Abstracts

Rationale: Traumatic brain injury is a major cause of acquired epilepsy. Seizures may occur because of the acute injury or progressive post-traumatic changes in brain metabolism, blood flow and homeostasis. Phenytoin is effective in treatment of acute seizures but failed to prevent post-traumatic epilepsy (PTE). Anticonvulsant efficacy of Phenobarbital is low with a greater risk of developing PTE. Understanding the mechanisms of anticonvulsant resistance and development of PTE is a critical for understanding the epilepsy and development of more efficient therapy for prevention and prophylaxis of PTE. Methods: Extracellular field potential recordings, two-photon imaging of Clomeleon, lactate and lactate dehydrogenase production assays were used to monitor neuronal network activity, intracellular chloride concentration([Cl-]i) and neuronal cell death. Results: Hippocampal slices were incubated for six-seven weeks, during which a latent one-two week period was followed by spontaneous seizure activity and electrical status epilepticus. Phenytoin exerted powerful acute concentration-dependent anticonvulsive effects (Berdichevsky et al., 2012). Chronic anticonvulsive efficacy of phenytoin progressively decreased demonstrating no antiepileptic action in this model. Washout of phenytoin was followed by a sharp increase in recurrent seizure activity. Phenobarbital was much effective at controlling post-traumatic seizures at the earlier stage of epileptogenesis. Anticonvulsive efficacy of phenobarbital decreased from 60-70 % to 0-10% during four-five weeks of epileptogenesis. Anticonvulsive efficacy of phenobarbital was correlated with intracellular chloride concentration ([Cl-]i) and GABA action. We found a correlation between seizure severity and frequency, increases in [Cl-]i and phenobarbital efficacy. Bumetanide, a sodium-potassium-chloride (NKCC1) co-transporter blocker, significantly increased anticonvulsive efficacy of phenobarbital. High concentration of furosemide (NKCC1 and potassium-chloride (KCC2) co-transporter blocker) controlled acute seizures at all stages of epileptogenesis, but failed to reduce interictal epileptiform discharges and prevent epilepsy. Conclusions: In conclusion, our data suggest a complex mechanism of anticonvulsant resistance that involves chronic post-traumatic chloride accumulation and alterations in GABA-mediated inhibition. More effective prevention of post-traumatic and seizure-induced neuronal chloride accumulation may comprise a new strategy for both anticonvulsive and antiepileptogenic therapy.