Abstract 2344: Video-EEG Reveals Subclinical Ischemic Seizures And Limited Efficacy Of Phenobarbital In Neonatal Mice

Ischemia in the immature brain is an important cause of neonatal seizures. The exact timing of neonatal stroke onset is usually unclear and the diagnosis delayed until presentation with seizures a few to several hours later. Optimal seizure treatment in neonates remains uncharacterized and the widely used drug phenobarbital has limited clinical efficacy. Developmental profiles of chloride co-transporter expression and function in immature brains have been proposed to dictate the age dependent anti-seizure efficacy of GABA-agonists and this switch is known to occur in P8-9 mouse pups. To investigate the anti-seizure efficacy of the first line anticonvulsant and GABA A -agonist phenobarbital (PB) and NKCC1 antagonist bumetanide (BTN) as adjunct treatment on neonatal ischemic-seizures, we utilized synchronous video-EEG and unilateral carotid-ligation to produce acute ischemic-seizures in postnatal day 7 and 10 CD1 mice. Quantitative analyses of pre- and post-treatment EEGs were done using Pinnacle (Pinnacle technology Inc., KS) seizure scoring and Insight software (Persyst development corp., AZ) for evaluation of seizure grades (clinical vs. subclinical or electrographic) and treatment efficacy. Severity of acute ischemic seizures and incidence of subclinical seizures was higher at P7 and a gender-specific susceptibility was detected in males that correlated with a lag in KCC2 expression levels in naive males compared to age-matched females, not detected at P10. However, the P7 brains were comparatively more resistant to infarcts unlike at P10 when they occurred frequently. PB showed a better efficacy at P10. BTN treatment 1h following PB however failed to act as an efficacious adjunct therapy and aggravated subclinical seizures in P10 females. At P7, both PB and add-on BTN treatment failed to stop seizures. EEG power (0.5-32 Hz) was lowered after PB treatment at both ages. Post-ischemic down-regulation of KCC2 expression was detected at both ages tested compared to age-matched naive brains. This study showed that 1. Quantification of subclinical ictal events better evaluate anti-seizure efficacy of treatments and 2. The down-regulation of KCC2 in ischemia may further decrease the efficacy of drug actions that are dependent on a hyperpolarizing chloride gradient for their anticonvulsant action. This decrease in efficacy failed to be rescued by blocking the immature chloride co-transporter NKCC1.