Abstracts

Rationale: Status Epilepticus (SE) is common in neonates and infants, and is associated with adverse developmental outcomes. However, the role of neonatal SE in these injury is uncertain. Until now, we have lacked an animal model in which SE induces neuronal injury during the neonatal period. We have developed a model of SE in post-natal day 7 (P7) rat pups, with 70% survival and extensive acute neuronal injury in many brain regions, and report the long-term sequellae associated with this model. Methods: We developed an animal model of SE in P7 rats, which are developmentally close to human neonates. Rat pups were injected ip with high dose lithium (5 mEq/kg) on P6, and the next morning with high dose pilocarpine (320 mg/kg), plus methylscopolamine to reduce secretions (1 mg/kg). This model was derived from a model of cholinergic SE (Tetz et al, 2006), and was adapted by us for use in P7 pups. Pups were kept in a special warming chamber to maintain their normal temperature (34-35°C). EEGs were recorded in selected animals and showed continuous seizures for 59.4 ± 6.3 min. O2 saturation was measured non-invasively from paw probes in selected animals, and showed no significant hypoxemia during or after SE. Animals were perfused with 4% phosphate-buffered paraformaldehyde 6 or 24 hrs after SE, or kept chronically for studies of behavior and epileptogenicity. Results: At 24 hours, a few Fluoro-Jade B (FJB) stained cells were found in the hippocampal formation and in extrahippocampal structures of sham control pups, as expected at that age. Six hours after SE onset, neuronal injury was significantly different from controls in neocortex, thalamus, dorsal CA3 and dorsal dentate gyrus. Twenty-four hrs after SE onset, significant neuronal injury was observed in CA1/subiculum, CA3, dentate gyrus, thalamus, neocortex, amygdala, piriform cortex, lateral entorhinal cortex, hypothalamus, caudate putamen, globus pallidus, ventral pallidum, and nucleus accumbens. At 24 hrs post-SE, caspase-3a immunoreactivity (IR) was significantly increased in CA1/subiculum, thalamus, and neocortex compared to sham. These caspase-3a-IR neurons had fragmented nuclei, suggesting that SE triggered an irreversible form of cell injury. At least 6 weeks after SE, both acquisition and retention in the Morris Water Maze were impaired in animals subjected to SE, compared to sham controls. Half of post-SE rats showed recurrent spontaneous seizure-like bursts of polyspikes lasting 5-10 seconds, accompanied by behavioral arrest, which were never seen in control rats. Convulsive activity was not seen in either group. Conclusions: We have developed a model of SE in P7 rat pups, which combines high survival (70% at 24hrs), widespread neuronal injury, chronic deficits in spatial learning and epileptogenesis. These studies suggest that the immature brain may be vulnerable to severe forms of SE, even during the perinatal period. Funding: Supported by grant 1 UO1 NS074926 from NINDS, by a Merit Review grant from the Veterans Health Administration, and by the James and Debbie Cho Foundation.