Complex spectrum of phenobarbital effects in a mouse model of neonatal hypoxia-induced seizures

Sean M M Quinlan,David C Henshall,Stephen F Madden,Eleanor J Molloy,Eva M Jimenez-Mateos,Geraldine B Boylan,Natalia Rodriguez-Alvarez

doi:10.1038/s41598-018-28044-2

Abstract

Seizures in neonates, mainly caused by hypoxic-ischemic encephalopathy, are thought to be harmful to the brain. Phenobarbital remains the first line drug therapy for the treatment of suspected neonatal seizures but concerns remain with efficacy and safety. Here we explored the short- and long-term outcomes of phenobarbital treatment in a mouse model of hypoxia-induced neonatal seizures. Seizures were induced in P7 mice by exposure to 5% O2 for 15 minutes. Immediately after hypoxia, pups received a single dose of phenobarbital (25 mg.kg−1) or saline. We observed that after administration of phenobarbital seizure burden and number of seizures were reduced compared to the hypoxic period; however, PhB did not suppress acute histopathology. Behavioural analysis of mice at 5 weeks of age previously subjected to hypoxia-seizures revealed an increase in anxiety-like behaviour and impaired memory function compared to control littermates, and these effects were not normalized by phenobarbital. In a seizure susceptibility test, pups previously exposed to hypoxia, with or without phenobarbital, developed longer and more severe seizures in response to kainic acid injection compared to control mice. Unexpectedly, mice treated with phenobarbital developed less hippocampal damage after kainic acid than untreated counterparts. The present study suggests phenobarbital treatment in immature mice does not improve the long lasting functional deficits induces by hypoxia-induced seizures but, unexpectedly, may reduce neuronal death caused by exposure to a second seizure event in later life.

Highlights

Seizures are most prevalent during the neonatal period, defined as the first 28 days of life in a term infant, affecting 3–5 in every 1000 live births[1]
We first evaluated the effects of PhB on hypoxia-induced neonatal seizures in post-natal day 7 (P7) mice, an age-appropriate model for neonatal seizures in humans[21,22,23]
P7 pups subjected to normoxia or hypoxia-induced seizures were injected with a single dose of vehicle or PhB (25 mg.kg−1, which falls within the normal dose used in the clinic (20–40 mg.kg−1)[15] immediately upon re-oxygenation and electrographic activity was evaluated (Fig. 1A)

Summary

Introduction

Seizures are most prevalent during the neonatal period, defined as the first 28 days of life in a term infant, affecting 3–5 in every 1000 live births[1]. Diagnosis of seizures in the neonatal period remains a challenge, resulting in over-diagnosis and, as a consequence, over-treatment of infants[4]. Studies in animal models suggest that exposure to PhB during the neonatal period produces long-lasting structural and functional changes in the brain[14]. For the first time, we sought to analyse the acute and chronic effects of PhB treatment in a mouse model of hypoxia-induced seizures[21]. In this model, P7 mice were exposed either to normoxia or hypoxia and PhB or vehicle (saline). Our results corroborate other work indicating PhB exposure is probably harmful to the immature brain and point, unexpectedly, to protection against later-life seizure-damage

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Conclusion