Abstracts

Rationale: Several animal models that induce status epilepticus with chemoconvulsants have shown differences across developmental ages in behavioral correlates of seizure activity, threshold for evoking a seizure, and susceptibility to seizure induced injury. However, in part because of technical difficulties obtaining high quality EEG recordings in pre-weaned animals, our knowledge of electrographic activity during status epilepticus in rat pups younger than postnatal day 12 is quite limited. The development of a novel miniature wireless telemetry system for immature animals with good signal to noise ratio allows for a more detailed examination of EEG activity during status epilepticus.Methods: The lithium pilocarpine model was used to study EEG recordings during status epilepticus. Sprague Dawley rat pups were implanted with a miniature wireless telemetry device on post natal day 6. Status epilepticus was induced on postnatal day 7 with intraperitoneal injection of pilocarpine (50 mg/kg). Animals were pretreated 14-16 h before pilocarpine treatment with LiCl (127 mg/kg). Status epilepticus was monitored for at least 4 h with continuous video-EEG recordings to observe both behavioral and electrographic seizure activity. P7 treated animals were compared to both animals that did not receive pilocarpine and also older immature animals treated at P13 and P20.Results: Both behavioral manifestations of seizure activity and electrographic evidence of seizures could be observed at P7. Animals displayed low-amplitude, discontinuous, rhythmic polyspike and sharp wave activity that was not observed in any of the control animals. Behavioral correlates included myoclonic jerks, tonic stiffening, single limb clonus, and behavioral arrest. However, there were also occasional examples of EEG confirmed seizure activity where no behavioral changes were observed, suggesting that some seizure activity in this age group is subclinical. Compared to P7 rats, P13 and P20 rats more consistently displayed prolonged higher amplitude spike and wave activity, and, in addition to the behaviors observed in P7 rats, had robust tonic-clonic seizure activity (Racine scale 4-5).Conclusions: EEG seizure activity can be successfully recorded after treatment with lithium pilocarpine in immature animals as young as P7. In very immature animals, EEG monitoring is able to detect more epileptic abnormalities during status epilepticus than observation of behavioral seizures alone. This novel miniature wireless telemetry system allows us to identify both normal and abnormal EEG patterns not previously observed in immature rats.