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

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.

The Anti-inflammatory Compound Candesartan Cilexetil Improves Neurological Outcomes in a Mouse Model of Neonatal Hypoxia

“…Day 1 (habituation day), mice were allowed to explore the arena without objects (10 min) followed by 3 sessions with two objects (10 min each session); on day 2 (test day), mice were placed in the same arena with one of the objects moved to a novel position. Object exploration was manually recorded and defined as the time mice were interacting with the objects with their nose or paw within 1 cm of the objects (3). To calculate the percentage of time with the novel-object, the following equation was used: (A)/(A+B) * 100.…”

“…All mice receiving KA were recorded for both electrographic (EEG) and behavioral seizures. Electrode implantation, EEG recording and quantification were performed as previously described (3, 33). Briefly, mice were injected with KA and monitored for 60 min post-KA.…”

“…Common clinical practice is to suppress neonatal seizures by using pharmacotherapies that boost inhibitory drive; such as phenobarbital. Response rates to phenobarbital are poor however, and treatment does not attenuate long-term neurological comorbidities (1–3). There are also concerns that phenobarbital and other anti-seizure medications may be neurotoxic at this age (4).…”

Neonatal Seizures and Purinergic Signalling

“…Nevertheless, this makes the immature brain more susceptible to seizures and therapies targeting GABA may even potentiate seizures and excitotoxicity. There are multiple studies raising concern with phenobarbital's safety due to potentiation of neuronal damage and behavioural deficits observed in rodent models [5,67,68] and various reports of patients developing behavioural abnormalities in later life [69]. In fact, Torolina et al observed that phenobarbital and midazolam exacerbate neonatal seizure damage even at subclinical doses [68].…”

“…Current treatment strategies aim to reduce the hyperexcitability of brain tissue via the use of anti-seizure drugs (ASDs), with phenobarbital being the first-line drug for neonatal seizures. ASDs, however, fail to resolve seizures in 50% of infants and may exacerbate symptoms and later life neurological deficits [2,5]. Therefore, there is a pressing need to identify novel treatment options with higher response rates and without affecting normal development of the brain.…”