Abstracts

Rationale: Pentobarbital is still extensively prescribed for pediatric epilepsy in developing countries and a favorable medication for refractory status epilepticus. As an allosteric regulator of GABAA receptors pentobarbital exerts its anti-epileptic action via facilitating inhibitory GABAergic transmission. However, patients frequently show pharmacological resistance to pentobarbital. Pentobarbital can even exacerbate seizures in pediatric epileptic patients or those who suffered from prolonged seizures. Additionally, pentobarbital has been shown to cause behavioral disorders, such as attention deficit hyperactive disorder. The mechanism underlying these paradoxical effects of pentobarbital is not completely understood. In light of the recent findings of the role of chloride co-transporters in GABAA transmission and poor efficacy of pentobarbital, we examined if KCC2 plays any role in pharmacological resistance and hyperexcitatory action of pentobarbital in immature (3-4 weeks old) rats that suffered from severe prolonged seizures in the pilocarpine model.Methods: Sprague-Dawley rats were treated with rapamycin via i.p injection for three days followed by pilocarpine at 255 mg/kg. Seizure activities were monitored via video-EEG recordings. Pentobarbital was administered at 25 mg/kg via i.p. injection and residual behavioral and electrographic seizure activity was recorded. Hyperlocomotor activity was monitored immediately following pentobarbital injection by counting beam breaks.Results: We found that immature rats (3-4 weeks old) that were pretreated with rapamycin developed very severe seizures to a low dose of pilocarpine at 255 mg/kg. Although pentobarbital at 25 mg/kg can fully anesthetize all control rats as well as those that developed mild seizures induced by pilocarpine at 255 mg/kg, it does not effectively suppress seizures in rats that developed severe seizures induced by rapamycin and pilocarpine cotreatment. Additionally, about 40% of rats showed aberrant hyperlocomotor activity. We found that severe seizures induced by rapamycin and pilocarpine cotreatment down-regulates the membrane KCC2 in the thalamus. Furthermore, rats which received infusion of KCC2 inhibitors into thalamus not only developed severe seizures to pilocarpine, but also exhibited pharmacological resistance and hyperlocomotor activity to pentobarbital.Conclusions: We found immature rats that developed the most severe seizures demonstrated pharmacological resistance and hyperexcitation in response to pentobarbital along with down regulation of thalamic KCC2. This is in line with the clinical observation that hyperactivity is more frequently observed in pediatric epileptic patients with early age of onset or prolonged severe seizures when treated with barbiturates. Our data provide new insight into pharmacological resistance to pentobarbital and comorbidity such as hyperactivity or ADHD in pediatric epilepsy.