neuronal injury (by Fluoro-Jade B), cell-mediated inflammation and breakdown of the blood-brain barrier (by IHC) were studied 48 h following SE onset.Results: Time to terminate SE after initiation of hypothermia was 198 ± 41 min in normothermics and 12 ± 2 min in hypothermics (p<0.0001). During the 24h following the initiation of cooling, deep hypothermia reduced the number of seizures by 65% (p<0.001), the number of spikes by 91% (p<0.0001), cumulative seizure time by 60% (p<0.01), the time needed for EEG power to decline to twice the pre-seizure baseline by 94% (p<0.0001), and the time in high-amplitude discharges by 55% (p<0.01). However, 3:36 -17:21 hours after re-warming, isolated seizures were found in 8 out of 17 animals, and in one animal, SE returned. At 48 hours, normothermic SE rats displayed extensive neuronal injury in many brain regions including hippocampus, dentate gyrus, amygdala, entorhinal and pyriform cortices, thalamus, caudate/putamen and frontoparietal neocortex. There was widespread breakdown of the blood-brain barrier, and extensive macrophage infiltration in areas of neuronal injury. In the hypothermic group, SE-induced neuronal injury, blood-brain barrier leakage and macrophage-mediated inflammation were eliminated in most animals.Conclusions: These results suggest that deep hypothermia may open a new therapeutic avenue for the treatment of RSE and for the prevention of its long-term consequences. Funding: Supported by VHA Research Service (CW) and NINDS (grant UO1 NS074926; CW).