Abstracts

Rationale: Febrile seizures (FS) affect nearly 5% of children under age 5 in the United States. Preclinical efficacy evaluation of effective and safe drug therapy to prevent and stop FS using a clinically relevant animal model is urgently needed. We developed a new model of FS that combines the innate immune activator, lipopolysaccharide (LPS), with hyperthermia-induced seizures to simulate fever, a regulated increase in body temperature from an immune challenge, rather than hyperthermia alone. We used this model to test the efficacy of an L-type calcium channel blocker (nimodipine) to prevent prolonged seizures induced by fever.Methods: P11 Long Evans rat pups were implanted with mouse EEG head mounts (Pinnacle). On P14, rats were injected with saline or LPS (200 ug/kg, i.p.) 2 h prior to induction of seizures. Hyperthermia (HT) was induced by positioning a commercial hairdryer or heat lamp over a Plexiglas chamber to maintain core body temperature between 38-42 C for 30 min. EEG, latency, threshold temperature, and total number of seizures were quantified. In separate experiments, wild type and Cx3cr1GFP/- mice were injected with LPS (100 ug/kg, i.p.) 2.5 h prior to heat lamp induction of FS. Blood was collected for cytokine assay 2-24 h after seizures. In a third experiment, rats were injected either with vehicle (DMSO) or nimodipine (2.5 mg/kg in DMSO) 30 minutes prior to undergoing seizure induction using a heat lamp. Results: There was a significant increase in seizure susceptibility in rats and mice subjected to FS compared to HT alone using either the hairdryer or heat lamp methods. LPS priming decreased latency to seizure onset (rat hairdryer: p<0.0001, mice heat lamp: p<0.002) and threshold temperature (p< 0.01, p<0.002) and caused more severe seizures (p<0.003). FS significantly activated IL-1 , IL-6, TNF- production in the blood, while HT alone had only modest and transient effects. Nearly a two-fold increase in microglia was noted in Cx3cr1GFP/- mice primed with LPS (FS) compared to controls. EEG confirmed electrographic correlates of seizures. Nimodipine (2.5 mg/kg) reduced both the incidence and duration of convulsive FS in rat pups: 81% of controls compared to 18% of nimodipine-treated pups progressed to convulsions (p<0.05). Nimodipine also reduced the duration of ictal discharges from 59 21 sec in control to 5 5 sec in nimodipine-treated rats (p<0.05) during the period of HT, while the duration of abnormal interictal activity was unaffected.Conclusions: Systemic injection of LPS primes the brain to more rapidly respond to hyperthermia, exacerbates seizures, activates microglia and triggers pro-inflammatory cytokine response. We used this model of FS to demonstrate that a drug that blocks L-type calcium channels can reduce the incidence and duration of convulsive FS in rat pups. Because nimodipine is already FDA approved and safe, it holds promise as a novel therapy to stop and prevent seizures triggered by high fever. Effective treatment may reduce the risk of long term neurological consequences of uncontrolled recurrent or prolonged FS.