Acute Seizure Activity in Neonatal Inflammation-sensitized Hypoxic-ischemic Brain Injury

Background: Hypoxic-ischemic encephalopathy (HIE) is a severe brain injury in newborns that affects 1.5 per 1000 live births worldwide and is the most common cause of neonatal seizures. Even with therapeutic hypothermia (TH), the only approved therapy for HIE at present, infants who survive HIE are at high risk for persistent neurodevelopmental deficits such as epilepsy and cerebral palsy. Perinatal infections, such as chorioamnionitis, are a common and significant risk factor for HIE. Previous studies have shown that infection in the setting of HIE has a poorer response to TH and poorer outcomes overall. There is no current specific neuroprotective therapy for infants with HIE complicated by infection. A more complete understanding of acute seizure activity following HIE complicated by infection will provide crucial opportunities for innovative therapies for this at-risk neonatal population. The objective of this study is to characterize acute seizure activity in HI brain injury complicated by infection compared to HI brain injury alone.

Methods: Neonatal mice (P9) were stereotactically implanted with electroencephalography (EEG) headsets and divided into the following 3 groups: sham, hypoxia-ischemia (HI), and inflammation-sensitized HI. HI injury was achieved at P10 utilizing the Vannucci model of unilateral carotid artery ligation followed by 8% hypoxia for 1 hour. Inflammation-sensitization, an established model for the inflammatory reaction associated with an infection that allows for good subject survivability, was achieved at P10 utilizing E. coli lipopolysaccharide (LPS) injection. All groups underwent continuous video EEG recording at baseline, during post-ligation, 8% hypoxia, and post-hypoxia. Video EEGs were then analyzed for electrographic seizure activity and behavior. Seizure behaviors were classified using a neonatal mouse behavioral seizure score (BSS) (Kadam 2009).

Results: All neonatal mice in the HI (n = 5 [3 female, 3 male]) and inflammation-sensitized HI (n = 7 [2 female, 5 male]) groups had electrographic seizures during ligation recovery, 8% hypoxia, and post-hypoxia. No mice in the sham group (n = 4 [3 female, 1 male]) exhibited electrographic seizure activity. Peak seizure burden occurred during 8% hypoxia and males appeared to have more seizure events compared to females in both experimental groups. There was no significant difference between the average number of non-convulsive (BSS 0-2) versus convulsive (BSS 4-6) seizures between inflammation-sensitized HI versus HI alone. Seizure duration was increased in inflammation-sensitized HI versus HI alone (mean = 78.95 vs 61.22).

Conclusion: Our preliminary data show that neonatal mice subjected to inflammation-sensitized HI exhibit a longer duration of electrographic seizure activity compared to neonatal mice subjected to HI alone. The next steps include further analyses of video EEGs, including background attenuation and power spectrogram comparisons, between the HI and inflammation-sensitized HI groups. Additional experiments to investigate sex differences in acute seizure activity in both experimental groups are actively ongoing.